Bulletin of the American Physical Society
2019 Fall Meeting of the APS Division of Nuclear Physics
Volume 64, Number 12
Monday–Thursday, October 14–17, 2019; Crystal City, Virginia
Session EN: Gluon Spin in proton-proton Collisions |
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Chair: Jinlong Zhang Room: Salon K |
Tuesday, October 15, 2019 8:30AM - 8:42AM |
EN.00001: Direct photon cross section and double helicity asymmetry at mid-rapidity in $\vec{p}$+$\vec{p}$ collisions at $\sqrt{s}$ = 510 GeV Zhongling Ji Double helicity asymmetries $A_{LL}$ in hadron, jet and direct photon production in $\vec{p}$+$\vec{p}$ collisions at the Relativistic Heavy Ion Collider (RHIC) are sensitive to the gluon helicity contribution to the proton's spin. Unlike hadrons and jet, direct photon production provides clean access to the polarized gluon distribution since there is no hadronization. However, the small direct photon production cross section compared to that of $\pi^0$ and jet production has so far limited its utility in extracting the polarized gluon distribution. With recent increases in RHIC luminosity, we expect this limitation to be partially overcome and try to revisit this ``golden'' measurement of polarized gluons based on RHIC data from 2013. This analysis measures the direct photon cross section and $A_{LL}$ from the data collected employing the PHENIX detector at mid-rapidity ($|\eta| <$ 0.35). This will be the first direct photon cross section and $A_{LL}$ measurement in $\vec{p}$+$\vec{p}$ at $\sqrt{s}$ = 510 GeV with this detector. In this talk I will present the status of direct photon cross section and $A_{LL}$ analysis. [Preview Abstract] |
Tuesday, October 15, 2019 8:42AM - 8:54AM |
EN.00002: Longitudinal Double-Spin Asymmetry for Inclusive and Di-Jet Production in Polarized Proton Collisions at $\sqrt{s}=200$ GeV Nicholas Lukow \noindent The contribution of the gluon helicity to the spin of the proton is being studied through the use of the unique capability of the Relativistic Heavy Ion Collider (RHIC) to collide polarized protons at $\sqrt{s}=200\,$GeV and $\sqrt{s}=510\,$GeV. The kinematic coverage of the Solenoidal Tracker At RHIC (STAR) allows access to gluons through quark-gluon and gluon-gluon scattering processes which dominate jet production at low and medium transverse momentum. The polarized gluon distribution function, $\Delta g(x)$, can be constrained through a global analysis by measuring the longitudinal double-spin asymmetry ($A_{LL}$) of inclusive jet and di-jet production. \noindent Inclusive jet $A_{LL}$ results published by STAR at mid-rapidity ($|\eta| < 1$ ) at $\sqrt{s}=200\,$GeV have been used in global analyses and show a non-zero truncated first moment of $\Delta g(x)$ for momentum fraction, $x$, greater than 0.05. An additional data sample of $43\,$pb$^{-1}$ has been collected in 2015. This new data sample is 115\% larger than the previous sample and will improve the precision of $\Delta g(x)$ for $x>0.05$. The status of this new inclusive jet analysis will be presented along with the status of a di-jet analysis using the same data. [Preview Abstract] |
Tuesday, October 15, 2019 8:54AM - 9:06AM |
EN.00003: Probing Gluon Polarization in the Proton with Jets at STAR Carl Gagliardi The STAR Collaboration at RHIC is exploring the gluon polarization in the proton with a broad range of inclusive jet and dijet measurements in polarized $pp$ collisions. STAR measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for inclusive jet production in $pp$ collisions at 200 GeV provided the first clear evidence that the gluons in the proton with momentum fraction $x > 0.05$ are polarized. Recently, STAR completed the analysis of $A_{LL}$ for inclusive jets and dijets in 510 GeV $pp$ collisions, based on data that were recorded during 2012. The high statistical precision of the 2012 data required the development of new analysis procedures to minimize systematic uncertainties. Together, the measurements provide important new constraints on both the magnitude and $x$ dependence of the gluon polarization. The results are consistent with the previous measurements at 200 GeV in the overlapping kinematic region, $x > 0.05$, and extend the sensitivity down to $x \approx 0.015$. The final 2012 inclusive jet and dijet $A_{LL}$ analysis and results will be discussed, as well as the first ever measurement of $A_{LL}$ for the underlying event. A status report will also be given regarding other recent STAR gluon polarization measurements. [Preview Abstract] |
Tuesday, October 15, 2019 9:06AM - 9:18AM |
EN.00004: Understanding the Gluon's Contribution to the Spin of the Proton using a $\pi^0$ $A_{LL}$ Measurement with the STAR Experiment at RHIC Adam Gibson The origin of the proton's intrinsic spin has remained a puzzle for 30 years. The STAR experiment at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) has played a major role in showing that the spins of gluons with at least a moderate fraction ($x$) of the proton's momentum play a role at least as important as the spins of quarks. But, a significant fraction of the proton's spin remains unaccounted for. So, a major goal in nuclear physics is to constrain the gluon polarization distribution $\Delta g(x)$ at low $x$ and thus understand the spin contribution from low-$x$ gluons. At STAR, strategies toward this end include analyzing larger datasets, using higher center-of-mass energy proton collisions, and forward detectors. Building on a published result from a 2006 dataset, our measurement of the inclusive $\pi^0$ $A_{LL}$ with the intermediate pseudorapidity Endcap ElectroMagnetic Calorimeter (EEMC, $1.09 < \eta < 2.00$) in a large dataset (82 pb$^{-1}$ collected by STAR in 2012) utilizes these strategies and is complementary to other measurements at STAR. The status of the measurement will be presented including recent efforts at a data-driven approach. [Preview Abstract] |
Tuesday, October 15, 2019 9:18AM - 9:30AM |
EN.00005: R&D for the Forward Silicon Tracker at STAR Te-Chuan Huang The STAR experiment at the Relativistic Heavy Ion Collider is planning to extend its capability to the forward pseudorapidity region (2.5 $<$ $\eta$ $<$ 4). A set of detector upgrades, including a silicon tracker and small thin gap chambers as the Forward Tracking System (FTS), an electromagnetic and hadronic calorimeter as the Forward Calorimeter System (FCS), are currently designed and will be constructed and installed after the phase II of the Beam Energy Scan program. These upgrades will help STAR to address some open questions in QCD physics, examples are, nucleon spin structure, parton saturation, and transport properties of matter in relativistic heavy ion collisions. In this presentation, I will focus on the hardware R\&D of the silicon tracker in the FTS, as well as the results from simulations on the performance of the tracking system. [Preview Abstract] |
Tuesday, October 15, 2019 9:30AM - 9:42AM |
EN.00006: The STAR Forward Calorimeter Upgrade: Performance and Prototype David Kapukchyan The STAR experiment at the Relativistic Heavy Ion Collider, RHIC, is installing an upgrade consisting of tracking (small thin gap chambers and silicon) and electromagnetic and hadronic calorimetry at forward pseudorapidity, $2.5<\eta<4.0$, for pp, pA and AA running after the beam-energy-scan II. The new detectors will utilize the unique capabilities of RHIC to collide polarized protons and heavy ions to explore novel measurements in cold QCD such as the nucleon spin structure, parton saturation, and transport properties of matter in relativistic heavy ion collisions. The new calorimeter system consisting of a hodoscope preshower and both electromagnetic and hadron calorimeters have been tested at the Fermilab test beam. The full system prototype has been installed and successfully ran during the 2019 RHIC run. This talk will discuss the results of the tests, integration, and performance of the prototype in heavy ion collisions. [Preview Abstract] |
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