Showing 1–50 of 61 results for author: Harris, P

Dissecting Parton Showers with Multi-Point Energy Correlators

Authors: Mark Gonzalez, Philip Harris, Kyle Lee, Ian Moult, Simon Rothman

Abstract: The last several years have seen tremendous progress in the ability to both compute and measure multi-point correlations in energy flux. The highly differential nature of energy correlators makes them ideal probes of multi-collinear factorization and azimuthal structure within jets. In this paper, we explore the phenomenology of four-point correlators in jet substructure. We identify experimentall… ▽ More The last several years have seen tremendous progress in the ability to both compute and measure multi-point correlations in energy flux. The highly differential nature of energy correlators makes them ideal probes of multi-collinear factorization and azimuthal structure within jets. In this paper, we explore the phenomenology of four-point correlators in jet substructure. We identify experimentally realizable projections that probe different factorization channels onto splitting tensors and splitting functions. We perform a detailed phenomenological study using both Herwig and Pythia. By comparing parton shower results with analytic calculations in kinematic limits, we are able to disentangle intrinsic spin correlations from kinematic azimuthal correlations. In experimentally accessible kinematic regions, we find the spin correlations are subdominant, strongly motivating a complete calculation of the four-point correlator in QCD to provide a test of the parton shower results. We also present parameterizations and analysis algorithms that can be used experimentally. Our work sets the stage for the experimental measurement of these observables at the LHC, and their use as probes of the next generation of parton showers. △ Less

Submitted 8 July, 2026; originally announced July 2026.

Comments: 42 pages, many beautiful figures

Flash from the Past: New Gamma-Ray Constraints on Light CP-even Scalar from SN1987A

Authors: Yue Yu, Writasree Maitra, P. S. Bhupal Dev, Jean-Franccois Fortin, Steven P. Harris, Kuver Sinha, Yongchao Zhang

Abstract: We derive new constraints on light CP-even scalars using old gamma-ray observations in the direction of SN1987A by the Solar Maximum Mission (SMM) satellite. Light scalars can be abundantly produced in the supernova core via the nucleon bremsstrahlung process, can stream out of the supernova-environment and decay into photons -- either primary photons or secondary photons from lepton-antilepton pa… ▽ More We derive new constraints on light CP-even scalars using old gamma-ray observations in the direction of SN1987A by the Solar Maximum Mission (SMM) satellite. Light scalars can be abundantly produced in the supernova core via the nucleon bremsstrahlung process, can stream out of the supernova-environment and decay into photons -- either primary photons or secondary photons from lepton-antilepton pairs -- thus leading to a gamma-ray signal. From the non-observation of excess photon flux by SMM after the detection of the neutrino burst from SN1987A, we set new constraints on the mixing angle of the CP-even scalar with the Standard Model Higgs boson. △ Less

Submitted 9 March, 2026; originally announced March 2026.

Comments: 15 pages, 11 figures

Shock-induced chiral magnetic effect

Authors: Steven P. Harris, Srimoyee Sen

Abstract: Weak-interaction-mediated chiral imbalance generation in idealized massless electrons during core-collapse supernovae was once proposed to be the source of strong magnetic fields found in neutron stars. The effect goes by the name of chiral plasma instability (CPI). However, it was found that a finite electron mass damps out this process, inactivating the instability and preventing magnetic field… ▽ More Weak-interaction-mediated chiral imbalance generation in idealized massless electrons during core-collapse supernovae was once proposed to be the source of strong magnetic fields found in neutron stars. The effect goes by the name of chiral plasma instability (CPI). However, it was found that a finite electron mass damps out this process, inactivating the instability and preventing magnetic field growth. In this work we show that the instability can survive in the presence of abrupt density and temperature perturbation that drives the system sufficiently far out of weak equilibrium. As an example, we work with such perturbations generated by shockwaves which are common during both core collapse as well as neutron star mergers. We find that the chiral imbalance resulting from shock waves, under the right conditions of density and temperature, can sustain the chiral plasma instability despite the damping from the electron mass. Additionally, in an already magnetized medium, the chiral magnetic effect resulting from shock wave density and temperature perturbation can generate substantial ohmic heating. Our results imply that shockwaves generated in core-collapse supernovae and merging neutron stars can act as a source of strong heating in a magnetized medium as well as CPI. △ Less

Submitted 10 August, 2026; v1 submitted 24 February, 2026; originally announced February 2026.

Comments: 22 pages, 8 figures (published version)

Bulk viscosity from neutron decays to dark baryons in neutron star matter

Authors: Steven P. Harris, C. J. Horowitz

Abstract: The existence of a dark baryon that mixes with the neutron leads to the possibility of neutron decay into a dark sector. Such dark decays have been studied as possibly relevant for the neutron decay anomaly and for their potential impacts on neutron stars. The most popular formulation is a dark sector consisting of a dark baryon $χ$ and a dark scalar $φ$, where a neutron in vacuum decays 1% or les… ▽ More The existence of a dark baryon that mixes with the neutron leads to the possibility of neutron decay into a dark sector. Such dark decays have been studied as possibly relevant for the neutron decay anomaly and for their potential impacts on neutron stars. The most popular formulation is a dark sector consisting of a dark baryon $χ$ and a dark scalar $φ$, where a neutron in vacuum decays 1% or less of the time via the channel $n\rightarrow χ+φ$. In this work, we consider the effect of this additional neutron decay channel on transport in neutrons star mergers. We find that the neutron dark decay rate in medium is quite slow, and thus the dark baryons modify the dense matter equation of state in a way that decreases the Urca bulk viscosity by, at most, a factor of 2-3. However, if the neutron dark decay was to occur more rapidly, then the bulk viscosity at merger temperatures of tens of MeV would be strongly enhanced, potentially rapidly damping oscillations in merger environments and therefore providing a signature of slowly equilibrating matter in the merger. △ Less

Submitted 16 April, 2026; v1 submitted 30 September, 2025; originally announced September 2025.

Comments: v2: Matches version accepted by Phys.Rev.D

t-channel dark matter at the LHC -- a whitepaper

Authors: Chiara Arina, Benjamin Fuks, Luca Panizzi, Michael J. Baker, Alan S. Cornell, Jan Heisig, Benedikt Maier, Rute Pedro, Dominique Trischuk, Diyar Agin, Alexandre Arbey, Giorgio Arcadi, Emanuele Bagnaschi, Kehang Bai, Disha Bhatia, Mathias Becker, Alexander Belyaev, Ferdinand Benoit, Monika Blanke, Jackson Burzynski, Jonathan M. Butterworth, Antimo Cagnotta, Lorenzo Calibbi, Linda M. Carpenter, Xabier Cid Vidal , et al. (45 additional authors not shown)

Abstract: This report, summarising work achieved in the context of the LHC Dark Matter Working Group, investigates the phenomenology of $t$-channel dark matter models, spanning minimal setups with a single dark matter candidate and mediator to more complex constructions closer to UV-complete models. For each considered class of models, we examine collider, cosmological and astrophysical implications. In add… ▽ More This report, summarising work achieved in the context of the LHC Dark Matter Working Group, investigates the phenomenology of $t$-channel dark matter models, spanning minimal setups with a single dark matter candidate and mediator to more complex constructions closer to UV-complete models. For each considered class of models, we examine collider, cosmological and astrophysical implications. In addition, we explore scenarios with either promptly decaying or long-lived particles, as well as featuring diverse dark matter production mechanisms in the early universe. By providing a unified analysis framework, numerical tools and guidelines, this work aims to support future experimental and theoretical efforts in exploring $t$-channel dark matter models at colliders and in cosmology. △ Less

Submitted 14 September, 2025; v1 submitted 14 April, 2025; originally announced April 2025.

Comments: 101 pages, 55 figures; report of the LHC Dark Matter Working Group on t-channel dark matter models; version accepted by EPJC

Report number: CERN-LPCC-2025-001, IRMP-CP3-25-07, TTK-25-07

Journal ref: Eur.Phys.J.C 85 (2025) 975

Product Manifold Machine Learning for Physics

Authors: Nathaniel S. Woodward, Sang Eon Park, Gaia Grosso, Jeffrey Krupa, Philip Harris

Abstract: Physical data are representations of the fundamental laws governing the Universe, hiding complex compositional structures often well captured by hierarchical graphs. Hyperbolic spaces are endowed with a non-Euclidean geometry that naturally embeds those structures. To leverage the benefits of non-Euclidean geometries in representing natural data we develop machine learning on… ▽ More Physical data are representations of the fundamental laws governing the Universe, hiding complex compositional structures often well captured by hierarchical graphs. Hyperbolic spaces are endowed with a non-Euclidean geometry that naturally embeds those structures. To leverage the benefits of non-Euclidean geometries in representing natural data we develop machine learning on $\mathcal P \mathcal M$ spaces, Cartesian products of constant curvature Riemannian manifolds. As a use case we consider the classification of "jets", sprays of hadrons and other subatomic particles produced by the hadronization of quarks and gluons in collider experiments. We compare the performance of $\mathcal P \mathcal M$-MLP and $\mathcal P \mathcal M$-Transformer models across several possible representations. Our experiments show that $\mathcal P \mathcal M$ representations generally perform equal or better to fully Euclidean models of similar size, with the most significant gains found for highly hierarchical jets and small models. We discover significant correlation between the degree of hierarchical structure at a per-jet level and classification performance with the $\mathcal P \mathcal M$-Transformer in top tagging benchmarks. This is a promising result highlighting a potential direction for further improving machine learning model performance through tailoring geometric representation at a per-sample level in hierarchical datasets. These results reinforce the view of geometric representation as a key parameter in maximizing both performance and efficiency of machine learning on natural data. △ Less

Submitted 9 December, 2024; originally announced December 2024.

