Hadron production from quark coalescence and jet fragmentation

Abstract

Transverse momentum spectra of pions, protons, and antiprotons in Au + Au collisions at intermediate RHIC energy √ s NN = 62 GeV are studied in a model that includes both quark coalescence from the dense partonic matter and fragmentation of the quenched perturbative minijet partons. The resulting baryon to meson ratio at intermediate transverse momenta is predicted to be larger than that seen in experiments at higher center of mass energies. Recently, there has been renewed interest in using the quark coalescence or recombination model to study hadron production in ultrarelativistic heavy ion reactions [1][2][3][4][5][6][7][8][9]. These studies were largely triggered by two surprising observations in measured hadron spectra from Au + Au collision at √ s NN = 200 GeV at the BNL Relativistic Heavy Ion Collider (RHIC) [1,[10][11][12]. The first was the nearly similar yield of protons and pions at intermediate transverse momentum (2 GeV < p T < 5 GeV), which is at variance with the expectation from the fragmentation of minijets produced from initial hard processes. The second was the so-called "quark number scaling" of hadron elliptic flow v 2h (p T ), i.e., the transverse momentum dependence becomes universal if both v 2h and transverse momentum p T are divided by the number of constituent quarks in the hadron. Both phenomena have a simple explanation if hadronization of the thermally equilibrated and collectively flowing partonic matter formed in these collisions proceeds through the coalescence of quarks of constituent masses [3][4][5][6].The description of hadronization of the quark-gluon plasma formed in heavy ion collision at relativistic energies by quark coalescence was first introduced in models such as ALCOR [13] and MICOR [14]. Emphases of these earlier studies were on particle yields and their ratios. Recent studies have been more concerned with observables that are related to collective dynamics and production of hadrons with relatively large transverse momenta. Furthermore, effects of minijet partons from initial hard processes have also been included through their independent fragmentation as well as coalescence with soft partons in the quark-gluon plasma [3,4]. The latter provides a new mechanism for the hadronization of minijet partons produced in relativistic heavy ion collisions. The interplay between quark coalescence and minijet fragmentation has been found to be essential for understanding measured inclusive hadron spectra at moderate and high transverse momenta. In particular, the observed jetlike features of these hadrons [15] seem to also support the scenario that they are produced from the coalescence of minijets with the thermal partons in the produced quark-gluon plasma. If confirmed by more exclusive data from experiments and by further theoretical studies, hadronization via quark coalescence then represents a new probe of the quark-gluon plasma formed in relativistic heavy ion collisions, and its hadronization mechanism, as well as that of the minijet partons produced in these collision...

Properties of particle production at large transverse momentum in Au+Au and Cu+Cu collisions at RHIC

“…This may indicate a similar energy loss of quarks and gluons in the medium formed in high energy heavy ion collisions. GeV is consistent with quark coalescence models [5]. However a detailed comparison of the p/π + andp/π − ratios to predictions from model shows there is a lack of quantitative agreement.…”

“…They will also help in probing the difference in the energy loss of quarks and gluons in the medium [3,4]. The energy dependence of baryon to meson ratio at the intermediate p T region from 2 -6 GeV/c will address the specific prediction from the quark coalescence models of a higher baryon to meson ratio at √ s NN = 62.4 GeV compared to √ s NN = 200 GeV [5]. At high p T (> 6 GeV/c) the p/π ratio can provide information on quark and gluon jet conversions in the medium formed in heavy ion collisions [6].…”

Coalescence Models for Hadron Formation from Quark-Gluon Plasma

“…3 they can be explained solely by wave function effects, resonance contributions and contributions from higher Fock states in hadrons (51,108,115). If the scaling feature were accidental and strongly dependent on details of the phase space distribution, the very different dynamical evolution at LHC might lead to much stronger scaling violations there.…”

ϕ and Ω production in relativistic heavy-ion collisions in a dynamical quark coalescence model

“…Although we have shown in the present study that the anisotropic flows of φ mesons and baryons are not sensitive to the strange quark mass used in the dynamical coalescence model if the same strange quark distribution is used, using massive partons in the AMPT model not only is expected to affect the transversemomentum spectra of partons but also may influence their anisotropic flow and thus that of produced hadrons. Also, it is important to include in future studies the contribution from high-momentum jets [69] as they are expected to affect the production of φ mesons and baryons as well as their anisotropic flows at intermediate and high transverse momenta.…”