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Single and double coincidence nucleon spectra in the weak decay of Lambda hypernuclei

Recent progress has been experienced in the field of hypernuclear weak decay, especially concerning the ratio of the neutron- to proton-induced Lambda non-mesonic decay rates, G_n/G_p. Theoretical analyses of nucleon coincidence data have been performed in a finite nucleus framework. They led to the extraction of G_n/G_p values in agreement with pure theoretical estimates, thus providing an evidence for the solution of a longstanding puzzle. Here we present an alternative approach to the problem, based on a nuclear matter formalism extended to finite nuclei via the local density approximation. The work is motivated by the exigence to make the determination of G_n/G_p from data less model dependent. One-meson-exchange potentials are used for describing both the one- and two-nucleon induced decays, Lambda N -> n N and Lambda N N -> n N N. For the latter, treated within a microscopic approach, the channels Lambda n n -> n n n and Lambda p p -> n p p are included in addition to the mode Lambda n p -> n n p already considered, in a phenomenological way, in previous studies. The propagation of the final nucleons in the residual nucleus is simulated by an intranuclear cascade code. We evaluate single and double coincidence nucleon spectra for the non-mesonic decay of C-12-Lambda. Through the comparison of our predictions with KEK coincidence data we determine G_n/G_p=0.43 \pm 0.10 for this hypernucleus, confirming previous finite nucleus analyses.