Weak Decays of Hypernuclei

Abstract

I present the main theoretical attempts carried out during the last few years to understand the weak hyperon-nucleon interaction through the comparison with hypernuclear decay observables, as well as the present perspectives and research avenues in the field.

The manuscript is organized as follow. The field of hypernuclear decay is presented in the Introduction. In Sect. 2 I discuss the possible modes for a hyperon to decay, the mesonic channel (Λ → πN) and the non-mesonic channel (Λ N ⇒ N N), which constitutes the dominant mode when the decay takes place in the medium. In Sect. 3 I concentrate in two different methods to evaluate the mesonic decay rate in a finite nucleus, the Propagator Method and the Wave Function Method. In Sect. 4 I present the finite nucleus calculation of the non-mesonic decay rate, again using two methods, the Polarization Propagator Method supplied by a Local Density Approximation, and a direct Finite Nucleus calculation. In this same Section, I discuss how to calculate the partial and total decay rates, and present the various models existing in the literature to describe the weak |ΔS| = 1 ΛN ⇒ NN transition potential, with special emphasis in the One-Meson-Exchange model. Sections 5 and 6 are devoted to the study of the role played by the strong interaction in hypernuclear decay, paying special attention to the effect of final state interactions of the nucleons emitted after the weak decay with the residual medium. The theoretical framework to evaluate the asymmetry in the distribution of protons coming from the decay of polarized hypernuclei is approached in Sect. 7, with the corresponding comparison with present experimental data. Recent attempts to obtain a model independent description of the weak decay process are tackled in Sect. 8. And finally, Sect. 9 presents the summary and some issues that, in my opinion, are especially worthy to address in the future.