Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session LC: 3D Parton Structure of Hadrons: Transverse Momentum Distributions II |
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Chair: Daniel Pitonyak, Lebanon Valley College Room: Studio 2 |
Wednesday, October 13, 2021 2:00PM - 2:12PM |
LC.00001: Quark Sivers Function at Small-x: Spin-Dependent Odderon and the Sub-Eikonal Evolution M. Gabriel G Santiago, Yuri V Kovchegov We apply the formalism developed earlier (Kovchegov and Sievert, 2019) for studying transverse momentum dependent parton distribution functions (TMDs) at small Bjorken-x to construct the small-x asymptotics of the quark Sivers function. First, we explicitly construct the complete fundamental "polarized Wilson line" operator to sub-sub-eikonal order. We then express the quark Sivers function in terms of dipole scattering amplitudes containing various components of the "polarized Wilson line" and show that the dominant term which contributes to the quark Sivers function at small-x is the spin-dependent odderon, confirming the recent results of Dong, Zheng and Zhou (2019). We analyze the sub-eikonal corrections to the quark Sivers function and construct new small-x evolution equations resumming double-logarithmic powers of αs ln2 (1/x) with αs the strong coupling constant. We solve the corresponding novel evolution equations in the large_Nc limit, obtaining a sub-eikonal correction to the spin-dependent odderon contribution. |
Wednesday, October 13, 2021 2:12PM - 2:24PM |
LC.00002: Transverse Λ/$\bar{\Lambda}$ Hyperon Polarization Measurements at LHCb Cynthia Nunez Spontaneous transverse Λ (uds) polarization observed over four decades ago contradicted early leading order perturbative QCD calculations. Recent studies have linked the polarization to the process of hadronization, where hyperon polarization from unpolarized proton-proton collisions comes from either including higher order twist-3 collinear multi-parton correlation matrix elements or convolution of a twist-2 transverse-momentum dependent parton distribution function with a transverse-momentum dependent fragmentation function. Measurements of hyperon polarization from unpolarized p-p and p-Pb collisions, along with e+e- and semi-inclusive deep inelastic scattering measurements can put us in a better position to understand this decades-old question in QCD. The high energy from the LHC, which produces hyperons in abundance, and the coverage and precision measurement possibilities from LHCb’s particle identification and forward geometry will be ideal to study polarization of various hyperons as a function of both pT and xF. The status of Λ/$\bar{\Lambda}$ polarization measurements performed for p-Pb collisions, $\sqrt{s} = 5.02$ TeV, at LHCb will be presented. |
Wednesday, October 13, 2021 2:24PM - 2:36PM |
LC.00003: Transverse Λ Polarization in e+e- collisions Fanyi Zhao, Leonard Gamberg, Zhong-bo Kang, Ding Yu Shao, John D Terry In single-inclusive e+e- annihilation, when the transverse momentum of the produced Λ baryon is measured with respect to the thrust axis, a transverse momentum dependent (TMD) factorization formalism is required and the polarization is generated by the TMD polarizing fragmentation function (TMD PFF), D1T⊥. However, when the transverse momentum of the Λ baryon is measured with respect to the momentum of the initial leptons, a collinear twist-3 formalism is required and the polarization is generated by the intrinsic collinear twist-3 fragmentation function DT . In this talk, we develop a TMD formalism for Λ polarization and present a recent twist-3 formalism that was established to describe Λ polarization. For phenomenology, we demonstrate that the Λ polarization at OPAL and Belle can be described using the twist-2 TMD factorization formalism and make a theoretical prediction for this polarization in the collinear twist-3 formalism at Belle. |
Wednesday, October 13, 2021 2:36PM - 2:48PM |
LC.00004: Beam spin asymmetries of π+π0 and π-π0 dihadrons from SIDIS at CLAS12 Christopher J Dilks Spin asymmetries provide a wide range of insights into nucleon structure and hadronization. Recent measurements of beam spin asymmetries of π+π- dihadrons from SIDIS at CLAS12 provide the first empirical evidence of a nonzero G1⊥, the parton helicity-dependent dihadron fragmentation function (DiFF) encoding spin-momentum correlations in hadronization. These measurements have been extended to help further characterize H1⊥ and H1∠, the DiFFs dependent on parton transverse spin, via a multidimensional partial wave analysis, giving access to the dependence on the interference of dihadrons of particular polarizations. Reconstruction of π0s allows for further extension of these measurements to π+π0 and π-π0 dihadrons. The DiFFs describing π+π- production differ from those describing π+π0 and π-π0 production, which involve different quark flavors along with a strong suppression of the exclusive diffractive contribution. This presentation will focus on comparisons of beam spin asymmetries for these three dihadron flavors, which will help shed light on a more comprehensive picture of dihadron fragmentation. |
