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Title: Measurement of Direct Photon Production in p+p Collisions at sqrt(s)=200 GeV

Abstract

Cross sections for midrapidity production of direct photons in p+p collisions at the Relativistic Heavy Ion Collider (RHIC) are reported for transverse momenta of 3 < pT < 16 GeV/c. Next-to-leading order perturbative QCD (pQCD) describes the data well for pT >5 GeV/c, where the uncertainties of the measurement and theory are comparable. We also report on the effect of requiring the photons to be isolated from parton jet energy. The observed fraction of isolated photons is well described by pQCD for pT >7 GeV/c.

Authors:
 [1];  [2];  [1];  [1];  [1];  [1];  [1];  [3];  [1];  [1];  [2];  [4]
  1. ORNL
  2. University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL)
  3. University of Tennessee, Knoxville (UTK)
  4. The
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
932004
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 74 ATOMIC AND MOLECULAR PHYSICS; CROSS SECTIONS; HEAVY IONS; PHOTONS; PRODUCTION; QUANTUM CHROMODYNAMICS

Citation Formats

Awes, Terry C, Batsouli, Sotiria, Cianciolo, Vince, Efremenko, Yuri V, Plasil, F, Read Jr, Kenneth F, Silvermyr, David O, Sorensen, Soren P, Stankus, Paul W, Young, Glenn R, Zhang, Chun, and PHENIX, Collaboration. Measurement of Direct Photon Production in p+p Collisions at sqrt(s)=200 GeV. United States: N. p., 2007. Web.
Awes, Terry C, Batsouli, Sotiria, Cianciolo, Vince, Efremenko, Yuri V, Plasil, F, Read Jr, Kenneth F, Silvermyr, David O, Sorensen, Soren P, Stankus, Paul W, Young, Glenn R, Zhang, Chun, & PHENIX, Collaboration. Measurement of Direct Photon Production in p+p Collisions at sqrt(s)=200 GeV. United States.
Awes, Terry C, Batsouli, Sotiria, Cianciolo, Vince, Efremenko, Yuri V, Plasil, F, Read Jr, Kenneth F, Silvermyr, David O, Sorensen, Soren P, Stankus, Paul W, Young, Glenn R, Zhang, Chun, and PHENIX, Collaboration. Mon . "Measurement of Direct Photon Production in p+p Collisions at sqrt(s)=200 GeV". United States. doi:.
@article{osti_932004,
title = {Measurement of Direct Photon Production in p+p Collisions at sqrt(s)=200 GeV},
author = {Awes, Terry C and Batsouli, Sotiria and Cianciolo, Vince and Efremenko, Yuri V and Plasil, F 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 = {Cross sections for midrapidity production of direct photons in p+p collisions at the Relativistic Heavy Ion Collider (RHIC) are reported for transverse momenta of 3 < pT < 16 GeV/c. Next-to-leading order perturbative QCD (pQCD) describes the data well for pT >5 GeV/c, where the uncertainties of the measurement and theory are comparable. We also report on the effect of requiring the photons to be isolated from parton jet energy. The observed fraction of isolated photons is well described by pQCD for pT >7 GeV/c.},
doi = {},
journal = {Physical Review Letters},
number = 1,
volume = 98,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Cross sections for midrapidity production of direct photons in p+p collisions at the Relativistic Heavy Ion Collider (RHIC) are reported for transverse momenta of 3<p{sub T}<16 GeV/c. Next-to-leading order perturbative QCD (pQCD) describes the data well for p{sub T}>5 GeV/c, where the uncertainties of the measurement and theory are comparable. We also report on the effect of requiring the photons to be isolated from parton jet energy. The observed fraction of isolated photons is well described by pQCD for p{sub T}>7 GeV/c.
  • PHENIX has measured the e{sup +}e{sup -} pair continuum in sq root(s{sub NN})=200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e{sup +}e{sup -} yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the phi and the J/psi meson, the yield is consistent with expectations from correlated cc-bar production, although other mechanisms are not ruled out. In the low-mass region, below the phi, the p+p inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, themore » Au+Au minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of 4.7+-0.4{sup stat}+-1.5{sup syst}+-0.9{sup model}. At low mass (m{sub ee}<0.3 GeV/c{sup 2}) and high p{sub T} (1<p{sub T}<5 GeV/c) an enhanced e{sup +}e{sup -} pair yield is observed that is consistent with production of virtual direct photons. This excess is used to infer the yield of real direct photons. In central Au+Au collisions, the excess of the direct photon yield over the p+p is exponential in p{sub T}, with inverse slope T=221+-19{sup stat}+-19{sup syst} MeV. Hydrodynamical models with initial temperatures ranging from T{sub init}approx =300-600 MeV at times of 0.6-0.15 fm/c after the collision are in qualitative agreement with the direct photon data in Au+Au. For low p{sub T}<1 GeV/c the low-mass region shows a further significant enhancement that increases with centrality and has an inverse slope of Tapprox =100 MeV. Theoretical models underpredict the low-mass, low-p{sub T} enhancement.« less
  • We report a measurement of high-p{sub T} inclusive {pi}{sup 0}, {eta}, and direct photon production in p+p and d+Au collisions at {radical}s{sub NN} = 200 GeV at midrapidity (0 < {eta} < 1). Photons from the decay {pi}{sup 0} {yields} {gamma}{gamma} were detected in the barrel electromagnetic calorimeter of the STAR experiment at the Relativistic Heavy Ion Collider. The {eta} {yields} {gamma}{gamma} decay was also observed and constituted the first {eta} measurement by STAR. The first direct photon cross-section measurement by STAR is also presented; the signal was extracted statistically by subtracting the {pi}{sup 0}, {eta}, and {omega}(782) decay backgroundmore » from the inclusive photon distribution observed in the calorimeter. The analysis is described in detail, and the results are found to be in good agreement with earlier measurements and with next-to-leading-order perturbative QCD calculations.« less
  • We report a measurement of high-p{sub T} inclusive {pi}{sup 0}, {eta}, and direct photon production in p + p and d + Au collisions at {radical}s{sub NN} = 200 GeV at midrapidity (0 < {eta} < 1). Photons from the decay {pi}{sup 0} {yields} {gamma}{gamma} were detected in the Barrel Electromagnetic Calorimeter of the STAR experiment at the Relativistic Heavy Ion Collider. The {eta} {yields} {gamma}{gamma} decay was also observed and constituted the first {eta} measurement by STAR. The first direct photon cross section measurement by STAR is also presented, the signal was extracted statistically by subtracting the {pi}{sup 0},more » {eta}, and {omega}(782) decay background from the inclusive photon distribution observed in the calorimeter. The analysis is described in detail, and the results are found to be in good agreement with earlier measurements and with next-to-leading order perturbative QCD calculations.« less
  • Correlations of charged hadrons of 1 < p{sub T} < 10 Gev/c with high p{sub T} direct photons and {pi}{sup 0} mesons in the range 5 < p{sub T} < 15 Gev/c are used to study jet fragmentation in the {gamma} + jet and dijet channels, respectively. The magnitude of the partonic transverse momentum, k{sub T}, is obtained by comparing to a model incorporating a Gaussian k{sub T} smearing. The sensitivity of the associated charged hadron spectra to the underlying fragmentation function is tested and the data are compared to calculations using recent global fit results. The shape of themore » direct photon-associated hadron spectrum as well as its charge asymmetry are found to be consistent with a sample dominated by quark-gluon Compton scattering. No significant evidence of fragmentation photon correlated production is observed within experimental uncertainties.« less