Related papers: Direct vs. resolved photon: an exercise in factori…
The dependence of the photon structure on the photon virtuality, Q^2, is studied by measuring the reaction e^+p\to e^+ + {\rm jet} + {\rm jet} + {\rm X} at photon-proton centre-of-mass energies 134 < W < 223 GeV. Events have been selected…
Manifestation of QCD improved partonic structure of longitudinally polarized virtual photons in hard collisions is discussed. As an example, dijet production in ep collisions at HERA is investigated in detail.
We have studied the reaction $ep \to ep \gamma$ in the kinematics corresponding to electron scattering at small angles and photon scattering at large angles, where proton bremsstrahlung dominates. The analysis is based on the direct…
Photon-proton ($\gamma p$) interactions with~$Q^2<10^{-2}$~GeV$^2$ and deep-inelastic scattering ($\gamma^* p$) interactions with photon virtualities $Q^2>5$~GeV$^2$ are studied at the high energy electron-proton collider HERA. The…
Di-jet photoproduction in polarized ep collisions at HERA is studied as a possible tool to determine the parton content of circularly polarized photons. The concept of the `effective parton density' approximation is extended to the…
We generalize our previous model for $\gamma^* p$ scattering to $\gamma \gamma$ scattering. Performing a new simultaneous fit to $\gamma^* p$ and $\gamma \gamma$ total cross section we find an optimal set of parameters to describe both…
Jet tomography, the study of differential energy loss of hard scattered partons to infer the density profile of the medium, is greatly improved by precise knowledge of the initial energy of the hard probe. As photons are not strongly…
An NLO photon parton parametrization is presented based on the existing $F_2^\gamma$ measurements from $e^+e^-$ data and the low-$x$ proton structure function from $ep$ interactions. Also included in the extraction of the NLO parton…
Some recent developments in the physics of photon induced reactions are discussed. My presentation is biased towards HERA physics with the other summary talk (of David Miller) being biased towards the gamma-gamma topics. Within the context…
We calculate the photon production cross-section in $pA$ collisions under the assumption that the nucleus has reached the saturation regime, while the proton can be described by the standard parton distribution functions. We show that due…
We study the reaction mechanism for the photoproduction of the Lambda(1520), based on an effective Lagrangian approach. We investigate each contribution of the s-, u-, t-channel processes and contact term, separately. One of the most…
We investigate the production of direct photons in heavy ion collisions within the modified bottom-up thermalization scenario, which we show to be related to the thermalizing Glasma framework. The dynamics of the parton system up to…
$\gamma$-jet production is considered one of the best probes of the hot quark-gluon plasma in high-energy heavy-ion collisions since the direct $\gamma$ can be used to gauge the initial energy and momentum of the associated jet. This is…
In this note, we formulate the notions of the direct and inverse problems and contact points for the Feynman diagrams. For the electron-photon interaction case, the solutions of these direct and inverse problems are presented. The…
Present data on the partonic content of the photon from LEP, TRISTAN and HERA accelerators are reviewed and the essential aspects of the underlying ideas and methods are pointed out. Results of the unpolarized photon structure function F_2…
Direct photons are a powerful tool for elucidating the properties of the hot QCD matter in heavy-ion collisions. They are conventionally estimated by assuming prompt photon contributions in proton-proton collisions and thermal and prompt…
The production of J/Psi mesons in gamma gamma collisions allows for a test of factorization in color-octet processes as predicted by NRQCD and observed at the Tevatron. We calculate the cross sections for J/Psi production with direct and…
A real photon has a complicated nature, whereby it may remain unresolved or fluctuate into a vector meson or a perturbative q-qbar pair. In gamma-gamma events, this gives three by three combinations of the nature of the two incoming…
Results of relativistic calculations of the direct knockout (DKO) mechanism for the photon induced removal of a proton from a target nucleus over a wide range of energies and nuclei are presented. Spectroscopic factors used in the…
Hard photons emitted from energetic heavy ion collisions are very interesting since they do not experience nuclear interaction, and therefore they are useful to explore properties of nuclear matter. We investigated hard photon production…