Strangeness production in ultrarelativistic heavy-ion collisions. II. Evolution of flavor composition in scaling hydrodynamics

Abstract

Bjorken's hydrodynamic description of the space-time evolution of the central rapidity region in ultrarelativistic heavy-ion collisions is extended to incorporate the chemical processes which affect the strangeness abundance. Scaling hydrodynamic equations which contain the rate equation for strangeness production and annihilation both in the plasma phase and in the hadron gas phase are integrated numerically assuming an almost adiabatic first-order phase transition from plasma to hadron gas. It is found that if a plasma is initially formed the resultant K / T ratio will be enhanced by about a factor of 3 from that in pp collisions. However, this ratio is still smaller than that in an equilibrium hadron gas and hence cannot be considered a direct signal of plasma formation.

The Search for the Quark-Gluon Plasma

“…It should be noted that some increase in the production of strange hadrons, especially kaons and Λ-hyperons, in nucleus-nucleus collisions can result from purely hadronic interactions [230,231,232]. However, the enhancement in the Λ yield measured over a large rapidity interval [225] is difficult to describe by a cascade of hadronic interactions.…”

QGP theory: Status and perspectives

“…However, the estimated chemical equilibration times may not be sufficiently rapid to cause chemical equilibration before hadronization: calculations based on boost-invariant hydrodynamics with rate-equations for quark production [50][51][52], pQCD rate-equations [53] or the Parton Cascade Model [54] all indicate that chemical equilibration (and strangeness saturation) cannot be achieved during realistic life-times of the deconfined phase. It has been suggested (e.g.…”

Strangeness evolution in the central region of a heavy-ion collision with transverse flow effects

“…3c shows n/neq if the rate term in hadron phase is reduced by a factor 10 [ll]. Here neq and s are calculated directly from the flow; n is obtained by numerically integrating the kinetic equations (4)(5)(6)(7)(8)(9)(10).…”