Wednesday, October 13, 2021 2:48PM - 3:00PM |
LC.00005: Transverse Spin Dependent Azimuthal Correlations of Charged Pion Pairs in $p^{\uparrow}p$ Collisions at $\sqrt s = 200$ GeV at STAR Babu R Pokhrel At leading twist, the transversity distribution function, $h^{q}_{1}(x)$, where $x$ is the longitudinal momentum fraction of the proton carried by quark $q$, encodes the transverse spin structure of the nucleon. Extraction of it is difficult because of its chiral-odd nature. In polarized proton-proton ($p^\uparrow p$) collisions, it can be coupled with a spin-dependent fragmentation function. This coupling leads to experimentally measurable oppositely charged hadron-pair (di-hadron) azimuthal correlations, $A_{UT}$, between the spin of the fragmenting quark and the final state di-hadron, which directly probes $h_{1}^{q}(x)$. The STAR experiment at RHIC has previously measured non-zero $A_{UT}$ for $\pi^+\pi^-$ pairs using $p^\uparrow p$ collisions at $\sqrt{s} = 200$ GeV from 2006, corresponding to an integrated luminosity, $L$, of $1.8\ \mathrm{pb^{-1}}$. In 2015, STAR collected $L\sim 48\ \mathrm{pb^{-1}}$ of $p^{\uparrow}p$ data at $\sqrt{s}=200$ GeV. This dataset provides highest precision $A_{UT}$ measurements at $\sqrt{s}=200$ GeV to date, which covers quark momentum fractions $0.1\textless x\textless 0.4$, sensitive to valence quark $h_{1}^{q}(x)$. We will present preliminary results on $A_{UT}$ for $\pi^+\pi^-$pairs based on this dataset. |
Wednesday, October 13, 2021 3:00PM - 3:12PM |
LC.00006: Transverse Spin Dependent Azimuthal Correlations of Charged Pion Pairs in $p^{\uparrow}p$ collisions at $\sqrt{s} = 510$ GeV at STAR Navagyan Ghimire The transversity distribution $h^q_1(x)$ describes transversely polarized quarks inside a transversely polarized nucleon. As $h^q_1(x)$ is chiral-odd, it can only be accessed via a process where it couples to another chiral-odd function, such as the spin-dependent interference fragmentation function (IFF) in $p^\uparrow p$ collisions. The coupling of $h^q_1(x)$ and IFF yields an experimentally measurable di-hadron correlation asymmetry, $A_{UT}$. To access $h^q_1(x)$ at high $Q^2$, where QCD framework is well understood, precise measurement of $A_{UT}$ at high center-of-mass energy, $\sqrt s$, is crucial. Previously, the STAR experiment at RHIC measured non-zero $A_{UT}$ using $p^\uparrow p$ data from 2011 at $\sqrt s= 500$ GeV with an integrated luminosity of $25$ pb$^{-1}$. In 2017, STAR collected $\sim 350$ pb$^{-1}$ of $p^\uparrow p$ data at $\sqrt s=510$ GeV which will significantly improve the statistical precision of $A_{UT}$ measurement and thus further constrain global fits of $h^q_1(x)$, especially for $0.07 |
Wednesday, October 13, 2021 3:12PM - 3:24PM |
LC.00007: Gauge-invariant TMD factorization for Drell-Yan hadronic tensor at small $x$ Ian Balitsky The Drell-Yan hadronic tensor is calculated in the Sudakov region $s\gg Q^2\gg q_\perp^2$ |
Wednesday, October 13, 2021 3:24PM - 3:36PM |
LC.00008: Nuclear Modifications to Transverse Momentum Distributions John D Terry, Mishary Alrashed, Hongxi Xing, Zhong-bo Kang, Daniele Paolo Anderle We perform the first simultaneous global QCD extraction of the transverse momentum dependent (TMD) Parton Distribution Functions in nuclei and the nuclear modified TMD Fragmentation Functions, which encode the three-dimensional information on the partonic structure of nuclei, and hadron formation in a nuclear medium, respectively. This analysis takes into account the world data from semi-inclusive electron-nucleus deep inelastic scattering and Drell-Yan di-lepton production in proton-nucleus collisions, comprising a total of 126 data points from 6 data sets. We quantify for the first time the broadening of partonic distributions in nuclei comparing with those in free nucleons. We also make predictions for the ongoing JLab 12 GeV program and future EIC measurements, which will further constrain the three-dimensional partonic structure of nuclei. |
Wednesday, October 13, 2021 3:36PM - 3:48PM |
LC.00009: Chasing QCD Signatures in Nuclei via Color Transparency Study Lamiaa El Fassi Over the last few decades several experiments have used atomic nuclei as unique laboratories to probe the internal structure of the strongly interacting particles, namely hadrons. Indeed, the nucleus could be used as a revealing medium of the time evolution of elementary configurations of the hadron wave function. One of the ordinary approaches used to probe this picture involves searching for the onset of various phenomena, which are naturally predicted by Quantum Chromo Dynamics (QCD), the theory of strong interactions. One such phenomena is the Color Transparency (CT). It refers to the production and propagation of a small size hadron-like configuration which, under specific conditions, stays intact in a transparent nuclear medium. In this talk, I will briefly review the status of the experimental search for CT effects and highlight the upcoming Jefferson Lab experiment that will study CT at higher momentum transfer using the CLAS12 spectrometer. |
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