105 research outputs found
Dilepton production by dynamical quasiparticles in the strongly interacting quark gluon plasma
The dilepton production by the constituents of the strongly interacting
quark-gluon-plasma (sQGP) is addressed. In order to make quantitative
predictions at realistically low plasma temperatures (O(T_c)), experimentally
relevant low dilepton mass (O(1 GeV)) and strong coupling (alphaS=0.5-1), we
take into account not only the higher order pQCD reaction mechanisms, but also
the non-perturbative spectral functions (off-shellness) and self-energies of
the quarks, anti-quarks and gluons thus going beyond the leading twist. For
this purpose, our calculations utilize parametrizations of the non-perturbative
propagators for quarks and gluons provided by the dynamical quasi-particle
model (DQPM) matched to reproduce lattice data. The DQPM describes QCD
properties in terms of single-particle Green's functions (in the sense of a
two-particle irreducible approach) and leads to the notion of the constituents
of the sQGP being effective quasiparticles, which are massive and have broad
spectral functions (due to large interaction rates). In the present work, we
derive the off-shell cross sections of dilepton production in the reactions
q+qbar->l^+l^- (Drell-Yan mechanism), q+qbar->g+l^+l^- (quark annihilation with
the gluon Bremsstrahlung in the final state), q(qbar)+g->q(qbar)+l^+l^- (gluon
Compton scattering), g->q+qbar+l^+l^- and q(qbar)->q(qbar)+g+l^+l^- (virtual
gluon decay, virtual quark decay) in the sQGP by dressing the quark and gluon
lines in the perturbative diagrams with the DQPM propagators for quarks and
gluons.Comment: RevTex style, 16 pages, 16 figure
Modelling Drell-Yan pair production in pbar-p
We predict the triple differential cross section of the unpolarized Drell-Yan
process at sqrt(S)=6 GeV. The model incorporates primordial parton transverse
momentum and quark off-shellness effects caused by the initial state
interaction.Comment: 4 pages, AIP style, talk given at the conference LEAP'05 (Low Energy
Antiproton Physics
Dilepton radiation by vector mesons and off-shell partons in the hot and dense medium
According to the dynamical quasiparticle model (DQPM) - matched to reproduce
lattice QCD results in thermodynamic limit, - the constituents of the strongly
interacting quark-gluon plasma (sQGP) are massive and off-shell quasi-particles
(quarks and gluons) with broad spectral functions. In order to address the
electromagnetic radiation of the sQGP, we derive off-shell cross sections of
q+qbar->gamma*, q+qbar->gamma*+glue and q+glue->gamma*+q(qbar+glue->gamma*qbar)
reactions taking into account the effective propagators for quarks and gluons
from the DQPM. Dilepton production in In+In collisions at 158 AGeV is studied
by implementing these processes into the parton-hadron-string dynamics (PHSD)
transport approach. The microscopic PHSD transport approach describes the full
evolution of the heavy-ion collision: from the dynamics of quasi-particles in
the sQGP phase (when the local energy density is above ~1 GeV/fm^3) through
hadronization and to the following hadron interactions and off-shell
propagation after the hadronization. A comparison to the data of the NA60
Collaboration shows that the low mass dilepton spectra are well described by
including a collisional broadening of vector mesons, while the spectra in the
intermediate mass range are dominated by off-shell quark-antiquark
annihilation, quark Bremsstrahlung and gluon-Compton scattering in the
nonperturbative QGP. In particular, the observed softening of the mT spectra at
intermediate masses (1 GeV < M < 3 GeV) is approximately reproduced.Comment: Talk given at the XIII International Conference on Hadron
Spectroscopy (HADRON 09), November 29 - December 4, 2009, Tallahassee,
Florida; two references added in version
Electromagnetic probes of the QGP
We investigate the properties of the QCD matter across the deconfinement
phase transition in the scope of the parton-hadron string dynamics (PHSD)
transport approach. We present here in particular the results on the
electromagnetic radiation, i.e. photon and dilepton production, in relativistic
heavy-ion collisions. By comparing our calculations for the heavy-ion
collisions to the available data, we determine the relative importance of the
various production sources and address the possible origin of the observed
strong elliptic flow of direct photons. We argue that the different
centrality dependence of the hadronic and partonic sources for direct photon
production in nucleus-nucleus collisions can be employed to shed some more
light on the origin of the photon "puzzle". While the dilepton spectra at
low invariant mass show in-medium effects like an enhancement from multiple
baryonic resonance formation or a collisional broadening of the vector meson
spectral functions, the dilepton yield at high invariant masses (above 1.1 GeV)
is dominated by QGP contributions for central heavy-ion collisions at
ultra-relativistic energies. This allows to have an independent view on the
parton dynamics via their electromagnetic massive radiation.Comment: 12 pages, Proceedings of the 3rd International Conference on 'New
Frontiers in Physics 2014', Kolymbari, Cret
Ground state correlations in Deep Inelastic Scattering and the Drell-Yan process
Non-perturbative corrections to the LO cross section formulae for DIS and the
Drell-Yan process were calculated. The interaction of partons was taken into
account via dressing the incoming quark lines with spectral functions. We found
the effect of ground state correlation in DIS to be large in the region of
small Bjorken x and low momentum transfer Q. For a quark width of the order of
200 MeV, the deviation from parton model cross section reaches as much as 50%
for Q^2=10 GeV^2. On the other hand, for the values of Q well above the
resonance region, the effect of ISI turned out to be small in DIS, but still
substantial for the triple differential Drell-Yan cross section. Our
calculations show that the shape of the high mass Drell-Yan pair transverse
momentum distribution is fully determined by quark off-shellness. From
comparison to the resent data on the Drell-Yan cross section from NuSea
collaboration, we obtained for the quark width in the nucleon the value about
200 MeV.Comment: Talk presented on "IV international conference on Perspectives in
Hadronic Physics", to be published in the proceedings, 6 pages, 5 figures,
uses EPJ styl
Prediction for the transverse momentum distribution of Drell-Yan dileptons at GSI-PANDA
We predict the triple differential cross section of the Drell-Yan process
(pbar p -> l^+l^-X) in the kinematical regimes relevant for the upcoming PANDA
experiment, using a model that accounts for quark virtuality as well as
primordial transverse momentum. We find a cross section magnitude of up to 10
nb in the low mass region. A measurement with 10% accuracy is desirable in
order to constrain the partonic transverse momentum dispersion and the spectral
function width within +-50 MeV and to study their evolution with M and sqrt(s).Comment: 4 pages, 7 figures, RevTex; the published version: typos corrected,
minor changes to the tex
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