Showing 1–50 of 97 results for author: Batell, B

Leggett-Garg Inequality Violation in Muon $g-2$ Experiments

Authors: Brian Batell, Morgan Cassidy, Kun Cheng

Abstract: We present the first study of Leggett-Garg inequality violation in polarized muon spin precession. We formulate a procedure to reconstruct temporal correlators of the longitudinal muon polarization from measured time-dependent muon decay spectra and apply it to publicly available Fermilab Muon $g-2$ data corresponding to approximately $10$ billion muon decays. Using a simplified model of the detec… ▽ More We present the first study of Leggett-Garg inequality violation in polarized muon spin precession. We formulate a procedure to reconstruct temporal correlators of the longitudinal muon polarization from measured time-dependent muon decay spectra and apply it to publicly available Fermilab Muon $g-2$ data corresponding to approximately $10$ billion muon decays. Using a simplified model of the detector acceptance and efficiency, the Leggett-Garg inequality is found to be violated with a single-bin significance of $5.5σ$, while combining neighboring bins further increases the significance. While our analysis is limited by systematic uncertainties associated with the detector modeling, a dedicated experimental analysis could reduce these uncertainties toward the statistical level, $\mathcal{O}(10^{-3})$, potentially enabling one of the most precise measurements of temporal quantum correlations. △ Less

Submitted 18 June, 2026; originally announced June 2026.

Report number: PITT-PACC-2608

Majoron Dark Matter, High-Scale Seesaw, and Leptogenesis

Authors: Brian Batell, Arnab Dasgupta, Swapnil Dutta, Akshay Ghalsasi

Abstract: We study the cosmology and observational probes of majoron dark matter in a high-scale seesaw framework with spontaneously broken lepton number. Right-handed neutrinos naturally generate light neutrino masses and can realize thermal leptogenesis, while the associated majoron is a light pseudo-Nambu-Goldstone boson that can be cosmologically stable and serve as a viable dark matter candidate for su… ▽ More We study the cosmology and observational probes of majoron dark matter in a high-scale seesaw framework with spontaneously broken lepton number. Right-handed neutrinos naturally generate light neutrino masses and can realize thermal leptogenesis, while the associated majoron is a light pseudo-Nambu-Goldstone boson that can be cosmologically stable and serve as a viable dark matter candidate for sub-MeV masses. We analyze both pre-inflationary and post-inflationary histories of lepton number breaking. In the pre-inflationary scenario, majoron dark matter is produced by misalignment and constrained by CMB isocurvature. In the post-inflationary scenario, the majoron abundance receives nonthermal contributions from spatially averaged misalignment, majoron radiation from global cosmic strings, and the collapse of the string-domain wall network, as well as a thermally produced component. This scenario can also be probed by future searches for the stochastic gravitational wave background produced by cosmic strings. We map the viable majoron dark matter parameter space and examine complementary probes from X-ray and soft gamma ray searches for majoron decays to photons, black hole superradiance, and Lyman-$α$ forest observations. These results demonstrate that majoron dark matter offers a distinctive cosmological probe of high-scale lepton number breaking and thermal leptogenesis. △ Less

Submitted 1 June, 2026; originally announced June 2026.

Comments: 42 pages, 5 figures

Report number: PITT-PACC-2606

Phasing out Dark Matter Isocurvature with Thermal Misalignment

Authors: Brian Batell, Akshay Ghalsasi, Subhajit Ghosh, Mudit Rai

Abstract: Thermal misalignment provides an alternative to the standard misalignment mechanism for the cosmological production of scalar dark matter. In this framework, feeble couplings to particles in the thermal bath generate a finite-temperature potential that drives the scalar towards large field values early in the radiation era, dynamically inducing the misalignment before the onset of scalar oscillati… ▽ More Thermal misalignment provides an alternative to the standard misalignment mechanism for the cosmological production of scalar dark matter. In this framework, feeble couplings to particles in the thermal bath generate a finite-temperature potential that drives the scalar towards large field values early in the radiation era, dynamically inducing the misalignment before the onset of scalar oscillations. As a result, the relic abundance is controlled primarily by particle masses and couplings rather than the initial field value. As a light spectator field, the scalar acquires inflationary fluctuations that are uncorrelated with the adiabatic curvature mode, generically sourcing isocurvature perturbations. We show that, unlike standard misalignment, where light scalars are strongly constrained by cosmic microwave background bounds on dark matter isocurvature for high-scale inflation, thermal misalignment can naturally suppress the isocurvature signal. This occurs through a novel late-time phase offset between the background zero mode and the superhorizon perturbations, which reduces the final dark matter density contrast. Thermal misalignment therefore provides a new and generic route to isocurvature-safe scalar dark matter. △ Less

Submitted 18 March, 2026; originally announced March 2026.

Comments: 30 pages, 4 figures

Report number: PITT-PACC-2605, UT-WI-09-2026, MI-HET-881

$i$-incidental $N$-naturalness

Authors: Brian Batell, Akshay Ghalsasi, Wenjie Huang, Matthew Low

Abstract: $N$-naturalness is a novel solution to the electroweak hierarchy problem which posits $N… ▽ More $N$-naturalness is a novel solution to the electroweak hierarchy problem which posits $N$ copies of the Standard Model with varying Higgs mass-squared parameters. Reheating proceeds through a "reheaton" particle that deposits most of its energy density into the Standard Model and small but potentially measurable fractions into the other copies. Typically the sector with the lightest negative Higgs mass-squared is identified as the Standard Model. We demonstrate that $N$-naturalness admits a broader class of realizations in which the Standard Model is identified with a heavier sector, rather than being restricted to the lightest. This is made possible by resonant mixing between the reheaton and the Higgs, which generically causes one sector to be preferentially reheated and to acquire the largest share of the energy density, singling it out as the Standard Model. We demonstrate that this scenario is consistent with current cosmological bounds on new relativistic degrees of freedom and overclosure constraints from heavy stable relics, while future cosmic microwave background and high redshift surveys will probe significant portions of the remaining parameter space. Furthermore, we highlight the possibility of a novel stochastic gravitational wave spectrum from the many cosmological first order QCD phase transitions occurring across the other sectors. △ Less

Submitted 16 December, 2025; originally announced December 2025.

Comments: 38 pages, 5 figures

Letter of Intent: The Forward Physics Facility

Authors: Luis A. Anchordoqui, John K. Anders, Akitaka Ariga, Tomoko Ariga, David Asner, Jeremy Atkinson, Alan J. Barr, Larry Bartoszek, Brian Batell, Hans Peter Beck, Florian U. Bernlochner, Bipul Bhuyan, Jianming Bian, Aleksey Bolotnikov, Silas Bosco, Jamie Boyd, Nick Callaghan, Gabriella Carini, Michael Carrigan, Kohei Chinone, Matthew Citron, Isabella Coronado, Peter Denton, Albert De Roeck, Milind V. Diwan , et al. (89 additional authors not shown)

Abstract: The Forward Physics Facility (FPF) is a proposed extension of the HL-LHC program designed to exploit the unique scientific opportunities offered by the intense flux of high energy neutrinos, and possibly new particles, in the far-forward direction. Located in a well-shielded cavern 627 m downstream of one of the LHC interaction points, the facility will support a broad and ambitious physics progra… ▽ More The Forward Physics Facility (FPF) is a proposed extension of the HL-LHC program designed to exploit the unique scientific opportunities offered by the intense flux of high energy neutrinos, and possibly new particles, in the far-forward direction. Located in a well-shielded cavern 627 m downstream of one of the LHC interaction points, the facility will support a broad and ambitious physics program that significantly expands the discovery potential of the HL-LHC. Equipped with four complementary detectors -- FLArE, FASER$ν$2, FASER2, and FORMOSA -- the FPF will enable breakthrough measurements that will advance our understanding of neutrino physics, quantum chromodynamics, and astroparticle physics, and will search for dark matter and other new particles. With this Letter of Intent, we propose the construction of the FPF cavern and the construction, integration, and installation of its experiments. We summarize the physics case, the facility design, the layout and components of the detectors, as well as the envisioned collaboration structure, cost estimate, and implementation timeline. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Report number: CERN-PBC-Notes-2025-010

Journal ref: Nucl.Phys.B 1026 (2026) 117398

Extended Color Twin Higgs

Authors: Brian Batell, Thomas Cochran, Logan Page, Christopher B. Verhaaren

Abstract: We describe a novel variation of the mirror Twin Higgs model in which the color gauge group in both sectors is extended to SU(4$)_c$ and spontaneously broken to SU(3$)_c$ exclusively in the visible sector. Through this process, the mirror $Z_2$ symmetry is spontaneously broken, allowing for a phenomenologically viable electroweak vacuum alignment. This structure produces interesting collider signa… ▽ More We describe a novel variation of the mirror Twin Higgs model in which the color gauge group in both sectors is extended to SU(4$)_c$ and spontaneously broken to SU(3$)_c$ exclusively in the visible sector. Through this process, the mirror $Z_2$ symmetry is spontaneously broken, allowing for a phenomenologically viable electroweak vacuum alignment. This structure produces interesting collider signatures, including heavy vectors and fermions with fractional electric charges. The twin sector, with unbroken SU(4$)_c$, produces interesting cosmological characteristics, such as the possibility to reduce $ΔN_\text{eff}$ and stable spin-0 baryons. The enlarged top quark sector required by the extended color gauge symmetry preserves naturalness, with even less tuning than the original twin Higgs in many circumstances. △ Less

Submitted 13 August, 2025; originally announced August 2025.

Comments: 22 pages + Appendices, 9 figures

Cosmological Histories in Neutrino Portal Dark Matter

Authors: Amro E. B. Abdelrahim, Brian Batell, Joshua Berger, David McKeen, Barmak Shams Es Haghi

Abstract: We explore the diverse cosmological histories of a dark sector that is connected to the Standard Model (SM) via a Dirac sterile neutrino. The dark sector consists of a complex scalar and a Dirac fermion dark matter (DM) candidate protected by a global $U(1)$ stabilizing symmetry. Assuming the dark sector has negligible initial abundance and is populated from reactions in the SM thermal plasma duri… ▽ More We explore the diverse cosmological histories of a dark sector that is connected to the Standard Model (SM) via a Dirac sterile neutrino. The dark sector consists of a complex scalar and a Dirac fermion dark matter (DM) candidate protected by a global $U(1)$ stabilizing symmetry. Assuming the dark sector has negligible initial abundance and is populated from reactions in the SM thermal plasma during the radiation era, we show that the cosmological histories of the dark sector fall into four qualitatively distinct scenarios, each one characterized by the strengths of the portal couplings involving the sterile neutrino mediator. By solving Boltzmann equations, both semi-analytically and numerically, we explore these thermal histories and transitions between them in detail, including the time evolution of the temperature of the dark sector and the number densities of its ingredients. We also discuss how these various histories may be probed by cosmology, direct detection, indirect detection, collider searches, and electroweak precision tests. △ Less

Submitted 10 June, 2025; originally announced June 2025.

