star focus: Charmed hadron production at low transverse momentum at RHIC
Highlights from the STAR paper Charmed hadron production at low transverse momentum in Au+Au collisions at RHIC submitted recently to Physical Review Letters.
Posted: Jun 27, 2008

Charm quarks are likely to be produced only in the early stages and can be a unique tool to probe the partonic matter created in relativistic heavy-ion collisions at RHIC energies. Studies of the number of binary collision (calculated using Glauber model) scaling of the total charm cross section from d+Au to Au+Au collisions can be used to test if charm production is exclusively at the initial impact of colliding heavy ions. The total charm production cross section is also an important input in models of J/Psi production via charm quark coalescence in a Quark Gluon Plasma.

STAR experiment has reported measurements of charmed hadron production at mid-rapidity from analysis of D0 --> K pi, muon(electron) from semileptonic charm decays in minimum bias and central Au+Au collisions and d+Au collisions at center of mass energy of 200 GeV at RHIC. The mid-rapidity charm cross section per nucleon-nucleon collisions are extracted from a combination of the above three measurements covering the transverse momentum range which contributes to ~ 90% of the integrated cross section. The charm production cross section at mid-rapidity is observed to scale with number of binary interactions from d+Au to central Au+Au collisions. This is shown in the figure. This confirms the expected scaling of hard production processes with binary interactions among incoming nucleons so that charm quarks can be used as a calibrated probe of the early stage dynamics of the system. The FONLL calculation is the band in figure. The ratio of the minimum bias data over theory calculation is 4.3 +/- 0.5(stat.) +/- 1.2(syst.) +9.4(theory) -3.3(theory). The upper theory value reproduces our result.

Further details can be found in the following STAR paper -
Charmed hadron production at low transverse momentum in Au+Au collisions at RHIC - arXiv:0805.0364.

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