Weak decay of Λ in nuclei: quarks versus mesons

Abstract

Decays of Λ in nuclei, nonmesonic mode, are studied by using the ΛN → N N weak transition potential derived from the meson exchange mechanism and the direct quark mechanism. The decay rates are calculated both for the Λ in symmetric nuclear matter and light hypernuclei. We consider the exchange of six mesons (π, K, η, ρ, ω, K * ). The form factor in the meson exchange mechanism and short range correlation are carefully studied.

Nonmesonic weak decay dynamics from proton spectra of Λ-hypernuclei

“…[22][23][24] Both groups announced a branching ratio Γ 0 2 /Γ N M ∼ 25 − 30 %. The first group obtained this result from the single and double coincidence nucleon spectra in 12 Λ C, and the second one from proton kinetic energy spectra in 5 Λ He, 7 Λ Li, 9 Λ Be, 11 Λ B, 12 Λ C, 13 Λ C, 15 Λ N and 16 Λ O. A branching ratio for the 2N -NM decay channel of this magnitude is consistent with the prediction made by Bauer and Garbarino.…”

“…[22][23][24] Both groups announced a branching ratio Γ 0 2 /Γ N M ∼ 25 − 30 %. The first group obtained this result from the single and double coincidence nucleon spectra in 12 Λ C, and the second one from proton kinetic energy spectra in 5 Λ He, 25 On the other hand, the one-particle proton and neutron kinetic energy spectra in 4 Λ He measured at BNL 26 are accounted for reasonably well theoretically by considering only the 1N -NM decay mode. 8,9 The above mentioned experiments, together with several others performed during the last few decades, 23,[27][28][29][30][31][32][33][34][35] represent very important advances in our knowledge about NM decay.…”

“…11 Nothing has been stated so far regarding the effect of the SRCs on the 2N -NM decay. The theoretical scene becomes even more complex when effects of the quark degrees of freedom, 12,13 the 2π-exchanges, [14][15][16][17] and the axial-vector a 1 -meson exchange 16,17 are considered.…”

Nonmesonic Weak Decay of A-Hypernuclei within Independent-Particle Shell-Model

“…One proceeds similarly with the Eqs. ( 19), (23), and (31). It turns out that the expressions within the IPSM-b can be obtained from those of IPSM-a through the replacements:…”

“…The deficiency of the OPE model was attributed to effects of short range physics, which should be quite important in view of the large momentum transfers involved. Although there have been some attempts to account for this fact by making use of quark models to compute the shortest range part of the transition potential [19][20][21][22][23], most of the theoretical work opted for the addition of other, heavier mesons in the exchange process [6,10,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. None of these models gives fully satisfactory results.…”