Comments: 48 pages, 11 figures

Report number: PITT-PACC-2502, UTWI-15-2025

MATHUSLA: An External Long-Lived Particle Detector to Maximize the Discovery Potential of the HL-LHC

Authors: Branden Aitken, Cristiano Alpigiani, Juan Carlos Arteaga-Velázquez, Mitchel Baker, Kincso Balazs, Jared Barron, Brian Batell, Austin Batz, Yan Benhammou, Tamara Alice Bud, Karen Salomé Caballero-Mora, John Paul Chou, David Curtin, Albert de Roeck, Miriam Diamond, Mariia Didenko, Keith R. Dienes, William Dougherty, Liam Andrew Dougherty, Marco Drewes, Sameer Erramilli, Erez Etzion, Arturo Fernández Téllez, Grace Finlayson, Oliver Fischer , et al. (48 additional authors not shown)

Abstract: We present the current status of the MATHUSLA (MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles) long-lived particle (LLP) detector at the HL-LHC, covering the design, fabrication and installation at CERN Point 5. MATHUSLA40 is a 40 m-scale detector with an air-filled decay volume that is instrumented with scintillator tracking detectors, to be located near CMS. Its large size, close pr… ▽ More We present the current status of the MATHUSLA (MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles) long-lived particle (LLP) detector at the HL-LHC, covering the design, fabrication and installation at CERN Point 5. MATHUSLA40 is a 40 m-scale detector with an air-filled decay volume that is instrumented with scintillator tracking detectors, to be located near CMS. Its large size, close proximity to the CMS interaction point and about 100 m of rock shielding from LHC backgrounds allows it to detect LLP production rates and lifetimes that are one to two orders of magnitude beyond the ultimate reach of the LHC main detectors. This provides unique sensitivity to many LLP signals that are highly theoretically motivated, due to their connection to the hierarchy problem, the nature of dark matter, and baryogenesis. Data taking is projected to commence with the start of HL-LHC operations. We summarize the new 40m design for the detector that was recently presented in the MATHUSLA Conceptual Design Report, alongside new realistic background and signal simulations that demonstrate high efficiency for the main target LLP signals in a background-free HL-LHC search. We argue that MATHUSLA's uniquely robust expansion of the HL-LHC physics reach is a crucial ingredient in CERN's mission to search for new physics and characterize the Higgs boson with precision. △ Less

Submitted 1 April, 2025; originally announced April 2025.

Comments: Input to the 2026 update of the European Strategy for Particle Physics. 10 pages + references. 7 figures, 2 tables. This submission draws heavily from, and acts as an executive summary of, the MATHUSLA CDR (arXiv:2503.20893), but makes additional points and is a standalone separate document. arXiv admin note: substantial text overlap with arXiv:2503.20893

Conceptual Design Report for the MATHUSLA Long-Lived Particle Detector near CMS

Authors: Branden Aitken, Cristiano Alpigiani, Juan Carlos Arteaga-Velázquez, Mitchel Baker, Kincso Balazs, Jared Barron, Brian Batell, Austin Batz, Yan Benhammou, Tamara Alice Bud, Karen Salomé Caballero-Mora, John Paul Chou, David Curtin, Albert de Roeck, Miriam Diamond, Mariia Didenko, Keith R. Dienes, William Dougherty, Liam Andrew Dougherty, Marco Drewes, Sameer Erramilli, Erez Etzion, Arturo Fernández Téllez, Grace Finlayson, Oliver Fischer , et al. (48 additional authors not shown)

Abstract: We present the Conceptual Design Report (CDR) for the MATHUSLA (MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles) long-lived particle detector at the HL-LHC, covering the design, fabrication and installation at CERN Point 5. MATHUSLA is a 40 m-scale detector with an air-filled decay volume that is instrumented with scintillator tracking detectors, to be located near CMS. Its large size,… ▽ More We present the Conceptual Design Report (CDR) for the MATHUSLA (MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles) long-lived particle detector at the HL-LHC, covering the design, fabrication and installation at CERN Point 5. MATHUSLA is a 40 m-scale detector with an air-filled decay volume that is instrumented with scintillator tracking detectors, to be located near CMS. Its large size, close proximity to the CMS interaction point and about 100 m of rock shielding from HL-LHC backgrounds allows it to detect LLP production rates and lifetimes that are one to two orders of magnitude beyond the ultimate sensitivity of the HL-LHC main detectors for many highly motivated LLP signals. Data taking is projected to commence with the start of HL-LHC operations. We present a new 40m design for the detector: its individual scintillator bars and wavelength-shifting fibers, their organization into tracking layers, tracking modules, tower modules and the veto detector; define a high-level design for the supporting electronics, DAQ and trigger system, including supplying a hardware trigger signal to CMS to record the LLP production event; outline computing systems, civil engineering and safety considerations; and present preliminary cost estimates and timelines for the project. We also conduct detailed simulation studies of the important cosmic ray and HL-LHC muon backgrounds, implementing full track/vertex reconstruction and background rejection, to ultimately demonstrate high signal efficiency and $\ll 1$ background event in realistic LLP searches for the main physics targets at MATHUSLA. This sensitivity is robust with respect to detector design or background simulation details. Appendices provide various supplemental information. △ Less

Submitted 26 March, 2025; originally announced March 2025.

Comments: 71 pages, 28 figures, 5 tables

The Forward Physics Facility at the Large Hadron Collider

Authors: Luis A. Anchordoqui, Akitaka Ariga, Tomoko Ariga, Alan J. Barr, Brian Batell, Jianming Bian, Jamie Boyd, Matthew Citron, Albert De Roeck, Milind V. Diwan, Jonathan L. Feng, Christopher S. Hill, Felix Kling, Steven Linden, Toni Mäkelä, Kostas Mavrokoridis, Josh McFayden, Hidetoshi Otono, Juan Rojo, Dennis Soldin, Anna Stasto, Sebastian Trojanowski, Matteo Vicenzi, Wenjie Wu

Abstract: The Forward Physics Facility (FPF) is a proposal developed to exploit the unique scientific potential made possible by the intense hadron beams produced in the far-forward direction at the high luminosity LHC (HL-LHC). Housed in a well-shielded cavern 627 m from the LHC interactions, the facility will enable a broad and deep scientific programme which will greatly extend the physics capability of… ▽ More The Forward Physics Facility (FPF) is a proposal developed to exploit the unique scientific potential made possible by the intense hadron beams produced in the far-forward direction at the high luminosity LHC (HL-LHC). Housed in a well-shielded cavern 627 m from the LHC interactions, the facility will enable a broad and deep scientific programme which will greatly extend the physics capability of the HL-LHC. Instrumented with a suite of four complementary detectors -- FLArE, FASER$ν$2, FASER2 and FORMOSA -- the FPF has unique potential to shed light on neutrino physics, QCD, astroparticle physics, and to search for dark matter and other new particles. This contribution describes some of the key scientific drivers for the facility, the engineering and technical studies that have been made in preparation for it, the design of its four complementary experiments, and the status of the project's partnerships and planning. △ Less

Submitted 24 March, 2025; originally announced March 2025.

Comments: Contribution prepared for the 2025 update of the European Strategy for Particle Physics, 10 pages, 9 figures

Dark gauge-mediated supersymmetry breaking with a massless dark photon

Authors: Brian Batell, Yechan Kim, Hye-Sung Lee, Jiheon Lee

Abstract: We study dark gauge-mediated supersymmetry breaking (dark GMSB) in a theory with a new unbroken $U(1)_{D}$ local symmetry and massless dark photon. Messenger fields charged under both Standard Model and dark gauge symmetries produce new soft supersymmetry-breaking terms due to gauge kinetic mixing between $U(1)_Y$ hypercharge and $U(1)_D$. We show that large kinetic mixing induces significant dist… ▽ More We study dark gauge-mediated supersymmetry breaking (dark GMSB) in a theory with a new unbroken $U(1)_{D}$ local symmetry and massless dark photon. Messenger fields charged under both Standard Model and dark gauge symmetries produce new soft supersymmetry-breaking terms due to gauge kinetic mixing between $U(1)_Y$ hypercharge and $U(1)_D$. We show that large kinetic mixing induces significant distortions to the superpartner spectra relative to conventional GMSB. Notably, shifts in the Higgs soft masses impact the conditions for electroweak symmetry breaking, lowering the $μ$ parameter and yielding a relatively light Higgsino that may be accessible at the LHC. Furthermore, for very simple messenger representations, a very light bino-dark photino mixed state is present in the spectrum, which may be probed through exotic Higgs boson decays at future Higgs factories. We also examine the cosmological and phenomenological consequences of the messengers, the lightest of which is absolutely stable and carries fractional electric charge. △ Less

Submitted 14 May, 2025; v1 submitted 23 December, 2024; originally announced December 2024.

Comments: 45 pages, 20 figures. Version matching the publication in JHEP

Right-Handed Neutrino Masses from the Electroweak Scale

Authors: Brian Batell, Amit Bhoonah, Wenjie Huang

Abstract: Heavy right-handed neutrinos are highly motivated due to their connection with the origin of neutrino masses via the seesaw mechanism. If the right-handed neutrino Majorana mass is at or below the weak scale, direct experimental discovery of these states is possible in laboratory experiments. However, there is no a priori basis to expect right-handed neutrinos to be so light since the Majorana mas… ▽ More Heavy right-handed neutrinos are highly motivated due to their connection with the origin of neutrino masses via the seesaw mechanism. If the right-handed neutrino Majorana mass is at or below the weak scale, direct experimental discovery of these states is possible in laboratory experiments. However, there is no a priori basis to expect right-handed neutrinos to be so light since the Majorana mass is a technically natural parameter and could comfortably reside at any scale, including at scales far above the weak scale. Here we explore the possibility that the right-handed neutrino Majorana mass originates from electroweak symmetry breaking. Working within an effective theory with two Higgs doublets, nonzero lepton number is assigned to the bilinear operator built from the two Higgs fields, which is then coupled to the right-handed neutrino mass operator. In tandem with the neutrino Yukawa coupling, following electroweak symmetry breaking a seesaw mechanism operates, generating the light SM neutrino masses along with right-handed neutrinos with masses below the electroweak scale. This scenario leads to novel phenomenology in the Higgs sector, which may be probed at the LHC and at future colliders. There are also interesting prospects for neutrinoless double beta decay and lepton flavor violation. We also explore some theoretical aspects of the scenario, including the technical naturalness of the effective field theory and ultraviolet completions of the right-handed neutrino Majorana mass. △ Less

Submitted 11 November, 2024; originally announced November 2024.

