We report the first measurement of the inclusive jet and the dijet longitudinal double-spin asymmetries, $A_{LL}$, at midrapidity in polarized $pp$ collisions at a center-of-mass energy $\sqrt{s} = 510$ GeV. The inclusive jet $A_{LL}$ measurement is sensitive to the gluon helicity distribution down to a gluon momentum fraction of $x\approx 0.015$, while the dijet measurements, separated into four jet-pair topologies, provide constraints on the $x$ dependence of the gluon polarization. Both results are consistent with previous measurements made at $\sqrt{s}= 200$ GeV in the overlapping kinematic region, $x > 0.05$, and show good agreement with predictions from recent next-to-leading order global analyses.
Fractions of the next-to-leading-order cross section for inclusive jet production arising from quark-quark, quark-gluon and gluon-gluon scattering in pp collisions (200GeV)
Fractions of the next-to-leading-order cross section for inclusive jet production arising from quark-quark, quark-gluon and gluon-gluon scattering in pp collisions (500GeV)
The upper panel shows the jet yield vs detector jet pT in data and simulation for each of the three trigger categories. The lower three panels show the relative differences between data and simulation (JP0)
We present the measurement of the transverse single-spin asymmetry of weak boson production in transversely polarized proton-proton collisions at $\sqrt{s} = 500~\text{GeV}$ by the STAR experiment at RHIC. The measured observable is sensitive to the Sivers function, one of the transverse momentum dependent parton distribution functions, which is predicted to have the opposite sign in proton-proton collisions from that observed in deep inelastic lepton-proton scattering. These data provide the first experimental investigation of the non-universality of the Sivers function, fundamental to our understanding of QCD.
$P_{T}$ Recoil distribution of events simulated with PYTHIA 6.4 and reconstructed before and after the boson's PT correction has been applied.
Estimated background contributions for the $W^+ -> ev$ data yields.
Estimated background contributions for the $W^- -> ev$ data yields.
We report the first measurement of the parity violating single-spin asymmetries for midrapidity decay positrons and electrons from $W^{+}$ and $W^{-}$ boson production in longitudinally polarized proton-proton collisions at $\sqrt{s}=500 $GeV by the STAR experiment at RHIC. The measured asymmetries, $A^{W^+}_{L}=-0.27\pm 0.10\/({\rm stat.})\pm 0.02\/({\rm syst.}) \pm 0.03\/({\rm norm.})$ and $A^{W^-}_{L}=0.14\pm 0.19\/({\rm stat.})\pm 0.02 \/({\rm syst.})\pm 0.01\/({\rm norm.})$, are consistent with theory predictions, which are large and of opposite sign. These predictions are based on polarized quark and antiquark distribution functions constrained by polarized DIS measurements.
$E^e_T$ for W+ (bottom) and W− (top) events showing the candidate histograms in black, the full background estimates in blue and the signal distributions in yellow.
$E^e_T$ for W+ (bottom) and W− (top) events showing the candidate histograms in black, the full background estimates in blue and the signal distributions in yellow.
Longitudinal single-spin asymmetry, AL, for W± events as a function of the leptonic pseudorapidity, $\eta_e$, for 25 < $E^e_T$ < 50 GeV in comparison to theory predictions
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