Parton Coalescence and the Antiproton/Pion Anomaly at RHIC

Abstract

Coalescence of minijet partons with partons from the quark-gluon plasma formed in relativistic heavy ion collisions is suggested as the mechanism for production of hadrons with intermediate transverse momentum. The resulting enhanced antiproton and pion yields at intermediate transverse momenta give a plausible explanation for the observed large antiproton to pion ratio. With further increasing momentum, the ratio is predicted to decrease and approach the small value given by independent fragmentations of minijet partons after their energy loss in the quark-gluon plasma.

Anisotropic flow inCu+Aucollisions atsNN=200GeV

“…The transition from the partonic matter to the hadronic matter is achieved using a simple coalescence model, which combines the two nearest quark and antiquark into mesons and the three nearest quarks or antiquarks into baryons or antibaryons that are close to the invariant mass of these partons. The present coalescence model is thus somewhat different from the ones recently used extensively [33][34][35][36] for studying hadron production at intermediate transverse momenta. By using parton scattering cross sections of 6−10 mb, the AMPT model with string melting was able to reproduce both the centrality and transverse momentum (below 2 GeV/c) dependence of the elliptic flow [10] and pion interferometry [22] measured in Au + Au collisions at √ s = 130A GeV at RHIC [37,38].…”

Highlights from STAR

“…(b) baryons Nuclear modification factors from 5% most central Au+Au collisions at √ s NN =200 GeV [14,15,16] Quark coalescence or recombination models [17,18,19,20] for hadron formation offer an elegant explanation for the experimentally observed dependence on the number of constituent quarks. Within some of these models [18], hadrons at intermediate p T are dominantly formed by coalescing quarks stemming from a thermalized parton system, i.e.…”

Production of D0 meson in pp and PbPb Collisions at √SNN = 5.02 TeV with CMS

“…At low transverse momentum (p T ), the charm hadron v n coefficient can help quantify the extent to which charm quarks flow with the medium, which is a good measure of their interaction strength. The measurements of R AA and v n can also help explore the coalescence production mechanism for charm hadrons where charm quarks recombine with light quarks from the medium, which could also lead to positive charm hadron v n [8,9]. At high p T , the charm hadron v n coefficient can constrain the path length dependence of charm quark energy loss [10,11], complementary to the R AA measurements.…”