Comments: 12 pages, 7 figures

Report number: PITT-PACC-2411

Conversations and Deliberations: Non-Standard Cosmological Epochs and Expansion Histories

Authors: Brian Batell, Keith R. Dienes, Brooks Thomas, Scott Watson, Rouzbeh Allahverdi, Mustafa Amin, Kimberly K. Boddy, M. Sten Delos, Adrienne L. Erickcek, Akshay Ghalsasi, John T. Giblin Jr., James Halverson, Fei Huang, Andrew J. Long, Lauren Pearce, Barmak Shams Es Haghi, Jessie Shelton, Gary Shiu, Kuver Sinha, Tristan L. Smith

Abstract: This document summarizes the discussions which took place during the PITT-PACC Workshop entitled "Non-Standard Cosmological Epochs and Expansion Histories," held in Pittsburgh, Pennsylvania, Sept. 5-7, 2024. Much like the non-standard cosmological epochs that were the subject of these discussions, the format of this workshop was also non-standard. Rather than consisting of a series of talks from p… ▽ More This document summarizes the discussions which took place during the PITT-PACC Workshop entitled "Non-Standard Cosmological Epochs and Expansion Histories," held in Pittsburgh, Pennsylvania, Sept. 5-7, 2024. Much like the non-standard cosmological epochs that were the subject of these discussions, the format of this workshop was also non-standard. Rather than consisting of a series of talks from participants, with each person presenting their own work, this workshop was instead organized around free-form discussion blocks, with each centered on a different overall theme and guided by a different set of Discussion Leaders. This document is not intended to serve as a comprehensive review of these topics, but rather as an informal record of the discussions that took place during the workshop, in the hope that the content and free-flowing spirit of these discussions may inspire new ideas and research directions. △ Less

Submitted 7 November, 2024; originally announced November 2024.

Comments: 33 pages, LaTeX, 2 figures

Science and Project Planning for the Forward Physics Facility in Preparation for the 2024-2026 European Particle Physics Strategy Update

Authors: Jyotismita Adhikary, Luis A. Anchordoqui, Akitaka Ariga, Tomoko Ariga, Alan J. Barr, Brian Batell, Jianming Bian, Jamie Boyd, Matthew Citron, Albert De Roeck, Milind V. Diwan, Jonathan L. Feng, Christopher S. Hill, Yu Seon Jeong, Felix Kling, Steven Linden, Toni Mäkelä, Kostas Mavrokoridis, Josh McFayden, Hidetoshi Otono, Juan Rojo, Dennis Soldin, Anna Stasto, Sebastian Trojanowski, Matteo Vicenzi , et al. (1 additional authors not shown)

Abstract: The recent direct detection of neutrinos at the LHC has opened a new window on high-energy particle physics and highlighted the potential of forward physics for groundbreaking discoveries. In the last year, the physics case for forward physics has continued to grow, and there has been extensive work on defining the Forward Physics Facility and its experiments to realize this physics potential in a… ▽ More The recent direct detection of neutrinos at the LHC has opened a new window on high-energy particle physics and highlighted the potential of forward physics for groundbreaking discoveries. In the last year, the physics case for forward physics has continued to grow, and there has been extensive work on defining the Forward Physics Facility and its experiments to realize this physics potential in a timely and cost-effective manner. Following a 2-page Executive Summary, we present the status of the FPF, beginning with the FPF's unique potential to shed light on dark matter, new particles, neutrino physics, QCD, and astroparticle physics. We summarize the current designs for the Facility and its experiments, FASER2, FASER$ν$2, FORMOSA, and FLArE, and conclude by discussing international partnerships and organization, and the FPF's schedule, budget, and technical coordination. △ Less

Submitted 19 May, 2025; v1 submitted 6 November, 2024; originally announced November 2024.

Comments: revised version, accepted by EPJC

Report number: DESY-24-174

Journal ref: Eur. Phys. J. C 85 (2025) 4, 430

Lepton-Flavor-Violating ALP Signals with TeV-Scale Muon Beams

Authors: Brian Batell, Hooman Davoudiasl, Roman Marcarelli, Ethan T. Neil, Sebastian Trojanowski

Abstract: We explore the feasibility of using TeV-energy muons to probe lepton-flavor-violating (LFV) processes mediated by an axion-like particle (ALP) $a$ with mass $\mathcal{O}(10~\textrm{GeV})$. We focus on $μτ$ LFV interactions and assume that the ALP is coupled to a dark state $χ$, which can be either less or more massive than $a$. Such a setup is demonstrated to be consistent with $χ$ being a candida… ▽ More We explore the feasibility of using TeV-energy muons to probe lepton-flavor-violating (LFV) processes mediated by an axion-like particle (ALP) $a$ with mass $\mathcal{O}(10~\textrm{GeV})$. We focus on $μτ$ LFV interactions and assume that the ALP is coupled to a dark state $χ$, which can be either less or more massive than $a$. Such a setup is demonstrated to be consistent with $χ$ being a candidate for dark matter, in the experimentally relevant regime of parameters. We consider the currently operating NA64-$μ$ experiment and proposed FASER$ν$2 detector as both the target and the detector for the process $μA \to τA\, a$, where $A$ is the target nucleus. We also show that a possible future active muon fixed-target experiment operating at a 3 TeV muon collider or in its preparatory phase can provide an impressive reach for the LFV process considered, with future FASER$ν$2 data providing a pilot study towards that goal. The implications of the muon anomalous magnetic moment $(g-2)_μ$ measurements for the underlying model, in case of a positive signal, are also examined, and a sample UV completion is outlined. △ Less

Submitted 4 November, 2024; v1 submitted 22 July, 2024; originally announced July 2024.

Comments: 16 pages, 7 figures, matches published version

Report number: PITT-PACC-2404

Journal ref: Phys.Rev.D 110 (2024) 7, 075039

Cosmic Stability of Dark Matter from Pauli Blocking

Authors: Brian Batell, Wen Yin

Abstract: Why does dark matter (DM) live longer than the age of the Universe? Here we study a novel sub-eV scalar DM candidate whose stability is due to the Pauli exclusion of its fermionic decay products. We analyze the stability of the DM condensate against decays, scatterings (i.e., evaporation), and parametric resonance, delineating the viable parameter regions in which DM is cosmologically stable. In a… ▽ More Why does dark matter (DM) live longer than the age of the Universe? Here we study a novel sub-eV scalar DM candidate whose stability is due to the Pauli exclusion of its fermionic decay products. We analyze the stability of the DM condensate against decays, scatterings (i.e., evaporation), and parametric resonance, delineating the viable parameter regions in which DM is cosmologically stable. In a minimal scenario in which the scalar DM decays to a pair of new exotic fermions, we find that scattering can populate an interacting thermal dark sector component to energies far above the DM mass. This self-interacting dark radiation may potentially alleviate the Hubble tensions. Furthermore, our scenario can be probed through precise measurements of the halo mass function or the masses of dwarf spheroidal galaxies since scattering prevents the DM from becoming too dense. On the other hand, if the lightest neutrino stabilizes the DM, the cosmic neutrino background (C$ν$B) can be significantly altered from the $Λ$CDM prediction and thus be probed in the future by C$ν$B detection experiments. △ Less

Submitted 24 June, 2024; originally announced June 2024.

Comments: 47 pages, 5 figures

Report number: TU-1168, PITT-PACC-2403

Gravitational Waves from Nnaturalness

Authors: Brian Batell, Akshay Ghalsasi, Matthew Low, Mudit Rai

Abstract: We study the prospects for probing the Nnaturalness solution to the electroweak hierarchy problem with future gravitational wave observatories. Nnaturalness, in its simplest incarnation, predicts $N$ copies of the Standard Model with varying Higgs mass parameters. We show that in certain parameter regions the scalar reheaton transfers a substantial energy density to the sector with the smallest po… ▽ More We study the prospects for probing the Nnaturalness solution to the electroweak hierarchy problem with future gravitational wave observatories. Nnaturalness, in its simplest incarnation, predicts $N$ copies of the Standard Model with varying Higgs mass parameters. We show that in certain parameter regions the scalar reheaton transfers a substantial energy density to the sector with the smallest positive Higgs squared mass while remaining consistent with bounds on additional effective relativistic species. In this sector, all six quarks are much lighter than the corresponding QCD confinement scale, allowing for the possibility of a first-order chiral symmetry-breaking phase transition and an associated stochastic gravitational wave signal. We consider several scenarios characterizing the strongly-coupled phase transition dynamics and estimate the gravitational wave spectrum for each. Pulsar timing arrays (SKA), spaced-based interferometers (BBO, Ultimate-DECIGO, $μ$Ares, asteroid ranging), and astrometric measurements (THEIA) all have the potential to explore new regions of Nnaturalness parameter space, complementing probes from next generation cosmic microwave background radiation experiments. △ Less

Submitted 10 October, 2023; originally announced October 2023.

Comments: 35 pages, 4 figures

Report number: PITT-PACC-2119, MI-HET-815

Keeping it Simple: Simplified Frameworks for Long-Lived Particles at Neutrino Facilities

Authors: Brian Batell, Wenjie Huang, Kevin J. Kelly

Abstract: Modern-day accelerator neutrino facilities are excellent venues for searches for new-physics particles. Many distinct new-physics models predict overlapping signatures and phenomenology in these experiments. In this work, we advocate for the adoption of simplified frameworks when studying these types of new-physics signatures, which are characterized by a small number of primary variables, includi… ▽ More Modern-day accelerator neutrino facilities are excellent venues for searches for new-physics particles. Many distinct new-physics models predict overlapping signatures and phenomenology in these experiments. In this work, we advocate for the adoption of simplified frameworks when studying these types of new-physics signatures, which are characterized by a small number of primary variables, including particle masses, lifetimes, and production and decay modes/rates that most directly control signal event rates and kinematics. In particular, taking the example of long-lived particles that decay inside a neutrino detector as a test case, we study formulate and study simplified frameworks in the context of light scalars/fermions produced in kaon decays which then decay into final states containing an electron-positron pair. We show that using these simplified frameworks can allow for individual experimental analyses to be applicable to a wide variety of specific model scenarios. As a side benefit, we demonstrate that using this approach can allow for the T2K collaboration, by reinterpreting its search for Heavy Neutral Leptons, to be capable of setting world-leading limits on the Higgs-Portal Scalar model. Furthermore, we argue the simplified framework interpretation can serve as a bridge to model identification in the hopeful detection of a new-physics signal. As an illustration, we perform a first determination of the likelihood that, in the presence of a new-physics signal in a detector like the DUNE ND-GAr, multiple different new-physics hypotheses (such as the Higgs-Portal Scalar and Heavy Neutral Lepton ones) can be disentangled. We demonstrate that this model discrimination is favorable for some portions of detectable new-physics parameter space but for others, it is more challenging. △ Less

Submitted 29 August, 2023; v1 submitted 21 April, 2023; originally announced April 2023.

Comments: 22 pages, 10 figures. Updated to JHEP version

Journal ref: JHEP08(2023)092

Dynamics of Dark Matter Misalignment Through the Higgs Portal

Authors: Brian Batell, Akshay Ghalsasi, Mudit Rai

Abstract: A light singlet scalar field feebly coupled through the super-renormalizable Higgs portal provides a minimal and well-motivated realization of ultra-light bosonic dark matter. We study the cosmological production of dark matter in this model by elucidating the dynamics of two sources of scalar field misalignment generated during the radiation era. For large scalar masses (above order… ▽ More A light singlet scalar field feebly coupled through the super-renormalizable Higgs portal provides a minimal and well-motivated realization of ultra-light bosonic dark matter. We study the cosmological production of dark matter in this model by elucidating the dynamics of two sources of scalar field misalignment generated during the radiation era. For large scalar masses (above order $10^{-3}\,{\rm eV}$), dark matter is produced through thermal misalignment, by which the scalar field is driven towards large field values as a result of the finite-temperature effective potential. The dominance of thermal misalignment in this mass range leads to a sharp relic abundance prediction which is, to a significant extent, insensitive to the initial conditions of the scalar field. On the other hand, for low mass scalars (below order $10^{-5}\,{\rm eV}$), dark matter is produced via VEV misalignment, which is caused by the induced scalar field vacuum expectation value triggered by the electroweak phase transition. We show that the relic abundance in this low mass range is sensitive to the scalar field initial conditions. In the intermediate mass range, the relic abundance is a consequence of a competition between thermal misalignment and VEV misalignment, leading to novel forced resonance effects which cause a recurring enhancement and suppression in the late time oscillation amplitude as a function of the scalar mass. We compare our relic abundance predictions with constraints and projections from equivalence principle and inverse square law tests, stellar cooling, resonant molecular absorption, and observations of extra-galactic background light and diffuse X-ray backgrounds. New experimental ideas are needed to probe most of the cosmologically motivated regions of parameter space. △ Less

Submitted 12 January, 2024; v1 submitted 16 November, 2022; originally announced November 2022.

