Previous studies of proton and neutron spectra from Non-Mesonic Weak Decay of eight Lambda-Hypernuclei (A = 5-16) have been revisited. New values of the ratio of the two-nucleon and the one-proton induced decay widths, Gamma_2N/Gamma_p, are obtained
from single proton spectra, Gamma_2N/Gamma_p = 0.50 +/- 0.24, and from neutron and proton coincidence spectra, Gamma_2N/Gamma_p = 0.36 +/- 0.14stat +0.05sys -0.04sys , in full agreement with previously published ones. With these values, a method is developed to extract the one-proton induced decay width in units of the free Lambda decay width, Gamma_p/Gamma_Lambda, without resorting to Intra Nuclear Cascade models but by exploiting only experimental data, under the assumption of a linear dependence on A of the Final State Interaction contribution. This is the first systematic determination ever done and it agrees within the errors with recent theoretical calculations.
The pentaquark $Theta^+$ has been searched for via the $pi^-p to K^-X$ reaction with beam momenta of 1.92 and 2.01 GeV/$c$ at J-PARC. A missing mass resolution of 2 MeV (FWHM) was achieved but no sharp peak structure was observed. The upper limits on
the production cross section averaged over the scattering angle from 2$^{circ}$ to 15$^{circ}$ in the laboratory frame were found to be less than 0.28 $mu$b/sr at the 90% confidence level for both the 1.92- and 2.01-GeV/$c$ data. The systematic uncertainty of the upper limits was controlled within 10%. Constraints on the $Theta^+$ decay width were also evaluated with a theoretical calculation using effective Lagrangian. The present result implies that the width should be less than 0.36 and 1.9 MeV for the spin-parity of $1/2^+$ and $1/2^-$, respectively.
Search for the neutron-rich hypernucleus 9LHe is reported by the FINUDA experiment at DAFNE, INFN-LNF, studying (pi+, pi-) pairs in coincidence from the K-stop + 9Be --> 9LHe + pi+ production reaction followed by 9LHe --> 9Li + pi- weak decay. An upp
er limit of the production rate of 9LHe undergoing this two-body pi- decay is determined to be (2.3 +/- 1.9) 10-6/K-stop at 90% confidence level.
Three candidate events of the neutron-rich hypernucleus 6{Lambda}H were uniquely identified in the FINUDA experiment at DA{Phi}NE, Frascati, by observing {pi}+ mesons from the (K-stop,{pi}+) production reaction on 6Li targets, in coincidence with {pi
}-mesons from 6{Lambda}H rightarrow 6He+{pi}- weak decay. Details of the experiment and the analysis of its data are reported, leading to an estimate of (2.9pm2.0)cdot10-6/K- stop for the 6{Lambda}H production rate times the two-body {pi}- weak decay branching ratio. The 6{Lambda}H binding energy with respect to 5H + {Lambda} was determined jointly from production and decay to be B{Lambda} = (4.0 pm 1.1) MeV, assuming that 5H is unbound with respect to 3H + 2n by 1.7 MeV. The binding energy determined from production is higher, in each one of the three events, than that determined from decay, with a difference of (0.98 pm 0.74) MeV here assigned to the 0+g.s. rightarrow 1+ excitation. The consequences of this assignment to {Lambda} hypernuclear dynamics are briefly discussed.
Evidence for the neutron-rich hypernucleus 6{Lambda}H is presented from the FINUDA experiment at DA{Phi}NE, Frascati, studying ({pi}+, {pi}-) pairs in coincidence from the K- +6Li rightarrow 6 H+{pi}+ production reaction followed by 6{Lambda}H righta
rrow 6He + {pi}- weak decay. The production rate of 6{Lambda}H undergoing this two-body {pi}- decay is determined to be (2.9pm2.0)cdot10-6/K-. Its binding energy, evaluated jointly from production and decay, is B{Lambda}(6{Lambda}H) = (4.0pm1.1) MeV with respect to 5H+{Lambda}. A systematic difference of (0.98 pm 0.74) MeV between B{Lambda} values derived separately from decay and from production is tentatively assigned to the 6{Lambda}H 0+g.s. rightarrow 1+ excitation.
