  The equation of state of a baryon-symmetric hadronic matter with hard-sphere
interactions is studied. It is assumed that mesons are point-like, but baryons
and antibaryons have the same hard-core radius rB. Three possibilities are
considered: 1) the baryon-baryon and antibaryon-baryon interactions are the
same; 2) baryons do not interact with antibaryons; 3) the baryon-antibaryon and
meson-(anti)baryon interactions are negligible. By choosing the parameter
rB=0.3-0.6 fm, we calculate the nucleon to pion ratio as a function of
temperature and perform the fit of hadron yields measured in central Pb+Pb
collisions at the bombarding energy Ecm=2.76 TeV per nucleon pair. New
nontrivial effects in the interacting hadron resonance gas at temperatures
150-200 MeV are found.