MACK: Mismodeling Addressed with Contrastive Knowledge

Authors: Liam Rankin Sheldon, Dylan Sheldon Rankin, Philip Harris

Abstract: The use of machine learning methods in high energy physics typically relies on large volumes of precise simulation for training. As machine learning models become more complex they can become increasingly sensitive to differences between this simulation and the real data collected by experiments. We present a generic methodology based on contrastive learning which is able to greatly mitigate this… ▽ More The use of machine learning methods in high energy physics typically relies on large volumes of precise simulation for training. As machine learning models become more complex they can become increasingly sensitive to differences between this simulation and the real data collected by experiments. We present a generic methodology based on contrastive learning which is able to greatly mitigate this negative effect. Crucially, the method does not require prior knowledge of the specifics of the mismodeling. While we demonstrate the efficacy of this technique using the task of jet-tagging at the Large Hadron Collider, it is applicable to a wide array of different tasks both in and out of the field of high energy physics. △ Less

Submitted 17 October, 2024; originally announced October 2024.

Comments: 13 pages, 4 figures, Submission to SciPost

Journal ref: SciPost Phys. 18, 150 (2025)

Re-Simulation-based Self-Supervised Learning for Pre-Training Foundation Models

Authors: Philip Harris, Michael Kagan, Jeffrey Krupa, Benedikt Maier, Nathaniel Woodward

Abstract: Self-Supervised Learning (SSL) is at the core of training modern large machine learning models, providing a scheme for learning powerful representations that can be used in a variety of downstream tasks. However, SSL strategies must be adapted to the type of training data and downstream tasks required. We propose RS3L ("Re-simulation-based self-supervised representation learning"), a novel simulat… ▽ More Self-Supervised Learning (SSL) is at the core of training modern large machine learning models, providing a scheme for learning powerful representations that can be used in a variety of downstream tasks. However, SSL strategies must be adapted to the type of training data and downstream tasks required. We propose RS3L ("Re-simulation-based self-supervised representation learning"), a novel simulation-based SSL strategy that employs a method of re-simulation to drive data augmentation for contrastive learning in the physical sciences, particularly, in fields that rely on stochastic simulators. By intervening in the middle of the simulation process and re-running simulation components downstream of the intervention, we generate multiple realizations of an event, thus producing a set of augmentations covering all physics-driven variations available in the simulator. Using experiments from high-energy physics, we explore how this strategy may enable the development of a foundation model; we show how RS3L pre-training enables powerful performance in downstream tasks such as discrimination of a variety of objects and uncertainty mitigation. In addition to our results, we make the RS3L dataset publicly available for further studies on how to improve SSL strategies. △ Less

Submitted 24 February, 2025; v1 submitted 11 March, 2024; originally announced March 2024.

Comments: 14 pages, 8 figures

Journal ref: Phys. Rev. D 111 (2025) 3, 032010

New Constraints on Axion-Like Particles from IXPE Polarization Data for Magnetars

Authors: Ephraim Gau, Fazlollah Hajkarim, Steven P. Harris, P. S. Bhupal Dev, Jean-Francois Fortin, Henric Krawczynski, Kuver Sinha

Abstract: We derive new constraints on axion-like particles (ALPs) using precision $X$-ray polarization studies of magnetars. Specifically, we use the first detection of polarized $X$-rays from the magnetars 4U 0142+61 and 1RXS J170849.0-400910 by the Imaging $X$-ray Polarimetry Explorer (IXPE) to place bounds on the product of the ALP-photon and ALP-nucleon couplings, $g_{aγ}g_{aN}$, with $g_{aN}$ being re… ▽ More We derive new constraints on axion-like particles (ALPs) using precision $X$-ray polarization studies of magnetars. Specifically, we use the first detection of polarized $X$-rays from the magnetars 4U 0142+61 and 1RXS J170849.0-400910 by the Imaging $X$-ray Polarimetry Explorer (IXPE) to place bounds on the product of the ALP-photon and ALP-nucleon couplings, $g_{aγ}g_{aN}$, with $g_{aN}$ being responsible for ALP production in the core of the magnetar and $g_{aγ}$ controlling the ALP-photon conversion probability in the magnetosphere. These bounds are most sensitive to the magnetar core temperature, and we use two benchmark values of $1\times 10^8$ K and $5\times 10^8$ K to derive our constraints. For the latter choice, our bounds are competitive with the existing bounds on the coupling product coming from a combination of CAST (for $g_{aγ}$) and SN1987A (for $g_{aN}$). We advocate for more precise and extensive observational campaigns in the higher end of the $2~-~8~$keV spectral window, where ALP-induced polarization is the strongest. We further advocate for hard $X$-ray polarization studies of young, hot, near-Earth magnetars with strong magnetic fields. △ Less

Submitted 21 December, 2023; originally announced December 2023.

Comments: 27 pages, 9 figures, 3 tables

Report number: INT-PUB-23-053

Chained Quantile Morphing with Normalizing Flows

Authors: Samuel Bright-Thonney, Philip Harris, Patrick McCormack, Simon Rothman

Abstract: Accounting for inaccuracies in Monte Carlo simulations is a crucial step in any high energy physics analysis. It becomes especially important when training machine learning models, which can amplify simulation inaccuracies and introduce large discrepancies and systematic uncertainties when the model is applied to data. In this paper, we introduce a method to transform simulated events to better ma… ▽ More Accounting for inaccuracies in Monte Carlo simulations is a crucial step in any high energy physics analysis. It becomes especially important when training machine learning models, which can amplify simulation inaccuracies and introduce large discrepancies and systematic uncertainties when the model is applied to data. In this paper, we introduce a method to transform simulated events to better match data using normalizing flows, a class of deep learning-based density estimation models. Our proposal uses a technique called chained quantile morphing, which corrects a set of observables by iteratively shifting each entry according to a conditonal cumulative density function. We demonstrate the technique on a realistic particle physics dataset, and compare it to a neural network-based reweighting method. We also introduce a new contrastive learning technique to correct high dimensional particle-level inputs, which naively cannot be efficiently corrected with morphing strategies. △ Less

Submitted 27 September, 2023; originally announced September 2023.

Comments: 13 pages, 7 figures, 3 tables

Feebly Interacting Particles: FIPs 2022 workshop report

Authors: C. Antel, M. Battaglieri, J. Beacham, C. Boehm, O. Buchmüller, F. Calore, P. Carenza, B. Chauhan, P. Cladè, P. Coloma, P. Crivelli, V. Dandoy, L. Darmé, B. Dey, F. F. Deppisch, A. De Roeck, M. Drewes, B. Echenard, V. V. Flambaum, P. Foldenauer, C. Gatti, M. Giannotti, A. Golutvin, M. C. Gonzalez-Garcia, S. Gori , et al. (53 additional authors not shown)

Abstract: Particle physics today faces the challenge of explaining the mystery of dark matter, the origin of matter over anti-matter in the Universe, the origin of the neutrino masses, the apparent fine-tuning of the electro-weak scale, and many other aspects of fundamental physics. Perhaps the most striking frontier to emerge in the search for answers involves new physics at mass scales comparable to famil… ▽ More Particle physics today faces the challenge of explaining the mystery of dark matter, the origin of matter over anti-matter in the Universe, the origin of the neutrino masses, the apparent fine-tuning of the electro-weak scale, and many other aspects of fundamental physics. Perhaps the most striking frontier to emerge in the search for answers involves new physics at mass scales comparable to familiar matter, below the GeV-scale, or even radically below, down to sub-eV scales, and with very feeble interaction strength. New theoretical ideas to address dark matter and other fundamental questions predict such feebly interacting particles (FIPs) at these scales, and indeed, existing data provide numerous hints for such possibility. A vibrant experimental program to discover such physics is under way, guided by a systematic theoretical approach firmly grounded on the underlying principles of the Standard Model. This document represents the report of the FIPs 2022 workshop, held at CERN between the 17 and 21 October 2022 and aims to give an overview of these efforts, their motivations, and the decadal goals that animate the community involved in the search for FIPs. △ Less

Submitted 2 May, 2023; originally announced May 2023.

Comments: 383 pp, 176 figures

Report number: CERN-TH-2023-061 DESY-23-050 FERMILAB-PUB-23-149-PPD INFN-23-14-LNF JLAB-PHY-23-3789 LA-UR-23-21432 MITP-23-015

First Constraints on the Photon Coupling of Axion-like Particles from Multimessenger Studies of the Neutron Star Merger GW170817

Authors: P. S. Bhupal Dev, Jean-François Fortin, Steven P. Harris, Kuver Sinha, Yongchao Zhang

Abstract: We use multimessenger observations of the neutron star merger event GW170817 to derive new constraints on axion-like particles (ALPs) coupling to photons. ALPs are produced via Primakoff and photon coalescence processes in the merger, escape the remnant and decay back into two photons, giving rise to a photon signal approximately along the line-of-sight to the merger. We analyze the spectral and t… ▽ More We use multimessenger observations of the neutron star merger event GW170817 to derive new constraints on axion-like particles (ALPs) coupling to photons. ALPs are produced via Primakoff and photon coalescence processes in the merger, escape the remnant and decay back into two photons, giving rise to a photon signal approximately along the line-of-sight to the merger. We analyze the spectral and temporal information of the ALP-induced photon signal, and use the Fermi-LAT observations of GW170817 to derive our new ALP constraints. We also show the improved prospects with future MeV gamma-ray missions, taking the spectral and temporal coverage of Fermi-LAT as an example. △ Less

Submitted 27 February, 2024; v1 submitted 1 May, 2023; originally announced May 2023.