Comments: 34 pages, 6 figures; v2 : references added, JHEP version

Report number: PITT-PACC-2213

Prospects for exotic $h\rightarrow 4 τ$ decays in single and di-Higgs boson production at the LHC and future hadron colliders

Authors: Amit Adhikary, Shankha Banerjee, Rahool Kumar Barman, Brian Batell, Biplob Bhattacherjee, Camellia Bose, Zhuoni Qian, Michael Spannowsky

Abstract: We study the prospects for observing exotic decays of the Standard Model Higgs boson $h$ into light beyond the Standard Model scalars $a$ with mass $m_{a} \lesssim m_{h}/2$ in the single Higgs and Higgs pair production channels at the high luminosity run of the Large Hadron Collider (HL-LHC). Discovery prospects for single Higgs production in the gluon-gluon fusion and vector boson fusion modes wi… ▽ More We study the prospects for observing exotic decays of the Standard Model Higgs boson $h$ into light beyond the Standard Model scalars $a$ with mass $m_{a} \lesssim m_{h}/2$ in the single Higgs and Higgs pair production channels at the high luminosity run of the Large Hadron Collider (HL-LHC). Discovery prospects for single Higgs production in the gluon-gluon fusion and vector boson fusion modes with the Higgs boson decaying via the exotic mode $h \to aa \to 4τ$ are analyzed at the HL-LHC. The projected sensitivity for exotic Higgs decays in the non-resonant Higgs pair production channel $pp \to hh \to (h \to b\bar{b})(h \to aa \to 4τ) \to 2b4τ$ at the HL-LHC and a future $\sqrt{s}=100~$TeV hadron collider (FCC-hh) are also estimated. Furthermore, we study HL-LHC's potential reach for the Higgs-strahlung process in the $2b4τ$ channel, taking into account the contamination from non-resonant Higgs pair production. Finally, the potential reach for resonant Higgs pair production in the $2b4τ$ channel %$pp \to H \to (h \to b\bar{b})(h \to aa \to 4τ)$ at the HL-LHC is also explored for several choices of $\{m_{H},m_{a}\}$. Our studies suggest that significant improvements over existing bounds are achievable in several production channels, motivating new dedicated searches for $h \rightarrow aa \rightarrow 4 τ$ at the HL-LHC and future colliders. △ Less

Submitted 23 March, 2024; v1 submitted 14 November, 2022; originally announced November 2022.

Comments: 59 pages, 18 figures, 15 tables

Heavy Neutral Leptons at the Electron-Ion Collider

Authors: Brian Batell, Tathagata Ghosh, Tao Han, Keping Xie

Abstract: The future Electron-Ion Collider (EIC) at Brookhaven National Laboratory, along with its primary capacity to elucidate the nuclear structure, will offer new opportunities to probe physics beyond the Standard Model coupled to the electroweak sector. Among the best motivated examples of such new physics are new heavy neutral leptons (HNLs), which are likely to play a key role in neutrino mass genera… ▽ More The future Electron-Ion Collider (EIC) at Brookhaven National Laboratory, along with its primary capacity to elucidate the nuclear structure, will offer new opportunities to probe physics beyond the Standard Model coupled to the electroweak sector. Among the best motivated examples of such new physics are new heavy neutral leptons (HNLs), which are likely to play a key role in neutrino mass generation and lepton number violation. We study the capability of the EIC to search for HNLs, which can be produced in electron-proton collisions through charged current interactions as a consequence of their mixing with light neutrinos. We find that, with the EIC design energy and integrated luminosity, one is able to probe HNLs in the mass range of 1 GeV$-100$ GeV with mixing angles down to the order of $10^{-4} - 10^{-3}$ through the prompt decay, and $10^{-6} - 10^{-4}$ via the displaced decay signatures. We also consider the invisible mode where an HNL is undetected or decaying to dark sector particles. One could potentially probe heavy HNLs for mixing angles in the window $10^{-3}-10^{-2}$, provided SM background systematics can be brought under control. These searches are complementary to other probes of HNLs, such as neutrino-less double-$β$ decay, meson decay, fixed-target, and high-energy collider experiments. △ Less

Submitted 17 October, 2022; originally announced October 2022.

Comments: 31 pages, 15 figures, and 4 tables

Report number: HRI-RECAPP-2022-006, PITT-PACC-2107

TF08 Snowmass Report: BSM Model Building

Authors: Patrick J. Fox, Graham D. Kribs, Hitoshi Murayama, Amin Aboubrahim, Prateek Agrawal, Wolfgang Altmannshofer, Howard Baer, Avik Banerjee, Vernon Barger, Brian Batell, Kim V. Berghaus, Asher Berlin, Nikita Blinov, Diogo Buarque Franzosi, Giacomo Cacciapaglia, Cari Cesarotti, Nathaniel Craig, Csaba Csáki, Raffaele Tito D'Agnolo, Jordy De Vries, Aldo Deandrea, Matthew J. Dolan, Patrick Draper, Gilly Elor, JiJi Fan , et al. (31 additional authors not shown)

Abstract: We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for Snowmass 2021, focusing mainly on several whitepaper contributions to BSM model building (TF08) and closely related areas. We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for Snowmass 2021, focusing mainly on several whitepaper contributions to BSM model building (TF08) and closely related areas. △ Less

Submitted 6 October, 2022; originally announced October 2022.

Comments: 44 pages, 1 figure, Submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021). Topical Group Report for TF08 - BSM Model Building

Report of the Topical Group on Physics Beyond the Standard Model at Energy Frontier for Snowmass 2021

Authors: Tulika Bose, Antonio Boveia, Caterina Doglioni, Simone Pagan Griso, James Hirschauer, Elliot Lipeles, Zhen Liu, Nausheen R. Shah, Lian-Tao Wang, Kaustubh Agashe, Juliette Alimena, Sebastian Baum, Mohamed Berkat, Kevin Black, Gwen Gardner, Tony Gherghetta, Josh Greaves, Maxx Haehn, Phil C. Harris, Robert Harris, Julie Hogan, Suneth Jayawardana, Abraham Kahn, Jan Kalinowski, Simon Knapen , et al. (297 additional authors not shown)

Abstract: This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM mode… ▽ More This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection. △ Less

Submitted 18 October, 2022; v1 submitted 26 September, 2022; originally announced September 2022.

Comments: 108 pages + 38 pages references and appendix, 37 figures, Report of the Topical Group on Beyond the Standard Model Physics at Energy Frontier for Snowmass 2021. The first nine authors are the Conveners, with Contributions from the other authors

Dark Sector Physics at High-Intensity Experiments

Authors: Stefania Gori, Mike Williams, Phil Ilten, Nhan Tran, Gordan Krnjaic, Natalia Toro, Brian Batell, Nikita Blinov, Christopher Hearty, Robert McGehee, Philip Harris, Philip Schuster, Jure Zupan

Abstract: Is Dark Matter part of a Dark Sector? The possibility of a dark sector neutral under Standard Model (SM) forces furnishes an attractive explanation for the existence of Dark Matter (DM), and is a compelling new-physics direction to explore in its own right, with potential relevance to fundamental questions as varied as neutrino masses, the hierarchy problem, and the Universe's matter-antimatter as… ▽ More Is Dark Matter part of a Dark Sector? The possibility of a dark sector neutral under Standard Model (SM) forces furnishes an attractive explanation for the existence of Dark Matter (DM), and is a compelling new-physics direction to explore in its own right, with potential relevance to fundamental questions as varied as neutrino masses, the hierarchy problem, and the Universe's matter-antimatter asymmetry. Because dark sectors are generically weakly coupled to ordinary matter, and because they can naturally have MeV-to-GeV masses and respect the symmetries of the SM, they are only mildly constrained by high-energy collider data and precision atomic measurements. Yet upcoming and proposed intensity-frontier experiments will offer an unprecedented window into the physics of dark sectors, highlighted as a Priority Research Direction in the 2018 Dark Matter New Initiatives (DMNI) BRN report. Support for this program -- in the form of dark-sector analyses at multi-purpose experiments, realization of the intensity-frontier experiments receiving DMNI funds, an expansion of DMNI support to explore the full breadth of DM and visible final-state signatures (especially long-lived particles) called for in the BRN report, and support for a robust dark-sector theory effort -- will enable comprehensive exploration of low-mass thermal DM milestones, and greatly enhance the potential of intensity-frontier experiments to discover dark-sector particles decaying back to SM particles. △ Less

Submitted 10 September, 2022; originally announced September 2022.

Comments: Report of the RF6 Topical Group for Snowmass 2021

Exploring Dark Sector Portals with High Intensity Experiments

Authors: Brian Batell, Nikita Blinov, Christopher Hearty, Robert McGehee

Abstract: A broad program of searches at high intensity experiments during the coming decade and beyond will sensitively probe new light mediator particles interacting through the minimal renormalizable vector, Higgs, and neutrino portals as well as higher-dimension axion-like particle portals. These portals may link the visible and dark sectors and play a critical role in many proposed solutions to some of… ▽ More A broad program of searches at high intensity experiments during the coming decade and beyond will sensitively probe new light mediator particles interacting through the minimal renormalizable vector, Higgs, and neutrino portals as well as higher-dimension axion-like particle portals. These portals may link the visible and dark sectors and play a critical role in many proposed solutions to some of the big open questions in particle physics and cosmology. In this whitepaper, we survey the theoretical and experimental progress, status, and prospects in the study of minimal dark sector portals. △ Less

Submitted 29 September, 2022; v1 submitted 14 July, 2022; originally announced July 2022.

