Weak decays of 4He-Lambda

We measured the lifetime and the mesonic and non-mesonic decay rates of the 4He-Lambda hypernucleus. The hypernuclei were created using a 750 MeV/c momentum K- beam on a liquid 4He target by the reaction 4He(K-,pi-)4He-Lambda. The 4He-Lambda lifetime was directly measured using protons from Lambda p -> n p non-mesonic decay (also referred to as proton-stimulated decay) and was found to have a value of tau = 245 +/- 24 ps. The mesonic decay rates were determined from the observed numbers of pi-'s and pi0's as Gamma_pi-/Gamma_tot = 0.270 +/- 0.024 and Gamma_pi0/Gamma_tot = 0.564 +/- 0.036, respectively, and the values of the proton- and neutron-stimulated decay rates were extracted as Gamma_p/Gamma_tot = 0.169 +/- 0.019 and Gamma_n/Gamma_tot <= 0.032 (95% CL), respectively. The effects of final-state interactions and possible 3-body Lambda N N decay contributions were studied in the context of a simple model of nucleon-stimulated decay. Nucleon-nucleon coincidence events were observed and were used in the determination of the non-mesonic branching fractions. The implications of the results of this analysis were considered for the empirical Delta I = 1/2 rule and the decay rates of the 4H-Lambda hypernucleus.Comment: 15 pages, 11 figures, published in PRC, revised content to match published versio

A TOTAL ABSORPTION RANGE TELESCOPE - THE CARUZ

A total absorption range telescope, the CARUZ, has been constructed, calibrated and employed in a coincidence experiment at TRIUMF. The CARUZ measures time-of-flight (TOF), energy (E), differential energy (\u394E) and range quantities. The energy resolution of the CARUZ for 50 MeV pions is measured to be 2 MeV and is 2 MeV for 70 MeV protons. The measured quantities enable the CARUZ to easily discriminate \u3c0+ of energy 8\u201360 MeV from electrons or positrons, and from protons of energy up to 140 MeV. The response of the scintillators to the stopping pions was measured. With the inclusion of the energy from the decay muon, the response of the scintillators is almost linear in incident \u3c0+ energy. The response of the stopping \u3c0+ alone is fitted to Birk's formula with a result for the product kB = 0.0114 \ub1 0.0017 (cm/MeV)