Comments: 8+8 pages, 4+5 figures, some updates and minor changes, version to appear in PRL

Report number: INT-PUB-23-014

Journal ref: Phys. Rev. Lett. 132, 101003 (2024)

Search for ultralight axion dark matter in a side-band analysis of a 199Hg free-spin precession signal

Authors: C. Abel, N. J. Ayres, G. Ban, G. Bison, K. Bodek, V. Bondar, E. Chanel, C. B. Crawford, M. Daum, B. Dechenaux, S. Emmenegger, P. Flaux, W. C. Griffith, P. G. Harris, Y. Kermaidic, K. Kirch, S. Komposch, P. A. Koss, J. Krempel, B. Lauss, T. Lefort, O. Naviliat-Cuncic, P. Mohanmurthy, D. Pais, F. M. Piegsa , et al. (13 additional authors not shown)

Abstract: Ultra-low-mass axions are a viable dark matter candidate and may form a coherently oscillating classical field. Nuclear spins in experiments on Earth might couple to this oscillating axion dark-matter field, when propagating on Earth's trajectory through our Galaxy. This spin coupling resembles an oscillating pseudo-magnetic field which modulates the spin precession of nuclear spins. Here we repor… ▽ More Ultra-low-mass axions are a viable dark matter candidate and may form a coherently oscillating classical field. Nuclear spins in experiments on Earth might couple to this oscillating axion dark-matter field, when propagating on Earth's trajectory through our Galaxy. This spin coupling resembles an oscillating pseudo-magnetic field which modulates the spin precession of nuclear spins. Here we report on the null result of a demonstration experiment searching for a frequency modulation of the free spin-precession signal of \magHg in a \SI{1}{\micro\tesla} magnetic field. Our search covers the axion mass range $10^{-16}~\textrm{eV} \lesssim m_a \lesssim 10^{-13}~\textrm{eV}$ and achieves a peak sensitivity to the axion-nucleon coupling of $g_{aNN} \approx 3.5 \times 10^{-6}~\textrm{GeV}^{-1}$. △ Less

Submitted 31 March, 2023; v1 submitted 2 December, 2022; originally announced December 2022.

Comments: 18 pages, 4 images, submitted to SciPost Physics

Journal ref: SciPost Phys. 15, 058 (2023)

Snowmass 2021 Dark Matter Complementarity Report

Authors: Antonio Boveia, Mohamed Berkat, Thomas Y. Chen, Aman Desai, Caterina Doglioni, Alex Drlica-Wagner, Susan Gardner, Stefania Gori, Joshua Greaves, Patrick Harding, Philip C. Harris, W. Hugh Lippincott, Maria Elena Monzani, Katherine Pachal, Chanda Prescod-Weinstein, Gray Rybka, Bibhushan Shakya, Jessie Shelton, Tracy R. Slatyer, Amanda Steinhebel, Philip Tanedo, Natalia Toro, Yun-Tse Tsai, Mike Williams, Lindley Winslow , et al. (2 additional authors not shown)

Abstract: The fundamental nature of Dark Matter is a central theme of the Snowmass 2021 process, extending across all Frontiers. In the last decade, advances in detector technology, analysis techniques and theoretical modeling have enabled a new generation of experiments and searches while broadening the types of candidates we can pursue. Over the next decade, there is great potential for discoveries that w… ▽ More The fundamental nature of Dark Matter is a central theme of the Snowmass 2021 process, extending across all Frontiers. In the last decade, advances in detector technology, analysis techniques and theoretical modeling have enabled a new generation of experiments and searches while broadening the types of candidates we can pursue. Over the next decade, there is great potential for discoveries that would transform our understanding of dark matter. In the following, we outline a road map for discovery developed in collaboration among the Frontiers. A strong portfolio of experiments that delves deep, searches wide, and harnesses the complementarity between techniques is key to tackling this complicated problem, requiring expertise, results, and planning from all Frontiers of the Snowmass 2021 process. △ Less

Submitted 15 November, 2022; v1 submitted 13 November, 2022; originally announced November 2022.

Comments: 10 pages, 5 figures. Version prepared for inclusion in the Snowmass Book. Extended version at arXiv:2210.01770. v2: fixed authors and affiliations

Long Range Plan: Dense matter theory for heavy-ion collisions and neutron stars

Authors: Alessandro Lovato, Travis Dore, Robert D. Pisarski, Bjoern Schenke, Katerina Chatziioannou, Jocelyn S. Read, Philippe Landry, Pawel Danielewicz, Dean Lee, Scott Pratt, Fabian Rennecke, Hannah Elfner, Veronica Dexheimer, Rajesh Kumar, Michael Strickland, Johannes Jahan, Claudia Ratti, Volodymyr Vovchenko, Mikhail Stephanov, Dekrayat Almaalol, Gordon Baym, Mauricio Hippert, Jacquelyn Noronha-Hostler, Jorge Noronha, Enrico Speranza , et al. (39 additional authors not shown)

Abstract: Since the release of the 2015 Long Range Plan in Nuclear Physics, major events have occurred that reshaped our understanding of quantum chromodynamics (QCD) and nuclear matter at large densities, in and out of equilibrium. The US nuclear community has an opportunity to capitalize on advances in astrophysical observations and nuclear experiments and engage in an interdisciplinary effort in the theo… ▽ More Since the release of the 2015 Long Range Plan in Nuclear Physics, major events have occurred that reshaped our understanding of quantum chromodynamics (QCD) and nuclear matter at large densities, in and out of equilibrium. The US nuclear community has an opportunity to capitalize on advances in astrophysical observations and nuclear experiments and engage in an interdisciplinary effort in the theory of dense baryonic matter that connects low- and high-energy nuclear physics, astrophysics, gravitational waves physics, and data science △ Less

Submitted 7 November, 2022; v1 submitted 3 November, 2022; originally announced November 2022.

Comments: 70 pages, 3 figures, White Paper for the Long Range Plan for Nuclear Science

Report number: LA-UR-22-31648

Snowmass 2021 Cross Frontier Report: Dark Matter Complementarity (Extended Version)

Authors: Antonio Boveia, Mohamed Berkat, Thomas Y. Chen, Aman Desai, Caterina Doglioni, Alex Drlica-Wagner, Susan Gardner, Stefania Gori, Joshua Greaves, Patrick Harding, Philip C. Harris, W. Hugh Lippincott, Maria Elena Monzani, Katherine Pachal, Chanda Prescod-Weinstein, Gray Rybka, Bibhushan Shakya, Jessie Shelton, Tracy R. Slatyer, Amanda Steinhebel, Philip Tanedo, Natalia Toro, Yun-Tse Tsai, Mike Williams, Lindley Winslow , et al. (2 additional authors not shown)

Abstract: The fundamental nature of Dark Matter is a central theme of the Snowmass 2021 process, extending across all frontiers. In the last decade, advances in detector technology, analysis techniques and theoretical modeling have enabled a new generation of experiments and searches while broadening the types of candidates we can pursue. Over the next decade, there is great potential for discoveries that w… ▽ More The fundamental nature of Dark Matter is a central theme of the Snowmass 2021 process, extending across all frontiers. In the last decade, advances in detector technology, analysis techniques and theoretical modeling have enabled a new generation of experiments and searches while broadening the types of candidates we can pursue. Over the next decade, there is great potential for discoveries that would transform our understanding of dark matter. In the following, we outline a road map for discovery developed in collaboration among the frontiers. A strong portfolio of experiments that delves deep, searches wide, and harnesses the complementarity between techniques is key to tackling this complicated problem, requiring expertise, results, and planning from all Frontiers of the Snowmass 2021 process. △ Less

Submitted 23 July, 2024; v1 submitted 4 October, 2022; originally announced October 2022.

Comments: v3: fixed authorlist (on arXiv only)

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

Neural Embedding: Learning the Embedding of the Manifold of Physics Data

Authors: Sang Eon Park, Philip Harris, Bryan Ostdiek

Abstract: In this paper, we present a method of embedding physics data manifolds with metric structure into lower dimensional spaces with simpler metrics, such as Euclidean and Hyperbolic spaces. We then demonstrate that it can be a powerful step in the data analysis pipeline for many applications. Using progressively more realistic simulated collisions at the Large Hadron Collider, we show that this embedd… ▽ More In this paper, we present a method of embedding physics data manifolds with metric structure into lower dimensional spaces with simpler metrics, such as Euclidean and Hyperbolic spaces. We then demonstrate that it can be a powerful step in the data analysis pipeline for many applications. Using progressively more realistic simulated collisions at the Large Hadron Collider, we show that this embedding approach learns the underlying latent structure. With the notion of volume in Euclidean spaces, we provide for the first time a viable solution to quantifying the true search capability of model agnostic search algorithms in collider physics (i.e. anomaly detection). Finally, we discuss how the ideas presented in this paper can be employed to solve many practical challenges that require the extraction of physically meaningful representations from information in complex high dimensional datasets. △ Less

Submitted 14 August, 2022; v1 submitted 10 August, 2022; originally announced August 2022.

