Event Structure and Double Helicity Asymmetry in Jet Production from Polarized p+p Collisions at sqrt(s) = 200 GeV

Abstract

We report on event structure and double helicity asymmetry ($A_{L}L$) of jet production in longitudinally polarized p+p collisions at $\sqrt{s}$=200 GeV. Photons and charged particles were measured at midrapidity $|\eta |<0.35$ with the requirement of a high-momentum ($>2$ GeV/$c$) photon in each event. Measured event structure is compared with {\sc pythia} and {\sc geant} simulations. The shape of jets and the underlying event were well reproduced at this collision energy. For the measurement of jet $A_{LL}$, photons and charged particles were clustered with a seed-cone algorithm to obtain the cluster $p_T$ sum ($p_T^{\mathrm{reco}}$). The effect of detector response and the underlying events on $p_T^{\mathrm{reco}}$ was evaluated with the simulation. The production rate of reconstructed jets is satisfactorily reproduced with the NLO pQCD jet production cross section. For $4<p_T^{\mathrm{reco}}<12$ GeV/$c$ with an average beam polarization of $<P>=49$ we measured $A_{LL}=-0.0014\pm 0.0037^{\mathrm{stat}}$ at the lowest $p_T^{\mathrm{reco}}$ bin (4-5 GeV/$c$) and $-0.0181\pm 0.0282^{\mathrm{stat}}$ at the highest $p_T^{\mathrm{reco}}$ bin (10-12 GeV/$c$) with a beam polarization scale error of 9.4% and a $\pT$ scale error of 10%. Jets in the measured $p_T^{\mathrm{reco}}$ range arise primarily from hard-scattered gluons with momentum fraction $0.02<x<0.3$ according to {\sc pythia}. The measured $A_{LL}$ is compared with predictions that assume various $\Delta G(x)$ distributions based on the GRSV parameterization. The present result imposes the limit $-1.1<{\int }_{0.02}^{0.3}dx\Delta G(x,{\mu }^2=1{\mathrm{GeV}}^2)<0.4$ at 95% confidence level or ${\int }_{0.02}^{0.3}dx\Delta G(x,{\mu }^2=1{\mathrm{GeV}}^2)<0.5$ at 99% confidence level.

376 authors from 58 institutions, 18 pages, 22 figures, and 5 tables. Submitted to Physical Review D. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html

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