Excited hadrons as a signal for quark-gluon plasma formation

Abstract

At the quark-hadron transition, when quarks get confined to hadrons, certain orbitally excited states, namely those which have excitation energies above the respective $L = 0$ states of the same order as the transition temperature $T_c$, may form easily because of thermal velocities of quarks at the transition temperature. We propose that the ratio of multiplicities of such excited states to the respective $L = 0$ states can serve as an almost model independent signal for the quark-gluon plasma formation in relativistic heavy-ion collisions. For example, the ratio $R^*$ of multiplicities of $D_{SJ}^{*\pm}(2317)(J^P = 0^+)$ and $D_S^{*\pm}(2112)(J^P = 1^-)$ when plotted with respect to the center of mass energy of the collision $\sqrt{s}$ (or vs. centrality/number of participants), should show a jump at the value of $\sqrt{s}$ beyond which the QGP formation occurs. This should happen irrespective of the shape of the overall plot of $R^*$ vs. $\sqrt{s}$. Recent data from RHIC on $Λ^*/Λ$ vs. N$_{part}$ for large values of N$_{part}$ may be indicative of such a behavior, though there are large error bars. We give a list of several other such candidate hadronic states.