Tue·Aug 11, 2020Tuesday·August 11, 2020

1. 01*

   Measurements of the induced polarization in the quasi-elastic $A(e,e^{\prime }\vec{p})$ process in non-coplanar kinematics

   Sebouh J. Paul🇩🇪 · Tim Kolar · Tilen Brecelj🇸🇮 · Patrick Achenbach🇩🇪 · Hartmuth Arenhövel🇩🇪 · Adi Ashkenazi🇺🇸 · Jure Beričič🇺🇸 · Ralph Böhm🇩🇪 · Damir Bosnar🇭🇷 · Ethan Cline🇺🇸 · Erez O. Cohen🇮🇱 · Luka Debenjak and 35 other authors

   We report measurements of the induced polarization $\vec{P}$ of protons knocked out from ${}^2$H and ${}^{12}$C via the $A(e,e^{\prime }\vec{p})$ reaction. We have studied the dependence of $\vec{P}$ on two kinematic variables: the missing momentum $p_{\mathrm{miss}}$ and the "off-coplanarity" angle ${\varphi }_{pq}$ between the scattering and reaction planes. For the full 360$°$ range in ${\varphi }_{pq}$, both the normal ($P_y$) and, for the first time, the transverse ($P_x$) components of the induced polarization were measured with respect to the coordinate system associated with the scattering plane. $P_x$ vanishes in coplanar kinematics, however in non-coplanar kinematics, it is on the same scale as $P_y$. We find that the dependence on ${\varphi }_{pq}$ is sine-like for $P_x$ and cosine-like for $P_y$. For carbon, the magnitude of the induced polarization is especially large when protons are knocked out from the $p_{3/2}$ shell at very small $p_{\mathrm{miss}}$. For the deuteron, the induced polarization is near zero at small $|p_{\mathrm{miss}}|$, and its magnitude increases with $|p_{\mathrm{miss}}|$. For both nuclei such behavior is reproduced qualitatively by theoretical results, driven largely by the spin-orbit part of the final-state interactions. However, for both nuclei, sizeable discrepancies exist between experiment and theory.

   nucl-exPLB(2020)·5 citations
2. 02*

   Direct photon emission and influence of dynamical wave packets in an extended quantum molecular dynamics model

   C.Z. Shi · Y. G. Ma🇨🇳 · X. G. Cao🇨🇳 · D. Q. Fang🇨🇳 · W. B. He · C. Zhong🇨🇳

   Direct photon produced from first proton-neutron ($p$-$n$) collision during the early stage of heavy ion reaction is a sensitive probe to reflect energy and momentum distribution of nucleons. In this work, we embedded the hard photon production channel in an extended quantum molecular dynamics (EQMD) model, and took the direct photon as a possible probe to improve namely the Fermi motion in the EQMD model. A possible scheme is offered to handle the dynamical wave packet width within incoherent bremsstrahlung process. Direct photons calculated by our modified EQMD were compared with data of ${}^{14}$N + ${}^{12}$C at beam energies $E/A$ = 20, 30 and 40 MeV, and it is found that the yield, inverse slope and angular distribution of direct photons could be reasonably reproduced. In addition, asymmetric reaction systems of ${}^4$He + C and ${}^4$He + Zn at $E/A$ = 53 MeV are also simulated in this work. It is found that the symmetric angular distribution in the nucleon-nucleon ($N$-$N$) center-of-mass (c.m.) frame and the velocity of $the\gamma$-emission source can be reasonably obtained from our method although there is some quantitative differences.

   ↳ nucl-thnucl-exPRC(2020)·11 citations
3. 03*

   Axial and pseudoscalar form factors from charged current quasielastic neutrino-nucleon scattering

   Oleksandr Tomalak🇺🇸

   We study the scattering of neutrinos on polarized and unpolarized free nucleons, and also the polarization of recoil particles in these scatters. In contrast to electromagnetic processes, the parity-violating weak interaction gives rise to large spin asymmetries at leading order. Future polarization measurements could provide independent access to the proton axial structure and allow the first extraction of the pseudoscalar form factor from neutrino data without the conventional partially conserved axial current (PCAC) ansatz and assumptions about the pion-pole dominance. The pseudoscalar form factor can be accessed with precise measurements with muon (anti)neutrinos of a few hundreds $\mathrm{MeV}$ of energy or with tau (anti)neutrinos. The axial form factor can be extracted from scattering measurements using accelerator neutrinos of all energies.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2021)·15 citations
4. 04*