Snowmass White Paper: New flavors and rich structures in dark sectors

Authors: Philip Harris, Philip Schuster, Jure Zupan

Abstract: Dark matter can be part of a dark sector with non-minimal couplings to the Standard Model. Compared to many (minimal) benchmark models, such scenarios can result in significant modifications in experimental signatures and strongly impact experimental search sensitivity. In this white paper, we review several non-minimal dark sector models, including phenomenological consequences: models explaining… ▽ More Dark matter can be part of a dark sector with non-minimal couplings to the Standard Model. Compared to many (minimal) benchmark models, such scenarios can result in significant modifications in experimental signatures and strongly impact experimental search sensitivity. In this white paper, we review several non-minimal dark sector models, including phenomenological consequences: models explaining $(g-2)_μ$, inelastic dark matter, strongly interacting massive particles as dark matter candidates, and axions with flavorful couplings. The present exclusions and projected experimental sensitivities on these example dark sector models illustrate the robustness of the growing dark sector experimental effort -- both the broadness and the precision of existing searches -- probing theoretically interesting parameter space. They also illustrate some of the unique complementarity of different experimental approaches. △ Less

Submitted 18 July, 2022; originally announced July 2022.

Comments: Contribution to Snowmass 2021

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

Summarizing experimental sensitivities of collider experiments to dark matter models and comparison to other experiments

Authors: Antonio Boveia, Caterina Doglioni, Boyu Gao, Josh Greaves, Philip Harris, Katherine Pachal, Etienne Dreyer, Giuliano Gustavino, Robert Harris, Daniel Hayden, Tetiana Hrynova, Ashutosh Kotwal, Jared Little, Kevin Black, Tulika Bose, Yuze Chen, Sridhara Dasu, Haoyi Jia, Deborah Pinna, Varun Sharma, Nikhilesh Venkatasubramanian, Carl Vuosalo

Abstract: Comparisons of the coverage of current and proposed dark matter searches can help us to understand the context in which a discovery of particle dark matter would be made. In some scenarios, a discovery could be reinforced by information from multiple, complementary types of experiments; in others, only one experiment would see a signal, giving only a partial, more ambiguous picture; in still other… ▽ More Comparisons of the coverage of current and proposed dark matter searches can help us to understand the context in which a discovery of particle dark matter would be made. In some scenarios, a discovery could be reinforced by information from multiple, complementary types of experiments; in others, only one experiment would see a signal, giving only a partial, more ambiguous picture; in still others, no experiment would be sensitive and new approaches would be needed. In this whitepaper, we present an update to a similar study performed for the European Strategy Briefing Book performed within the dark matter at the Energy Frontier (EF10) Snowmass Topical Group We take as a starting point a set of projections for future collider facilities and a method of graphical comparisons routinely performed for LHC DM searches using simplified models recommended by the LHC Dark Matter Working Group and also used for the BSM and dark matter chapters of the European Strategy Briefing Book. These comparisons can also serve as launching point for cross-frontier discussions about dark matter complementarity. △ Less

Submitted 7 June, 2022; originally announced June 2022.

Comments: Submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021)

Displaying dark matter constraints from colliders with varying simplified model parameters

Authors: Andreas Albert, Antonio Boveia, Oleg Brandt, Eric Corrigan, Zeynep Demiragli, Caterina Doglioni, Etienne Dreyer, Boyu Gao, Josh Greaves, Ulrich Haisch, Philip Harris, Greg Landsberg, Alexander Moreno, Katherine Pachal, Priscilla Pani, Federica Piazza, Tim M. P. Tait, David Yu, Felix Yu, Lian-Tao Wang

Abstract: The search for dark matter is one of the main science drivers of the particle and astroparticle physics communities. Determining the nature of dark matter will require a broad approach, with a range of experiments pursuing different experimental hypotheses. Within this search program, collider experiments provide insights on dark matter which are complementary to direct/indirect detection experime… ▽ More The search for dark matter is one of the main science drivers of the particle and astroparticle physics communities. Determining the nature of dark matter will require a broad approach, with a range of experiments pursuing different experimental hypotheses. Within this search program, collider experiments provide insights on dark matter which are complementary to direct/indirect detection experiments and to astrophysical evidence. To compare results from a wide variety of experiments, a common theoretical framework is required. The ATLAS and CMS experiments have adopted a set of simplified models which introduce two new particles, a dark matter particle and a mediator, and whose interaction strengths are set by the couplings of the mediator. So far, the presentation of LHC and future hadron collider results has focused on four benchmark scenarios with specific coupling values within these simplified models. In this work, we describe ways to extend those four benchmark scenarios to arbitrary couplings, and release the corresponding code for use in further studies. This will allow for more straightforward comparison of collider searches to accelerator experiments that are sensitive to smaller couplings, such as those for the US Community Study on the Future of Particle Physics (Snowmass 2021), and will give a more complete picture of the coupling dependence of dark matter collider searches when compared to direct and indirect detection searches. By using semi-analytical methods to rescale collider limits, we drastically reduce the computing resources needed relative to traditional approaches based on the generation of additional simulated signal samples. △ Less

Submitted 22 March, 2022; originally announced March 2022.

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 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

Light scalars in neutron star mergers

Authors: P. S. Bhupal Dev, Jean-François Fortin, Steven P. Harris, Kuver Sinha, Yongchao Zhang

Abstract: Due to their unique set of multimessenger signals, neutron star mergers have emerged as a novel environment for studies of new physics beyond the Standard Model (SM). As a case study, we consider the simplest extension of the SM scalar sector involving a light CP-even scalar singlet $S$ mixing with the SM Higgs boson. These $S$ particles can be produced abundantly in neutron star mergers via the n… ▽ More Due to their unique set of multimessenger signals, neutron star mergers have emerged as a novel environment for studies of new physics beyond the Standard Model (SM). As a case study, we consider the simplest extension of the SM scalar sector involving a light CP-even scalar singlet $S$ mixing with the SM Higgs boson. These $S$ particles can be produced abundantly in neutron star mergers via the nucleon bremsstrahlung process. We show that the $S$ particles may either be trapped in or stream freely out of the merger remnant, depending on the $S$ mass, its mixing with the SM Higgs boson, and the temperature and baryon density in the merger. In the free-streaming region, the scalar $S$ will provide an extra channel to cool down the merger remnant, with cooling timescales as small as ${\cal O}$(ms). On the other hand, in the trapped region, the Bose gas of $S$ particles could contribute a larger thermal conductivity than the trapped neutrinos in some parts of the parameter space, thus leading to faster thermal equilibration than expected. Therefore, future observations of the early postmerger phase of a neutron star merger could effectively probe a unique range of the $S$ parameter space, largely complementary to the existing and future laboratory and supernova limits. In view of these results, we hope the merger simulation community will be motivated to implement the effects of light CP-even scalars into their simulations in both the free-streaming and trapped regimes. △ Less

Submitted 29 December, 2021; v1 submitted 10 November, 2021; originally announced November 2021.

Comments: 44 pages, 10 figures v2: Matches version to be published in JCAP. Added a discussion of the Boltzmann suppression of the emissivity (fig 5) that occurs for scalar particles with m_S >> T. Added some material on the role of pions

Report number: INT-PUB-21-024

Unveiling Hidden Physics at the LHC

Authors: Oliver Fischer, Bruce Mellado, Stefan Antusch, Emanuele Bagnaschi, Shankha Banerjee, Geoff Beck, Benedetta Belfatto, Matthew Bellis, Zurab Berezhiani, Monika Blanke, Bernat Capdevila, Kingman Cheung, Andreas Crivellin, Nishita Desai, Bhupal Dev, Rohini Godbole, Tao Han, Philip Harris, Martin Hoferichter, Matthew Kirk, Suchita Kulkarni, Clemens Lange, Kati Lassila-Perini, Zhen Liu, Farvah Mahmoudi , et al. (8 additional authors not shown)

Abstract: The field of particle physics is at the crossroads. The discovery of a Higgs-like boson completed the Standard Model (SM), but the lacking observation of convincing resonances Beyond the SM (BSM) offers no guidance for the future of particle physics. On the other hand, the motivation for New Physics has not diminished and is, in fact, reinforced by several striking anomalous results in many experi… ▽ More The field of particle physics is at the crossroads. The discovery of a Higgs-like boson completed the Standard Model (SM), but the lacking observation of convincing resonances Beyond the SM (BSM) offers no guidance for the future of particle physics. On the other hand, the motivation for New Physics has not diminished and is, in fact, reinforced by several striking anomalous results in many experiments. Here we summarise the status of the most significant anomalies, including the most recent results for the flavour anomalies, the multi-lepton anomalies at the LHC, the Higgs-like excess at around 96 GeV, and anomalies in neutrino physics, astrophysics, cosmology, and cosmic rays. While the LHC promises up to 4/ab of integrated luminosity and far-reaching physics programmes to unveil BSM physics, we consider the possibility that the latter could be tested with present data, but that systemic shortcomings of the experiments and their search strategies may preclude their discovery for several reasons, including: final states consisting in soft particles only, associated production processes, QCD-like final states, close-by SM resonances, and SUSY scenarios where no missing energy is produced. New search strategies could help to unveil the hidden BSM signatures, devised by making use of the CERN open data as a new testing ground. We discuss the CERN open data with its policies, challenges, and potential usefulness for the community. We showcase the example of the CMS collaboration, which is the only collaboration regularly releasing some of its data. We find it important to stress that individuals using public data for their own research does not imply competition with experimental efforts, but rather provides unique opportunities to give guidance for further BSM searches by the collaborations. Wide access to open data is paramount to fully exploit the LHCs potential. △ Less

Submitted 13 September, 2021; originally announced September 2021.

