Observation of enhanced baryon production using strange hadrons in oxygen-oxygen collisions

Abstract

A hot deconfined medium known as the quark-gluon plasma (QGP) is created in collisions of ultrarelativistic heavy nuclei. In these systems, hadron production is strongly modified relative to proton-proton (pp) interactions. In the hadron transverse momentum region 2 $\lt$ $p_\mathrm{T}$ $\lt$ 5 GeV, collective radial flow and quark coalescence are important mechanisms that can produce such modifications. While these effects are well-established for collisions of large ions, such as lead, it is unknown if they are present in systems produced using smaller ions. To address this question, the $p_\mathrm{T}$ spectra of two strange hadrons, K$^0_\mathrm{S}$ and $Λ$, are measured in oxygen-oxygen (OO) and pp collisions at a center-of-mass energy per nucleon pair of 5.36 TeV. The measurements are performed using the CMS detector at the LHC, and the OO and pp datasets correspond to integrated luminosities of 6.8 nb$^{-1}$ and 1.1 pb$^{-1}$, respectively. The spectral modification of K$^0_\mathrm{S}$ mesons in OO collisions relative to pp collisions is found to be similar to that of inclusive charged hadrons. Conversely, the $Λ$-to-K$^0_\mathrm{S}$ cross section ratio exhibits a pronounced enhancement in OO collisions when compared to pp collisions. The results provide the first observation of a baryon-to-meson enhancement in OO collisions and suggest the formation of a deconfined medium, offering insight into the roles of strangeness, radial flow, and quark coalescence in QGP.