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Last modified: Sat Sep 9 03:00:47 CEST 2006

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Workshop on Photoproduction at collider energies:
from RHIC and HERA to LHC

ECT* - Trento, January 15-19, 2007


workshop description

Photon-induced collisions at high-energy have received much recent theoretical and experimental attention as a fruitful tool to investigate strong and electromagnetic interactions. These collisions complement studies in $e^+e^-$, deep-inelastic $ep$ scattering, as well as $pp$ and $AA$ collisions. At the HERA $ep$ collider, photon-hadron processes provide precise information on QCD (parton evolution at low- $x$, hadronic structure of the photon, ...) via measurements of inclusive hard photoproduction (heavy-flavour, jets, prompt photons ...) and exclusive diffractive vector meson production.

Beams of protons and heavy-ions at BNL-RHIC ( $\sqrt{s_{_{NN}}}$ = 200 GeV) and CERN-LHC energies( $\sqrt{s_{_{NN}}}$ = 5.5 - 14 TeV) generate also strong electromagnetic fields which correspond to a high flux of equivalent photons with maximum energies: $E_{\gamma}^{max}\approx$ 3, 100 GeV respectively, which open up the possibility to study $\gamma\gamma$ and $\gamma$- $p,A$ processes in a kinematic regime ( $\sqrt{s_{_{\gamma\,N}}}\lesssim$ 1 TeV) so far unexplored. At RHIC, coherent photonuclear production of $\rho$ and $J/\psi $, as well as photon-photon production of $e^+e^-$ pairs has been studied in ultraperipheral collisions (UPC) of gold nuclei. Quarkonium production in $\gamma\,A$ collisions at RHIC and LHC energies is an excellent probe of the gluon distribution function $G_A(x,Q^2)$ in nuclei providing a complementary tool to study parton saturation effects at low- $x$.

At Tevatron and the LHC, the study of inclusive and diffractive (photon- and Pomeron-induced) processes, - characterized by protons or ions emitted in the forward direction, rapidity gap(s), and a cluster of produced particles at central rapidities -, is the subject of a vigorous scientific programme not only centered on QCD but also on Higgs and beyond-SM signals.

After 6 years of rich physics operation at HERA-II and RHIC, and less than one year before the start of the LHC, it seems a timely moment to have a workshop, gathering both theorists and experimentalists, to discuss the current status of investigations of photon-induced processes at RHIC, HERA and Tevatron and preparations for extension of these studies in $AA$ and $pp$ collisions at the LHC. We are planning on a series of overview talks on these subjects, with plenty of time for discussion.