Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session JF: Gluons and Sea Quarks |
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Chair: Ian Cloet, Argonne National Laboratory Room: Salon 6 |
Friday, October 27, 2017 10:30AM - 10:42AM |
JF.00001: Experiment E1039, polarized SeasQuest andi klein We have constructed a state-of-the-art, high luminosity polarized proton and deuteron target and propose to measure the Sivers asymmetry for the $\bar{u}$ and $\bar{d}$ sea quarks in the nucleon for four different Bjorken $x_B$ bins in the range $0.1 < x_B < 0.5$, using the Drell-Yan process at SeaQuest. We will: i) perform the first measurement of the Sivers asymmetry in Drell-Yan scattering for sea quarks; ii) determine the flavor dependence of the Sivers function for the $\bar{u}$ and $\bar{d}$ sea quarks iii) explore a unique range of virtualities and transverse momenta not accessible through $Z^0/W^\pm$ measurements; and iv) determine the sign and possibly the magnitude of the sea quark Sivers function in Drell-Yan for comparison to future sea quark Sivers function determinations in Semi Inclusive Deep Inelastic Scattering (SIDIS). Measuring a nonzero Sivers asymmetry would provide ``smoking gun'' evidence for nonzero orbital angular momentum of sea quarks; determination of the $\bar{u}$ and $\bar{d}$ Sivers function would allow comparison of the sea quark Sivers function flavor dependence to that for valence quarks; and measuring a sign change in the Sivers asymmetry between this measurement and future measurements at the EIC would test a fundamental prediction of QCD. [Preview Abstract] |
Friday, October 27, 2017 10:42AM - 10:54AM |
JF.00002: Measurement of Longitudinal Single-Spin Asymmetry for W Boson Production in Polarized p+p Collisions at STAR Amani Kraishan {The production of W-bosons in longitudinally polarized p+p collisions at RHIC is an ideal tool to study the spin-flavor structure of the proton at a high momentum scale, $Q\sim M_W$. $W^{-(+)}$ bosons are produced in $\bar u + d(\bar d+u ) $ collisions and can be detected through their leptonic decays, $e^{-}+\bar {\nu_e} (e^{+} + \nu _e)$. The charged lepton can be detected by the Time Projection Chamber $|\eta|< 1.3$ and the Electromagnetic Calorimeters (Barrel $|\eta|< 1.0 $ and EndCap $ 1< \eta< 2$). The parity-violating nature of the weak production process gives rise to large longitudinal single-spin asymmetries, $A_L$. The measurement of $A_L$ of W-bosons as a function of lepton pseudorapidity $\eta_e$ at STAR provides a unique probe to the valence and sea quark helicity distribution for the fractional momentum range of $0.05 < x < 0.2$ .\par In 2013 the STAR experiment collected an integrated luminosity about 250 pb^{-1 }\hspace{2mm} at \hspace{2mm} $\sqrt s $= 510 GeV with an average beam polarization of $\ 53 \%$. The preliminary results of W-bosons $A_{L}$ from 2013 data sample will be presented.} [Preview Abstract] |
Friday, October 27, 2017 10:54AM - 11:06AM |
JF.00003: Longitudinal Double-Spin Asymmetry A$_{\mathrm{LL}}$ for Inclusive Jet Production in Polarized Proton Collisions at $\surd $s $=$ 510 GeV Amilkar Quintero The STAR experiment at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory is carrying out a spin physics program in high-energy polarized proton collisions at center of mass energies up to 510 GeV, to gain a deeper insight into the spin structure and dynamics of the proton. The polarized gluon distribution function can be constrained in longitudinally polarized proton collisions through jet / di-jet production. Recent global analyses, which include results of the measurement of A$_{\mathrm{LL}}$ for inclusive jet production at 200 GeV at mid-rapidity at the STAR experiment, provide evidence of a non-zero gluon polarization in the measured range of partonic momentum fraction~of approximately 0.05\textless x\textless 0.3. We present preliminary results of the measurement of A$_{\mathrm{LL}}$ for inclusive jet production at 510 GeV. The higher center-of-mass energy allows to probe the polarized gluon distribution function at smaller x values. The data were recorded at the STAR experiment during the 2013 running period at mid-rapidity (\textbar $\eta $\textbar \textless 0.9). The integrated luminosity recorded at STAR used for this study is approximately 250 pb$^{\mathrm{-1}}$. We discuss and compare these results with previous STAR results and various next-to-leading order (NLO) calculations. [Preview Abstract] |
Friday, October 27, 2017 11:06AM - 11:18AM |
