BREAKUP OF RELATIVISTIC PI(-) ATOMS IN MATTER()PI()

The relativistic motion of atoms formed by pi(+) and pi(-) mesons in m atter is considered. Exact analytic expressions for the form factors o f hydrogen-like atoms for discrete-discrete transitions are obtained i n a form convenient for numerical calculations. The total and transiti on cross sections for the interaction of pi(+)pi(-) atoms with matter are calculated in the Born approximation. The evolution of atomic-stat e populations is treated in terms of kinetic equations. The method of calculation makes it possible to obtain the populations of discrete at omic states, as well as the probability of transitions to the continuo us spectrum (ionization). The proposed method yields the first experim ental estimate of the lifetime of the pi(+)pi(-) atom.