Elliptic Flow at Large Transverse Momenta from Quark Coalescence

We show that hadronization via quark coalescence enhances hadron elliptic flow at large $p_{\perp }$ 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 $dN/d\eta (b=0)\sim 1500–3000$ can explain the differential elliptic flow $v_2(p_{\perp })$ data for $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ reactions at $\sqrt{s}=130$ and $200A\mathrm{G}\mathrm{e}\mathrm{V}$ from BNL RHIC. In addition, $v_2(p_{\perp })$ could saturate at about 50% higher values for baryons than for mesons. If strange quarks have weaker flow than light quarks, hadron $v_2$ at high $p_{\perp }$ decreases with relative strangeness content.

Figure 1

Qualitative behavior of baryon and meson elliptic flow as a function of $p_{\perp }$ from quark coalescence.

Figure 2

Fit parameters $v_2^{\mathrm{m}\mathrm{a}\mathrm{x}}$ and $p_0$ as a function of transport opacity $\chi (b=0)$, for the $v_2(p_{\perp })$ results in Ref. 4.