Partonic coalescence in relativistic heavy ion collisions

Abstract

Using a covariant coalescence model, we study hadron production in relativistic heavy ion collisions from both soft partons in the quark-gluon plasma and hard partons in minijets. Including transverse flow of soft partons and independent fragmentation of minijet partons, the model is able to describe available experimental data on pion, kaon, and antiproton spectra. The resulting antiproton to pion ratio is seen to increase at low transverse momenta and reaches a value of about one at intermediate transverse momenta, as observed in experimental data at RHIC. A similar dependence of the antikaon to pion ratio on transverse momentum is obtained, but it reaches a smaller value at intermediate transverse momenta. At high transverse momenta, the model predicts that both the antiproton to pion and the antikaon to pion ratio decrease and approach those given by the perturbative QCD. Both collective flow effect and coalescence of minijet partons with partons in the quark-gluon plasma affect significantly the spectra of hadrons with intermediate transverse momenta. Elliptic flows of protons, Lambdas, and Omegas have also been evaluated from partons with elliptic flows extracted from fitting measured pion and kaon elliptic flows, and they are found to be consistent with available experimental data.

Energy loss, hadronization, and hadronic interactions of heavy flavors in relativistic heavy-ion collisions

“…The momentum dependence of the relative probability between fragmentation and coalescence will be calculated according to the Wigner functions in an instantaneous coalescence model. This coalescence model was first proposed for the production of light hadrons out of QGP fireballs [46][47][48][49], and then applied to the production of heavy flavor hadrons in nuclear collisions [39][40][41] and recently to partonic jet hadronization [50] as well. This model does not require the thermalization of the recombining partons and is easily extensible to simultaneously include various meson and baryon species, allowing for the normalization of the total coalescence probability over all possible hadronization channels.…”

Hadron production from quark coalescence and jet fragmentation

“…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 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 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].…”