ON THE PHOTOEXCITATION OF THE 2S-]2P TRANSITION IN LIGHT MUONIC ATOMS

It is known that the energy of the 2s --> 2p transition of light mu-at oms can be precisely measured by laser spectroscopy. Such measurements provide a good test of quantum electrodynamics predictions. Here we c onsider how the hyperfine muon-nucleus interaction effects on the phot oexcitation of this transition and on the subsequent X-rays emission. Besides the obvious change of the transition energy the hyperfine inte raction mixes the 2p1/2 and 2p3/2 orbits. This mixing is rather effect ive in mu-atoms of H-1, Li-7, Be-9, B-10 and B-11. Its taking into acc ount changes the photoexcitation cross-section of electric dipole tran sitions between the hyperfine components of the 2s and 2p orbits and a n angular X-rays distribution as well. These changes prove to be consi derable for some transitions. For example, in mu H-2 and mu Li-7 the c ross-section is decreased by factors of two and four respectively. In mu Be-9 it is increased by a factor of two. Moreover, in mu 1H the ang ular X-rays distribution becomes more anisotropic. Besides the above s ubject one more question is discussed here. The fact is that the laser experiments can give an information on the residual muon spin polariz ation at the 2s orbit and on the degree of alignment of the angular mu -atom momentum in this state. The polarization can be determined by me asuring an angular correlation between the X-rays emission direction a nd the momentum of a hard mu-decay electron. The alignment degree can be found by measuring an anisotropy of the angular X-rays distribution .