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The Present and Future of QCD
Authors:
P. Achenbach,
D. Adhikari,
A. Afanasev,
F. Afzal,
C. A. Aidala,
A. Al-bataineh,
D. K. Almaalol,
M. Amaryan,
D. Androić,
W. R. Armstrong,
M. Arratia,
J. Arrington,
A. Asaturyan,
E. C. Aschenauer,
H. Atac,
H. Avakian,
T. Averett,
C. Ayerbe Gayoso,
X. Bai,
K. N. Barish,
N. Barnea,
G. Basar,
M. Battaglieri,
A. A. Baty,
I. Bautista
, et al. (378 additional authors not shown)
Abstract:
This White Paper presents the community inputs and scientific conclusions from the Hot and Cold QCD Town Meeting that took place September 23-25, 2022 at MIT, as part of the Nuclear Science Advisory Committee (NSAC) 2023 Long Range Planning process. A total of 424 physicists registered for the meeting. The meeting highlighted progress in Quantum Chromodynamics (QCD) nuclear physics since the 2015…
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This White Paper presents the community inputs and scientific conclusions from the Hot and Cold QCD Town Meeting that took place September 23-25, 2022 at MIT, as part of the Nuclear Science Advisory Committee (NSAC) 2023 Long Range Planning process. A total of 424 physicists registered for the meeting. The meeting highlighted progress in Quantum Chromodynamics (QCD) nuclear physics since the 2015 LRP (LRP15) and identified key questions and plausible paths to obtaining answers to those questions, defining priorities for our research over the coming decade. In defining the priority of outstanding physics opportunities for the future, both prospects for the short (~ 5 years) and longer term (5-10 years and beyond) are identified together with the facilities, personnel and other resources needed to maximize the discovery potential and maintain United States leadership in QCD physics worldwide. This White Paper is organized as follows: In the Executive Summary, we detail the Recommendations and Initiatives that were presented and discussed at the Town Meeting, and their supporting rationales. Section 2 highlights major progress and accomplishments of the past seven years. It is followed, in Section 3, by an overview of the physics opportunities for the immediate future, and in relation with the next QCD frontier: the EIC. Section 4 provides an overview of the physics motivations and goals associated with the EIC. Section 5 is devoted to the workforce development and support of diversity, equity and inclusion. This is followed by a dedicated section on computing in Section 6. Section 7 describes the national need for nuclear data science and the relevance to QCD research.
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Submitted 4 March, 2023;
originally announced March 2023.
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Single $π^0$ Production Off Neutrons Bound in Deuteron with Linearly Polarized Photons
Authors:
C. Mullen,
S. Gardner,
D. I. Glazier,
S. J. D. Kay,
K. Livingston,
I. I. Strakovsky,
R. L. Workman,
S. Abt,
P. Achenbach,
F. Afzal,
Z. Ahmed,
C. S. Akondi,
J. R. M. Annand,
M. Bashkanov,
R. Beck,
M. Biroth,
N. S. Borisov,
A. Braghieri,
W. J. Briscoe,
F. Cividini,
C. Collicott,
S. Costanza,
A. Denig,
M. Dieterle,
E. J. Downie
, et al. (57 additional authors not shown)
Abstract:
The quasifree $\overrightarrowγ d\toπ^0n(p)$ photon beam asymmetry, $Σ$, has been measured at photon energies, $E_γ$, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49 to 148$^\circ$.…
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The quasifree $\overrightarrowγ d\toπ^0n(p)$ photon beam asymmetry, $Σ$, has been measured at photon energies, $E_γ$, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49 to 148$^\circ$. In this kinematic region, polarization observables are sensitive to contributions from the $Δ(1232)$ and $N(1440)$ resonances. The extracted values of $Σ$ have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID, and Bonn-Gatchina analyses; while a revised SAID fit, including the new $Σ$ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict $π^0n$ photoproduction observables, based on fits to published data in the channels $π^0p$, $π^+n$, and $π^-p$.
