Inclusive cross section and double-helicity asymmetry for pi(0) production at midrapidity in p plus p collisions at root s=510 GeV

Adare, Andrew
Apadula, Nicole
Campbell, Sarah
Ding, Lei
Hill, John
Hotvedt, Nels
Lajoie, John
Lebedev, Alexandre
Ogilvie, Craig
Patel, Milap
Perry, Joshua
Rinn, Timothy
Rosati, Marzia
Shaver, Alex
Shimomura, M.
Timilsina, Arbin
Whitaker, Shawn
et al.
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PHENIX measurements are presented for the cross section and double-helicity asymmetry (A(LL)) in inclusive pi(0) production at midrapidity from p + p collisions at root s = 510 GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-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 pi(0)A(LL) results follow an increasingly positive asymmetry trend with p(T) and root s with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on pi(0) and jet A(LL) and suggested a positive contribution of gluon polarization to the spin of the proton Delta G for the gluon momentum fraction range x > 0.05. The data presented here extend to a currently unexplored region, down to x similar to 0.01, and thus provide additional constraints on the value of Delta G.


This article is from Physical Review D 93 (2016): 011501, doi:10.1103/PhysRevD.93.011501. Posted with permission.