The decay of $Lambda$-hypernuclei without pion emission, known as Non Mesonic Weak Decay (NMWD), gives an effective tool to investigate $Delta$S=1 four-baryon interactions. It was theoretically suggested that the two-nucleon induced mechanism could p
lay a substantial role in reproducing the observed NMWD decay rates and nucleon spectra, but at present no direct evidence of such a mechanism has been obtained. The FINUDA experiment, exploiting the possibility to detect both charged and neutral particles coming from the hypernucleus decay, has allowed us to deduce the relative weight of the two nucleon induced decay rate to the total NMWD rate. The value of $Gamma_{2N}$/$Gamma_{NMWD}$=0.24$pm$${0.03_{stat}}^{+0.03_{sys}}_{{-{0.02_{sys}}}}$ has been deduced, with an error reduced by a factor more than two compared with the previous assessment.
New spectra from the FINUDA experiment of the Non Mesonic Weak Decay (NMWD) proton kinetic energy for 9(Lambda)Be, 11(Lambda)B, 12(Lambda)C, 13(Lambda)C, 15 (Lambda)N and 16(Lambda)O are presented and discussed along with the published data on 5(Lamb
da)He and 7(Lambda)Li. Exploiting the large mass number range and the low energy threshold (15 MeV) for the proton detection of FINUDA, an evaluation of both Final State Interactions (FSI) and the two nucleon induced NMWD contributions to the decay process has been done. Based on this evaluation, a linear dependence of FSI on the hypernuclear mass number A is found and for the two nucleon stimulated decay rate the experimental value of Gamma2/Gammap=0.43+-0.25 is determined for the first time. A value for the two nucleon stimulated decay rate to the total decay rate Gamma2/GammaNMWD=0.24+-0.10 is also extracted.
Novel data from the $K^{-}_{stop}A$ absorption reaction in light nuclei $^{6,7}$Li and $^{9}$Be are presented. The study aimed at finding $Lambda t$ correlations. Regardless of $A$, the $Lambda t$ pairs are preferentially emitted in opposite directio
ns. Reaction modeling predominantly assigns to the $K^-_{stop}AtoLambda t(N)A$ direct reactions the emission of the $Lambda t$ pairs whose yield is found to range from $10^{-3}$ to $10^{-4}$$/K^-_{stop}$. The experiment was performed with the FINUDA spectrometer at DA$Phi$NE (LNF).
The results of a measurement of the proton spectra following the Non--Mesonic Weak Decay of $mathrm{^5_{Lambda}He}$, $mathrm{^7_{Lambda}Li}$ and $mathrm{^{12}_{Lambda}C}$ are presented and discussed. The experiment was performed at the ($e^+$ $e^-$)
collider DA$Phi$NE at Laboratori Nazionale di Frascati of INFN. It is the first measurement for $mathrm{^7_{Lambda}Li}$, and for all the spectra the lower limit on the energy of the protons is 15 MeV, never reached before. All the spectra show a similar shape, namely a peak at around 80 MeV as expected for the free $Lambda p to np$ weak reaction, with a low energy rise that should be due to Final State Interactions and/or two--nucleon induced weak processes. The decay spectrum of $mathrm{^5_{Lambda}He}$ is somehow similar to the ones reported by previous measurements and theoretical calculations, but the same doesnt happen for the $mathrm{^{12}_{Lambda}C}$ one.
Correlated $Lambda d$ pairs emitted after the absorption of negative kaons at rest $K^{-}_{stop}Ato Lambda d A$ in light nuclei $^6Li$ and $^{12}C$ are studied. $Lambda$-hyperons and deuterons are found to be preferentially emitted in opposite direct
ions. The $Lambda d$ invariant mass spectrum of $^6Li$ shows a bump whose mass is 3251$pm$6 MeV/c$^2$. The bump mass (binding energy), width and yield are reported. The appearance of a bump is discussed in the realm of the [$bar{K}3N$] clustering process in nuclei. The experiment was performed with the FINUDA spectrometer at DA$Phi$NE (LNF).
