Probing Late-Stage Hadronic Interactions at High Baryon Density via $K^{*0}$ Production in the RHIC Beam Energy Scan Program

TL;DR

This study measures $K^{*0}$ meson yields across various energies at RHIC, revealing suppression in central collisions due to hadronic re-scattering, and explores energy-dependent hadronic interactions.

Contribution

First high-precision measurement of $K^{*0}$ production at multiple RHIC energies, highlighting the energy dependence of hadronic re-scattering effects.

Findings

Suppression of $K^{*0}$ in central collisions indicates re-scattering effects.

Charged kaon yields scale with charged-particle multiplicity across energies.

Stronger $K^{*0}/K$ suppression at lower energies supports energy-dependent hadronic interactions.

Abstract

A precision measurement of the $K^{*0}$ meson yield is reported in Au+Au collisions at $\sqrt{s_{NN}} = 7.7,\; 11.5,\; 14.6,\; 19.6,$ and $27~\mathrm{GeV}$ using the high-statistics data sample collected by the STAR experiment during the Beam Energy Scan II (BES-II) program at RHIC. The transeverse momentum ($p_{T}$)-integrated yield ratios $(K^{*0} + \overline{K^{*0}})/(K^{+} + K^{-})$ in central collisions show a suppression relative to peripheral collisions at the $(1.7\text{-}3.6)\,\sigma$ level, while a thermal model without final-stage rescattering overpredicts this ratio with a deviation of $(6.9\text{-}8.2)\,\sigma$. These results indicate a loss of the measured $K^{*0}$ signal in central collisions due to re-scattering of its hadronic decay products in the hadronic phase. The $p_{T}$-integrated yield of charged kaons exhibits an approximate scaling with charged-particle multiplicity, independent of collision energy and system size. A similar trend is observed for the short-lived $K^{*0}$ resonance, although significant deviations emerge at lower energies. At BES energies, the $K^{*0}/K$ ratio shows stronger suppression than at the highest RHIC and LHC energies within a given multiplicity bin, particularly in central and mid-central collisions. This behavior is consistent with changes in the effective hadronic interaction cross section and is supported by transport model calculations, which indicate dominant meson-baryon interactions at lower energies and meson-meson interactions at higher energies.