Lambda -nucleon interaction in nuclei probed by the quasifree 12C( pi +,K+) reaction.

It is shown that hypernuclei are produced in the quasifree region of the [sup 12]C([pi][sup +],[ital K][sup +])[sub [Lambda]][sup 12]C reaction where a free [Lambda] is expected to be knocked out from a nucleus. The production ratio, which gives the [Lambda]-nucleon cross section in a nucleus, was derived as a function of excitation energy of [sub [Lambda]][sup 12]C. It is shown that the [Lambda]-nucleon cross section in the nucleus has to be modified by both Pauli blocking and Fermi averaging to reproduce the observed ratio.