   Exploring the Collective Phenomenon at the Electron-Ion Collider

   Yu Shi🇨🇳 · Lei Wang🇨🇳 · Shu-Yi Wei🇮🇹 · Bo-Wen Xiao🇨🇳 · Liang Zheng🇨🇳

   Based on rare fluctuations in strong interactions, we argue that there is a strong physical resemblance between the high multiplicity events in photo-nuclear collisions and those in $pA$ collisions, in which interesting long range collective phenomena are discovered. This indicates that the collectivity can also be studied in certain kinematic region of the upcoming Electron-Ion Collider (EIC) where the incoming virtual photon has a sufficiently long lifetime. Using a model in the Color Glass Condensate formalism, we first show that the initial state interactions can explain the recent ATLAS azimuthal correlation results measured in the photo-nuclear collisions, and then we provide quantitative predictions for the long range correlations in $eA$ collisions in the EIC regime. With the unprecedented precision and the ability to change the size of the collisional system, the high luminosity EIC will open a new window to explore the physical mechanism responsible for the collective phenomenon.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2021)·23 citations
5. 05*

   Factorization and its Breaking in Dijet Single Transverse Spin Asymmetries in $pp$ Collisions

   Xiaohui Liu🇨🇳 · Felix Ringer🇺🇸 · Werner Vogelsang🇩🇪 · Feng Yuan🇺🇸

   We study factorization in single transverse spin asymmetries for dijet production in proton-proton collisions, by considering soft gluon radiation at one-loop order. We show that the associated transverse momentum dependent (TMD) factorization is valid at the leading logarithmic level. At next-to-leading-logarithmic (NLL) accuracy, however, we find that soft gluon radiation generates terms in the single transverse spin dependent cross section that differ from those known for the unpolarized case. As a consequence, these terms cannot be organized in terms of a spin independent soft factor in the factorization formula. We present leading logarithmic predictions for the single transverse spin dijet asymmetry for $pp$ collisions at RHIC, based on quark Sivers functions constrained by semi-inclusive deep inelastic scattering data. We hope that our results will contribute to a better understanding of TMD factorization breaking effects at NLL accuracy and beyond.

   ↳ hep-phhep-exnucl-exPRD(2020)·11 citations
6. 06*

   Magnetic moments of the octet, decuplet, low-lying charm, and low-lying bottom baryons in a nuclear medium

   Kazuo Tsushima🇧🇷

   We study the magnetic moments of the octet, decuplet, low-lying charm, and low-lying bottom baryons with nonzero light quarks in symmetric nuclear matter using the quark-meson coupling (QMC) model, which satisfies the constraint for the allowed maximum change (swelling) of the in-medium nucleon size derived from the $y$-scaling data for ${}^3$He$(e,e^{\prime })$ and ${}^{56}$Fe$(e,e^{\prime })$. The present QMC model also satisfies the expected allowed maximum enhancement of the nucleon magnetic moments in nuclear matter. Moreover, it has been proven that the calculated in-medium to free proton electromagnetic form factor (EMFF) ratios calculated within the QMC model, reproduce well the proton EMFF super ratio extracted from ${}^4\mathrm{He}(\vec{e},e^{\prime }\vec{p}{)}^3\mathrm{H}$ at Jefferson Laboratory (JLab). The medium modifications of the magnetic moments are estimated by evaluating the in-medium to free space baryon magnetic moment ratios to compensate the MIT bag deficiency to describe the free space octet baryon magnetic moments, where ratios are often measured directly in experiments even without knowing the absolute values, such as the free and bound proton electromagnetic form factors, as well as the European Muon Collaboration (EMC) effect to extract the structure function $F_2$ ratio of the bound to free nucleons by the corresponding cross section ratio. We also present the results calculated with the different current quark mass values for the strange and bottom quarks to see the possible impact. Furthermore, for a practical use, we give the explicit density dependent parametrizations for the vector potentials of the baryons and light-$(u,d)$ quarks, as well as for the effective masses of the baryons treated in this study, and of the mesons, $\omega ,\rho ,K,K^{\ast },\eta ,{\eta }^{\prime },D,D^{\ast },B$, and $B^{\ast }$.