Comments: Whitepaper including input from the workshop "Unveiling Hidden Physics Beyond the Standard Model at the LHC" (1-3 March 2021, online), 70 pages plus references, 17 figures, 7 tables

A FAIR and AI-ready Higgs boson decay dataset

Authors: Yifan Chen, E. A. Huerta, Javier Duarte, Philip Harris, Daniel S. Katz, Mark S. Neubauer, Daniel Diaz, Farouk Mokhtar, Raghav Kansal, Sang Eon Park, Volodymyr V. Kindratenko, Zhizhen Zhao, Roger Rusack

Abstract: To enable the reusability of massive scientific datasets by humans and machines, researchers aim to adhere to the principles of findability, accessibility, interoperability, and reusability (FAIR) for data and artificial intelligence (AI) models. This article provides a domain-agnostic, step-by-step assessment guide to evaluate whether or not a given dataset meets these principles. We demonstrate… ▽ More To enable the reusability of massive scientific datasets by humans and machines, researchers aim to adhere to the principles of findability, accessibility, interoperability, and reusability (FAIR) for data and artificial intelligence (AI) models. This article provides a domain-agnostic, step-by-step assessment guide to evaluate whether or not a given dataset meets these principles. We demonstrate how to use this guide to evaluate the FAIRness of an open simulated dataset produced by the CMS Collaboration at the CERN Large Hadron Collider. This dataset consists of Higgs boson decays and quark and gluon background, and is available through the CERN Open Data Portal. We use additional available tools to assess the FAIRness of this dataset, and incorporate feedback from members of the FAIR community to validate our results. This article is accompanied by a Jupyter notebook to visualize and explore this dataset. This study marks the first in a planned series of articles that will guide scientists in the creation of FAIR AI models and datasets in high energy particle physics. △ Less

Submitted 16 February, 2022; v1 submitted 4 August, 2021; originally announced August 2021.

Comments: 13 pages, 3 figures. v2: Accepted to Nature Scientific Data. Learn about the FAIR4HEP project at https://fair4hep.github.io. See our invited Behind the Paper Blog in Springer Nature Research Data Community at https://go.nature.com/3oMVYxo

ACM Class: I.2; J.2

Journal ref: Scientific Data volume 9, Article number: 31 (2022)

Axions: From Magnetars and Neutron Star Mergers to Beam Dumps and BECs

Authors: Jean-François Fortin, Huai-Ke Guo, Steven P. Harris, Doojin Kim, Kuver Sinha, Chen Sun

Abstract: We review topics in searches for axion-like-particles (ALPs), covering material that is complementary to other recent reviews. The first half of our review covers ALPs in the extreme environments of neutron star cores, the magnetospheres of highly magnetized neutron stars (magnetars), and in neutron star mergers. The focus is on possible signals of ALPs in the photon spectrum of neutron stars and… ▽ More We review topics in searches for axion-like-particles (ALPs), covering material that is complementary to other recent reviews. The first half of our review covers ALPs in the extreme environments of neutron star cores, the magnetospheres of highly magnetized neutron stars (magnetars), and in neutron star mergers. The focus is on possible signals of ALPs in the photon spectrum of neutron stars and gravitational wave/electromagnetic signals from neutron star mergers. We then review recent developments in laboratory-produced ALP searches, focusing mainly on accelerator-based facilities including beam-dump type experiments and collider experiments. We provide a general-purpose discussion of the ALP search pipeline from production to detection, in steps, and our discussion is straightforwardly applicable to most beam-dump type and reactor experiments. We end with a selective look at the rapidly developing field of ultralight dark matter, specifically the formation of Bose-Einstein Condensates (BECs). We review the properties of BECs of ultralight dark matter and bridge these properties with developments in numerical simulations, and ultimately with their impact on experimental searches. △ Less

Submitted 24 February, 2021; originally announced February 2021.

Comments: Invited review, submitted to IJMPD. 58 pages, 11 figures. Comments welcome

Report number: MI-TH-214,INT-PUB-21-004

The LHC Olympics 2020: A Community Challenge for Anomaly Detection in High Energy Physics

Authors: Gregor Kasieczka, Benjamin Nachman, David Shih, Oz Amram, Anders Andreassen, Kees Benkendorfer, Blaz Bortolato, Gustaaf Brooijmans, Florencia Canelli, Jack H. Collins, Biwei Dai, Felipe F. De Freitas, Barry M. Dillon, Ioan-Mihail Dinu, Zhongtian Dong, Julien Donini, Javier Duarte, D. A. Faroughy, Julia Gonski, Philip Harris, Alan Kahn, Jernej F. Kamenik, Charanjit K. Khosa, Patrick Komiske, Luc Le Pottier , et al. (22 additional authors not shown)

Abstract: A new paradigm for data-driven, model-agnostic new physics searches at colliders is emerging, and aims to leverage recent breakthroughs in anomaly detection and machine learning. In order to develop and benchmark new anomaly detection methods within this framework, it is essential to have standard datasets. To this end, we have created the LHC Olympics 2020, a community challenge accompanied by a… ▽ More A new paradigm for data-driven, model-agnostic new physics searches at colliders is emerging, and aims to leverage recent breakthroughs in anomaly detection and machine learning. In order to develop and benchmark new anomaly detection methods within this framework, it is essential to have standard datasets. To this end, we have created the LHC Olympics 2020, a community challenge accompanied by a set of simulated collider events. Participants in these Olympics have developed their methods using an R&D dataset and then tested them on black boxes: datasets with an unknown anomaly (or not). This paper will review the LHC Olympics 2020 challenge, including an overview of the competition, a description of methods deployed in the competition, lessons learned from the experience, and implications for data analyses with future datasets as well as future colliders. △ Less

Submitted 20 January, 2021; originally announced January 2021.

Comments: 108 pages, 53 figures, 3 tables

Magnetars and Axion-like Particles: Probes with the Hard X-ray Spectrum

Authors: Jean-François Fortin, Huai-Ke Guo, Steven P. Harris, Elijah Sheridan, Kuver Sinha

Abstract: Quiescent hard X-ray and soft gamma-ray emission from neutron stars constitute a promising frontier to explore axion-like-particles (ALPs). ALP production in the core peaks at energies of a few keV to a few hundreds of keV; subsequently, the ALPs escape and convert to photons in the magnetosphere. The emissivity goes as $\sim T^6$ while the conversion probability is enhanced for large magnetic fie… ▽ More Quiescent hard X-ray and soft gamma-ray emission from neutron stars constitute a promising frontier to explore axion-like-particles (ALPs). ALP production in the core peaks at energies of a few keV to a few hundreds of keV; subsequently, the ALPs escape and convert to photons in the magnetosphere. The emissivity goes as $\sim T^6$ while the conversion probability is enhanced for large magnetic fields, making magnetars, with their high core temperatures and strong magnetic fields, ideal targets for probing ALPs. We compute the energy spectrum of photons resulting from conversion of ALPs in the magnetosphere and then compare it against hard X-ray data from NuSTAR, INTEGRAL, and XMM-Newton, for a set of eight magnetars for which such data exists. Upper limits are placed on the product of the ALP-nucleon and ALP-photon couplings. For the production in the core, we perform a calculation of the ALP emissivity in degenerate nuclear matter modeled by a relativistic mean field theory. The reduction of the emissivity due to improvements to the one-pion exchange approximation is incorporated, as is the suppression of the emissivity due to proton superfluidity in the neutron star core. A range of core temperatures is considered, corresponding to different models of the steady heat transfer from the core to the stellar surface. For the subsequent conversion, we solve the coupled differential equations mixing ALPs and photons in the magnetosphere. The conversion occurs due to a competition between the dipolar magnetic field and the photon refractive index induced by the external magnetic field. Semi-analytic expressions are provided alongside the full numerical results. We also present an analysis of the uncertainty on the axion limits we derive due to the uncertainties in the magnetar masses, nuclear matter equation of state, and the proton superfluid critical temperature. △ Less

Submitted 15 July, 2021; v1 submitted 13 January, 2021; originally announced January 2021.