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Submitted 16 March, 2021; v1 submitted 15 March, 2021;
originally announced March 2021.
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Measurement of the Generalized Polarizabilities of the Proton at Intermediate $Q^2$
Authors:
H. Fonvieille,
J. Beričič,
L. Correa,
M. Benali,
P. Achenbach,
C. Ayerbe Gayoso,
J. C. Bernauer,
A. Blomberg,
R. Böhm,
D. Bosnar,
L. Debenjak,
A. Denig,
M. O. Distler,
E. J. Downie,
A. Esser,
I. Friščić,
S. Kegel,
Y. Kohl,
M. Makek,
H. Merkel,
D. G. Middleton,
M. Mihovilovič,
U. Müller,
L. Nungesser,
M. Paolone
, et al. (13 additional authors not shown)
Abstract:
Background: Generalized polarizabilities (GPs) are important observables to describe the nucleon structure, and measurements of these observables are still scarce. Purpose: This paper presents details of a virtual Compton scattering (VCS) experiment, performed at the A1 setup at the Mainz Microtron by studying the $e p \to e p γ$ reaction. The article focuses on selected aspects of the analysis. M…
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Background: Generalized polarizabilities (GPs) are important observables to describe the nucleon structure, and measurements of these observables are still scarce. Purpose: This paper presents details of a virtual Compton scattering (VCS) experiment, performed at the A1 setup at the Mainz Microtron by studying the $e p \to e p γ$ reaction. The article focuses on selected aspects of the analysis. Method: The experiment extracted the $P_{LL} -P_{TT} / ε$ and $P_{LT}$ structure functions, as well as the electric and magnetic GPs of the proton, at three new values of the four-momentum transfer squared $Q^2$: 0.10, 0.20 and 0.45 GeV$^2$. Results: We emphasize the importance of the calibration of experimental parameters. The behavior of the measured $e p \to e p γ$ cross section is presented and compared to the theory. A detailed investigation of the polarizability fits reveals part of their complexity, in connection with the higher-order terms of the low-energy expansion. Conclusions: The presented aspects are elements which contribute to minimize the systematic uncertainties and improve the precision of the physics results.
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Submitted 11 February, 2021; v1 submitted 20 August, 2020;
originally announced August 2020.
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Compton scattering from $^4$He at the TUNL HI$γ$S facility
Authors:
X. Li,
M. W. Ahmed,
A. Banu,
C. Bartram,
B. Crowe,
E. J. Downie,
M. Emamian,
G. Feldman,
H. Gao,
D. Godagama,
H. W. Grießhammer,
C. R. Howell,
H. J. Karwowski,
D. P. Kendellen,
M. A. Kovash,
K. K. H. Leung,
D. Markoff,
S. Mikhailov,
R. E. Pywell,
M. H. Sikora,
J. A. Silano,
R. S. Sosa,
M. C. Spraker,
G. Swift,
P. Wallace
, et al. (4 additional authors not shown)
Abstract:
Differential cross sections for elastic Compton scattering from $^4$He have been measured with high statistical precision at the High Intensity $γ$-ray Source at laboratory scattering angles of $55^\circ$, $90^\circ$, and $125^\circ$ using a quasi-monoenergetic photon beam with a weighted mean energy value of $81.3$ MeV. The results are compared to previous measurements and similar fore-aft asymme…
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Differential cross sections for elastic Compton scattering from $^4$He have been measured with high statistical precision at the High Intensity $γ$-ray Source at laboratory scattering angles of $55^\circ$, $90^\circ$, and $125^\circ$ using a quasi-monoenergetic photon beam with a weighted mean energy value of $81.3$ MeV. The results are compared to previous measurements and similar fore-aft asymmetry in the angular distribution of the differential cross sections is observed. This experimental work is expected to strongly motivate the development of effective-field-theory calculations of Compton scattering from $^4$He to fully interpret the data.
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Submitted 24 April, 2020; v1 submitted 14 December, 2019;
originally announced December 2019.
