Heavy-quark probes of the quark-gluon plasma and interpretation of recent data taken at the BNL Relativistic Heavy Ion Collider

Abstract

Thermalization and collective flow of charm (c) and bottom (b) quarks in ultrarelativistic heavy-ion collisions are evaluated based on elastic parton rescattering in an expanding quark-gluon plasma (QGP). We show that resonant interactions in a strongly interacting QGP (sQGP), as well as parton coalescence, can play an essential role in the interpretation of recent data from the BNL Relativistic Heavy-Ion Collider (RHIC), and thus illuminate the nature of the sQGP and its hadronization. Our main assumption, motivated by recent findings in lattice quantum chromodynamics, is the existence of D-and B-meson states in the sQGP, providing resonant cross sections for heavy quarks. Pertinent drag and diffusion coefficients are implemented into a relativistic Langevin simulation to compute transverse-momentum spectra and azimuthal asymmetries (v 2 ) of b-and c-quarks in Au-Au collisions at RHIC. After hadronization into D-and B-mesons using quark coalescence and fragmentation, associated electron-decay spectra and v 2 are compared to recent RHIC data. Our results suggest a reevaluation of radiative and elastic quark energy-loss mechanisms in the sQGP.

Collisional energy loss of heavy quarks

“…There is an ongoing debate on the underlying reasons, which could be possibly clarified by analyzing spectra from heavy flavor decays. An additional contribution of suppression, potentially important for the range of smaller (to medium) momenta, is the collisional energy loss by elastic processes as discussed in [10,11,12] and with further modifications in [13,14,15,16,17,18]. It will turn out that in our approach a fairly large collisional energy loss is predicted, although some comparisons between collisional and radiative contributions [19,20] indicate another picture where the collisional loss should be relatively small (∼ 20%) compared to the radiative one.…”

One-dimensional non-relativistic and relativistic Brownian motions: a microscopic collision model

“…4 However, if it should turn out that deviations from the standard Ju¨ttner-Maxwell distribution 4 We note, the applicability of simple kinematic models as discussed here is, in principle, limited to situations where high-energies quantum processes, as e.g., creation and annihilation of particles, can be neglected. p e r s o n a l c o p y persist in higher space dimensions as well, then this might be of relevance for calculating relativistic corrections in high-energy physics [50] and astrophysics (e.g., to the Sunyaev-Zeldovich effect [51,52]). For example, given P ¼ ðE; pÞ, the corresponding (1+1)-momentum vector wrt.…”

Dilepton radiation at the CERN super-proton synchrotron

“…The most important parameter is the transverse acceleration. More recent applications of the fireball model, both in the dilepton [15] and charm diffusion [77] context, have used larger values than in previous work [24,38], in the range a ⊥ = 0.08 − 0.1c 2 /fm. Here, we employ a ⊥ = 0.085c 2 /fm as in Ref.…”

“…As a note of caution, we remark that recent measurements at the Relativistic Heavy-Ion Collider (RHIC) report substantial modifications of heavy-quark spectra in Au-Au collisions, relative to p-p (as inferred from a suppression and elliptic flow of "non-photonic" single-electron spectra associated with semileptonic decays of open-charm (and -bottom) hadrons) [75,76]. Such (possibly nonperturbative [77]) medium modifications of the charm momentum spectra presumably translate into a softening of the invariantmass spectra of l + l − pairs as well. At the SPS, the shorter QGP lifetime is likely to lead to smaller effects, but an explicit measurement of the (delayed) charm decays has been presented recently [78].…”