Comments: v1: 44 pages, 15 figures. Comments welcome v2: Updated version with uncertainty bands on ALP couplings coming from different choices of the nuclear equation of state, the mass of the magnetar, and the model of proton singlet superfluidity. Calculation of n+p-->n+p+a clarified. Version matches that published in JCAP

Report number: INT-PUB-21-001

Quasi Anomalous Knowledge: Searching for new physics with embedded knowledge

Authors: Sang Eon Park, Dylan Rankin, Silviu-Marian Udrescu, Mikaeel Yunus, Philip Harris

Abstract: Discoveries of new phenomena often involve a dedicated search for a hypothetical physics signature. Recently, novel deep learning techniques have emerged for anomaly detection in the absence of a signal prior. However, by ignoring signal priors, the sensitivity of these approaches is significantly reduced. We present a new strategy dubbed Quasi Anomalous Knowledge (QUAK), whereby we introduce alte… ▽ More Discoveries of new phenomena often involve a dedicated search for a hypothetical physics signature. Recently, novel deep learning techniques have emerged for anomaly detection in the absence of a signal prior. However, by ignoring signal priors, the sensitivity of these approaches is significantly reduced. We present a new strategy dubbed Quasi Anomalous Knowledge (QUAK), whereby we introduce alternative signal priors that capture some of the salient features of new physics signatures, allowing for the recovery of sensitivity even when the alternative signal is incorrect. This approach can be applied to a broad range of physics models and neural network architectures. In this paper, we apply QUAK to anomaly detection of new physics events at the CERN Large Hadron Collider utilizing variational autoencoders with normalizing flow. △ Less

Submitted 11 June, 2021; v1 submitted 6 November, 2020; originally announced November 2020.

Comments: 25 pages, 9 figures

Journal ref: J. High Energ. Phys. 2021, 30 (2021)

Transport in neutron star mergers

Authors: Steven P. Harris

Abstract: After an introduction to the QCD phase diagram, the nuclear equations of state, and neutron star mergers, I discuss three projects related to transport and nuclear matter in neutron star mergers. The first is the nature of beta equilibrium in the portion of a merger that is transparent to neutrinos. We calculate the weak interaction (Urca) rates and find that the beta equilibrium condition needs t… ▽ More After an introduction to the QCD phase diagram, the nuclear equations of state, and neutron star mergers, I discuss three projects related to transport and nuclear matter in neutron star mergers. The first is the nature of beta equilibrium in the portion of a merger that is transparent to neutrinos. We calculate the weak interaction (Urca) rates and find that the beta equilibrium condition needs to be modified by adding an additional chemical potential, which changes slightly the particle content in neutrino-transparent beta equilibrium. Secondly, we calculate the bulk viscosity in neutrino-transparent nuclear matter in conditions encountered in neutron star mergers. Bulk viscosity arises from a phase lag between the pressure and density in the nuclear matter, which is due to the finite rate of beta equilibration. When bulk viscosity is sufficiently strong, which happens when the equilibration rate nearly matches the frequency of the density oscillation, it can noticeably dampen the oscillation. We find that in certain thermodynamic conditions likely encountered in mergers, oscillations in nuclear matter can be damped on timescales on the order of 10 milliseconds, so we conclude that bulk viscosity should be included in merger simulations. Finally, we study thermal transport due to axions in neutron star mergers. We conclude that axions are never trapped in mergers, but instead escape, carrying energy away from the merger. We calculate the cooling time due to the energy carried away by axions and find that within current constraints on the axion-nucleon coupling, axions could cool fluid elements in mergers on timescales which could affect the dynamics of the merger. △ Less

Submitted 19 May, 2020; originally announced May 2020.

Comments: Thesis, based on the works: arXiv:1705.09880, arXiv:1803.00662, arXiv:1907.03795, and arXiv:2003.09768

Journal ref: ProQuest Dissertations Publishing, 2020. 27836728

Axions in neutron star mergers

Authors: Steven P. Harris, Jean-Francois Fortin, Kuver Sinha, Mark G. Alford

Abstract: Supernovae and cooling neutron stars have long been used to constrain the properties of axions, such as their mass and interactions with nucleons and other Standard Model particles. We investigate the prospects of using neutron star mergers as a similar location where axions can be probed in the future. We examine the impact axions would have on mergers, considering both the possibility that they… ▽ More Supernovae and cooling neutron stars have long been used to constrain the properties of axions, such as their mass and interactions with nucleons and other Standard Model particles. We investigate the prospects of using neutron star mergers as a similar location where axions can be probed in the future. We examine the impact axions would have on mergers, considering both the possibility that they free-stream through the dense nuclear matter and the case where they are trapped. We calculate the mean free path of axions in merger conditions, and find that they would free-stream through the merger in all thermodynamic conditions. In contrast to previous calculations, we integrate over the entire phase space while using a relativistic treatment of the nucleons, assuming the matrix element is momentum-independent. In particular, we use a relativistic mean field theory to describe the nucleons, taking into account the precipitous decrease in the effective mass of the nucleons as density increases above nuclear saturation density. We find that within current constraints on the axion-neutron coupling, axions could cool nuclear matter on timescales relevant to neutron star mergers. Our results may be regarded as first steps aimed at understanding how axions affect merger simulations and potentially interface with observations. △ Less

Submitted 18 June, 2020; v1 submitted 21 March, 2020; originally announced March 2020.

Comments: v2: matches version accepted by JCAP

An approach to constraining the Higgs width at the LHC and HL-LHC

Authors: Philip Coleman Harris, Dylan Sheldon Rankin, Cristina Mantilla Suarez

Abstract: Despite the discovery of the Higgs boson decay in five separate channels many parameters of the Higgs boson remain largely unconstrained. In this paper, we present a new approach to constraining the Higgs total width by requiring the Higgs to be resolved as a single high p$_T$ jet and measuring the inclusive Higgs boson cross section. To measure the inclusive Higgs boson cross section, we rely on… ▽ More Despite the discovery of the Higgs boson decay in five separate channels many parameters of the Higgs boson remain largely unconstrained. In this paper, we present a new approach to constraining the Higgs total width by requiring the Higgs to be resolved as a single high p$_T$ jet and measuring the inclusive Higgs boson cross section. To measure the inclusive Higgs boson cross section, we rely on new approaches from machine learning and a modified jet reconstruction. This approach is found to be complementary to the existing off-shell width measurement and, with the full HL-LHC luminosity, is capable of yielding similar sensitivity to the off-shell projections. We outline the theoretical and experimental limitations and present a path towards making this approach a truly model-independent measurement of the Higgs boson total width. △ Less

Submitted 4 October, 2019; originally announced October 2019.

Comments: 27 pages, 12 figures, 1 appendix

Damping of density oscillations in neutrino-transparent nuclear matter

Authors: Mark G. Alford, Steven P. Harris

Abstract: We calculate the bulk-viscous dissipation time for adiabatic density oscillations in nuclear matter at densities of 1-7 times nuclear saturation density and at temperatures ranging from 1 MeV, where corrections to previous low-temperature calculations become important, up to 10 MeV, where the assumption of neutrino transparency is no longer valid. Under these conditions, which are expected to occu… ▽ More We calculate the bulk-viscous dissipation time for adiabatic density oscillations in nuclear matter at densities of 1-7 times nuclear saturation density and at temperatures ranging from 1 MeV, where corrections to previous low-temperature calculations become important, up to 10 MeV, where the assumption of neutrino transparency is no longer valid. Under these conditions, which are expected to occur in neutron star mergers, damping of density oscillations arises from beta equilibration via weak interactions. We find that for 1 kHz oscillations the shortest dissipation times are in the 5 to 20 ms range, depending on the equation of state, which means that bulk viscous damping could affect the dynamics of a neutron star merger. For higher frequencies the dissipation time can be even shorter. △ Less

Submitted 27 September, 2019; v1 submitted 8 July, 2019; originally announced July 2019.

Comments: 13 pages v2: Matches journal version

Journal ref: Phys. Rev. C 100, 035803 (2019)

Novel tools and observables for jet physics in heavy-ion collisions

Authors: Harry Arthur Andrews, Liliana Apolinario, Redmer Alexander Bertens, Christian Bierlich, Matteo Cacciari, Yi Chen, Yang-Ting Chien, Leticia Cunqueiro Mendez, Michal Deak, David d'Enterria, Fabio Dominguez, Philip Coleman Harris, Krzysztof Kutak, Yen-Jie Lee, Yacine Mehtar-Tani, James Mulligan, Matthew Nguyen, Chang Ning-Bo, Dennis Perepelitsa, Gavin Salam, Martin Spousta, Jose Guilherme Milhano, Konrad Tywoniuk, Marco Van Leeuwen, Marta Verweij , et al. (3 additional authors not shown)

Abstract: Studies of fully-reconstructed jets in heavy-ion collisions aim at extracting thermodynamical and transport properties of hot and dense QCD matter. Recently, a plethora of new jet substructure observables have been theoretically and experimentally developed that provide novel precise insights on the modifications of the parton radiation pattern induced by a QCD medium. This report, summarizing the… ▽ More Studies of fully-reconstructed jets in heavy-ion collisions aim at extracting thermodynamical and transport properties of hot and dense QCD matter. Recently, a plethora of new jet substructure observables have been theoretically and experimentally developed that provide novel precise insights on the modifications of the parton radiation pattern induced by a QCD medium. This report, summarizing the main lines of discussion at the 5th Heavy Ion Jet Workshop and CERN TH institute "Novel tools and observables for jet physics in heavy-ion collisions" in 2017, presents a first attempt at outlining a strategy for isolating and identifying the relevant physical processes that are responsible for the observed medium-induced jet modifications. These studies combine theory insights, based on the Lund parton splitting map, with sophisticated jet reconstruction techniques, including grooming and background subtraction algorithms. △ Less

Submitted 30 April, 2020; v1 submitted 10 August, 2018; originally announced August 2018.

