High energy scattering and emission in QED&QCD media

A formalism for the evaluation of the intensity of photon and gluon bremsstrahlung in QED and QCD condensed media is presented which considers general interactions beyond the Fokker-Planck approximation, the angular distribution of the final particles and admits finite or structured target calculations. The Fokker-Planck results of Migdal/Zakharov and the BDMPS group are recovered under the adequate approximations as particular cases. Weinberg's soft photon theorem is shown to saturate the LPM suppression in the soft regime. The angle integrated intensity under realistic screened interactions is always larger than the Fokker-Planck evaluation and the changes can not be accounted for by a single definition of the medium transpor

Transverse spectrum of bremsstrahlung in finite condensed media

A formalism is presented in which the radiation of photons off high energy electrons during a multiple scattering process with finite condensed media can be evaluated for a general interaction. We show that the arising Landau-Pomeranchuk-Migdal suppression for finite size targets saturates at some characteristic photon energy. Medium coherence effects in the photon dispersion relation can be also considered leading to a dielectric suppression or transition radiation effects in the soft part of the spectrum. The main results of our formulation are presented for a Debye screened interaction and its well-known Fokker-Planck approximation, showing that for finite size targets or for the angular distributions of the final particles the differences between both scenarios cannot be reconciled into a single redefinition of the medium transport parameter (q^). Our predictions are in very good agreement with the experimental data collected at SLACWe thank the grant María de Maeztu Unit of Excellence of Spain and the support of Xunta de Galicia under the Project No. ED431C2017. This paper has been partially done under the Project No. FPA2017-83814-P of Ministerio de Ciencia, Innovación y Universidades (Spain)S

Thermal behavior and entanglement in Pb-Pb and p-p collisions

The thermalization of the particles produced in collisions of small objects can be achieved by quantum entanglement of the partons of the initial state as was analyzed recently in proton-proton collisions. We extend such study to Pb-Pb collisions and to different multiplicities of proton-proton collisions. We observe that, in all cases, the effective temperature is approximately proportional to the hard scale of the collision. We show that such a relation between the thermalization temperature and the hard scale can be explained as a consequence of the clustering of the color sources. The fluctuations of the number of parton states decrease with multiplicity in Pb-Pb collisions as long as the width of the transverse-momentum distribution decreases, contrary to the p−p case. We relate these fluctuations to the temperature fluctuations by means of a Langevin equation for the white stochastic noise. We show that the multiplicity parton distribution for events with at least one hard parton collision is a Γ distribution. We use this result to compute the entanglement entropy, showing that the leading term is the logarithm of the number of partons, meaning that the n microstates are equally probable and the entropy is maximal. There is another contribution related to the inverse of the normalized parton number fluctuation, which at very high energy changes the behavior from ln n to ln √nWe are grateful for a grant from the María de Maeztu Unit of Excellence of Spain and the support of Xunta de Galicia under Project No. ED431C2017. This work has been partially carried out under Project No. FPA2017-83814-P of Ministerio de Ciencia, Innovación y Universidades (Spain)S