Comments: 21 pages, 8 figures; contribution to Snowmass 2021; v2 and v3: minor changes, references added

Dark Sector Studies with Neutrino Beams

Authors: Brian Batell, Joshua Berger, Vedran Brdar, Alan D. Bross, Janet M. Conrad, Patrick deNiverville, Valentina De Romeri, Bhaskar Dutta, Saeid Foroughi-Abari, Matheus Hostert, Joshua Isaacson, Ahmed Ismail, Sudip Jana, Wooyoung Jang, Nicholas W. Kamp, Kevin J. Kelly, Doojin Kim, Felix Kling, Mathieu Lamoureux, David McKeen, Jong-Chul Park, Gianluca Petrillo, Adam Ritz, Seodong Shin, Tyler B. Smith , et al. (7 additional authors not shown)

Abstract: An array of powerful neutrino-beam experiments will study the fundamental properties of neutrinos with unprecedented precision in the coming years. Along with their primary neutrino-physics motivations, there has been growing recognition that these experiments can carry out a rich program of searches for new, light, weakly-coupled particles that are part of a dark sector. In this white paper, we r… ▽ More An array of powerful neutrino-beam experiments will study the fundamental properties of neutrinos with unprecedented precision in the coming years. Along with their primary neutrino-physics motivations, there has been growing recognition that these experiments can carry out a rich program of searches for new, light, weakly-coupled particles that are part of a dark sector. In this white paper, we review the diverse theoretical motivations for dark sectors and the capabilities of neutrino beam experiments to probe a wide range of models and signatures. We also examine the potential obstacles that could limit these prospects and identify concrete steps needed to realize an impactful dark sector search program in this and coming decades. △ Less

Submitted 5 September, 2022; v1 submitted 14 July, 2022; originally announced July 2022.

Comments: 66 pages, 24 figures, 6 tables; Contribution to Snowmass 2021; v2: minor changes, references added

A Snowmass Whitepaper: Dark Matter Production at Intensity-Frontier Experiments

Authors: G. Krnjaic, N. Toro, A. Berlin, B. Batell, N. Blinov, L. Darme, P. DeNiverville, P. Harris, C. Hearty, M. Hostert, K. J. Kelly, D. McKeen, S. Trojanowski, Y. -D. Tsai

Abstract: Dark matter particles can be observably produced at intensity-frontier experiments, and opportunities in the next decade will explore important parameter space motivated by thermal DM models, the dark sector paradigm, and anomalies in data. This whitepaper describes the motivations, detection strategies, prospects and challenges for such searches, as well as synergies and complementarity both with… ▽ More Dark matter particles can be observably produced at intensity-frontier experiments, and opportunities in the next decade will explore important parameter space motivated by thermal DM models, the dark sector paradigm, and anomalies in data. This whitepaper describes the motivations, detection strategies, prospects and challenges for such searches, as well as synergies and complementarity both within RF6 and across HEP. △ Less

Submitted 5 September, 2022; v1 submitted 1 July, 2022; originally announced July 2022.

Comments: 37 pages, 13 figures, comments and feedback welcome. Updated discussion of proton beam dump searches, minor edits to text and title for clarity. Core message unchanged

DarkQuest: A dark sector upgrade to SpinQuest at the 120 GeV Fermilab Main Injector

Authors: Aram Apyan, Brian Batell, Asher Berlin, Nikita Blinov, Caspian Chaharom, Sergio Cuadra, Zeynep Demiragli, Adam Duran, Yongbin Feng, I. P. Fernando, Stefania Gori, Philip Harris, Duc Hoang, Dustin Keller, Elizabeth Kowalczyk, Monica Leys, Kun Liu, Ming Liu, Wolfgang Lorenzon, Petar Maksimovic, Cristina Mantilla Suarez, Hrachya Marukyan, Amitav Mitra, Yoshiyuki Miyachi, Patrick McCormack , et al. (14 additional authors not shown)

Abstract: Expanding the mass range and techniques by which we search for dark matter is an important part of the worldwide particle physics program. Accelerator-based searches for dark matter and dark sector particles are a uniquely compelling part of this program as a way to both create and detect dark matter in the laboratory and explore the dark sector by searching for mediators and excited dark matter p… ▽ More Expanding the mass range and techniques by which we search for dark matter is an important part of the worldwide particle physics program. Accelerator-based searches for dark matter and dark sector particles are a uniquely compelling part of this program as a way to both create and detect dark matter in the laboratory and explore the dark sector by searching for mediators and excited dark matter particles. This paper focuses on developing the DarkQuest experimental concept and gives an outlook on related enhancements collectively referred to as LongQuest. DarkQuest is a proton fixed-target experiment with leading sensitivity to an array of visible dark sector signatures in the MeV-GeV mass range. Because it builds off of existing accelerator and detector infrastructure, it offers a powerful but modest-cost experimental initiative that can be realized on a short timescale. △ Less

Submitted 15 March, 2022; originally announced March 2022.

Comments: Contribution to Snowmass 2021; 37 pages, 35 figures, 2 tables

The Present and Future Status of Heavy Neutral Leptons

Authors: Asli M. Abdullahi, Pablo Barham Alzas, Brian Batell, Alexey Boyarsky, Saneli Carbajal, Animesh Chatterjee, Jose I. Crespo-Anadon, Frank F. Deppisch, Albert De Roeck, Marco Drewes, Alberto Martin Gago, Rebeca Gonzalez Suarez, Evgueni Goudzovski, Athanasios Hatzikoutelis, Marco Hufnagel, Philip Ilten, Alexander Izmaylov, Kevin J. Kelly, Juraj Klaric, Joachim Kopp, Suchita Kulkarni, Mathieu Lamoureux, Gaia Lanfranchi, Jacobo Lopez-Pavon, Oleksii Mikulenko , et al. (20 additional authors not shown)

Abstract: The existence of non-zero neutrino masses points to the likely existence of multiple SM neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as Heavy Neutral Leptons (HNLs). In this white paper we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological… ▽ More The existence of non-zero neutrino masses points to the likely existence of multiple SM neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as Heavy Neutral Leptons (HNLs). In this white paper we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological impacts. We discuss the importance of continuing to search for HNLs, and its potential impact on our understanding on key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenarios. △ Less

Submitted 15 March, 2022; originally announced March 2022.

Comments: 82 pages, 34 figures. Contribution to Snowmass 2021

Heavy Neutral Lepton Searches at the Electron-Ion Collider: A Snowmass Whitepaper

Authors: Brian Batell, Tathagata Ghosh, Tao Han, Keping Xie

Abstract: In this whitepaper, we consider the model of heavy neutral leptons (HNLs) as an example to explore the potential of new physics searches at the Electron-Ion Collider (EIC). We propose two broad categories of search strategies depending on the HNL lifetime: direct searches for the prompt decay of HNLs with a short lifetime and displaced vertex searches for long-lived ones. After identifying the mos… ▽ More In this whitepaper, we consider the model of heavy neutral leptons (HNLs) as an example to explore the potential of new physics searches at the Electron-Ion Collider (EIC). We propose two broad categories of search strategies depending on the HNL lifetime: direct searches for the prompt decay of HNLs with a short lifetime and displaced vertex searches for long-lived ones. After identifying the most promising signals and the corresponding backgrounds, we perform a detailed simulation to estimate the sensitivity of the EIC to HNLs, accounting for detector thresholds, resolutions, and geometric acceptance. We derive projections for the EIC reach to the HNL squared mixing angle as a function of the HNL mass under the electron flavor mixing dominance hypothesis. Our findings indicate that the EIC can provide comparable sensitivity to the existing constraints for the prompt searches, while the displaced vertex searches can cover substantial new ground for HNLs in the 1-10 GeV mass range. Our proposed strategies are generally applicable to other new physics scenarios as well and motivate additional phenomenological exploration and dedicated future searches at the EIC. △ Less

Submitted 10 March, 2023; v1 submitted 13 March, 2022; originally announced March 2022.

Comments: Contribution to Snowmass 2021, 7 pages, 2 figures

Report number: PITT-PACC-2206

Review of Neutral Naturalness

Authors: Brian Batell, Matthew Low, Ethan T. Neil, Christopher B. Verhaaren

Abstract: The hierarchy between the mass parameter of the Higgs boson and larger mass scales becomes ever more puzzling as experiments explore higher energies. Neutral naturalness is the umbrella term for symmetry-based explanations for these hierarchies whose quark symmetry partners are not charged under the SU(3) color gauge group of the Standard Model. Though the first manifestations of this idea predate… ▽ More The hierarchy between the mass parameter of the Higgs boson and larger mass scales becomes ever more puzzling as experiments explore higher energies. Neutral naturalness is the umbrella term for symmetry-based explanations for these hierarchies whose quark symmetry partners are not charged under the SU(3) color gauge group of the Standard Model. Though the first manifestations of this idea predate the physics runs of the Large Hadron Collider, since the Higgs discovery this paradigm has grown and developed to include a wide variety of concrete realizations with connections to intriguing collider signals. Determining the phenomenology of such models often requires the characterization - typically relying on lattice calculations - of a new confining gauge symmetry. This presents additional motivation to further develop our understanding of nonperturbative field theory as well as to pursue specific lattice studies. The wide range of suggested hidden sectors also produces a variety of dark matter candidates, intersections with astrophysics and cosmology, and ties to neutrinos and flavor. In this review, we orient the reader within both this growing collection of specific models and the physical phenomena they produce. We also survey the often less familiar dynamics of hidden-sector glueballs and quirks. In addition to providing a guide to past efforts, we reveal interesting directions for further study. △ Less

Submitted 18 December, 2025; v1 submitted 10 March, 2022; originally announced March 2022.

Comments: 70 pages, 23 figures; v1: contribution to Snowmass 2021; v2: Minor typos, updated references. v3: major expansion of review for Physics Reports

Report number: PITT-PACC-2205

Journal ref: Phys. Rept. 1165 (2026) 1-49

The Forward Physics Facility at the High-Luminosity LHC

Authors: Jonathan L. Feng, Felix Kling, Mary Hall Reno, Juan Rojo, Dennis Soldin, Luis A. Anchordoqui, Jamie Boyd, Ahmed Ismail, Lucian Harland-Lang, Kevin J. Kelly, Vishvas Pandey, Sebastian Trojanowski, Yu-Dai Tsai, Jean-Marco Alameddine, Takeshi Araki, Akitaka Ariga, Tomoko Ariga, Kento Asai, Alessandro Bacchetta, Kincso Balazs, Alan J. Barr, Michele Battistin, Jianming Bian, Caterina Bertone, Weidong Bai , et al. (211 additional authors not shown)

Abstract: High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Mod… ▽ More High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential. △ Less

Submitted 9 March, 2022; originally announced March 2022.

Comments: 429 pages, contribution to Snowmass 2021

Report number: UCI-TR-2022-01, CERN-PBC-Notes-2022-001, FERMILAB-PUB-22-094-ND-SCD-T, INT-PUB-22-006, BONN-TH-2022-04

Physics Opportunities for the Fermilab Booster Replacement

Authors: John Arrington, Joshua Barrow, Brian Batell, Robert Bernstein, Nikita Blinov, S. J. Brice, Ray Culbertson, Patrick deNiverville, Vito Di Benedetto, Jeff Eldred, Angela Fava, Laura Fields, Alex Friedland, Andrei Gaponenko, Corrado Gatto, Stefania Gori, Roni Harnik, Richard J. Hill, Daniel M. Kaplan, Kevin J. Kelly, Mandy Kiburg, Tom Kobilarcik, Gordan Krnjaic, Gabriel Lee, B. R. Littlejohn , et al. (27 additional authors not shown)

Abstract: This white paper presents opportunities afforded by the Fermilab Booster Replacement and its various options. Its goal is to inform the design process of the Booster Replacement about the accelerator needs of the various options, allowing the design to be versatile and enable, or leave the door open to, as many options as possible. The physics themes covered by the paper include searches for dark… ▽ More This white paper presents opportunities afforded by the Fermilab Booster Replacement and its various options. Its goal is to inform the design process of the Booster Replacement about the accelerator needs of the various options, allowing the design to be versatile and enable, or leave the door open to, as many options as possible. The physics themes covered by the paper include searches for dark sectors and new opportunities with muons. △ Less

Submitted 8 March, 2022; originally announced March 2022.

