16 research outputs found
Photons from anisotropic Quark-Gluon-Plasma
We calculate medium photons due to Compton and annihilation processes in an
anisotropic media. The effects of time-dependent momentum-space anisotropy of
{\em Quark-Gluon-Plasma} (QGP) on the medium photon production are discussed.
Such an anisotropy can results from the initial rapid longitudinal expansion of
the matter, created in relativistic heavy ion collisions. A phenomenological
model for the time-dependence of the parton hard momentum scale,
, and anisotropy parameter, , has been used to
describe the plasma space-time evolution. We find significant dependency of
photon yield on the isotropization time (). It is shown that the
introduction of early time momentum-space anisotropy can enhance the photon
production by a factor of (in the central rapidity region) for {\em
free streaming} ({\em collisionally-broadened}) {\em interpolating} model if we
assume fixed initial condition. On the other hand, enforcing the fixed final
multiplicity significantly reduces the enhancement of medium photon production.Comment: 15 pages, 19 figures, few refs added, one new paragraph is added in
introduction, published in Physical Rev.
Measuring the isotropization time of quark-gluon plasma from direct photons at energies available at the BNL Relativistic Heavy Ion Collider (RHIC)
We calculate transverse momentum distribution of direct photons from various
sources by taking into account the initial state momentum anisotropy of {\em
Quark-Gluon-Plasma} (QGP) and late stage transverse flow effects. The total
photon yield, calculated for various combinations of initial conditions,
transition temperatures, is then compared with the recent measurement of photon
transverse momentum distribution by the PHENIX collaboration. It is shown that
the presence of such an anisotropy can describe the PHENIX photon data better
than the isotropic case. We show that the isotropization time thus extracted
remains of the order of 1 fm/c and is almost insensitive to the initial
conditions used.Comment: 12 pages, 11 eps figure
Nuclear modification factor in an anisotropic {\em Quark-Gluon-Plasma}
We calculate the nuclear modification factor () of light hadrons by
taking into account the initial state momentum anisotropy of the quark gluon
plasma (QGP) expected to be formed in relativistic heavy ion collisions. Such
an anisotropy can result from the initial rapid longitudinal expansion of the
matter. A phenomenological model for the space time evolution of the
anisotropic QGP is used to obtain the time dependence of the anisotropy
parameter and the hard momentum scale, . The result is then
compared with the PHENIX experimental data to constrain the isotropization time
scale, for fixed initial conditions (FIC). It is shown that
the extracted value of lies in the range . However, using fixed final multiplicity (FFM) condition does
not lead to any firm conclusion about the extraction of the isotropization
time. The present calculation is also extended to contrast with the recent
measurement of nuclear modification factor by ALICE collaboration at
TeV. It is argued that in the present approach, the extraction
of at this energy is uncertain and, therfore, refinement of
the model is necessary. The sensitivity of the results on the initial
conditions has been discussed. We also present the nuclear modification factor
at LHC energies with TeV.Comment: 18 pages, 9 eps figures, Accepted for publication in Physical Review