   ↳ hep-phastro-ph.HEhep-exnucl-ex+1PTEP·35 citations
7. 07*

   A Hybrid Renormalization Scheme for Quasi Light-Front Correlations in Large-Momentum Effective Theory

   Xiangdong Ji🇺🇸 · Yizhuang Liu🇨🇳 · Andreas Schäfer🇩🇪 · Wei Wang🇨🇳 · Yi-Bo Yang🇨🇳 · Jian-Hui Zhang🇨🇳 · Yong Zhao🇺🇸

   In large-momentum effective theory (LaMET), calculating parton physics starts from calculating coordinate-space-$z$ correlation functions $\tilde{h}(z,a,P^z)$ in a hadron of momentum $P^z$ in lattice QCD. Such correlation functions involve both linear and logarithmic divergences in lattice spacing $a$, and thus need to be properly renormalized. We introduce a hybrid renormalization procedure to match these lattice correlations to those in the continuum $\overline{\mathrm{MS}}$ scheme, without introducing extra non-perturbative effects at large $z$. We analyze the effect of $\mathcal{O}({\Lambda }_{\mathrm{QCD}})$ ambiguity in the Wilson line self-energy subtraction involved in this hybrid scheme. To obtain the momentum-space distributions, we recommend to extrapolate the lattice data to the asymptotic $z$-region using the generic properties of the coordinate space correlations at moderate and large $P^z$, respectively.

   ↳ hep-phhep-exhep-latnucl-ex+1NPB(2021)·148 citations
8. 08*

   Quartic cumulant of baryon number in the presence of QCD critical point

   D. Mroczek🇺🇸 · J. Noronha-Hostler🇺🇸 · A. R. Nava Acuna🇺🇸 · C. Ratti🇺🇸 · P. Parotto🇩🇪 · M.A. Stephanov🇺🇸

   In the context of the ongoing search for the QCD critical point at the Relativistic Heavy-Ion Collider, we study the equation of state near the critical point in the temperature and baryon chemical potential plane. We use the parametric representation introduced in earlier literature, which maps the universal 3D Ising equation of state onto the QCD phase diagram using several non-universal parameters. We focus on the quartic cumulant of the baryon number, or baryon number susceptibility~${\chi }_4^B$, which can be accessed experimentally via net-proton fluctuation kurtosis measurements. It was originally predicted, through universality arguments based on the {\em leading} singular contribution, that ${\chi }_4^B$ and net-proton kurtosis should show a specific non-monotonic behavior due to the critical point. In particular, when following the freeze-out curve on the phase diagram by decreasing beam energy, the kurtosis is expected to dip, and then peak, when the beam energy scan passes close to the critical point. We study the effects of the non-universal and thus far unknown parameters of the Ising-to-QCD mapping on the behavior of~${\chi }_4^B$. We find that, while the peak remains a solid feature, the presence of the critical point does not necessarily cause a dip in ${\chi }_4^B$ on the freezeout line {\em below} the transition temperature. The critical point contribution to the dip appears only for a narrow set of mapping parameters, when subleading singular terms are sufficiently suppressed.

   ↳ nucl-thhep-phnucl-exPRC(2021)·53 citations
9. 09*

   Transverse Single-Spin Asymmetries of Midrapidity Direct Photons, Neutral Pions, and Eta Mesons in 200 GeV Polarized Proton-Proton Collisions at PHENIX

   Nicole Lewis🇺🇸

   Experimental observations of strikingly large transverse single-spin asymmetries (TSSAs) opened a window into quark and gluon dynamics present in hadronic collisions, revealing large spin-momentum correlations within nucleons and in the process of forming hadrons. Though originally measured in lower energy fixed target experiments, they have been found to persist in collisions with momentum transfer well into the perturbative regime of quantum chromodynamics (QCD) and yet their origin remains poorly understood. TSSA measurements have allowed for the development of both transverse momentum dependent and collinear twist-3 descriptions of nonperturbative spin-momentum correlations for both initial- and final-state effects. Results are presented for the TSSAs of direct photons, neutral pions, and eta mesons in the pseudorapidity range $|\eta |<0.35$ from $p^{\uparrow }+p$ collisions with $\sqrt{s}=200$ GeV at PHENIX. As hadrons, ${\pi }^0$ and $\eta$ mesons are sensitive to both initial- and final-state effects. At midrapidity, ${\pi }^0$ and $\eta$ measurements are sensitive to the dynamics of gluons along with a mix of quark flavors. These results are a factor of three increase in statistical precision and extend to higher transverse momentum when compared with previous PHENIX measurements in this kinematic region. Because direct photon production does not include hadronization, the direct photon TSSA is only sensitive to spin-momentum correlations in the proton. The kinematics of this result in particular make the direct photon TSSA a clean probe of gluon dynamics in the transversely polarized proton. All three of these asymmetries will help constrain the twist-3 trigluon collinear correlation function as well as the gluon Sivers function, improving our knowledge of spin-dependent gluon dynamics in QCD.

   ↳ hep-exnucl-ex1 citation

* 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.