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Title: Inclusive Cross Section and Double Helicity Asymmetry for {pi} 0 Production in p+p Collisions at s = 200 GeV: Implications for the Polarized Gluon Distribution in the Proton

Abstract

The PHENIX experiment presents results from the Relativistic Heavy Ion Collider 2005 run with polarized proton collisions at sqrt(s)=200 GeV, for inclusive {pi}{sup 0} production at midrapidity. Unpolarized cross section results are given for transverse momenta p{sub T}=0.5 to 20 GeV/c, extending the range of published data to both lower and higher p{sub T}. The cross section is described well for p{sub T}<1 GeV/c by an exponential in p{sub T}, and, for p{sub T}>2 GeV/c, by perturbative QCD. Double helicity asymmetries ALL are presented based on a factor of 5 improvement in uncertainties as compared to previously published results, due to both an improved beam polarization of 50%, and to higher integrated luminosity. These measurements are sensitive to the gluon polarization in the proton. Using one representative model of gluon polarization it is demonstrated that the gluon spin contribution to the proton spin is significantly constrained.

Authors:
 [1];  [2];  [3];  [2];  [3];  [4];  [2];  [2];  [4];  [2];  [2];  [3];  [5]
  1. University of Colorado, Boulder
  2. ORNL
  3. University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL)
  4. University of Tennessee, Knoxville (UTK)
  5. The
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
932050
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review D; Journal Volume: 76; Journal Issue: 5
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ASYMMETRY; CROSS SECTIONS; DISTRIBUTION; GLUONS; HELICITY; PRODUCTION; PROTONS

