Elliptic Flow at Large Transverse Momenta from Quark Coalescence

Abstract

We show that hadronization via quark coalescence enhances hadron elliptic flow at large p ⊥ relative to that of partons at the same transverse momentum. Therefore, compared to earlier results based on covariant parton transport theory, more moderate initial parton densities dN/dη(b = 0) ∼ 1500 − 3000 can explain the differential elliptic flow v2(p ⊥ ) data for Au + Au reactions at √ s = 130 and 200A GeV from RHIC. In addition, v2(p ⊥ ) could saturate at about 50% higher values for baryons than for mesons. If strange quarks have weaker flow than light quarks, hadron v2 at high p ⊥ decreases with relative strangeness content.

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].…”

“…We note that these parton cross sections are significantly smaller than that needed to reproduce the parton elliptic flow from the hydrodynamic model [41]. The resulting hadron elliptic flows in the AMPT model with string melting are, however, amplified by modeling hadronization via quark coalescence [36], leading to a satisfactory reproduction of experimental data. As shown earlier in Refs.…”

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.…”