Measurements of double-helicity asymmetries in inclusive production in longitudinally polarized collisions at GeV

Adare, A.*; Imai, Kenichi; Hasegawa, Shoichi   ; Nagamiya, Shoji; Sako, Hiroyuki   ; Sato, Susumu  ; Tanida, Kiyoshi   ; PHENIX Collaboration*; 328 of others*

We report the double-helicity asymmetry, , in inclusive production at forward rapidity as a function of transverse momentum and rapidity . The data analyzed were taken during GeV longitudinally polarized collisions at the Relativistic Heavy Ion Collider in the 2013 run using the PHENIX detector. At this collision energy, particles are predominantly produced through gluon-gluon scatterings, thus is sensitive to the gluon polarization inside the proton. We measured by detecting the decay daughter muon pairs within the PHENIX muon spectrometers in the rapidity range . In this kinematic range, we measured the to be . The can be expressed to be proportional to the product of the gluon polarization distributions at two distinct ranges of Bjorken : one at moderate range where recent data of jet and double helicity spin asymmetries have shown evidence for significant gluon polarization, and the other one covering the poorly known small-x region Thus our new results could be used to further constrain the gluon polarization for .