Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session LN: Hadrons II |
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Chair: Kyungseon Joo, Jefferson Lab |
Saturday, October 31, 2020 10:30AM - 10:42AM |
LN.00001: Chasing QCD Signatures in Nuclei 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 Chromodynamics (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. [Preview Abstract] |
Saturday, October 31, 2020 10:42AM - 10:54AM |
LN.00002: Search for the Onset of Color Transparency in Protons Deepak Bhetuwal Color transparency (CT) is a unique prediction of Quantum Chromodynamics (QCD) where the final (and/or initial) state interactions of hadrons with the nuclear medium are suppressed for exclusive processes at high momentum transfers. \\[-0.3mm] \linebreak During the spring of 2018, the experiment E1206107 dedicated to measure the Proton Transparency was the first to run in Hall C at Jefferson Lab using the upgraded 12 GeV electron beam. Our experiment used the High Momentum Spectrometer (HMS) and the new Super High Momentum Spectrometer (SHMS) in coincidence, to measure the proton knockout from the $^{12}$C(e,e$^{'}$p) reaction to extract the proton nuclear transparency over the Q$^2\,=\,8\,-\,14.3$ (GeV/c)$^2$ range. Additional $^1$H(e,e$^{'}$p) measurements, in the same range, were used to determine the elementary process.} A rise in the proton transparency as a function of Q$^2$ is predicted to be a signature of the onset of CT. \linebreak This talk will summarize the status of the experiment analysis and some preliminary results. [Preview Abstract] |
Saturday, October 31, 2020 10:54AM - 11:06AM |
LN.00003: Study of hard color singlet exchange in dijet events with proton-proton collisions at $\sqrt{s}= 13$ TeV Cristian Baldenegro A study of pp collision events where the two leading jets are separated by a pseudorapidity gap void of radiation, is presented. Both jets have $p_\text{T, jet} > 40$ GeV and $1.4 < |\eta_\text{jet}| < 4.7$, with $\eta_\text{jet-1}\times \eta_\text{jet-2} < 0$. The analysis is based on data collected by the CMS experiment during a low luminosity high-$\beta^*$ run in 2015 at $\sqrt{s} = 13$ TeV, with an integrated luminosity of $0.66~\mathrm{pb}^{-1}$. The number of charged particles with transverse momentum $p_\text{T} > 200$ MeV in $-1 < \eta < 1$ is used to discriminate color-singlet exchange (CSE) dijet events from color-exchange dijet events. The fraction of CSE dijet events to all dijet events with similar kinematics, $f_\text{CSE}$, is presented as a function of various kinematic variables of interest. The results are compared to previous measurements and to perturbative quantum chromodynamics predictions. A first study of jet-gap-jet events with a leading proton using data collected jointly by the CMS and TOTEM experiments is presented. The protons are detected with the Roman pot detectors of TOTEM. The ratio $f_\text{CSE}$ in this sample is found to be $2.91 \pm 0.70~\mathrm{(stat)} ^{+ 1.02}_{- 0.94}~\mathrm{(syst)}$ times larger than in inclusive dijet production. [Preview Abstract] |
Saturday, October 31, 2020 11:06AM - 11:18AM |
LN.00004: The Constituent Counting Rule and Omega Photoproduction Trevor Reed, Christopher Leon, Frank Vera, Lei Guo, Brian Raue The constituent counting ruling (CCR) has been found to hold for numerous hard, exclusive processes. It predicts the differential cross section at high energies and fixed $\cos \theta_{c.m.}$ should follow $ \frac{d \sigma}{dt} \sim \frac{1}{s^{n-2}}$, where $n$ is the minimal number of constituents involved in the reaction. An in-depth examination of applying the CCR to the reaction $\gamma p \rightarrow \omega p$ at $\theta_{c.m.}\sim 90^\circ$ is provided. CLAS data with an energy range of $s = 5 - 8$ GeV$^2$, where the CCR has been shown to work in other reactions, is used in this analysis. The data selected to test the CCR is done so on the basis of momentum transfer, the Mandelstam variable $t$. A Taylor-series expansion of the fitting function is implemented to take advantage of data from nearby angle bins in the analysis. Na\"{i}vely, this reaction would have $n=9$ (or $n=10$ if the photon is in a $q\bar{q}$ state) and scaling of $\sim s^{-7}$ ($s^{-8}$) is expected. Instead, a scaling of $s^{-(9.08 \pm 0.11)}$ was observed. [Preview Abstract] |
Saturday, October 31, 2020 11:18AM - 11:30AM |
