Are direct photons a clean signal of a thermalized quark gluon plasma?

Physics – High Energy Physics – High Energy Physics - Phenomenology

Scientific paper

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0


31 pages, 12 eps figures, version to appear in PRD

Scientific paper


Direct photon production from a quark gluon plasma (QGP) in thermal equilibrium is studied directly in real time. In contrast to the usual S-matrix calculations, the real time approach is valid for a QGP that formed and reached LTE a short time after a collision and of finite lifetime ($\sim 10-20 \mathrm{fm}/c$ as expected at RHIC or LHC). We point out that during such finite QGP lifetime the spectrum of emitted photons carries information on the initial state. There is an inherent ambiguity in separating the virtual from the observable photons during the transient evolution of the QGP. We propose a real time formulation to extract the photon yield which includes the initial stage of formation of the QGP parametrized by an effective time scale of formation $\Gamma^{-1}$. This formulation coincides with the S-matrix approach in the infinite lifetime limit. It allows to separate the virtual cloud as well as the observable photons emitted during the pre- equilibrium stage from the yield during the QGP lifetime. We find that the lowest order contribution $\mathcal{O}(\alpha_{em})$ which does \emph{not} contribute to the S-matrix approach, is of the same order of or larger than the S-matrix contribution during the lifetime of the QGP for a typical formation time $\sim 1 \mathrm{fm}/c$. The yield for momenta $\gtrsim 3 \mathrm{Gev}/c$ features a power law fall-off $\sim T^3 \Gamma^2/k^{5}$ and is larger than that obtained with the S-matrix for momenta $\geq 4 \mathrm{Gev}/c$. We provide a comprehensive numerical comparison between the real time and S-matrix yields and study the dynamics of the build-up of the photon cloud and the different contributions to the radiative energy loss. The reliability of the current estimates on photon emission is discussed.

No associations


Say what you really think

Search for scientists and scientific papers. Rate them and share your experience with other people.


Are direct photons a clean signal of a thermalized quark gluon plasma? does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Are direct photons a clean signal of a thermalized quark gluon plasma?, we encourage you to share that experience with our community. Your opinion is very important and Are direct photons a clean signal of a thermalized quark gluon plasma? will most certainly appreciate the feedback.

Rate now


Profile ID: LFWR-SCP-O-548042

All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.