Volume 134, number 7 PHYSICS LETTERS A 23 January 1989 COLLISION-INDUCED SPIN FLIP IN ISOTOPES OF MUONIC HYDROGEN L. BRACCI Dipartimento di Fjsjca dell’Uni~ersitàdi Pisa and INFNSezione di Pisa, Pisa, Italy C. CHICCOLI, P. PASINI INFNSezione di Bologna and CNAF, Bologna, Italy G. FIORENTINI Dipartimento di Fisica dell’Università di Cagliari and INFNSezione di Cagliari, Cagliari, italy V.S. MELEZHIK Joint Institute for Nuclear Research, Dubna, USSR and J. WOZNIAK Institute ofPhysics and Nuclear Techniques, KrakOw, Poland Received 28 September 1988; revised manuscript received 29 November 1988; accepted for publication 30 November 1988 Communicated by B. Fricke We present results for spin flip processes in muonic atoms. The calculations are performed in the framework of the adiabatic representation of the three-body Coulomb problem. The contribution of back decay is taken into account and comparison with available experimental data is reported. In the chain of phenomena leading to muon cat- tween the ground state (F= 0) and the excited state alyzed fusion [1] the number of processes which a (F= 1) is Et~I1”~~ = 0.182 eV and EM’~= 0.2373 eV muon can catalyze is ultimately determined by the respectively. For (dl.t) atoms the ground and excited interplay of several different rates (mesomolecule level have F= ~ and F= ~ respectively, the splitting formation, fusion, transfer etc.). In the case of iden- being E~~I?~ = 0.0485 eV. tical nuclei (dj.t + d process for instance) a marked We perform the calculations of the spin flip cross dependence of the mesomolecule formation rate on sections in the framework of the adiabatic represen- the state of the hyperfine structure (HFS) of the col- tation of the three-body Coulomb problem. In the liding muonic atom has been noted [21. As a con- hamiltonian the only spin dependent term is the con- sequence it is interesting to estimate the population tact interaction between the muon and the nuclei, of the HFS states in the range of temperatures which is responsible of the HFS splitting. Total spin T~1000 K, where experiments are currently per- S of the nuclei-plus-muon system is conserved and formed. This requires the calculation of the spin flip spin flip occurs because of the exchange interaction cross sections, up to the energy (E~1 eV), where due to the symmetry of the total wave function. As the distribution of muonic atoms is still appreciable. a consequence, for p—p and t—t collisions spin flip is We recall some data about the HFS of muonic hy- allowed only for S= ~. For d—d both S= ~ and drogen. For (pji) and (tJ.L) atoms the splitting be- 5= ~ are allowed. 435