In-medium modifications of hadron masses and chemical freeze-out in ultra-relativistic heavy-ion collisions

We confront the hypothesis of chemical freeze-out in ultra-relativistic hea vy-ion collisions with the hypothesis of large modifications of hadron mass es in nuclear medium. We find that the thermal-model predictions for the ra tios of particle multiplicities are sensitive to the values of in-medium ha dronic masses. In particular, the pi(+)/p and K+/p ratios decrease by about 30% when the masses of all hadrons (except for pseudo-Goldstone bosons) ar e scaled down by 30%. (C) 2000 Published by Elsevier Science B.V. All right s reserved.