Comments: 25 pages, report from the CERN TH institute "Novel tools and observables for jet physics in heavy-ion collisions", version accepted for publication in J. Phys. G

Report number: CERN-TH-2018-186, LU-TP 18-14, IFJPAN-IV-2018-8, MCNET-18-19

Machine Learning Uncertainties with Adversarial Neural Networks

Authors: Christoph Englert, Peter Galler, Philip Harris, Michael Spannowsky

Abstract: Machine Learning is a powerful tool to reveal and exploit correlations in a multi-dimensional parameter space. Making predictions from such correlations is a highly non-trivial task, in particular when the details of the underlying dynamics of a theoretical model are not fully understood. Using adversarial networks, we include a priori known sources of systematic and theoretical uncertainties duri… ▽ More Machine Learning is a powerful tool to reveal and exploit correlations in a multi-dimensional parameter space. Making predictions from such correlations is a highly non-trivial task, in particular when the details of the underlying dynamics of a theoretical model are not fully understood. Using adversarial networks, we include a priori known sources of systematic and theoretical uncertainties during the training. This paves the way to a more reliable event classification on an event-by-event basis, as well as novel approaches to perform parameter fits of particle physics data. We demonstrate the benefits of the method explicitly in an example considering effective field theory extensions of Higgs boson production in association with jets. △ Less

Submitted 3 January, 2019; v1 submitted 23 July, 2018; originally announced July 2018.

Comments: 10 pages, 6 figures, v2: published version

Report number: IPPP/18/61

Prospects for a measurement of the $W$ boson mass in the all-jets final state at hadron colliders

Authors: Marat Freytsis, Philip Harris, Andreas Hinzmann, Ian Moult, Nhan Tran, Caterina Vernieri

Abstract: Precise measurements of the mass of the $W$ boson are important to test the overall consistency of the Standard Model of particle physics. The current best measurements of the $W$ boson mass come from single production measurements at hadron colliders in its decay mode to a lepton (electron or muon) and a neutrino and pair production of $W$ bosons at lepton colliders, where also the decay mode of… ▽ More Precise measurements of the mass of the $W$ boson are important to test the overall consistency of the Standard Model of particle physics. The current best measurements of the $W$ boson mass come from single production measurements at hadron colliders in its decay mode to a lepton (electron or muon) and a neutrino and pair production of $W$ bosons at lepton colliders, where also the decay mode of the $W$ boson to hadrons has been considered. In this study, prospects for a measurement of the $W$ boson mass in the all-jet final state at hadron colliders are presented. The feasibility of this measurement takes advantage of numerous recent developments in the field of jet substructure. Compared to other methods for measuring the $W$ mass, a measurement in the all-jets final state would be complementary in methodology and have systematic uncertainties orthogonal to previous measurements. We have estimated the main experimental and theoretical uncertainties affecting a measurement in the all-jet final state. With new trigger strategies, a statistical uncertainty for the measurement of the mass difference between the $Z$ and $W$ bosons of 30 MeV could be reached with HL-LHC data corresponding to 3000 fb$^{-1}$ of integrated luminosity. However, in order to reach that precision, the current understanding of non-perturbative contributions to the invariant mass of $W\to q\bar{q}'$ and $Z\to b\bar{b}$ jets will need to be refined. Similar strategies will also allow the reach for generic boosted resonances searches in hadronic channels to be extended. △ Less

Submitted 8 February, 2019; v1 submitted 19 July, 2018; originally announced July 2018.

Comments: 23 pages, 10 figures, 6 tables, Fig.10 updated

Report number: FERMILAB-PUB-18-315-E

Journal ref: JHEP 1902 (2019) 003

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

Beta equilibrium in neutron star mergers

Authors: Mark G. Alford, Steven P. Harris

Abstract: We show that the commonly used criterion for beta equilibrium in neutrino-transparent dense nuclear matter becomes invalid as temperatures rise above 1 MeV. Such temperatures are attained in neutron star mergers. By numerically computing the relevant weak interaction rates we find that the correct criterion for beta equilibrium requires an isospin chemical potential that can be as large as 10-20 M… ▽ More We show that the commonly used criterion for beta equilibrium in neutrino-transparent dense nuclear matter becomes invalid as temperatures rise above 1 MeV. Such temperatures are attained in neutron star mergers. By numerically computing the relevant weak interaction rates we find that the correct criterion for beta equilibrium requires an isospin chemical potential that can be as large as 10-20 MeV, depending on the temperature at which neutrinos become trapped. △ Less

Submitted 21 December, 2018; v1 submitted 1 March, 2018; originally announced March 2018.

Comments: Section on neutrino mean free paths added. Discussion and plot of effect of isospin chemical potential on beta-equilibrium proton fraction added

Journal ref: Phys. Rev. C 98, 065806 (2018)

Search for axion-like dark matter through nuclear spin precession in electric and magnetic fields

Authors: C. Abel, N. J. Ayres, G. Ban, G. Bison, K. Bodek, V. Bondar, M. Daum, M. Fairbairn, V. V. Flambaum, P. Geltenbort, K. Green, W. C. Griffith, M. van der Grinten, Z. D. Grujić, P. G. Harris, N. Hild, P. Iaydjiev, S. N. Ivanov, M. Kasprzak, Y. Kermaidic, K. Kirch, H. -C. Koch, S. Komposch, P. A. Koss, A. Kozela , et al. (23 additional authors not shown)

Abstract: We report on a search for ultra-low-mass axion-like dark matter by analysing the ratio of the spin-precession frequencies of stored ultracold neutrons and $^{199}$Hg atoms for an axion-induced oscillating electric dipole moment of the neutron and an axion-wind spin-precession effect. No signal consistent with dark matter is observed for the axion mass range… ▽ More We report on a search for ultra-low-mass axion-like dark matter by analysing the ratio of the spin-precession frequencies of stored ultracold neutrons and $^{199}$Hg atoms for an axion-induced oscillating electric dipole moment of the neutron and an axion-wind spin-precession effect. No signal consistent with dark matter is observed for the axion mass range $10^{-24}~\textrm{eV} \le m_a \le 10^{-17}~\textrm{eV}$. Our null result sets the first laboratory constraints on the coupling of axion dark matter to gluons, which improve on astrophysical limits by up to 3 orders of magnitude, and also improves on previous laboratory constraints on the axion coupling to nucleons by up to a factor of 40. △ Less

Submitted 21 August, 2017; originally announced August 2017.

Journal ref: Phys. Rev. X 7, 041034 (2017)

Recommendations of the LHC Dark Matter Working Group: Comparing LHC searches for heavy mediators of dark matter production in visible and invisible decay channels

Authors: Andreas Albert, Mihailo Backovic, Antonio Boveia, Oliver Buchmueller, Giorgio Busoni, Albert De Roeck, Caterina Doglioni, Tristan DuPree, Malcolm Fairbairn, Marie-Helene Genest, Stefania Gori, Giuliano Gustavino, Kristian Hahn, Ulrich Haisch, Philip C. Harris, Dan Hayden, Valerio Ippolito, Isabelle John, Felix Kahlhoefer, Suchita Kulkarni, Greg Landsberg, Steven Lowette, Kentarou Mawatari, Antonio Riotto, William Shepherd , et al. (5 additional authors not shown)

Abstract: Weakly-coupled TeV-scale particles may mediate the interactions between normal matter and dark matter. If so, the LHC would produce dark matter through these mediators, leading to the familiar "mono-X" search signatures, but the mediators would also produce signals without missing momentum via the same vertices involved in their production. This document from the LHC Dark Matter Working Group sugg… ▽ More Weakly-coupled TeV-scale particles may mediate the interactions between normal matter and dark matter. If so, the LHC would produce dark matter through these mediators, leading to the familiar "mono-X" search signatures, but the mediators would also produce signals without missing momentum via the same vertices involved in their production. This document from the LHC Dark Matter Working Group suggests how to compare searches for these two types of signals in case of vector and axial-vector mediators, based on a workshop that took place on September 19/20, 2016 and subsequent discussions. These suggestions include how to extend the spin-1 mediated simplified models already in widespread use to include lepton couplings. This document also provides analytic calculations of the relic density in the simplified models and reports an issue that arose when ATLAS and CMS first began to use preliminary numerical calculations of the dark matter relic density in these models. △ Less

Submitted 17 March, 2017; v1 submitted 16 March, 2017; originally announced March 2017.

Comments: 19 pages, 4 figures; v2: author list and LaTeX problem fixed

Report number: CERN-LPCC-2017-01

Fractal based observables to probe jet substructure of quarks and gluons

Authors: Joe Davighi, Philip Harris

Abstract: New jet observables are defined which characterize both fractal and scale-dependent contributions to the distribution of hadrons in a jet. These infrared safe observables, named Extended Fractal Observables (EFOs), have been applied to quark-gluon discrimination to demonstrate their potential utility. The EFOs are found to be individually discriminating and only weakly correlated to variables used… ▽ More New jet observables are defined which characterize both fractal and scale-dependent contributions to the distribution of hadrons in a jet. These infrared safe observables, named Extended Fractal Observables (EFOs), have been applied to quark-gluon discrimination to demonstrate their potential utility. The EFOs are found to be individually discriminating and only weakly correlated to variables used in existing discriminators. Consequently, their inclusion improves discriminator performance, as here demonstrated with particle level simulation from the parton shower. △ Less

Submitted 9 May, 2018; v1 submitted 2 March, 2017; originally announced March 2017.

