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

TL;DR

This paper measures resonance production in heavy-ion and proton-proton collisions at RHIC to investigate the hadronic medium's evolution and freeze-out dynamics through resonance decay, regeneration, and suppression patterns.

Contribution

It provides new measurements of resonance spectra and ratios at RHIC, revealing the effects of hadronic interactions and freeze-out conditions on resonance properties.

Findings

Resonance yields and ratios indicate significant hadronic re-scattering effects.

Mass and width modifications suggest in-medium interactions.

Nuclear modification factors show particle-type dependence at intermediate pT.

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.