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Cross Section for $γn \to π^0 n$ measured at Mainz/A2
Authors:
W. J. Briscoe,
M. Hadzimehmedovi,
A. E. Kudryavtsev,
V. V. Kulikov,
M. A. Martemianov,
I. I. Strakovsky,
A. Svarc,
V. E. Tarasov,
R. L. Workman,
S. Abt,
P. Achenbach,
C. S. Akondi,
F. Afzal,
P. Aguar-Bartolome,
Z. Ahmed,
J. R. M. Annand,
H. J. Arends,
K. Bantawa,
M. Bashkanov,
R. Beck,
M. Biroth,
N. Borisov,
A. Braghieri,
S. A. Bulychjov,
F. Cividini
, et al. (67 additional authors not shown)
Abstract:
The $γn \to π^0 n$ differential cross section evaluated for 27 energy bins span the photon-energy range 290-813 MeV (W = 1.195-1.553 GeV) and the pion c.m. polar production angles, ranging from 18 deg to 162 deg, making use of model-dependent nuclear corrections to extract pi0 production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross sec…
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The $γn \to π^0 n$ differential cross section evaluated for 27 energy bins span the photon-energy range 290-813 MeV (W = 1.195-1.553 GeV) and the pion c.m. polar production angles, ranging from 18 deg to 162 deg, making use of model-dependent nuclear corrections to extract pi0 production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross section was measured. The tagged photon beam produced by the 883-MeV electron beam of the Mainz Microtron MAMI was used for the 0-meson production. Our accumulation of 3.6 x 10^6 $γn \to π^0 n$ events allowed a detailed study of the reaction dynamics. Our data are in reasonable agreement with previous A2 measurements and extend them to lower energies. The data are compared to predictions of previous SAID, MAID, and BnGa partial-wave analyses and to the latest SAID fit MA19 that included our data. Selected photon decay amplitudes $N^* \to γn$ at the resonance poles are determined for the first time.
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Submitted 7 August, 2019;
originally announced August 2019.
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Study of $η$ and $η'$ photoproduction at MAMI
Authors:
V. L. Kashevarov,
P. Ott,
S. Prakhov,
P. Adlarson,
F. Afzal,
Z. Ahmed,
C. S. Akondi,
J. R. M. Annand,
H. J. Arends,
R. Beck,
A. Braghieri,
W. J. Briscoe,
F. Cividini,
R. Codling,
C. Collicott,
S. Costanza,
A. Denig,
E. J. Downie,
M. Dieterle,
M. I. Ferretti Bondy,
L. V. Filkov,
A. Fix,
S. Gardner,
S. Garni,
D. I. Glazier
, et al. (65 additional authors not shown)
Abstract:
The reactions $γp\to ηp$ and $γp\to η' p$ have been measured from their thresholds up to the center-of-mass energy $W=1.96$GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections were obtained with unprecedented accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section and excitation func…
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The reactions $γp\to ηp$ and $γp\to η' p$ have been measured from their thresholds up to the center-of-mass energy $W=1.96$GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections were obtained with unprecedented accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section and excitation functions for $η$ photoproduction at the energies in vicinity of the $η'$ threshold, $W=1896$MeV ($E_γ=1447$MeV). This behavior is explained in a revised $η$MAID isobar model by a significant branching of the $N(1895)1/2^-$ nucleon resonance to both, $ηp$ and $η' p$, confirming the existence and constraining the properties of this poorly known state.
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Submitted 2 January, 2017;
originally announced January 2017.
