We report the double-helicity asymmetry, ALLJ/psi, in inclusive J/psi production at forward rapidity as a function of transverse momentum p_T 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/psi particles are predominantly produced through gluon-gluon scatterings, thus ALLJ/psi is sensitive to the gluon polarization inside the proton. We measured ALLJ/psi by detecting the decay daughter muon pairs mu^+mu^- within the PHENIX muon spectrometers in the rapidity range 1.2<|y|<2.2. In this kinematic range, we measured the ALLJ/psi to be 0.012 0.010 (stat) 0.003 (syst). The ALLJ/psi 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 pi^0 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.著者所属: 日本原子力研究開発機構(JAEA)