Speaker
Description
Understanding the proton spin structure in terms of quark and gluon degrees of freedom is one of the key open questions in the field of hadron physics. Gluon helicity, ∆g(x), related measurements play an important role in solving this “Spin Puzzle”. The polarized proton+proton collisions at the Relativistic Heavy Ion Collider provide unique opportunities for studying ∆g(x) by accessing it via a variety of probes through gluon-gluon or quark-gluon interactions at leading order. The double-helicity spin asymmetries (ALL) for π0 and jet production were measured at PHENIX and STAR, respectively, in 2009 using polarized p + p collisions at 200 GeV center-of-mass energy, revealing for the first time evidence of nonzero ∆g(x) for Bjorken-x in the range 0.05 < x < 0.2. Yet ∆g(x) for x < 0.05 is still poorly constrained. In this talk, we will report recent PHENIX measurements sensitive to the gluon polarization. The π0 ALL measurements at central rapidity (|η| < 0.35) at √s = 510 GeV can provide constraints on gluon polarization down to x near 10−2. At forward rapidity (1.2 < |y| < 2.2), also at 510 GeV, the measurement of ALL for J/ψ production has sensitivity to ∆g(x) for x ≈ 2 × 10−3.
