The production cross section of heavy quarks in real and virtual photon-photon collisions has been studied. The unintegrated gluon density in the photon was obtained using the CCFM evolution equation for the first time. The gluon density was implemented in the Monte Carlo generator CASCADE, and cross sections for heavy quark production in e + e − collisions were calculated and compared to LEP d...

Prompt photon production has been known to be a sensitive probe to the gluon luminosity inside a hadron because it is mainly produced by quark-gluon scattering. For the same reason prompt photon production should also be sensitive to the anomalous couplings of gluons to quarks. We will examine the effects of two specific anomalous couplings – chromoelectric and chromomagnetic dipole moments of ...

Prompt photon production has been known to be a sensitive probe to the gluon luminosity inside a hadron because it is mainly produced by quark-gluon scattering. For the same reason prompt photon production should also be sensitive to the anomalous couplings of gluons to quarks. We will examine the effects of two specific anomalous couplings – chromoelectric and chromomagnetic dipole moments of ...

We calculate the photon production cross section arising from the hard scattering of partons in nuclear collisions by taking into account the intrinsic parton transverse momentum distribution and the next-to-leading-order contributions. As first pointed out by Owens, the inclusion of the intrinsic transverse momentum distribution of partons leads to an enhancement of photon production cross sec...

Results from the PHENIX experiment on direct-photon production in Au+Au collisions at √ sNN = 200 GeV for transverse momenta 1 . pT . 13 GeV/c are presented. Direct-photon yields at high pT scale as expected for particle production in hard processes. This supports jetquenching models which attribute the suppression of high-pT hadrons to the energy loss of fast partons in the quark-gluon plasma....

A study of the J/ψ-meson photoproduction at large transverse momentum at HERA energies via the charm quark excitation in the photon is presented. Based on perturbative QCD, nonrelativistic quark model and photon structure function formalism, our calculation demonstrates that the charm content of the photon may be very important for the J/ψ photoproduction at the large transverse momentum. It is...

The present theoretical knowledge about photons and hard photoproduction processes, i.e. the production of jets, light and heavy hadrons, quarkonia, and prompt photons in photon-photon and photon-hadron collisions, is reviewed. Virtual and polarized photons and prompt photon production in hadron collisions are also discussed. The most important leading and next-to-leading order QCD results are ...

Recent experimental results of the Crystal-Barrel/TAPS collaboration at ELSA are presented. The experiments used a tagged photon beam incident on proton and neutron targets. Multiple photon final states were detected in the hermetically closed Crystal Barrel/TAPS detector setup, enabling the reconstruction of various neutral meson production channels. In addition to cross sections also photon b...

Direct photon production and W + jet production are processes of great interest for a number of reasons. Direct photon production is important for determinations of gluon distributions whileW + jet production is relevant for estimating backgrounds to new physics. Near threshold for the production of the final state in these processes one can resum logarithmic corrections originating from soft g...

We report on recent work concerning the phenomenology of initial-state partonkT effects in direct-photon production and related processes in hadron collisions. After a brief summary of a kT -smearing model, we present a study of recent results on fixed-target and collider direct-photon production, using complementary data on diphoton and pion production that provide empirical guidance on the re...