Inclusive cross section and double-helicity asymmetry forπ0production at midrapidity inp+pcollisions ats

Abstract

PHENIX measurements are presented for the cross section and double-helicity asymmetry (ALL) in inclusive π 0 production at midrapidity from p+p collisions at √ s = 510 GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbativequantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. The π 0 ALL results follow an increasingly positive asymmetry trend with pT and √ s with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on π 0 and jet ALL, and suggested a positive contribution of gluon polarization to the spin of the proton ∆G for the gluon momentum fraction range x > 0.05. The data presented here extend to a currently unexplored region, down to x ∼ 0.01, and thus provide additional constraints on the value of ∆G.

Nucleon spin structure functions at NNLO in the presence of target mass corrections and higher twist effects

“…In addition to the DIS and SIDIS fixed-target data, a remarkable amount of data from longitudinally polarized proton-proton collisions at the RHIC has become available recently [122,123]. The RHIC data can be expected to further constrain the gluon helicity distribution especially at the small momentum fractions, down to x ∼ 0.01 [16,73,105,124]. The double-helicity asym-metries for jet and π 0 production are directly sensitive to the gluon helicity distribution over a small range of x, because of the dominance of gluon-gluon and quarkgluon initiated subprocesses in the kinematic range accessed by PHENIX at the RHIC [125].…”

“…Current phenomenological spin-dependent parton distribution function (PDF) analysis uses the spindependent DIS measurements on g p,n,d 1 (x, Q 2 ) and g p,n,d 2 (x, Q 2 ), see Table I. Beside these data sets, one can also include the recent PHENIX measurement on neutral-pion π 0 productions [15,16] at √ s = 200, 510 GeV and inclusive jet production from the STAR Collaboration [17] in polarized proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC). The longitudinal single-spin asymmetries in W ± weak boson production [18,19] from polarized proton-proton collisions also can be used.…”

Measurement of double helicity asymmetries ($A_{LL}$) at mid- and forward rapidities in longitudinally polarized $p+p$ collisions at $\sqrt{s}$ = 510 GeV with PHENIX experiment

“…The central π 0 asymmetries at 200 [1] and 510 GeV [3] are displayed in Fig. 1 as a function of x T = p T / √ s. One clearly sees the increasingly nonzero asymmetries with increasing x T .…”

Analytical approaches to the determination of spin-dependent parton distribution functions at NNLO approximation

“…In addition, the nucleon spin structure has been always a fundamental question in high energy physics so it has been extensively studied both in theory and experiment in recent decades. From an experimental point of view, several experiments have been set up to study the longitudinal spin structure of the nucleon, such as COMPASS experiments at CERN [23][24][25], HERMES experiments at DESY [26][27][28], many experiments at Jefferson Laboratory (JLAB) [29][30][31], and PHENIX and STAR experiments at the protonproton (pp) Relativistic Heavy Ion Collider (RHIC) [32][33][34][35]. The majority of this experimental information on spin-dependent PDFs come from the neutral-current inclusive and semi-inclusive deep inelastic scattering, DIS and SIDIS, with charged lepton beams ℓ ± and nuclear targets.…”