Event structure and double helicity asymmetry in jet production from polarized p plus p collisions at root s=200 GeV

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2011-07-21
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Adare, Andrew
Grau, Nathan
Ogilvie, Craig
Hill, John
Lajoie, John
Lebedev, Alexandre
Ogilvie, Craig
Pei, H.
Rosati, Marzia
Skutnik, S.
Vale, Carla
et al.
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Physics and Astronomy
Abstract

We report on the event structure and double helicity asymmetry (A(LL)) of jet production in longitudinally polarized p + p collisions at root s = 200 GeV. Photons and charged particles were measured by the PHENIX experiment at midrapidity vertical bar eta vertical bar < 0.35 with the requirement of a high-momentum (> 2 GeV/c) photon in the event. Event structure, such as multiplicity, p(T) density and thrust in the PHENIX acceptance, were measured and compared with the results from the PYTHIA event generator and the GEANT detector simulation. 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 pT sum (p(T)(reco)). The effect of detector response and the underlying events on p(T)(reco) was evaluated with the simulation. The production rate of reconstructed jets is satisfactorily reproduced with the next-to-leading-order and perturbative quantum chromodynamics jet production cross section. For 4< p(T)(reco) < 12 GeV/c with an average beam polarization of < P > = 49% we measured Lambda(LL) = -0.0014 +/- 0.0037(stat) at the lowest p(T)(reco) bin (4-5 GeV= c) and -0.0181 +/- 0.0282(stat) at the highest p(T)(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)(reco) range arise primarily from hard-scattered gluons with momentum fraction 0: 02 < x < 0: 3 according to PYTHIA. The measured A(LL) is compared with predictions that assume various Delta G(x) distributions based on the Gluck-Reya-Stratmann-Vogelsang parameterization. The present result imposes the limit -a.1 < integral(0.3)(0.02) dx Delta G(x, mu(2) = GeV2) < 0.4 at 95% confidence level or integral(0.3)(0.002) dx Delta G(x, mu(2) = 1 GeV2) < 0.5 at 99% confidence level.

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This article is published as Adare, A., S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander et al. "Event structure and double helicity asymmetry in jet production from polarized p+ p collisions at s= 200 GeV." Physical Review D 84, no. 1 (2011): 012006. DOI:10.1103/PhysRevD.84.012006. Posted with permission.

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