Speaker
Dr
Stefania Bufalino
(INFN-TORINO)
Description
The information coming from the study of the Lambda-hypernuclei weak decay channels complements the knowledge of strange nuclear systems obtained by both missing mass and gamma-ray spectroscopy measurements. Lambda-hypernuclei decay through both the mesonic weak
decay (MWD) and the non-mesonic weak decay (NMWD) processes.
In particular, recently, the two-nucleon induced (2N) NMWD has been studied quite extensively both experimentally and theoretically. The FINUDA experiment performed a complete analysis of the charged particles (pi− and p) spectra following the MWD and NMWD of 5(Lambda)He, 7(Lambda)Li, 9(Lambda)Be, 11(Lambda)B, 12(Lambda)C, 13(Lambda)C, 15(Lambda)N and 16(Lambda)O hypernuclei.
MWD spectra and decay rates have been obtained for 7(Lambda)Li, 9(Lambda)Be, 11(Lambda)B and 15(Lambda)N for the first
time and compared with previous measurements and calculations. The spin-parity assignment for 15(Lambda)Ng.s. = 3/2+ was made for the first time and the results have been published [1].
The FINUDA Collaboration also analyzed the proton energy spectra of 5(Lambda)He, 7(Lambda)Li, 9(Lambda)Be, 11(Lambda)B, 12(Lambda)C, 13(Lambda)C, 15(Lambda)N and 16(Lambda)O with good resolution (deltap/p=2% FWHM for protons of 80 MeV) and with a detection threshold of 15 MeV. All measured spectra showed a similar
behaviour, i.e. a bump at about 80 MeV, roughly at the energy expected from one-proton induced NMWD (with an incertitude of about 10 MeV due to several nuclear structure and interaction effects). The bump is quite well defined in the high energy portion, whereas at low
energies it is blurred in a continuum generated by FSI, superimposed to the 2N-induced NMWD contribution. With very simple hypotheses and a model–independent method the
contributions from FSI and 2N-induced NMWD were disentangled, providing a value of Gamma(2N)/Gamma(NMWD) of 0.24±0.10 [2]. This method was recently improved with the further detection of a neutron, from which we determined the value of
Gamma(2N)/Gamma(NMWD) with an error reduced respect to the previous FINUDA determination [2].
The value is in agreement, within the errors, with previous evaluations, model dependent or not, and with theoretical calculations.
Comparison of the FINUDA data with the available experimental results from KEK will be also presented.
References:
[1] M. Agnello et al., Phys. Lett. B 681 (2009) 139.
[2] M. Agnello et al., Phys. Lett. B 685 (2010) 247.
Primary author
Dr
Stefania Bufalino
(INFN-TORINO)
