Measurements of double-helicity asymmetries in inclusive J／ψ production in longitudinally polarized p+p collisions at √s=510 GeV
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We report the double-helicity asymmetry, AJ/ψLL, in inclusive J/ψ production at forward rapidity as a function of transverse momentum pT and rapidity |y|. The data analyzed were taken during √s=510 GeV longitudinally polarized p+p collisions at the Relativistic Heavy Ion Collider in the 2013 run using the PHENIX detector. At this collision energy, J/ψ particles are predominantly produced through gluon-gluon scatterings, thus AJ/ψLL is sensitive to the gluon polarization inside the proton. We measured AJ/ψLL by detecting the decay daughter muon pairs μ+μ− within the PHENIX muon spectrometers in the rapidity range 1.2<|y|<2.2. In this kinematic range, we measured the AJ/ψLL to be 0.012±0.010 (stat) ±0.003 (syst). The AJ/ψLL can be expressed to be proportional to the product of the gluon polarization distributions at two distinct ranges of Bjorken x: one at moderate range x≈5×10−2 where recent data of jet and π0 double helicity spin asymmetries have shown evidence for significant gluon polarization, and the other one covering the poorly known small-x region x≈2×10−3. Thus our new results could be used to further constrain the gluon polarization for x<5×10−2.
- Physical review D
Physical review D 94(11), 112008, 2016-12
American Physical Society