  We propose an intensity-dependent pion-nucleon coupling Hamiltonian within a
unitary multiparticle-production model of the AABS type in which the pion field
is represented by the thermal-density matrix. Using this Hamiltonian, we
explain the appearance of the negative- binomial (NB) distribution for pions
and the well-known empirical relation, the so-called Wroblewski relation. The
Hamiltonian of our model is expressed linearly in terms of the generators of
the SU(1,1) group.