Comments: [v1] 11 pages 4 figures [v2] 13 pages, 5 figures [v3] 9 pages, 7 figures. v2 added comment on how the observable can preserve infrared safety, updated acknowledgement, added diagram about visualization. v3 added comparison of performance in Herwig and Pythia, added comparison between two different EFO fitting functions, and added figure showing dependence on transverse momentum

Report number: DAMTP-2017-03-06

Journal ref: Eur.Phys.J. C78 (2018) no.4, 334

Towards the next generation of simplified Dark Matter models

Authors: Andreas Albert, Martin Bauer, Oliver Buchmueller, Jim Brooke, David G. Cerdeno, Matthew Citron, Gavin Davies, Annapaola de Cosa, Albert De Roeck, Andrea De Simone, Tristan Du Pree, John Ellis, Henning Flaecher, Malcolm Fairbairn, Alexander Grohsjean, Kristian Hahn, Ulrich Haisch, Philip C. Harris, Valentin V. Khoze, Greg Landsberg, Christopher McCabe, Bjoern Penning, Veronica Sanz, Christian Schwanenberger, Pat Scott , et al. (1 additional authors not shown)

Abstract: This White Paper is an input to the ongoing discussion about the extension and refinement of simplified Dark Matter (DM) models. Based on two concrete examples, we show how existing simplified DM models (SDMM) can be extended to provide a more accurate and comprehensive framework to interpret and characterise collider searches. In the first example we extend the canonical SDMM with a scalar mediat… ▽ More This White Paper is an input to the ongoing discussion about the extension and refinement of simplified Dark Matter (DM) models. Based on two concrete examples, we show how existing simplified DM models (SDMM) can be extended to provide a more accurate and comprehensive framework to interpret and characterise collider searches. In the first example we extend the canonical SDMM with a scalar mediator to include mixing with the Higgs boson. We show that this approach not only provides a better description of the underlying kinematic properties that a complete model would possess, but also offers the option of using this more realistic class of scalar mixing models to compare and combine consistently searches based on different experimental signatures. The second example outlines how a new physics signal observed in a visible channel can be connected to DM by extending a simplified model including effective couplings. This discovery scenario uses the recently observed excess in the high-mass diphoton searches of ATLAS and CMS for a case study to show that such a pragmatic approach can aid the experimental search programme to verify/falsify a potential signal and to study its underlying nature. In the next part of the White Paper we outline other interesting options for SDMM that could be studied in more detail in the future. Finally, we discuss important aspects of supersymmetric models for DM and how these could help to develop of more complete SDMM. △ Less

Submitted 25 February, 2017; v1 submitted 22 July, 2016; originally announced July 2016.

Physics at a 100 TeV pp collider: beyond the Standard Model phenomena

Authors: T. Golling, M. Hance, P. Harris, M. L. Mangano, M. McCullough, F. Moortgat, P. Schwaller, R. Torre, P. Agrawal, D. S. M. Alves, S. Antusch, A. Arbey, B. Auerbach, G. Bambhaniya, M. Battaglia, M. Bauer, P. S. Bhupal Dev, A. Boveia, J. Bramante, O. Buchmueller, M. Buschmann, J. Chakrabortty, M. Chala, S. Chekanov, C. -Y. Chen , et al. (89 additional authors not shown)

Abstract: This report summarises the physics opportunities in the search and study of physics beyond the Standard Model at a 100 TeV pp collider. This report summarises the physics opportunities in the search and study of physics beyond the Standard Model at a 100 TeV pp collider. △ Less

Submitted 2 June, 2016; originally announced June 2016.

Comments: 196 pages, 114 figures. Chapter 3 of the "Physics at the FCC-hh" Report

Report number: CERN-TH-2016-111

Cosmological constraints on Dark Matter models for collider searches

Authors: Tristan du Pree, Kristian Hahn, Philip Harris, Christos Roskas

Abstract: Searches for Dark Matter at the LHC are commonly described in terms of simplified models with scalar, pseudo-scalar, vector and axial-vector mediators. In this work we explore the constraints imposed on such models from the observed Dark Matter relic abundance. We present these constraints over a range of mediator masses relevant for the LHC and for future, higher energy colliders. We additionally… ▽ More Searches for Dark Matter at the LHC are commonly described in terms of simplified models with scalar, pseudo-scalar, vector and axial-vector mediators. In this work we explore the constraints imposed on such models from the observed Dark Matter relic abundance. We present these constraints over a range of mediator masses relevant for the LHC and for future, higher energy colliders. We additionally compute bounds from a photon line search for the decay of a pseudo-scalar mediator to di-photons that includes the mediator mass region near 750 GeV. Finally, we compare cosmological constraints with the reach of a possible future 100 TeV circular hadron collider, indirect, and direct detection experiments. △ Less

Submitted 28 March, 2016; originally announced March 2016.

Comments: 16 pages, 6 figures

Recommendations on presenting LHC searches for missing transverse energy signals using simplified $s$-channel models of dark matter

Authors: Antonio Boveia, Oliver Buchmueller, Giorgio Busoni, Francesco D'Eramo, Albert De Roeck, Andrea De Simone, Caterina Doglioni, Matthew J. Dolan, Marie-Helene Genest, Kristian Hahn, Ulrich Haisch, Philip C. Harris, Jan Heisig, Valerio Ippolito, Felix Kahlhoefer, Valentin V. Khoze, Suchita Kulkarni, Greg Landsberg, Steven Lowette, Sarah Malik, Michelangelo Mangano, Christopher McCabe, Stephen Mrenna, Priscilla Pani, Tristan du Pree , et al. (8 additional authors not shown)

Abstract: This document summarises the proposal of the LHC Dark Matter Working Group on how to present LHC results on $s$-channel simplified dark matter models and to compare them to direct (indirect) detection experiments. This document summarises the proposal of the LHC Dark Matter Working Group on how to present LHC results on $s$-channel simplified dark matter models and to compare them to direct (indirect) detection experiments. △ Less

Submitted 14 March, 2016; originally announced March 2016.

Comments: LHC Dark Matter Working Group document, 21pages, 4 figures

Report number: CERN-LPCC-2016-001

Thinking outside the ROCs: Designing Decorrelated Taggers (DDT) for jet substructure

Authors: James Dolen, Philip Harris, Simone Marzani, Salvatore Rappoccio, Nhan Tran

Abstract: We explore the scale-dependence and correlations of jet substructure observables to improve upon existing techniques in the identification of highly Lorentz-boosted objects. Modified observables are designed to remove correlations from existing theoretically well-understood observables, providing practical advantages for experimental measurements and searches for new phenomena. We study such obser… ▽ More We explore the scale-dependence and correlations of jet substructure observables to improve upon existing techniques in the identification of highly Lorentz-boosted objects. Modified observables are designed to remove correlations from existing theoretically well-understood observables, providing practical advantages for experimental measurements and searches for new phenomena. We study such observables in $W$ jet tagging and provide recommendations for observables based on considerations beyond signal and background efficiencies. △ Less

Submitted 8 June, 2016; v1 submitted 29 February, 2016; originally announced March 2016.

Report number: FERMILAB-PUB-16-046-PPD

Journal ref: JHEP 05 (2016) 156

Closing up on Dark Sectors at Colliders: from 14 to 100 TeV

Authors: Philip Harris, Valentin V. Khoze, Michael Spannowsky, Ciaran Williams

Abstract: We investigate the reach of the LHC Run 2 and that of a future circular hadron collider with up to 100 TeV centre of mass energy for the exploration of potential Dark Matter sectors. These dark sectors are conveniently and broadly described by simplified models. The simplified models we consider provide microscopic descriptions of interactions between the Standard Model partons and the dark sector… ▽ More We investigate the reach of the LHC Run 2 and that of a future circular hadron collider with up to 100 TeV centre of mass energy for the exploration of potential Dark Matter sectors. These dark sectors are conveniently and broadly described by simplified models. The simplified models we consider provide microscopic descriptions of interactions between the Standard Model partons and the dark sector particles mediated by the four basic types of messenger fields: scalar, pseudo-scalar, vector or axial-vector. Our analysis extends and updates the previously available results for the LHC at 8 and 14 TeV to 100 TeV for models with all four messenger types. We revisit and improve the analysis at 14 TeV, by studying a variety of analysis techniques, concluding that the most discriminating variables correspond to the missing transverse energy and the azimuthal angle between jets in the final state. Going to 100 TeV, the limits on simplified models of Dark Matter are enhanced significantly, in particular for heavier mediators and dark sector particles, for which the available phase space at the LHC is restricted. The possibility of a 100 TeV collider provides an unprecedented coverage of the dark sector basic parameters and a unique opportunity to pin down the particle nature of Dark Matter and its interactions with the Standard Model. △ Less

Submitted 9 September, 2015; originally announced September 2015.

Comments: 16 pages, 11 figures

Report number: IPPP/15/20, DCPT/15/36

Journal ref: Phys. Rev. D 93, 054030 (2016)