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

Abstract

A precision measurement of the $K^{\ast 0}$ 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 $(K^{\ast 0}+\overline{K^{\ast 0}})/(K^{+}+K^{-})$ 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 $K^{\ast 0}$ 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 $K^{\ast 0}$ resonance, although significant deviations emerge at lower energies. At BES energies, the $K^{\ast 0}/K$ 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.

17 pages, 6 figures, 2 tables

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