Comments: Snowmass white paper

Report number: FERMILAB-FN-1145, LA-UR-22-21987

Hadrophilic Dark Sectors at the Forward Physics Facility

Authors: Brian Batell, Jonathan L. Feng, Max Fieg, Ahmed Ismail, Felix Kling, Roshan Mammen Abraham, Sebastian Trojanowski

Abstract: Models with light dark sector and dark matter particles motivate qualitatively new collider searches. Here we carry out a comprehensive study of hadrophilic models with U(1)$_B$ and U(1)$_{B-3L_τ}$ gauge bosons coupled to light dark matter. The new mediator particles in these models couple to quarks, but have suppressed couplings to leptons, providing a useful foil to the well-studied dark photon… ▽ More Models with light dark sector and dark matter particles motivate qualitatively new collider searches. Here we carry out a comprehensive study of hadrophilic models with U(1)$_B$ and U(1)$_{B-3L_τ}$ gauge bosons coupled to light dark matter. The new mediator particles in these models couple to quarks, but have suppressed couplings to leptons, providing a useful foil to the well-studied dark photon models. We consider current bounds from accelerator and collider searches, rare anomaly-induced decays, neutrino non-standard interactions, and dark matter direct detection. Despite the many existing constraints, these models predict a range of new signatures that can be seen in current and near future experiments, including dark gauge boson decays to the hadronic final states $π^+ π^- π^0$, $π^0 γ$, $K^+ K^-$, and $K_S K_L$ in FASER at LHC Run 3, enhancements of $ν_τ$ scattering rates in far-forward neutrino detectors, and thermal dark matter scattering in FLArE in the HL-LHC era. These models therefore motivate an array of different experiments in the far-forward region at the LHC, as could be accommodated in the proposed Forward Physics Facility. △ Less

Submitted 6 July, 2022; v1 submitted 19 November, 2021; originally announced November 2021.

Comments: v2: Updated to PRD version, results unchanged v3: Corrected a minor typo in Eq. 13, results unchanged

The Forward Physics Facility: Sites, Experiments, and Physics Potential

Authors: Luis A. Anchordoqui, Akitaka Ariga, Tomoko Ariga, Weidong Bai, Kincso Balazs, Brian Batell, Jamie Boyd, Joseph Bramante, Mario Campanelli, Adrian Carmona, Francesco G. Celiberto, Grigorios Chachamis, Matthew Citron, Giovanni De Lellis, Albert De Roeck, Hans Dembinski, Peter B. Denton, Antonia Di Crecsenzo, Milind V. Diwan, Liam Dougherty, Herbi K. Dreiner, Yong Du, Rikard Enberg, Yasaman Farzan, Jonathan L. Feng , et al. (56 additional authors not shown)

Abstract: The Forward Physics Facility (FPF) is a proposal to create a cavern with the space and infrastructure to support a suite of far-forward experiments at the Large Hadron Collider during the High Luminosity era. Located along the beam collision axis and shielded from the interaction point by at least 100 m of concrete and rock, the FPF will house experiments that will detect particles outside the acc… ▽ More The Forward Physics Facility (FPF) is a proposal to create a cavern with the space and infrastructure to support a suite of far-forward experiments at the Large Hadron Collider during the High Luminosity era. Located along the beam collision axis and shielded from the interaction point by at least 100 m of concrete and rock, the FPF will house experiments that will detect particles outside the acceptance of the existing large LHC experiments and will observe rare and exotic processes in an extremely low-background environment. In this work, we summarize the current status of plans for the FPF, including recent progress in civil engineering in identifying promising sites for the FPF and the experiments currently envisioned to realize the FPF's physics potential. We then review the many Standard Model and new physics topics that will be advanced by the FPF, including searches for long-lived particles, probes of dark matter and dark sectors, high-statistics studies of TeV neutrinos of all three flavors, aspects of perturbative and non-perturbative QCD, and high-energy astroparticle physics. △ Less

Submitted 25 May, 2022; v1 submitted 22 September, 2021; originally announced September 2021.

Comments: revised version, accepted by Physics Reports

Report number: BNL-222142-2021-FORE, CERN-PBC-Notes-2021-025, DESY-21-142, FERMILAB-CONF-21-452-AE-E-ND-PPD-T, KYUSHU-RCAPP-2021-01, LU TP 21-36, PITT-PACC-2118, SMU-HEP-21-10, UCI-TR-2021-22

Journal ref: Phys. Rept. 968 (2022), 1-50

Thermal Misalignment of Scalar Dark Matter

Authors: Brian Batell, Akshay Ghalsasi

Abstract: The conventional misalignment mechanism for scalar dark matter depends on the initial field value, which governs the oscillation amplitude and present-day abundance. We present a mechanism by which a feeble (Planck-suppressed) coupling of dark matter to a fermion in thermal equilibrium drives the scalar towards its high-temperature potential minimum at large field values, dynamically generating mi… ▽ More The conventional misalignment mechanism for scalar dark matter depends on the initial field value, which governs the oscillation amplitude and present-day abundance. We present a mechanism by which a feeble (Planck-suppressed) coupling of dark matter to a fermion in thermal equilibrium drives the scalar towards its high-temperature potential minimum at large field values, dynamically generating misalignment before oscillations begin. Unlike conventional misalignment production, the dark matter abundance is dictated by microphysics and not by initial conditions. As an application of the generic mechanism, we discuss a realistic scenario in which dark matter couples to the muon. △ Less

Submitted 9 September, 2021; originally announced September 2021.

Comments: 5 pages, 3 figures

Report number: PITT-PACC-2119

Renormalizable Models of Flavor-Specific Scalars

Authors: Brian Batell, Ayres Freitas, Ahmed Ismail, David McKeen, Mudit Rai

Abstract: New light singlet scalars with flavor-specific couplings represent a phenomenologically distinctive and flavor-safe alternative to the well-studied possibility of Higgs-portal scalars. However, in contrast to the Higgs portal, flavor-specific couplings require an ultraviolet completion involving new heavy states charged under the Standard Model gauge symmetries, leading to a host of additional nov… ▽ More New light singlet scalars with flavor-specific couplings represent a phenomenologically distinctive and flavor-safe alternative to the well-studied possibility of Higgs-portal scalars. However, in contrast to the Higgs portal, flavor-specific couplings require an ultraviolet completion involving new heavy states charged under the Standard Model gauge symmetries, leading to a host of additional novel phenomena. Focusing for concreteness on a scenario with up quark-specific couplings, we investigate two simple renormalizable completions, one with an additional vector-like quark and another featuring an extra scalar doublet. We consider the implications of naturalness, flavor- and CP-violation, electroweak precision observables, and direct searches for the new states at the LHC. These bounds, while being model-dependent, are shown to probe interesting regions in the parameter space of the scalar mass and its low-energy effective coupling, complementing the essential phenomenology of the low-energy effective theory at a variety of low and medium energy experiments. △ Less

Submitted 16 July, 2021; originally announced July 2021.

Comments: 42 pages, 8 figures

Report number: PITT-PACC-2114

Discovering Dark Matter at the LHC through Its Nuclear Scattering in Far-Forward Emulsion and Liquid Argon Detectors

Authors: Brian Batell, Jonathan L. Feng, Ahmed Ismail, Felix Kling, Roshan Mammen Abraham, Sebastian Trojanowski

Abstract: The LHC may produce light, weakly-interacting particles that decay to dark matter, creating an intense and highly collimated beam of dark matter particles in the far-forward direction. We investigate the prospects for detecting this dark matter in two far-forward detectors proposed for a future Forward Physics Facility: FASER$ν$2, a 10-tonne emulsion detector, and FLArE, a 10- to 100-tonne LArTPC.… ▽ More The LHC may produce light, weakly-interacting particles that decay to dark matter, creating an intense and highly collimated beam of dark matter particles in the far-forward direction. We investigate the prospects for detecting this dark matter in two far-forward detectors proposed for a future Forward Physics Facility: FASER$ν$2, a 10-tonne emulsion detector, and FLArE, a 10- to 100-tonne LArTPC. We focus here on nuclear scattering, including elastic scattering, resonant pion production, and deep inelastic scattering, and devise cuts that efficiently remove the neutrino-induced background. In the invisibly-decaying dark photon scenario, DM-nuclear scattering probes new parameter space for dark matter masses 5 MeV $\lesssim m_χ \lesssim$ 500 MeV. When combined with the DM-electron scattering studied previously, FASER$ν$2 and FLArE will be able to discover dark matter in a large swath of the cosmologically-favored parameter space with MeV $\lesssim m_χ \lesssim $ GeV. △ Less

Submitted 31 August, 2021; v1 submitted 1 July, 2021; originally announced July 2021.

Comments: 28 pages, 8 figures, 4 tables. Version published in PRD

Report number: PITT-PACC-2113, UCI-TR-2021-15

Journal ref: Phys. Rev. D 104, 035036 (2021)

Inelastic Dark Matter at the Fermilab Short Baseline Neutrino Program

Authors: Brian Batell, Joshua Berger, Luc Darmé, Claudia Frugiuele

Abstract: We study the sensitivity of the Fermilab Short-Baseline Neutrino (SBN) experiments, MicroBooNE, ICARUS, and SBND, to MeV- to GeV-scale inelastic dark matter interacting through a dark photon mediator. These models provide interesting scenarios of light thermal dark matter, which, while challenging to probe with direct and indirect detection experiments, are amenable to accelerator-based searches.… ▽ More We study the sensitivity of the Fermilab Short-Baseline Neutrino (SBN) experiments, MicroBooNE, ICARUS, and SBND, to MeV- to GeV-scale inelastic dark matter interacting through a dark photon mediator. These models provide interesting scenarios of light thermal dark matter, which, while challenging to probe with direct and indirect detection experiments, are amenable to accelerator-based searches. We consider production of the dark sector states with both the Fermilab Booster 8 GeV and NuMI 120 GeV proton beams and study the signatures of scattering and decay of the heavy excited dark state in the SBN detectors. These distinct signatures probe complementary regions of parameter space. All three experiments will be able to cover new ground, with an excellent near-term opportunity to search for cosmologically motivated targets explaining the observed dark matter abundance. △ Less

Submitted 8 June, 2021; originally announced June 2021.

