Hypernuclear weak decay studies with FINUDA

Abstract

The FINUDA experiment has recently completed an extensive study of the weak decay of p-shell Λ-hypernuclei including both mesonic and non-mesonic modes. Charged mesonic decay rates have been determined based on the analysis of π − kinetic energy spectra, never measured before. The study of proton spectra from non-mesonic weak decay for p-shell hypernuclei, both single and in coincidence with a neutron, has triggered the investigation of the two-nucleon induced ΛN N → nN N decay channel: its weight has been evaluated to be Γ 2 /Γ NM = 0.21 ± 0.07 stat +0.03 sys −0.02 sys . Finally, a direct experimental evidence of the occurrence of the weak reaction Λnp → nnp in nuclei is presented for the first time. Three events have been found which can be attributed to 7 Λ Li and 9 Λ Be two-nucleon induced non-mesonic weak decay; the kinematical analysis is discussed here.

Strangeness nuclear physics: a critical review on selected topics

“…The obtained Γ np width can be used to obtain Γ 2 by following the theoretical predictions of Ref. [225]; moreover, by assuming again that Γ n /Γ p is independent of the Hypernuclear species and using for this ratio the data obtained by KEK [238], the FINUDA final result is: From [246].…”

“…[26]. Finally, thanks to the large solid angle coverage of the FINUDA apparatus (∼ 2π srad) and to its detection efficiency for neutrons and for protons with low kinetic energy, it has been possible to find one event [246] in which also the second neutron from pn-induced NMWD was detected, for which the angles between each neutron and the proton, and between the two neutrons are greater than π/2, which is the maximum angle expected for a simple nucleon-nucleon scattering. The projection of this event, occurring on a 7 Li target, onto the ρ−φ plane of the apparatus is shown in figure 41.…”

“…Pictorial representation of the Λnp → nnp event seen by FINUDA on a 7 Li target. The blue track represents the trajectory of the π − from the hypernucleus formation reaction.From[246].…”

Experimental Studies on the Weak Decay of Λ-Hypernuclei

“…1 the contribution from process (4), without resorting to any Intra-Nuclear Cascade (INC) calculation, as it was done instead by other research Groups [29,30]. This way, it was possible to get a first evaluation of Γ 2N /Γ p and Γ 2N /Γ NMWD ratios and to provide the first purely experimental evidence of the occurrence of reaction (4) [31].…”

Production of strangeness −1 and −2 hypernuclei within a field theoretic model

“…Furthermore, since in these reactions a proton in the target nucleus is converted into a hyperon, it leads to the production of neutron rich hypernuclei (see, e.g., Ref. [33]), which may carry exotic features such as a halo structure. It can produce many mirror hypernuclear systems which would enable the study of the charge symmetry breaking with strangeness degrees of freedom.…”