Overview of charm production at RHIC

Abstract

Abstract. In this presentation, I discussed a) the charm total cross-section and its comparisons to measurements at other beam energies and pQCD calculations; b) the semileptonic decay of charmed hadrons and the sensitivity of non-photonic leptons to charm quark collective flow and freeze-out; c) semileptonic decayed electron spectrum at high transverse momentum, its comparison to FONLL in p+p and d+Au collisions, and heavy-quark energy loss in Au+Au collisions.In relativistic heavy-ion collisions, charm quarks are believed to be produced in the early stage via initial gluon fusion and their production cross-section can be evaluated using perturbative QCD [1]. Study of the N bin scaling properties of the charm total cross-section in p+p, d+Au and Au+Au collisions can test if heavy-flavor quarks, which are used as a probe, are produced exclusively at the initial impact. The interactions of heavy quarks with the medium provide a unique tool for probing the hot and dense matter created in ultra-relativistic heavy-ion collisions at the early times. At RHIC energies, heavy quark energy loss [2], charm quark coalescence [3,4,5,6], the effect of J/ψ production from charm quark coalescence on the interpretation of possible J/ψ suppression due to color screening [7], and charm flow [8,9,10] have been proposed as important tools in studying the properties of matter created in heavy ion collisions. The last three effects depend strongly on the charm total cross-section and spectrum at low p T .Since the beginning of RHIC operation, PHENIX and STAR collaborations have made pioneer measurements in charm related physics [11,12,13,14,15,16] ‡. New measurements presented at this conference are: (i) muon spectra at forward rapidity (1.4 < |y| < 2.2) from charm semileptonic decay by PHENIX Collaboration [16]. This enables us to study the rapidity dependence of nuclear effects of charm production.(ii) muon spectra at low p T (0.17 < p T < 0.25 GeV/c) from charm semileptonic decay by STAR Collaboration [15]. This improves the charm total cross-section measurements and better constrains the charm spectrum for studying the charm radial flow. ‡ The overviews of charm elliptic flow and quarkonium can be found elsewhere [17,18]

Parton energy loss in an expanding quark-gluon plasma: Radiative vs. collisional

“…Although the pQCD calculations [24] predict that the bottom contribution dominates at p T ∼ > 5 GeV, this possibility cannot be excluded since the pQCD results in the charm mass region are very fragile, say, the calculations of Ref. [24] underestimates the normalization of the experimental electron spectrum by a factor of about 5 [25]. The same situations occurs for the D-meson production [26].…”

Heavy quark production at LHC in the color dipole formalism

“…As the rcBK dipole cross section can be calculated only for small x (≤ 10 −2 ), we are not able to obtain results for heavy quark production at the lowest energies. We compare our results with the experimental data obtained by the PHENIX collaboration [14,15] (circles), by the UA2 Collaboration [38] (up triangles) and with data extracted from cosmic ray measurements [39] (diamonds). We also show the theoretical results obtained with the k T factorization scheme [40] (squares) and with FONLL [41] (down triangles).…”

Heavy-flavor production in pp and heavy-ion collisions in QCD up-to-LHC energies

“…There one can see the absence of nuclear effects in the PHENIX data from pp to central Au-Au collisions, and in STAR data from d-Au to central Au-Au collisions, in both cases at the level of 20% accuracy. Concerning the PHENIX data presented in [38], they do not present any visible dependence of the charm production cross section on the number of collision participant nucleons, N part , in Au-Au collisions at different centralities.…”

“…One can also see the different data obtained by the PHENIX and the STAR collaborations. This discrepancy is discussed in detail in references [38,39]. Experimental fixed target data are taken from [32] and [33], the RHIC point [34], and the UA2 Collaboration data from [35] (all are shown by points).…”

“…Experimental fixed target data are taken from [32] and [33], the RHIC point [34], and the UA2 Collaboration data from [35] (all are shown by points). PHENIX data [25,26] and STAR data [27] in nuclear collisions are shown by squares and triangles, respectively, while cosmic rays data [38] are shown by diamonds. The solid curve shows the theoretical result obtained in the k T -factorization approach, the dashed curve corresponds to NLO QCD with only gluon-gluon fusion contribution, and the dash-dotted curve corresponds to the total NLO QCD result.…”