Tue·Mar 9, 2021Tuesday·March 9, 2021

1. 01*

   Determination of two-photon exchange via $e^{+}p/e^{-}p$ Scattering with CLAS12

   Jan C. Bernauer🇺🇸 · Volker D. Burkert🇺🇸 · Ethan Cline🇺🇸 · Axel Schmidt🇺🇸 · Youri Sharabian🇺🇸

   The proton elastic form factor ratio shows a discrepancy between measurements using the Rosenbluth technique in unpolarized beam and target experiments and measurements using polarization degrees of freedom. The proposed explanation of this discrepancy is uncorrected hard two-photon exchange (TPE), a type of radiative correction that is conventionally neglected. The effect size and agreement with theoretical predictions has been tested recently by three experiments. While the results support the existence of a small two-photon exchange effect, they cannot establish that theoretical treatments are valid. At larger momentum transfers, theory remains untested. This proposal aims to measure two-photon exchange over an extended and so far largely untested $Q^2$ and $\epsilon$ range with high precision using the {\tt CLAS12} experiment. Such data are crucial to clearly confirm or rule out TPE as the driver for the discrepancy as well as test several theoretical approaches, believed valid in different parts of the tested $Q^2$ range.

   nucl-exEPJA(2021)·9 citations
2. 02*

   Distribution amplitudes of light diquarks

   Ya Lu🇨🇳 · Daniele Binosi🇮🇹 · Minghui Ding🇮🇹 · Craig D. Roberts🇨🇳 · Hui-Yu Xing🇨🇳 · Chang Xu🇨🇳

   Accumulating evidence indicates that soft quark+quark (diquark) correlations play an important role in the structure and interactions of hadrons constituted from three or more valence-quarks; so, it is worth developing insights into diquark structure. Using a leading-order truncation of those equations needed to solve continuum two-valence-body bound-state problems, the leading-twist two-parton distribution amplitudes (DAs) of light-quark scalar and pseudovector diquarks are calculated. The diquark DAs are narrower and taller than the asymptotic profile that characterises mesons. Consequently, the valence quasiparticles in a diquark are less likely to carry a large light-front fraction of the system's total momentum than those in a meson. These features may both influence the form of baryon DAs and be transmitted to diquark distribution functions (DFs), in which case their impact will be felt, e.g. in the proton's $u$ and $d$ valence-quark DFs.

   ↳ hep-phhep-exhep-latnucl-ex+1EPJA(2021)·16 citations
3. 03*

   The Asymmetry of Antimatter in the Proton

   J. Dove🇺🇸 · B. Kerns🇺🇸 · R. E. McClellan🇺🇸 · S. Miyasaka🇯🇵 · D. H. Morton🇺🇸 · K. Nagai🇯🇵 · S. Prasad🇺🇸 · F. Sanftl🇯🇵 · M. B. C. Scott🇺🇸 · A. S. Tadepalli🇺🇸 · C. A. Aidala🇺🇸 · J. Arrington🇺🇸 and 55 other authors

   The fundamental building blocks of the proton, quarks and gluons, have been known for decades. However, we still have an incomplete theoretical and experimental understanding of how these particles and their dynamics give rise to the quantum bound state of the proton and its physical properties, such as for example its spin. The two up and the single down quarks that comprise the proton in the simplest picture account only for a few percent of the proton mass, the bulk of which is in the form of quark kinetic and potential energy and gluon energy from the strong force. An essential feature of this force, as described by quantum chromodynamics, is its ability to create matter-antimatter quark pairs inside the proton that exist only for a very short time. Their fleeting existence makes the antimatter quarks within protons difficult to study, but their existence is discernible in reactions where a matter-antimatter quark pair annihilates. In this picture of quark-antiquark creation by the strong force, the probability distributions as a function of momentum for the presence of up and down antimatter quarks should be nearly identical, since their masses are quite similar and small compared to the mass of the proton. In the present manuscript, we show evidence from muon pair production measurements that these distributions are significantly different, with more abundant down antimatter quarks than up antimatter quarks over a wide range of momentum. These results revive interest in several proposed mechanisms as the origin of this antimatter asymmetry in the proton that had been disfavored by the previous results and point to the future measurements that can distinguish between these mechanisms.

   ↳ hep-phhep-exnucl-exNature(2021)·123 citations
4. 04*

   Deep learning stochastic processes with QCD phase transition

   Lijia Jiang🇩🇪 · Lingxiao Wang🇩🇪 · Kai Zhou🇩🇪

   It is non-trivial to recognize phase transitions and track dynamics inside a stochastic process because of its intrinsic stochasticity. In this paper, we employ the deep learning method to classify the phase orders and predict the damping coefficient of fluctuating systems under Langevin's description. As a concrete set-up, we demonstrate this paradigm for the scalar condensation in QCD matter near the critical point, in which the order parameter of chiral phase transition can be characterized in a $1+1$-dimensional Langevin equation for $\sigma$ field. In a supervised learning manner, the Convolutional Neural Networks(CNNs) accurately classify the first-order phase transition and crossover based on $\sigma$ field configurations with fluctuations. Noise in the stochastic process does not significantly hinder the performance of the well-trained neural network for phase order recognition. For mixed dynamics with diverse dynamical parameters, we further devise and train the machine to predict the damping coefficients $\eta$ in a broad range. The results show that it is robust to extract the dynamics from the bumpy field configurations.

