  We report the first direct observation of excited state muon transfer in
hydrogen/deuterium mixtures by direct measurement of q_1s, the probability that
a mu-p atom, which is initially formed in an excited state, reaches the 1s
ground state. The dependence of q_1s on deuterium concentration c_d was
measured for two different densities at cryogenic temperatures using charge
coupled devices (CCDs) to detect the muonic X rays. First results based on the
analysis of the K_alpha-lines of the two isotopes are presented.
