2003/05/31 by D. Boyanovsky, H. J. de Vega · 1 citation
Physics and Astronomy · #High-Energy Particle Collisions Research #Large Hadron Collider #Matrix (chemical analysis) #Nuclear physics #Observable #Order (exchange) #Particle physics #Particle physics theoretical and experimental studies #Photon #Physics #Plasma #Quantum Chromodynamics and Particle Interactions #Quantum mechanics #Quark #Quark–gluon plasma #Thermal equilibrium #Virtual particle #Yield (engineering) #hep-ex #hep-ph #nucl-ex #nucl-th
paper · pdf · doi:10.1103/physrevd.68.065018
published as Phys.Rev. D68 (2003) 065018 · 31 pages, 12 eps figures, version to appear in PRD
arxiv created 2003/07/29 · openalex publication_date 2003/09/23 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Direct photon production from a quark-gluon plasma (QGP) in thermal equilibrium is studied directly in real time. In contrast with the usual S-matrix calculations, the real time approach is valid for a QGP that formed and reached local thermal equilibrium a short time after a collision and of finite lifetime (\ensuremath∼10--20fm/c as expected at BNL RHIC or CERN LHC). We point out that during such a 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 \ensuremathΓ^\ensuremath-1. This formulation coincides with the S-matrix approach in the infinite lifetime limit. It allows us to separate the virtual cloud as well as the observable photons emitted during the preequilibrium stage from the yield during the QGP lifetime. We find that the lowest order contribution O(\ensuremathαem) which does 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 \ensuremath∼1fm/c. The yield for momenta \ensuremath\gtrsim3GeV/c features a power law fall-off \ensuremath∼T3\ensuremathΓ2/k5 and is larger than that obtained with the S-matrix for momenta >~4GeV/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 as well as theoretical uncertainties on the details of the initial state are discussed.