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 Tc, 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 (QGP) formation in relativistic heavy-ion collisions. For example, the ratio R* of multiplicities of and when plotted with respect to the center-of-mass energy of the collision (or vs. centrality/number of participants), should show a jump at the value of beyond which the QGP formation occurs. This should happen irrespective of the shape of the overall plot of R* vs. . Recent data from RHIC on Λ*/Λ vs. Npart for large values of Npart may be indicative of such a behavior, though there are large error bars. We give a list of several other such candidate hadronic states.