A GLOBAL QCD STUDY OF DIRECT PHOTON PRODUCTION

Abstract

A global QCD analysis of the direct photon production process from both fixed target and collider experiments is presented. These data sets now completely cover the parton $x$ range from 0.01 to 0.6, thereby providing a stringent test of perturbative QCD and parton distributions. Previous detailed studies of direct photons emphasized fixed target data. We find most data sets have a steeper $p_t$ distribution than the QCD prediction. Neither global fits with new parton distributions nor improved photon fragmentation functions can resolve this problem since the deviation occurs at different $x$ values for experiments at different energies. A more likely explanation is the need for additional broadening of the $k_t$ of the initial state partons. The magnitude and the possible physical origin of this effect are investigated and discussed.

8 page Latex file using epsf.sty for figures. 6 eps figures submitted separately in uuencoded file.

References in corpus (1)

• Global QCD Analysis and the CTEQ Parton Distributions

Cited by in corpus (63)

• Improved Parton Distributions from Global Analysis of Recent Deep Inelastic Scattering and Inclusive Jet Data
• Single Transverse-Spin Asymmetries in Hadronic Pion Production
• Prospects for Spin Physics at RHIC
• A new critical study of photon production in hadronic collisions
• Resummation of Threshold Corrections for Single-Particle Inclusive Cross Sections
• Parton intrinsic motion in inclusive particle production: unpolarized cross sections, single spin asymmetries and the Sivers effect
• Structure Functions of the Nucleon and their Interpretation
• High-p_T pion and kaon production in relativistic nuclear collisions
• Recoil and Threshold Corrections in Short-distance Cross Sections
• Direct Photons from Relativistic Heavy-Ion Collisions
• Evidence for Parton kT Effects in High pT Particle Production
• kt Effects in Direct-Photon Production
• Semi-Inclusive Deeply Inelastic Scattering at Small q_T
• The Isolated Photon Cross Section in p pbar Collisions at sqrt(s) = 1.8 TeV
• Photon Pair Production with Soft Gluon Resummation in Hadronic Interactions
• Constraints on the Proton's Gluon Distribution from Prompt Photon Production
• Unification of the $k_T$ and threshold resummations
• Direct Photon Production in Association With A Heavy Quark At Hadron Colliders
• Large Transverse Momentum Jet Production and the Gluon Distribution Inside the Proton
• Soft-gluon resummation and NNLO corrections for direct photon production
• Charmonia production in hadron colliders and the extraction of colour-octet matrix elements
• Ratio of the Isolated Photon Cross Sections at \sqrt{s} = 630 and 1800 GeV
• Electroweak corrections to hadronic photon production at large transverse momenta
• Search for Scalar Top and Scalar Bottom Quarks in $p\bar{p}$ collisions at $\sqrt{s}=1.8$ TeV
• The Isolated Photon Cross Section in the Central and Forward Rapidity Regions in p-pbar Collisions at sqrt(s) = 1.8 TeV
• Measurement of correlated $\mu -overlineb$ jet cross sections in $p\bar{p}$ collisions at $\sqrt{s}=1.8$ TeV
• Difficulties in the description of Drell-Yan processes at moderate invariant mass and high transverse momentum
• Study of the Uncertainty of the Gluon Distribution
• Origin of the $k_T$ smearing in direct photon production
• Comments on the high-$Q^2$ HERA anomaly
• Production of pizero and eta mesons at large transverse momenta in pp and pBe interactions at 530 and 800 GeV/c
• Single jet and prompt-photon inclusive production with multi-Regge kinematics: From Tevatron to LHC
• Measurement of direct photon production at Tevatron fixed target energies
• Study of the effective transverse momentum of partons in the proton using prompt photons in photoproduction at HERA
• Direct photon cross section with conversions at CDF
• Prompt photon hadroproduction at high energies in the k_T-factorization approach
• Search for Second and Third Generation Leptoquarks Including Production via Technicolor Interactions in $p\bar{p}$ collisions at $\sqrt{s}=1.8$ TeV
• Observation of Isolated High-ET Photons in Photoproduction at HERA
• Threshold resummation for the prompt-photon cross section revisited
• Saturating Cronin effect in ultrarelativistic proton-nucleus collisions
• Probing Polarized Parton Distributions with Meson Photoproduction
• Isolated-photon production in polarized pp collisions
• Prompt photon hadroproduction at high energies in off-shell gluon-gluon fusion
• Examination of direct-photon and pion production in proton-nucleon collisions
• Multiple Parton Emission Effects in Next-to-Leading Order Direct Photon Production
• Recoil and Power Corrections in High-x_T Direct-Photon Production
• Transverse momentum distribution in hadrons. What can we learn from QCD?
• J/psi Production at the LHC
• Prompt photons at RHIC
• Study of isolated prompt photon production in $p$-Pb collisions for the ALICE kinematics
• Measuring Polarized Gluon and Quark Distributions with Meson Photoproduction
• Isolated Photons at Hadron Colliders at O($\alpha alph{a}_s^2$) (I): Spin Averaged Case
• Inclusive Prompt Photon Production in Polarized pp Collisions at HERA-N
• High energy resummation of direct photon production at hadronic colliders
• Nuclear Effects in Prompt Photon Production at the Large Hadron Collider
• Cronin effect for protons and pions in pA collisions
• Enhanced Minijet Production in $A-A$ Collisions from Gluons with Large Transverse Momenta
• Probing nuclear modifications of parton distribution functions through the isolated prompt photon production at the LHC
• Photon Production from a Quark--Gluon Plasma
• Direct-Photon Production from SPS to RHIC Energies
• Production of pizero and eta mesons at large transverse momenta in pi-p and pi-Be interactions at 515 GeV/c
• Modified parton distributions and the HERA high-Q^2 anomaly
• High $p_T$ correlations of $\gamma$ and charged hadrons at RHIC