Citation Formats

Adare, A., Awes, Terry C, Batsouli, Sotiria, Cianciolo, Vince, Efremenko, Yuri, Mahurin, R., Read Jr, Kenneth F, Silvermyr, David O, Sorensen, Soren P, Stankus, Paul W, Young, Glenn R, Zhang, Chun, and PHENIX, Collaboration. Inclusive Cross Section and Double Helicity Asymmetry for {pi}0 Production in p+p Collisions at s = 200 GeV: Implications for the Polarized Gluon Distribution in the Proton. United States: N. p., 2007. Web.
Adare, A., Awes, Terry C, Batsouli, Sotiria, Cianciolo, Vince, Efremenko, Yuri, Mahurin, R., Read Jr, Kenneth F, Silvermyr, David O, Sorensen, Soren P, Stankus, Paul W, Young, Glenn R, Zhang, Chun, & PHENIX, Collaboration. Inclusive Cross Section and Double Helicity Asymmetry for {pi}0 Production in p+p Collisions at s = 200 GeV: Implications for the Polarized Gluon Distribution in the Proton. United States.
Adare, A., Awes, Terry C, Batsouli, Sotiria, Cianciolo, Vince, Efremenko, Yuri, Mahurin, R., Read Jr, Kenneth F, Silvermyr, David O, Sorensen, Soren P, Stankus, Paul W, Young, Glenn R, Zhang, Chun, and PHENIX, Collaboration. Mon . "Inclusive Cross Section and Double Helicity Asymmetry for {pi}0 Production in p+p Collisions at s = 200 GeV: Implications for the Polarized Gluon Distribution in the Proton". United States. doi:.
@article{osti_932050,
title = {Inclusive Cross Section and Double Helicity Asymmetry for {pi}0 Production in p+p Collisions at s = 200 GeV: Implications for the Polarized Gluon Distribution in the Proton},
author = {Adare, A. and Awes, Terry C and Batsouli, Sotiria and Cianciolo, Vince and Efremenko, Yuri and Mahurin, R. and Read Jr, Kenneth F and Silvermyr, David O and Sorensen, Soren P and Stankus, Paul W and Young, Glenn R and Zhang, Chun and PHENIX, Collaboration},
abstractNote = {The PHENIX experiment presents results from the Relativistic Heavy Ion Collider 2005 run with polarized proton collisions at sqrt(s)=200 GeV, for inclusive {pi}{sup 0} production at midrapidity. Unpolarized cross section results are given for transverse momenta p{sub T}=0.5 to 20 GeV/c, extending the range of published data to both lower and higher p{sub T}. The cross section is described well for p{sub T}<1 GeV/c by an exponential in p{sub T}, and, for p{sub T}>2 GeV/c, by perturbative QCD. Double helicity asymmetries ALL are presented based on a factor of 5 improvement in uncertainties as compared to previously published results, due to both an improved beam polarization of 50%, and to higher integrated luminosity. These measurements are sensitive to the gluon polarization in the proton. Using one representative model of gluon polarization it is demonstrated that the gluon spin contribution to the proton spin is significantly constrained.},
doi = {},
journal = {Physical Review D},
number = 5,
volume = 76,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The PHENIX experiment presents results from the Relativistic Heavy Ion Collider 2005 run with polarized proton collisions at {radical}(s)=200 GeV, for inclusive {pi}{sup 0} production at midrapidity. Unpolarized cross section results are given for transverse momenta p{sub T}=0.5 to 20 GeV/c, extending the range of published data to both lower and higher p{sub T}. The cross section is described well for p{sub T}<1 GeV/c by an exponential in p{sub T}, and, for p{sub T}>2 GeV/c, by perturbative QCD. Double helicity asymmetries A{sub LL} are presented based on a factor of 5 improvement in uncertainties as compared to previously published results,more » due to both an improved beam polarization of 50%, and to higher integrated luminosity. These measurements are sensitive to the gluon polarization in the proton. Using one representative model of gluon polarization it is demonstrated that the gluon spin contribution to the proton spin is significantly constrained.« less
  • The double helicity asymmetry in neutral pion production for p{sub T} = 1 to 12 GeV/c was measured with the PHENIX experiment to access the gluon-spin contribution, {Delta}G, to the proton spin. Measured asymmetries are consistent with zero, and at a theory scale of {mu}{sup 2} = 4 GeV{sup 2} a next to leading order QCD analysis gives {Delta}G{sup [0.02,0.3]} = 0.2, with a constraint of -0.7 < {Delta}G{sup [0.02,0.3]} < 0.5 at {Delta}{chi}{sup 2} = 9 ({approx}3{sigma}) for the sampled gluon momentum fraction (x) range, 0.02 to 0.3. The results are obtained using predictions for the measured asymmetries generatedmore » from four representative fits to polarized deep inelastic scattering data. We also consider the dependence of the {Delta}G constraint on the choice of the theoretical scale, a dominant uncertainty in these predictions.« less
  • The double helicity asymmetry in neutral pion production for p{sub T}=1 to 12 GeV/c was measured with the PHENIX experiment to access the gluon-spin contribution, DELTAG, to the proton spin. Measured asymmetries are consistent with zero, and at a theory scale of mu{sup 2}=4 GeV{sup 2} a next to leading order QCD analysis gives DELTAG{sup [0.02,0.3]}=0.2, with a constraint of -0.7<DELTAG{sup [0.02,0.3]}<0.5 at DELTAchi{sup 2}=9 (approx3sigma) for the sampled gluon momentum fraction (x) range, 0.02 to 0.3. The results are obtained using predictions for the measured asymmetries generated from four representative fits to polarized deep inelastic scattering data. We alsomore » consider the dependence of the DELTAG constraint on the choice of the theoretical scale, a dominant uncertainty in these predictions.« less
  • The double helicity asymmetry in neutral pion production for p{sub T} = 1 to 12 GeV/c was measured with the PHENIX experiment to access the gluon-spin contribution, {Delta}G, to the proton spin. Measured asymmetries are consistent with zero, and at a theory scale of {mu}{sup 2} = 4 GeV{sup 2} a next to leading order QCD analysis gives {Delta}G{sup [0.02,0.3]} = 0.2, with a constraint of -0.7 < {Delta}G{sup [0.02,0.3]} < 0.5 at {Delta}{chi}{sup 2} = 9 (-3{sigma}) for the sampled gluon momentum fraction (x) range, 0.02 to 0.3. The results are obtained using predictions for the measured asymmetries generatedmore » from four representative fits to polarized deep inelastic scattering data. We also consider the dependence of the {Delta}G constraint on the choice of the theoretical scale, a dominant uncertainty in these predictions.« less
  • We present an improved measurement of the double helicity asymmetry for {pi}{sup 0} production in polarized proton-proton scattering at {radical}(s)=200 GeV employing the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The improvements to our previous measurement come from two main factors: Inclusion of a new data set from the 2004 RHIC run with higher beam polarizations than the earlier run and a recalibration of the beam polarization measurements for the earlier run, which resulted in reduced uncertainties and increased beam polarizations. The results are compared to a Next to Leading Order (NLO) perturbative Quantum Chromodynamics (pQCD) calculation withmore » a range of polarized gluon distributions.« less