NUCLEUS FRAGMENTATION AT LIMITED ENERGY-TRANSFER IN PION-NUCLEON COLLISIONS AT 3.15 AND 1.4 GEV C/

The pion-nucleus transitions of the type A(pi,pi'p(d))X, where pi' is the leading secondary pion emitted at a small angle (theta < 8-degrees ) and carrying over a half of the initial beam momentum, and p is a cu mulative proton (deuteron) emitted backwards with a production angle i n the 120 - 160-degrees interval, are studied. The 3.15 (1.4) GeV/c pi on beam is brought into collision with the Al and Pb (Ti and Fe) targe ts in the FOCUS detector at ITEP. The influence of the energy transfer epsilon = E(pi) - E(pi') to the leading pion on the shape of the cumu lative proton (deuteron) spectrum is investigated. The invariant cumul ative proton function f=p-1dsigma/dT is fitted with a functional form C exp(-T/T0) for both the reaction under consideration and the inclusi ve A(pi, p)X process observed in the same experiment. The deviation of the parameter T0 at low epsilon from its inclusive value, associated with the deviation of the cumulative proton spectrum from the exponent ial form, is interpreted as a kinematical boundary effect. To account for the kinematical boundary, die invariant function is taken in the f orm f is similar to (1 - T/epsilon) epsilon/T0 for epsilon < epsilon* and f is similar to (1 - T/epsilon)epsilon*/T0* for epsilon greater- than-or-equal-to epsilon, where epsilon* is the mean energy of the lo cal excitation of nuclear matter, beginning from which the function f becomes constant. The saturation of the local excitation leads to the scaling behavior of the invariant function. The global fit of all spec tra of cumulative protons yields epsilon'= 0.9 - 1.0 GeV.