skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Effects of the running of the QCD coupling on the energy loss in the quark-gluon plasma

Abstract

Finite temperature modifies the running of the QCD coupling {alpha}{sub s}(k,T) with resolution k. After calculating the thermal quark and gluon masses self-consistently, we determine the quark-quark and quark-gluon cross sections in the plasma based on the running coupling. We find that the running coupling enhances these cross sections by factors of two to four depending on the temperature. We also compute the energy loss (dE/dx) of a high-energy quark in the plasma as a function of temperature. Our study suggests that, beside t-channel processes, inverse Compton scattering is a relevant process for a quantitative understanding of the energy loss of an incident quark in a hot plasma.

Authors:
 [1];  [1];  [2]
  1. Institute for Theoretical Physics, University of Heidelberg, Philosophenweg 19, 69120 Heidelberg (Germany)
  2. (Germany)
Publication Date:
OSTI Identifier:
21020078
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. D, Particles Fields; Journal Volume: 75; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevD.75.054031; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; COMPTON EFFECT; COUPLING; CROSS SECTIONS; ENERGY LOSSES; GLUONS; QUANTUM CHROMODYNAMICS; QUARK MATTER; QUARK-GLUON INTERACTIONS; QUARK-QUARK INTERACTIONS; QUARKS; REST MASS; T CHANNEL

Citation Formats

Braun, Jens, Pirner, Hans-Juergen, and Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, 69117 Heidelberg. Effects of the running of the QCD coupling on the energy loss in the quark-gluon plasma. United States: N. p., 2007. Web. doi:10.1103/PHYSREVD.75.054031.
Braun, Jens, Pirner, Hans-Juergen, & Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, 69117 Heidelberg. Effects of the running of the QCD coupling on the energy loss in the quark-gluon plasma. United States. doi:10.1103/PHYSREVD.75.054031.
Braun, Jens, Pirner, Hans-Juergen, and Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, 69117 Heidelberg. Thu . "Effects of the running of the QCD coupling on the energy loss in the quark-gluon plasma". United States. doi:10.1103/PHYSREVD.75.054031.
@article{osti_21020078,
title = {Effects of the running of the QCD coupling on the energy loss in the quark-gluon plasma},
author = {Braun, Jens and Pirner, Hans-Juergen and Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, 69117 Heidelberg},
abstractNote = {Finite temperature modifies the running of the QCD coupling {alpha}{sub s}(k,T) with resolution k. After calculating the thermal quark and gluon masses self-consistently, we determine the quark-quark and quark-gluon cross sections in the plasma based on the running coupling. We find that the running coupling enhances these cross sections by factors of two to four depending on the temperature. We also compute the energy loss (dE/dx) of a high-energy quark in the plasma as a function of temperature. Our study suggests that, beside t-channel processes, inverse Compton scattering is a relevant process for a quantitative understanding of the energy loss of an incident quark in a hot plasma.},
doi = {10.1103/PHYSREVD.75.054031},
journal = {Physical Review. D, Particles Fields},
number = 5,
volume = 75,
place = {United States},
year = {Thu Mar 01 00:00:00 EST 2007},
month = {Thu Mar 01 00:00:00 EST 2007}
}
  • The non-Abelian analogue of the Landau-Pomeranchuk-Migdal effect is investigated in perturbative QCD. Extending our previous studies, the suppression of induced soft bremsstrahlung due to multiple scatterings of quarks in the spinor representation is considered. The effective formation time of gluon radiation due to the color interference is shown to depend on the color representation of the emitting parton, and an improved formula for the radiative energy loss is derived that interpolates between the factorization and Bethe-Heitler limits.
  • The energy loss {ital dE}/{ital dx} for a heavy quark propagating through a quark-gluon plasma is calculated to leading order in the QCD coupling constant. Simple formulas for {ital dE}/{ital dx} are obtained in the regions {ital E}{much lt}{ital M}{sub {ital Q}}{sup 2}/{ital T} and {ital E}{much gt}{ital M}{sub {ital Q}}{sup 2}/{ital T}, where {ital M}{sub {ital Q}} is the mass of the heavy quark and {ital T} is the temperature. The crossover energy between the two regions is determined to be approximately 1.8{ital M}{sub {ital Q}}{sup 2}/{ital T}. Under conditions relevant to ultrarelativistic heavy-ion collisions, charm quarks and bottommore » quarks lie on opposite sides of the crossover energy and therefore experience significantly different energy losses.« less
  • We compute the leading-order collisional energy loss of a heavy quark propagating through a quark-gluon plasma in which the quark and gluon distributions are anisotropic in momentum space. Following the calculation outlined for QED in an earlier work we indicate the differences encountered in QCD and their effect on the collisional energy loss results. For a 20 GeV bottom quark we show that momentum-space anisotropies can result in the collisional heavy-quark energy loss varying with the angle of propagation by up to 50%. For low velocity quarks we show that anisotropies result in energy gain instead of energy loss withmore » the energy gain focused in such a way as to accelerate particles along the anisotropy direction thereby reducing the momentum-space anisotropy. A relation between the origin of this negative energy loss and the presence of plasma instabilities in the system is pointed out.« less
  • We discuss the average collisional energy loss dE/dx of a heavy quark crossing a quark-gluon plasma, in the limit of high quark energy E>>M{sup 2}/T, where M is the quark mass and T<<M is the plasma temperature. In the fixed coupling approximation, at leading order dE/dx{proportional_to}{alpha}{sub s}{sup 2}, with a coefficient which is logarithmically enhanced. The soft logarithm arising from t-channel scattering off thermal partons is well known, but a collinear logarithm from u-channel exchange had previously been overlooked. We also determine the constant beyond those leading logarithms. We then generalize our calculation of dE/dx to running coupling. We estimatemore » the remaining theoretical uncertainty of dE/dx, which turns out to be quite large under Relativistic Heavy Ion Collider conditions. Finally, we point out an approximate relation between dE/dx and the QCD Debye mass, from which we derive an upper bound to dE/dx for all quark energies.« less
  • We analyze heavy quark free energies in 2-flavor QCD at finite temperature and the corresponding heavy quark potential at zero temperature. Static quark-antiquark sources in color singlet, octet and color averaged channels are used to probe thermal modifications of the medium. The temperature dependence of the running coupling, {alpha}{sub qq}(r,T), is analyzed at short and large distances and is compared to zero temperature as well as quenched calculations. In part, we also compare our results to recent findings in 3-flavor QCD. We find that the characteristic length scale below which the running coupling shows almost no temperature dependence is almostmore » twice as large as the Debye screening radius. Our analysis supports recent findings which suggest that {chi}{sub c} and {psi}{sup '} are suppressed already at the (pseudo) critical temperature and thus give a probe for quark gluon plasma production in heavy ion collision experiments, while J/{psi} may survive the transition and will dissolve at higher temperatures.« less