These proceedings show the preliminary results of the dijet longitudinal double spin asymmetry $A_{LL}$ in polarized proton-proton collisions at $\sqrt{s} = 200$ GeV for the pseudorapidity range $|η| \le 0.8$. The integrated luminosity of 10.6 pb$^{-1}$ used in this analysis was collected during RHIC Run-9. This result is presented as a function of the dijet invariant mass in multiple pseudorapidity acceptances. The division into different pseudorapidity regions allows the kinematics of the hard interaction to be constrained and information about the shape of $Δg(x)$ to be extracted for the first time. Comparisons are made with expectations from various different theoretical scenarios of polarized parton distributions of the proton.
PHENIX has a well defined program for measuring the polarized gluon distribution in the nucleon. We measure the gluon polarization in the proton with polarized $p$-$p$ collisions at PHENIX. The measurements of gluon polarization $via$ the direct-photon production and the heavy-flavor production can be significantly improved by the silicon vertex tracker upgrade. We have studied the possible improvements of the gluon polarization measurements using Monte Carlo simulation and they are shown and discussed in this paper.
The gluon polarization contribution to the proton spin is an integral part to solve the longstanding proton spin puzzle. At the Relativistic Heavy Ion Collider (RHIC), the STAR experiment has measured jets produced in mid-pseudo-rapidity, $|η| < $ 1.0, and full azimuth, $ϕ$, from longitudinally polarized $pp$ collisions to study the gluon polarization in the proton. At center of mass energies $\sqrt{s} =$ 200 and 510 GeV, jet production is dominated by hard QCD scattering processes such as gluon-gluon ($gg$) and quark-gluon ($qg$), thus making the longitudinal double-spin asymmetry ($A_{LL}$) …
Jets produced in the pseudo-rapidity range, $-1.0 < η< 1.0$, from $pp$ collisions at RHIC kinematics are dominated by quark-gluon and gluon-gluon scattering processes. Therefore the longitudinal double spin asymmetry $A_{LL}$ for jets is an effective channel to explore the longitudinal gluon polarization in the proton. At STAR, jets are reconstructed in full azimuth, from the charged-particle tracks seen by the Time Projection Chamber and electro-magnetic energy deposited in the Barrel and Endcap electro-magnetic calorimeters at both $\sqrt{s} = $ 200 and 510 GeV. Early STAR inclusive jet $A_{…
We perform the first simultaneous global QCD analysis of spin-averaged and spin-dependent parton distribution functions (PDFs), including single jet production data from unpolarized and polarized hadron collisions. We critically assess the impact of SU(3) flavor symmetry and PDF positivity assumptions on the quark and gluon helicity PDFs, and find strong bias from these, particularly on the gluon polarization. The simultaneous analysis allows for the first time extraction of individual helicity-aligned and antialigned PDFs with a consistent treatment of uncertainties.
Institute of Frontier and Interdisciplinary Science, Key Laboratory of Particle Physics and Particle Irradiation (MOE), Shandong University（山东大学前沿交叉科学研究院，粒子物理与粒子辐照教育部重点实验室）；School of Physics and Technology, University of Jinan（济南大学物理科学与技术学院）
Direct Estimate of the Gluon Polarization in the Nucleon
结合来自HERMES、SMC和COMPASS合作的关于高p_T强子产生中的不对称性的数据，我们对质子中的净胶子极化DeltaG进行了第一次粗略的直接估计。虽然这些数据采样的x范围有限，但它们没有提供DeltaG很大的暗示。使用强子不对称性数据固定不同理论参数化的归一化，我们发现DeltaG \sim 0.5的典型中心值，具有相似量级的不确定性。Δ G \ge 2的值不受Δ chi ^2 \sim 9到20的影响，这取决于所使用的参数化。
The gluon transversity distribution in the deuteron is defined by the matrix element between linearly-polarized deuteron states, and it could be investigated in proton-deuteron collisions in addition to lepton-deuteron scattering. The linear polarization of photon is often used, whereas it is rarely used for the spin-1 deuteron. Therefore, it is desirable to express deuteron-reaction cross sections in term of conventional deuteron spin polarizations for actual experimental measurements. In this work, we investigate how proton-deuteron Drell-Yan cross sections are expressed by the conventional …
Inclusive cross section and double helicity asymmetry for π^0 production in p+p collisions at sqrt(s)=200 GeV: Implications for the polarized gluon distribution in the proton
We present a systematic study on the influence of spatial correlations between the proton constituents, in our case gluonic hot spots, their size and their number on the symmetric cumulant SC(2,3), at the eccentricity level, within a Monte Carlo Glauber framework [1]. When modeling the proton as composed by 3 gluonic hot spots, the most common assumption in the literature, we find that the inclusion of spatial correlations is indispensable to reproduce the negative sign of SC(2,3) in the highest centrality bins as dictated by data. Further, the subtle interplay between the different scales of …
Probing Gluon Linear Polarization with Dihadron Fragmentation in $χ_b$ Decays
Beijing University of Chemical Technology（北京化工大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；China Center of Advanced Science and Technology（中国科学技术中心）；Center for High Energy Physics, Peking University（北京大学高能物理中心）
Accessing gluon polarization with high-$P_T$ hadrons in SIDIS
Wichita State University（威奇托州立大学）；South China Normal University（华南师范大学）；University of California, Los Angeles（加州大学洛杉矶分校）；Jefferson Lab（杰弗逊实验室）；University of Adelaide（阿德莱德大学）
$J/ψ$- or $Υ$-pair production at the LHC are promising processes to study the gluon transverse momentum distributions (TMDs) which remain very poorly known. In this article, we improve on previous results by including the TMD evolution in the computation of the observables such as the pair-transverse-momentum spectrum and asymmetries arising from the linear polarization of gluons inside unpolarized protons. We show that the azimuthal asymmetries generated by the gluon polarization are reduced compared to the tree level case but are still of measurable size (in the 5%-10% range). Such asymmetri…
We propose to utilize the polarization information of the $Z$ bosons in $ZZ$ production, via the gluon-gluon fusion process $gg\to ZZ$, to probe the $Zt\bar{t}$ gauge coupling. The contribution of longitudinally polarized $Z$ bosons is sensitive to the axial-vector component ($a_t$) of the $Zt\bar{t}$ coupling. We demonstrate that the angular distribution of the charged lepton from $Z$ boson decays serves well for measuring the polarization of $Z$ bosons and the determination of $a_t$. We show that $ZZ$ production via the $gg\to ZZ$ process complement to $Zt\bar{t}$ and $tZj$ productions in me…
Gluon Generalized TMD signatures at the EIC from exclusive heavy (axial-)vector meson production
University of Connecticut（康涅狄格大学）；Shandong University（山东大学）；Shandong Institute of Advanced Technology（山东高等技术研究院）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）
The longitudinal spin transfer represents the probability density of producing longitudinally polarized hadrons from longitudinally polarized quarks or circularly polarized gluons. It thus was usually measured in polarized reactions or high-energy collisions where weak interaction dominates. In this work, we propose the dihadron polarization correlation as a novel probe of this quantity. Such an observable does not require the fragmenting partons to be polarized and therefore can be measured in the currently available experimental facilities, such as Belle, RHIC, Tevatron, and the LHC. We make…
