Abstract
We present a calculation of direct photon production at next-to-leading order of QCD and a matching of this calculation with parton showers using POWHEG BOX. Based on simulations with POWHEG+PYTHIA, we perform a detailed phenomenological analysis of PHENIX data on prompt photon production and photon-hadron jet correlations in pp collisions at RHIC, considerably improving the description of these data with respect to previous calculations, and we suggest additional interesting analyses.
Highlights
Collaboration, and an inverse slope parameter was extracted from the pT -spectrum for 020% central collisions
Tomas Jezo,a Michael Klasenb and Florian Konigb aUniversita di Milano-Bicocca and INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy bInstitut fur Theoretische Physik, Westfalische Wilhelms-Universitat Munster, Wilhelm-Klemm-Straße 9, D-48149 Munster, Germany E-mail: tomas.jezo@mib.infn.it, michael.klasen@uni-muenster.de, florian.koenig@uni-muenster.de Abstract: We present a calculation of direct photon production at next-to-leading order of QCD and a matching of this calculation with parton showers using POWHEG BOX
We report on a re-calculation and validation of direct photon production at next-to-leading order (NLO) in section 2, a matching of this calculation with parton showers (PS) using POWHEG BOX [28] in section 3, and in section 4 on a successful phenomenological √reanalysis of PHENIX data on photon and photon-hadron production in pp collisions at s = 200 GeV, which form the baseline for the corresponding analyses in heavy-ion collisions
Summary
Direct photon production proceeds at LO through the partonic processes qq → γg and qg → γq. For photons with finite transverse momenta, they appear only in the final state and are canceled by the corresponding dipole terms arising from collinear factorisation. The LO direct and purely partonic fragmentation processes scale formally with O(ααs) and O(αs2), respectively. The latter must still be convoluted with fragmentation functions (FFs), which scale as. For the numerical evaluation of our NLO direct and LO fragmentation results, we computed the scalar loop integrals using LoopTools 2.13 [29]. Important advantages of NLO over LO calculations are a more reliable (typically larger) normalisation of the total cross section, its stabilisation with respect to variations of the unphysical renormalisation and factorisation scales, and improved descriptions of kinematic distributions. Disadvantages with respect to Monte Carlo generators are the restriction to at most one additional parton and the absence of hadronisation effects
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