A brief introduction to the physics of ultraperipheral collisions at collider energies is given. Photon-hadron (proton/ nucleus) and photon-photon interactions can be studied in a hitherto unexplored energy regime. 1 Some features of Ultraperipheral Collisions (UPC) Photon-photon and photon-hadron interactions can also be studied in hadron-hadron collisions [1]. This may be surprising since in ...

It is shown how the increase of classical threshold for hard photon absorption on far infrared background can be achieved with the use of deformed kinematics, described by κ-deformation of Poincaré symmetries in bicrossproduct basis. We consider the dependence of absorption threshold on the scattering angles for ingoing photons as well as outgoing e − e pair. We discuss in detail the threshold ...

PHENIX has measured low momentum direct photons at 200 GeV via their external conversions to di-electron pairs on a specific detector material. The advantage of this method along with the selection of this detector material is a purity to large extent in photon identification. We present the results of the measurements of low momentum direct photons at 39 GeV and 62.4 GeV based on the same exte...

At the Mott transition of a quark/meson plasma, mesons become un-bound. This leads to the eeect of critical scattering, which is studied by investigating photon pair production due to the process q q !. This process can proceed either via direct annihilation or via the formation of a mesonic resonance. It is shown that the latter channel leads to an enhancement of photon pairs with invariant ma...

At linear colliders, the e + e − luminosity is limited by beam-collision effects, which determine the required emittances of beams in damping rings (DRs). While in γγ collisions at the photon collider, these effects are absent, and so smaller emittances are desirable. In present damping rings designs, nominal DR parameters correspond to those required for e + e − collisions. In this note, I wou...

At the Mott transition of a quark/meson plasma, mesons become unbound. This leads to the effect of critical scattering, which is studied by investigating photon pair production due to the process qq̄ → γγ. This process can proceed either via direct annihilation or via the formation of a mesonic resonance. It is shown that the latter channel leads to an enhancement of photon pairs with invariant ...

A novel method of electron beam cooling is considered which can be used for linear colliders. The electron beam is cooled during collision with focused powerful laser pulse. With reasonable laser parameters (laser flash energy about 10 J) one can decrease transverse beam emittances by a factor about 10 per one stage. The ultimate transverse emittances are much below of that given by other metho...