JF.00004: Using Longitudinally Polarized Proton+Proton Collisions To Constrain the Polarized Gluon Distribution Through Dijet Measurements at $\sqrt{s} = 510$ GeV at STAR Daniel Olvitt, Jr The production of jets from polarized p+p collisions at STAR is dominated by quark-gluon and gluon-gluon scattering. The dijet double spin asymmetry ($A_{LL}$) is sensitive to the polarized gluon distribution ($\Delta g(x)$). Dijets are also advantageous because the parton momentum fraction, x, of initial partons may be reconstructed to first order from the final state measurements. New data from 2013 with an estimated 250 pb$^{-1}$, at a beam polarization of $\sim$55\% at $\sqrt{s}$ = 510 GeV, has a figure of merit $\sim$3 times that of the 2012 data collected at $\sqrt{s}$ = 510 GeV. This talk will discuss the new dijet $A_{LL}$ preliminary results, this data use $\sim$40\% of the total 2013 data. The 2013 results are consistent with the published STAR dijet $A_{LL}$ measurements at $\sqrt{s}$ = 200 GeV, and the preliminary 2012 dijet $A_{LL}$. The 2013 dijet $A_{LL}$ is also consistent with global fits from DSSV and NNPDF collaborations, that incorporate the published STAR inclusive jet $A_{LL}$ at $\sqrt{s}$ = 200 GeV. [Preview Abstract] |
Friday, October 27, 2017 11:18AM - 11:30AM |
JF.00005: Updates on the Strange Sea Contributions to the Nucleon Spin. Fatiha Benmokhtar Understanding the spin structure of the nucleon in terms of quarks and gluons has been the goal of intense investigations during the last decades. The determination of strangeness is challenging and the only way of determining the strange distribution accurately from data is to improve the semi-inclusive information. In this talk I will present most recent updates on the strange sea spin measurements, and will talk about the preparation for the determination of the strange sea contribution to the nucleon spin through the pseudo-scalar method using semi-inclusive Kaon detection technique with CLAS12 at Jefferson Lab. A hybrid Ring Imaging CHerenkov (RICH) detector is under construction and will be used for pion-kaon-proton separation in the 3 to 8 GeV/c momentum range. Contributions from the Duquesne group will be presented. [Preview Abstract] |
Friday, October 27, 2017 11:30AM - 11:42AM |
JF.00006: Illuminating QCD and Nucleon Structure Through the Study of Hadrons Within Jets at STAR James Drachenberg The experiments of the RHIC spin program have provided critical insight into the spin structure of the nucleon, in particular shedding light on the roles played by gluon and sea-quark helicity. Over the last decade, theoretical and experimental engagement of transverse-spin phenomena have unlocked tantalizing opportunities for new insight into nucleon structure, e.g.~with higher dimensions in partonic momentum space. STAR data collected in 2011 at $\sqrt{s}=500$ GeV and 2012 at $200$ GeV reveal the first observations of transverse single-spin asymmetries in the azimuthal distributions of hadrons within jets from polarized proton collisions. These data combined with measurements from deep inelastic scattering and recent phenomenological breakthroughs may illuminate longstanding questions: Do factorization and universality extend to the transverse-momentum-dependent (TMD) picture in proton+proton collisions, e.g.~through the Collins mechanism? How do TMD functions evolve with changing kinematics? [Preview Abstract] |
Friday, October 27, 2017 11:42AM - 11:54AM |
JF.00007: Constraining the Sea Quark Distributions Through W$^\pm$ Cross Section Ratio Measurements at STAR Matthew Posik Over the years, extractions of parton distribution functions (PDFs) have become more precise, however there are still regions where more data are needed to improve constraints. One such distribution is the sea quark distribution near the valence region, in particular the $\bar{d}/\bar{u}$ distribution. Currently, measurements in the high-x region still have large uncertainties and suggest different trends for this distribution. The charged W cross section ratio is sensitive to the unpolarized sea quark distributions and could be used to help constrain the $\bar{d}/\bar{u}$ distribution. Through $pp$ collisions, the STAR experiment at RHIC, is well equipped to measure the e$^{\pm}$ leptonic decays of W$^{\pm}$ bosons in the mid-rapidity range $\left(|\eta| \leq 1 \right)$ at $\sqrt{s}$ = 500/510 GeV. At these kinematics STAR is sensitive to quark distributions near Bjorken-x of 0.16. STAR can also extend the sea quark sensitivity to higher x by measuring the leptonic decays in the forward rapidity range 1.1 $< \eta <$ 2.0. STAR runs from 2011 through 2013 have collected about 350 pb$^{-1}$ of data. Presented here are preliminary results for the 2011-2012 W cross section ratios ($\sim$100 pb$^{-1}$), and an update on the 2013 W cross section analysis ($\sim$250 pb$^{-1}$). [Preview Abstract] |
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