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Photoproduction of the $ω$ meson off the proton near threshold
Authors:
I. I. Strakovsky,
S. Prakhov,
Y. I. Azimov,
P. Aguar-Bartolome,
J. R. M. Annand,
H. J. Arends,
K. Bantawa,
R. Beck,
V. Bekrenev,
H. Berghaeuser,
A. Braghieri,
W. J. Briscoe,
J. Brudvik,
S. Cherepnya,
R. F. B. Codling,
C. Collicott,
S. Costanza,
B. T. Demissie,
E. J. Downie,
P. Drexler,
L. V. Fil'kov,
D. I. Glazier,
R. Gregor,
D. J. Hamilton,
E. Heid
, et al. (49 additional authors not shown)
Abstract:
An experimental study of $ω$ photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The $γp\toωp$ differential cross sections are measured from threshold to the incident-photon energy $E_γ=1.40$ GeV ($W=1.87$ GeV for the center-of-mass energy) with 15-MeV binning in $E_γ$ and fu…
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An experimental study of $ω$ photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The $γp\toωp$ differential cross sections are measured from threshold to the incident-photon energy $E_γ=1.40$ GeV ($W=1.87$ GeV for the center-of-mass energy) with 15-MeV binning in $E_γ$ and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the $ωN$ scattering length $α_{ωp}$ is provided.
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Submitted 21 May, 2015; v1 submitted 13 July, 2014;
originally announced July 2014.
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Real and Virtual Compton Scattering: the nucleon polarisabilities
Authors:
E. J. Downie,
H. Fonvieille
Abstract:
We give an overview of low-energy Compton scattering (gamma^(*) p --> gamma p) with a real or virtual incoming photon. These processes allow the investigation of one of the fundamental properties of the nucleon, i.e. how its internal structure deforms under an applied static electromagnetic field. Our knowledge of nucleon polarisabilities and their generalization to non-zero four-momentum transfer…
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We give an overview of low-energy Compton scattering (gamma^(*) p --> gamma p) with a real or virtual incoming photon. These processes allow the investigation of one of the fundamental properties of the nucleon, i.e. how its internal structure deforms under an applied static electromagnetic field. Our knowledge of nucleon polarisabilities and their generalization to non-zero four-momentum transfer will be reviewed, including the presently ongoing experiments and future perspectives.
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Submitted 7 September, 2011; v1 submitted 1 June, 2011;
originally announced June 2011.
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Study of the gp-->etap reaction with the Crystal Ball detector at the Mainz Microtron(MAMI-C)
Authors:
E. F. McNicoll,
S. Prakhov,
I. I. Strakovsky,
P. Aguar-Bartolomepmainz,
L. K. Akasoy,
J. R. M. Annand,
H. J. Arends,
R. A. Arndt,
Ya. I. Azimov,
K. Bantawa,
R. Beck,
V. S. Bekrenev,
H. Berghaeuser,
A. Braghieri,
D. Branford,
W. J. Briscoe,
J. Brudvik,
S. Cherepnya,
R. F. B. Codling,
B. T. Demissie,
E. J. Downie,
P. Drexler,
L. V. Fil'kov,
A. Fix,
B. Freehart
, et al. (59 additional authors not shown)
Abstract:
The gp-->etap reaction has been measured with the Crystal Ball and TAPS multiphoton spectrometers in the energy range from the production threshold of 707 MeV to 1.4 GeV (1.49 =< W >= 1.87 GeV). Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz Microtron MAMI-C and momentum analyzed by the Glasgow Tagging Spectrometer were used for the eta-meson production. Our accumulation…
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The gp-->etap reaction has been measured with the Crystal Ball and TAPS multiphoton spectrometers in the energy range from the production threshold of 707 MeV to 1.4 GeV (1.49 =< W >= 1.87 GeV). Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz Microtron MAMI-C and momentum analyzed by the Glasgow Tagging Spectrometer were used for the eta-meson production. Our accumulation of 3.8 x 10^6 gp-->etap-->3pi0p-->6gp events allows a detailed study of the reaction dynamics. The gp-->etap differential cross sections were determined for 120 energy bins and the full range of the production angles. Our data show a dip near W = 1680 MeV in the total cross section caused by a substantial dip in eta production at forward angles. The data are compared to predictions of previous SAID and MAID partial-wave analyses and to thelatest SAID and MAID fits that have included our data.
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Submitted 25 September, 2010; v1 submitted 5 July, 2010;
originally announced July 2010.