Comments: 18 pages, 8 figures, 2 tables

Report number: PITT-PACC-2111

Detecting Dark Matter with Far-Forward Emulsion and Liquid Argon Detectors at the LHC

Authors: Brian Batell, Jonathan L. Feng, Sebastian Trojanowski

Abstract: New light particles may be produced in large numbers in the far-forward region at the LHC and then decay to dark matter, which can be detected through its scattering in far-forward experiments. We consider the example of invisibly-decaying dark photons, which decay to dark matter through $A' \to χχ$. The dark matter may then be detected through its scattering off electrons $χe^- \to χe^-$. We cons… ▽ More New light particles may be produced in large numbers in the far-forward region at the LHC and then decay to dark matter, which can be detected through its scattering in far-forward experiments. We consider the example of invisibly-decaying dark photons, which decay to dark matter through $A' \to χχ$. The dark matter may then be detected through its scattering off electrons $χe^- \to χe^-$. We consider the discovery potential of detectors placed on the beam collision axis 480 m from the ATLAS interaction point, including an emulsion detector (FASER$ν$2) and, for the first time, a Forward Liquid Argon Experiment (FLArE). For each of these detector technologies, we devise cuts that effectively separate the single $e^-$ signal from the leading neutrino- and muon-induced backgrounds. We find that 10- to 100-tonne detectors may detect hundreds to thousands of dark matter events in the HL-LHC era and will sensitively probe the thermal relic region of parameter space. These results motivate the construction of far-forward emulsion and liquid argon detectors at the LHC, as well as a suitable location to accommodate them, such as the proposed Forward Physics Facility. △ Less

Submitted 16 April, 2021; v1 submitted 25 January, 2021; originally announced January 2021.

Comments: 35 pages, 10 figures, 7 tables, references added, matches published version

Report number: PITT-PACC-2101, UCI-TR-2021-01

Journal ref: Phys. Rev. D 103, 075023 (2021)

An Update to the Letter of Intent for MATHUSLA: Search for Long-Lived Particles at the HL-LHC

Authors: Cristiano Alpigiani, Juan Carlos Arteaga-Velázquez, Austin Ball, Liron Barak, Jared Barron, Brian Batell, James Beacham, Yan Benhammo, Karen Salomé Caballero-Mora, Paolo Camarri, Roberto Cardarelli, John Paul Chou, Wentao Cui, David Curtin, Miriam Diamond, Keith R. Dienes, Liam Andrew Dougherty, Giuseppe Di Sciascio, Marco Drewes, Erez Etzion, Rouven Essig, Jared Evans, Arturo Fernández Téllez, Oliver Fischer, Jim Freeman , et al. (58 additional authors not shown)

Abstract: We report on recent progress in the design of the proposed MATHUSLA Long Lived Particle (LLP) detector for the HL-LHC, updating the information in the original Letter of Intent (LoI), see CDS:LHCC-I-031, arXiv:1811.00927. A suitable site has been identified at LHC Point 5 that is closer to the CMS Interaction Point (IP) than assumed in the LoI. The decay volume has been increased from 20 m to 25 m… ▽ More We report on recent progress in the design of the proposed MATHUSLA Long Lived Particle (LLP) detector for the HL-LHC, updating the information in the original Letter of Intent (LoI), see CDS:LHCC-I-031, arXiv:1811.00927. A suitable site has been identified at LHC Point 5 that is closer to the CMS Interaction Point (IP) than assumed in the LoI. The decay volume has been increased from 20 m to 25 m in height. Engineering studies have been made in order to locate much of the decay volume below ground, bringing the detector even closer to the IP. With these changes, a 100 m x 100 m detector has the same physics reach for large c$τ$ as the 200 m x 200 m detector described in the LoI and other studies. The performance for small c$τ$ is improved because of the proximity to the IP. Detector technology has also evolved while retaining the strip-like sensor geometry in Resistive Plate Chambers (RPC) described in the LoI. The present design uses extruded scintillator bars read out using wavelength shifting fibers and silicon photomultipliers (SiPM). Operations will be simpler and more robust with much lower operating voltages and without the use of greenhouse gases. Manufacturing is straightforward and should result in cost savings. Understanding of backgrounds has also significantly advanced, thanks to new simulation studies and measurements taken at the MATHUSLA test stand operating above ATLAS in 2018. We discuss next steps for the MATHUSLA collaboration, and identify areas where new members can make particularly important contributions. △ Less

Submitted 3 September, 2020; originally announced September 2020.

Comments: 22 pages + references, 12 Figures

Report number: CERN-LHCC-2020-014, LHCC-I-031-ADD-1

Dark Scalars and Heavy Neutral Leptons at DarkQuest

Authors: Brian Batell, Jared A. Evans, Stefania Gori, Mudit Rai

Abstract: The proposed DarkQuest beam dump experiment, a modest upgrade to the existing SeaQuest/SpinQuest experiment, has great potential for uncovering new physics within a dark sector. We explore both the near-term and long-term prospects for observing two distinct, highly-motivated hidden sector benchmark models: heavy neutral leptons and Higgs-mixed scalars. We comprehensively examine the particle prod… ▽ More The proposed DarkQuest beam dump experiment, a modest upgrade to the existing SeaQuest/SpinQuest experiment, has great potential for uncovering new physics within a dark sector. We explore both the near-term and long-term prospects for observing two distinct, highly-motivated hidden sector benchmark models: heavy neutral leptons and Higgs-mixed scalars. We comprehensively examine the particle production and detector acceptance at DarkQuest, including an updated treatment of meson production, and light scalar production through both bremsstrahlung and gluon-gluon fusion. In both benchmark models, DarkQuest will provide an opportunity to probe previously inaccessible interesting regions of parameter space on a fairly short timescale when compared to other proposed experiments. △ Less

Submitted 18 August, 2020; originally announced August 2020.

Comments: 30 pages, 11 figures

Breaking Mirror Twin Color

Authors: Brian Batell, Wei Hu, Christopher B. Verhaaren

Abstract: We investigate simple extensions of the Mirror Twin Higgs model in which the twin color gauge symmetry and the discrete $Z_2$ mirror symmetry are spontaneously broken. This is accomplished in a minimal way by introducing a single new colored triplet, sextet, or octet scalar field and its twin along with a suitable scalar potential. This spontaneous $Z_2$ breaking allows for a phenomenologically vi… ▽ More We investigate simple extensions of the Mirror Twin Higgs model in which the twin color gauge symmetry and the discrete $Z_2$ mirror symmetry are spontaneously broken. This is accomplished in a minimal way by introducing a single new colored triplet, sextet, or octet scalar field and its twin along with a suitable scalar potential. This spontaneous $Z_2$ breaking allows for a phenomenologically viable alignment of the electroweak vacuum, and leads to dramatic differences between the visible and mirror sectors with regard to the residual gauge symmetries at low energies, color confinement scales, and particle spectra. In particular, several of our models feature a remnant $SU(2)$ or $SO(3)$ twin color gauge symmetry with a very low confinement scale in comparison to $Λ_{\rm QCD}$. Furthermore, couplings between the colored scalar and matter provide a new dynamical source of twin fermion masses, and due to the mirror symmetry, these lead to a variety of correlated visible sector effects that can be probed through precision measurements and collider searches. △ Less

Submitted 11 August, 2020; v1 submitted 22 April, 2020; originally announced April 2020.

Comments: 45 pages, 2 figures; Updated to published version

Report number: PITT-PACC-2002; UCI-TR-2020-08

Journal ref: JHEP 2008 (2020) 009

Probing the Higgs Portal at the Fermilab Short-Baseline Neutrino Experiments

Authors: Brian Batell, Joshua Berger, Ahmed Ismail

Abstract: The Fermilab Short-Baseline Neutrino (SBN) experiments, MicroBooNE, ICARUS, and SBND, are expected to have significant sensitivity to light weakly coupled hidden sector particles. Here we study the capability of the SBN experiments to probe dark scalars interacting through the Higgs portal. We investigate production of dark scalars using both the Fermilab Booster 8 GeV and NuMI 120 GeV proton beam… ▽ More The Fermilab Short-Baseline Neutrino (SBN) experiments, MicroBooNE, ICARUS, and SBND, are expected to have significant sensitivity to light weakly coupled hidden sector particles. Here we study the capability of the SBN experiments to probe dark scalars interacting through the Higgs portal. We investigate production of dark scalars using both the Fermilab Booster 8 GeV and NuMI 120 GeV proton beams, simulating kaons decaying to dark scalars and taking into account the beamline geometry. We also investigate strategies to mitigate backgrounds from beam-related neutrino scattering events. We find that SBND, with its comparatively short ${\cal O}(100\ {\rm m})$ baseline, will have the best sensitivity to scalars produced with Booster, while ICARUS, with its large detector volume, will provide the best limits on off-axis dark scalar production from NuMI. The SBN experiments can provide leading tests of dark scalars with masses in the 50 - 350 MeV range in the near term. Our results motivate dedicated experimental searches for dark scalars and other long-lived hidden sector states at these experiments. △ Less

Submitted 8 October, 2025; v1 submitted 25 September, 2019; originally announced September 2019.

Comments: 34 pages, 16 figures, updated references, v3: minor corrections to Figure 1; main results unchanged; v4: minor clarifications surround equation (4)

Report number: PITT-PACC-1906, OSU-HEP-19-07

Journal ref: Phys. Rev. D 100, 115039 (2019)

White Paper on New Opportunities at the Next-Generation Neutrino Experiments (Part 1: BSM Neutrino Physics and Dark Matter)

Authors: C. A. Argüelles, A. J. Aurisano, B. Batell, J. Berger, M. Bishai, T. Boschi, N. Byrnes, A. Chatterjee, A. Chodos, T. Coan, Y. Cui, A. de Gouvêa, P. B. Denton, A. De Roeck, W. Flanagan, R. P. Gandrajula, A. Hatzikoutelis, M. Hostert, B. Jones, B. J. Kayser, K. J. Kelly, D. Kim, J. Kopp, A. Kubik, K. Lang , et al. (25 additional authors not shown)

Abstract: With the advent of a new generation of neutrino experiments which leverage high-intensity neutrino beams for precision measurements, it is timely to explore physics topics beyond the standard neutrino-related physics. Given that the realm of beyond the standard model (BSM) physics has been mostly sought at high-energy regimes at colliders, such as the LHC at CERN, the exploration of BSM physics in… ▽ More With the advent of a new generation of neutrino experiments which leverage high-intensity neutrino beams for precision measurements, it is timely to explore physics topics beyond the standard neutrino-related physics. Given that the realm of beyond the standard model (BSM) physics has been mostly sought at high-energy regimes at colliders, such as the LHC at CERN, the exploration of BSM physics in neutrino experiments will enable complementary measurements at the energy regimes that balance that of the LHC. This is in concert with new ideas for high-intensity beams for fixed target and beam-dump experiments world-wide, e.g., those at CERN. The combination of the high intensity proton beam facilities and massive detectors for precision neutrino oscillation parameter measurements and for CP violation phase measurements will help make BSM physics reachable even in low energy regimes in accelerator based experiments. Large mass detectors with highly precise tracking and energy measurements, excellent timing resolution, and low energy thresholds will enable searches for BSM phenomena from cosmogenic origin, as well. Therefore, it is conceivable that BSM topics in the next generation neutrino experiments could be the dominant physics topics in the foreseeable future, as the precision of the neutrino oscillation parameter and CPV measurements continues to improve. In this spirit, this white paper provides a review of the current landscape of BSM theory in neutrino experiments in two selected areas of the BSM topics - dark matter and neutrino related BSM - and summarizes the current results from existing neutrino experiments to set benchmarks for both theory and experiment. This paper then provides a review of upcoming neutrino experiments throughout the next 10 - 15 year time scale and their capabilities to set the foundation for potential reach in BSM physics in the two aforementioned themes. △ Less

Submitted 18 October, 2019; v1 submitted 18 July, 2019; originally announced July 2019.

