Speaker
Pol Gossiaux
(Subatech)
Description
It is generally admitted that heavy quarks (c and b) created in the early stage of ultrarelativistic heavy ion collisions through hard processes are among the best probes of the later QGP stage. Perturbative QCD allows for the calculation of the production cross sections (in contradistinction to light quarks) and these cross sections have also been measured. Also the details of the chiral/confinement phase transition are less important than for light quarks because, due to its mass, the momentum of the heavy quark determines the momentum of the open charm hadrons. In addition, the momentum distribution at production and at the transition is very different from that expected if the heavy quarks are in thermal equilibrium with the plasma of light quarks and gluons. Therefore the modification of the initial momentum distribution by the interaction of the heavy quarks with the plasma carries information on the plasma properties.
The interaction of the heavy quark with the plasma has two parts, elastic collisions and radiative collisions. For the first a model was developed [1] in which the cross section of the elementary interactions are calculated by
perturbative QCD with a running coupling constant and an infrared behavior adjusted so as to match hard thermal loop calculations. Embedding these cross sections in the hydrodynamical description of the expanding plasma of Heinz and Kolb it was shown that the collisional energy loss underpredicts the measured energy loss of heavy mesons at large momenta as well as their elliptic flow by roughly a factor of two.
It is the purpose of the present work to extend our pQCD calculation toward the calculation of the radiative energy loss for heavy quarks at intermediate energies. To this end we compute the gluon emission cross section of a heavy quark colliding a light parton from the plasma in pQCD at leading order [2]. We first derive the high-energy approximation that naturally extends results obtained by Gunion and Bertsch for the light quark sector to heavy quarks. We next show that it is possible to compute the complete energy dependence of the result. This allows us to assess the range of applicability in energy of the high-energy approximation. We then extend the calculation to the case of intermediate energy, for which the invariant mass $s$ in the collision does not exceed the squared heavy quark mass $m_Q^2$ in large amounts. We discuss in particular the relevance of the dead cone effect as well as the consequences of a finite heavy quark energy, which is often neglected in the literature. For this purpose, we address quantities such as the average energy loss in a bath at finite temperature as well as the nuclear modification factor as a function of the transverse momentum.
References
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[1] P.B. Gossiaux and J. Aichelin, Phys Rev C78, 014904 (2008)
[2] J. Aichelin, P.B. Gossiaux and Th. Gousset arXiv:1307.5270, TBP in PRD
| On behalf of collaboration: | None |
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Author
Pol Gossiaux
(Subatech)
Co-authors
Joerg Aichelin
(University of Nantes)
Prof.
Thierry GOUSSET
(SUBATECH)
