$\Delta$, $K^{*}$ and $\rho$ Resonance Production and Their Probing of Freeze-out Dynamics at RHIC

Abstract

We report the measurements of the transverse momentum spectra and invariant mass distributions of $\Delta$(1232)$\to \pi p$, $K^*$(892)$^{0,\pm} \to \pi K$ and $\rho$(770)$^{0} \to \pi^{+} \pi^{-}$ in Au+Au and p+p collisions at $\sqrt{s_{NN}}$=200 GeV using the STAR TPC at RHIC. These resonances provide sensitive probes to examine the evolution dynamics in the hadronic medium through their decay and regeneration processes. The particle ratios of $K^*/K$, $K^*/\phi$, $\Delta$/p and $\rho/\pi$, the $K^*$, $\rho$ and $\Delta$ apparent masses and the dependence of these quantities on centrality provide evidence of dynamical interaction and re-scattering between hadrons close to freeze-out. The dependence of resonance yields on the strength of their hadronic cross sections and the lifetime between the freeze-outs will also be discussed. In the intermediate $p_{T}$ region ($2<p_T<4$ GeV/c), the nuclear modification factors ($R_{CP}$ and $R_{AA}$) of $K^*$ are similar to those of $K_{S}$ and smaller than those of baryons ($\Lambda$). In the intermediate $p_{T}$ region, no strong dependence on the particle masses is seen in the data.