   ↳ nucl-thnucl-exphysics.data-anPRD(2021)·34 citations
5. 05*

   Using Z boson events to study parton-medium interactions in PbPb collisions

   CMS Collaboration

   The spectra measurements of charged hadrons produced in the shower of a parton originating in the same hard scattering with a leptonically decaying Z boson, are reported in lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Both PbPb and pp data sets are recorded by the CMS experiment at the LHC, and correspond to an integrated luminosity of 1.7 nb${}^{-1}$ and 320 pb${}^{-1}$, respectively. Hadronic collision data with one reconstructed Z boson candidate with the transverse momentum $p_{\mathrm{T}}$ $>$ 30 GeV/$c$ are analyzed. The Z boson constrains the initial energy and direction of the associated parton. In heavy ion events, azimuthal angular distributions of charged hadrons with respect to the direction of a Z boson are sensitive to modifications of the in-medium parton shower and medium response. Compared to reference data from pp interactions, the results for central PbPb collisions indicate a modification of the angular correlations. The measurements of the fragmentation functions and $p_{\mathrm{T}}$ spectra of charged particles in Z boson events, which are sensitive to medium modifications of the parton shower longitudinal structure, are also reported. Significant modifications in central PbPb events compared to pp reference data are also found for these observables.

   ↳ hep-exnucl-exPRL(2022)·61 citations
6. 06*

   Improved $K_{e3}$ radiative corrections sharpen the $K_{\mu 2}$--$K_{l3}$ discrepancy

   Chien-Yeah Seng🇩🇪 · Daniel Galviz🇩🇪 · Mikhail Gorchtein🇩🇪 · Ulf-G. Meißner🇩🇪

   The measurements of $V_{us}$ in leptonic $(K_{\mu 2})$ and semileptonic $(K_{l3})$ kaon decays exhibit a $3\sigma$ disagreement, which could originate either from physics beyond the Standard Model or some large unidentified Standard Model systematic effects. Clarifying this issue requires a careful examination of all existing Standard Model inputs. Making use of a newly-proposed computational framework and the most recent lattice QCD results, we perform a comprehensive re-analysis of the electroweak radiative corrections to the $K_{e3}$ decay rates that achieves an unprecedented level of precision of $10^{-4}$, which improves the current best results by almost an order of magnitude. No large systematic effects are found, which suggests that the electroweak radiative corrections should be removed from the ``list of culprits'' responsible for the $K_{\mu 2}$--$K_{l3}$ discrepancy.

   ↳ hep-phhep-exhep-latnucl-ex+1JHEP(2021)·40 citations
7. 07*

   Science Requirements and Detector Concepts for the Electron-Ion Collider: EIC Yellow Report

   R. Abdul Khalek🇳🇱 · A. Accardi🇺🇸 · J. Adam🇺🇸 · D. Adamiak🇺🇸 · W. Akers🇺🇸 · M. Albaladejo🇺🇸 · A. Al-bataineh🇸🇦 · M. G. Alexeev🇮🇹 · F. Ameli🇮🇹 · P. Antonioli🇮🇹 · N. Armesto🇪🇸 · W. R. Armstrong🇺🇸 and 403 other authors

   This report describes the physics case, the resulting detector requirements, and the evolving detector concepts for the experimental program at the Electron-Ion Collider (EIC). The EIC will be a powerful new high-luminosity facility in the United States with the capability to collide high-energy electron beams with high-energy proton and ion beams, providing access to those regions in the nucleon and nuclei where their structure is dominated by gluons. Moreover, polarized beams in the EIC will give unprecedented access to the spatial and spin structure of the proton, neutron, and light ions. The studies leading to this document were commissioned and organized by the EIC User Group with the objective of advancing the state and detail of the physics program and developing detector concepts that meet the emerging requirements in preparation for the realization of the EIC. The effort aims to provide the basis for further development of concepts for experimental equipment best suited for the science needs, including the importance of two complementary detectors and interaction regions. This report consists of three volumes. Volume I is an executive summary of our findings and developed concepts. In Volume II we describe studies of a wide range of physics measurements and the emerging requirements on detector acceptance and performance. Volume III discusses general-purpose detector concepts and the underlying technologies to meet the physics requirements. These considerations will form the basis for a world-class experimental program that aims to increase our understanding of the fundamental structure of all visible matter

   ↳ physics.ins-dethep-exhep-phnucl-ex+1NPA(2022)·1653 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.