LN.00005: $\Lambda$ Fragmentation Study in the Current and Target Regions using CLAS Taya Chetry One of the basic phenomena of the quantum chromodynamics can be attributed to the so-called hadronization or fragmentation studies. In the hadronization process, the energetic struck quark transforms into color-neutral hadrons, effectively providing a probe to the confinement dynamics as well as the characteristic time-scales involved. These time-scales are significant to elucidate our understanding of the color-neutralization and subsequent non-perturbative formation of the observed hadrons. This talk will report the first-ever analysis of the semi-inclusive deep inelastic scattering of $\Lambda$ hyperons in the current and target fragmentation regions using the Jefferson Lab 5-GeV CLAS data-sets, which were taken with various nuclear targets (EG2 run). Results on multiplicity ratios and the transverse momentum broadening will be presented. The results from this work along with other EG2 meson studies exhibit a good benchmark for the upcoming CLAS12 color propagation measurements. [Preview Abstract] |
Saturday, October 31, 2020 11:30AM - 11:42AM |
LN.00006: SIDIS Single Pion Beam Spin Asymmetry measurements with CLAS 12 Paul Stoler, Stefan Diehl The CLAS12 detector at Jefferson Laboratory (JLab) started data taking with a polarized 10.6 GeV electron beam, interacting with an unpolarized liquid hydrogen target in February 2018. The collected statistics enable a high precision study of the structure function ratio F$_{\mathrm{LU}}^{\mathrm{sin\phi }}$/F$_{\mathrm{UU}}$ corresponding to the polarized electron beam spin asymmetry in semi-inclusive deep inelastic scattering. F$_{\mathrm{LU}}^{\mathrm{sin\phi }}$ is a twist-3 quantity which provides information about the quark gluon correlations in the nucleon. The contribution will present a simultaneous study of all three pion channels ($\pi^{\mathrm{+}}$, $\pi^{\mathrm{0}}$ and $\pi ^{\mathrm{-}})$ over a large kinematic range of z, x$_{\mathrm{B}}$, P$_{\mathrm{T}}$ and Q$^{\mathrm{2}}$ with virtualities Q$^{\mathrm{2}}$ ranging from 1 GeV$^{\mathrm{2\thinspace }}$up to 8 GeV$^{\mathrm{2}}$. Based on the available statistics, a fully multidimensional analysis becomes possible for the first time. The results will be compared with various model calculations. [Preview Abstract] |
Saturday, October 31, 2020 11:42AM - 11:54AM |
LN.00007: Dihadron beam spin asymmetries and partial waves from CLAS12, with sensitivity to $G_1^\perp$ Christopher Dilks Dihadron beam spin asymmetries present powerful probes of nucleon structure and hadronization, in particular, spin-momentum correlations in hadronization. Recent preliminary measurements at CLAS12 provide the first empirical evidence of a nonzero $G_1^\perp$, the parton helicity-dependent dihadron fragmentation function (DiFF), which encodes spin-momentum correlations in hadronization. A sign change is observed, with different behavior above and below the $\rho$ resonance. Moreover, the dihadron production cross section expands in partial waves, each containing a DiFF corresponding to the interference of dihadrons of particular polarizations; it turns out that $G_1^\perp$ needs the interference with a dihadron in a $p$-wave or higher order, that is, a dihadron with a nonzero angular momentum. Asymmetry amplitudes for each partial wave can be measured using a simultaneous fitting technique. This presentation focuses on updates to dihadron beam spin asymmetries at CLAS12, from 10.6 GeV electrons scattering on a proton target, along with prospects for learning more about nucleon structure and hadronization. [Preview Abstract] |
Saturday, October 31, 2020 11:54AM - 12:06PM |
LN.00008: First NLO calculation of quarkonium polarization in the improved color evaporation model Vincent Cheung, Ramona Vogt One of the best ways to understand hadronization in QCD is to study the production of quarkonium. The color evaporation model (CEM) and Nonrelativistic QCD (NRQCD) can describe production yields rather well but spin-related measurements like the polarization are stronger tests. In this talk, we will present the first NLO calculation of quarkonium polarization in the improved color evaporation model (ICEM) by considering all diagrams at the order of $\alpha_s^3$ and integrating over all color states. [Preview Abstract] |
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