Report number: Reports on Progress in Physics, Volume 83, Number 12

Breaking Mirror Twin Hypercharge

Authors: Brian Batell, Christopher B. Verhaaren

Abstract: The Twin Higgs scenario stabilizes the Higgs mass through an approximate global symmetry and has remained natural in the face of increasingly stringent LHC bounds on colored top partners. Two basic structural questions in this framework concern the nature of the twin hypercharge gauge symmetry and the origin of the $\mathbb{Z}_2$ symmetry breaking needed to achieve the correct vacuum alignment. Bo… ▽ More The Twin Higgs scenario stabilizes the Higgs mass through an approximate global symmetry and has remained natural in the face of increasingly stringent LHC bounds on colored top partners. Two basic structural questions in this framework concern the nature of the twin hypercharge gauge symmetry and the origin of the $\mathbb{Z}_2$ symmetry breaking needed to achieve the correct vacuum alignment. Both questions are addressed in a simple extension of the Mirror Twin Higgs model with an exact $\mathbb{Z}_2$ symmetry and a scalar field that spontaneously breaks both twin hypercharge and $\mathbb{Z}_2$. Due to the $\mathbb{Z}_2$ symmetry and an approximate $U(2)$ symmetry in the potential, a new hypercharge scalar appears in the visible sector and, like the Higgs, is a pseudo-Nambu-Goldstone boson with a weak-scale mass. Couplings between the hypercharge scalar and matter provide a new dynamical source of twin sector fermion masses. Depending on the nature and size of these couplings, a variety of experimental signatures may arise, including quark and lepton flavor violation, neutrino masses and mixings as well as direct collider probes of the hypercharged scalar. These signals are correlated with the twin matter spectrum, which can differ dramatically from the visible one, including dynamical realizations of fraternal-like scenarios. △ Less

Submitted 7 December, 2019; v1 submitted 23 April, 2019; originally announced April 2019.

Comments: 34 pages, 3 figures; Updated to published version

Report number: PITT-PACC-1902

Journal ref: JHEP 1912 (2019) 010

Probing Light Dark Matter with a Hadrophilic Scalar Mediator

Authors: Brian Batell, Ayres Freitas, Ahmed Ismail, David McKeen

Abstract: We investigate the thermal cosmology and terrestrial and astrophysical phenomenology of a sub-GeV hadrophilic dark sector. The specific construction explored in this work features a Dirac fermion dark matter candidate interacting with a light scalar mediator that dominantly couples to the up-quark. The correct freeze-out relic abundance may be achieved via dark matter annihilation directly to hadr… ▽ More We investigate the thermal cosmology and terrestrial and astrophysical phenomenology of a sub-GeV hadrophilic dark sector. The specific construction explored in this work features a Dirac fermion dark matter candidate interacting with a light scalar mediator that dominantly couples to the up-quark. The correct freeze-out relic abundance may be achieved via dark matter annihilation directly to hadrons or through secluded annihilation to scalar mediators. A rich and distinctive phenomenology is present in this scenario, with probes arising from precision meson decays, proton beam dump experiments, colliders, direct detection experiments, supernovae, and nucleosynthesis. In the future, experiments such as NA62, REDTOP, SHiP, SBND, and NEWS-G will be able to explore a significant portion of the cosmologically motivated parameter space. △ Less

Submitted 12 December, 2018; originally announced December 2018.

Comments: 36 pages, 2 figures

Report number: PITT-PACC-1817

Journal ref: Phys. Rev. D 100, 095020 (2019)

Dark Matter Search in Nucleon, Pion, and Electron Channels from a Proton Beam Dump with MiniBooNE

Authors: MiniBooNE-DM Collaboration, A. A. Aguilar-Arevalo, M. Backfish, A. Bashyal, B. Batell, B. C. Brown, R. Carr, A. Chatterjee, R. L. Cooper, P. deNiverville, R. Dharmapalan, Z. Djurcic, R. Ford, F. G. Garcia, G. T. Garvey, J. Grange, J. A. Green, E. -C. Huang, W. Huelsnitz, I. L. de Icaza Astiz, G. Karagiorgi, T. Katori, W. Ketchum, T. Kobilarcik, Q. Liu , et al. (20 additional authors not shown)

Abstract: A search for sub-GeV dark matter produced from collisions of the Fermilab 8 GeV Booster protons with a steel beam dump was performed by the MiniBooNE-DM Collaboration using data from $1.86 \times 10^{20}$ protons on target in a dedicated run. The MiniBooNE detector, consisting of 818 tons of mineral oil and located 490 meters downstream of the beam dump, is sensitive to a variety of dark matter in… ▽ More A search for sub-GeV dark matter produced from collisions of the Fermilab 8 GeV Booster protons with a steel beam dump was performed by the MiniBooNE-DM Collaboration using data from $1.86 \times 10^{20}$ protons on target in a dedicated run. The MiniBooNE detector, consisting of 818 tons of mineral oil and located 490 meters downstream of the beam dump, is sensitive to a variety of dark matter initiated scattering reactions. Three dark matter interactions are considered for this analysis: elastic scattering off nucleons, inelastic neutral pion production, and elastic scattering off electrons. Multiple data sets were used to constrain flux and systematic errors, and time-of-flight information was employed to increase sensitivity to higher dark matter masses. No excess from the background predictions was observed, and 90$\%$ confidence level limits were set on the vector portal and leptophobic dark matter models. New parameter space is excluded in the vector portal dark matter model with a dark matter mass between 5 and 50$\,\mathrm{MeV}\,c^{-2}$. The reduced neutrino flux allowed to test if the MiniBooNE neutrino excess scales with the production of neutrinos. No excess of neutrino oscillation events were measured ruling out models that scale solely by number of protons on target independent of beam configuration at 4.6$σ$. △ Less

Submitted 29 March, 2019; v1 submitted 16 July, 2018; originally announced July 2018.

Comments: 19 pages, 25 figures, Data release: http://www-boone.fnal.gov/for_physicists/data_release/dark_matter_prd/ v2 Updated to published version

Report number: LA-UR-18-26421, FERMILAB-PUB-18-334-ND

Journal ref: Phys. Rev. D 98, 112004 (2018)

Long-Lived Particles at the Energy Frontier: The MATHUSLA Physics Case

Authors: David Curtin, Marco Drewes, Matthew McCullough, Patrick Meade, Rabindra N. Mohapatra, Jessie Shelton, Brian Shuve, Elena Accomando, Cristiano Alpigiani, Stefan Antusch, Juan Carlos Arteaga-Velázquez, Brian Batell, Martin Bauer, Nikita Blinov, Karen Salomé Caballero-Mora, Jae Hyeok Chang, Eung Jin Chun, Raymond T. Co, Timothy Cohen, Peter Cox, Nathaniel Craig, Csaba Csáki, Yanou Cui, Francesco D'Eramo, Luigi Delle Rose , et al. (63 additional authors not shown)

Abstract: We examine the theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of Standard Model (SM) extensions. LLPs are a common prediction of a wide range of theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). I… ▽ More We examine the theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of Standard Model (SM) extensions. LLPs are a common prediction of a wide range of theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). In most cases the LLP lifetime can be treated as a free parameter from the $μ$m scale up to the Big Bang Nucleosynthesis limit of $\sim 10^7$m. Neutral LLPs with lifetimes above $\sim$ 100m are particularly difficult to probe, as the sensitivity of the LHC main detectors is limited by challenging backgrounds, triggers, and small acceptances. MATHUSLA is a proposal for a minimally instrumented, large-volume surface detector near ATLAS or CMS. It would search for neutral LLPs produced in HL-LHC collisions by reconstructing displaced vertices (DVs) in a low-background environment, extending the sensitivity of the main detectors by orders of magnitude in the long-lifetime regime. In this white paper we study the LLP physics opportunities afforded by a MATHUSLA-like detector at the HL-LHC. We develop a model-independent approach to describe the sensitivity of MATHUSLA to BSM LLP signals, and compare it to DV and missing energy searches at ATLAS or CMS. We then explore the BSM motivations for LLPs in considerable detail, presenting a large number of new sensitivity studies. While our discussion is especially oriented towards the long-lifetime regime at MATHUSLA, this survey underlines the importance of a varied LLP search program at the LHC in general. By synthesizing these results into a general discussion of the top-down and bottom-up motivations for LLP searches, it is our aim to demonstrate the exceptional strength and breadth of the physics case for the construction of the MATHUSLA detector. △ Less

Submitted 5 March, 2019; v1 submitted 19 June, 2018; originally announced June 2018.

Comments: 213 pages, 73 figures. Extended Section 2 to add more detailed discussion of LLP reconstruction and analysis, and background rejection. Updated comparison of MATHUSLA RH neutrino sensitivity to other experiments. Updated analysis of long-lived ALPs produced in weak-scale processes and decaying to jets. Various clarifications, fixed typos, and added references. Results and conclusions unchanged

Flavor-specific scalar mediators

Authors: Brian Batell, Ayres Freitas, Ahmed Ismail, David McKeen

Abstract: New singlet scalar bosons have broad phenomenological utility and feature prominently in many extensions of the Standard Model. Such scalars are often taken to have Higgs-like couplings to SM fermions in order to evade stringent flavor bounds, e.g. by assuming Minimal Flavor Violation (MFV), which leads to a rather characteristic phenomenology. Here we describe an alternative approach, based on an… ▽ More New singlet scalar bosons have broad phenomenological utility and feature prominently in many extensions of the Standard Model. Such scalars are often taken to have Higgs-like couplings to SM fermions in order to evade stringent flavor bounds, e.g. by assuming Minimal Flavor Violation (MFV), which leads to a rather characteristic phenomenology. Here we describe an alternative approach, based on an effective field theory framework for a new scalar that dominantly couples to one specific SM fermion mass eigenstate. A simple flavor hypothesis ensures adequate suppression of new flavor changing neutral currents. We consider radiatively generated flavor changing neutral currents and scalar potential terms in such theories, demonstrating that they are often suppressed by small Yukawa couplings, and also describe the role of $CP$ symmetry. We further demonstrate that such scalars can have masses that are significantly below the electroweak scale while still being natural, provided they are sufficiently weakly coupled to ordinary matter. In comparison to other flavor scenarios, our framework is rather versatile since a single (or a few) desired scalar couplings may be investigated in isolation. We illustrate this by discussing in detail the examples of an up-specific scalar mediator to dark matter and a muon-specific scalar that may address the $\sim 3 σ$ muon anomalous magnetic moment discrepancy. △ Less

Submitted 18 October, 2018; v1 submitted 28 December, 2017; originally announced December 2017.

Comments: 37 pages, 7 figures. v2: references added, minor changes, conclusions unchanged; matches version published in PRD

Journal ref: Phys. Rev. D 98, 055026 (2018)