Ghislaine Coremans

A determination of the binding-energy values of light hypernuclei

Abstract The results of an experimental study of the binding energies of light hypernuclei are presented, based on a sample of 2008 uniquely identified π − mesonic decays. The problems of the calibration procedure and the selection criteria are discussed. Various aspects of the Λ -N interaction are reviewed in the light of these new results.

Total cross sections for ve and ve interactions and search for neutrino oscillations and decay

Abstract About 200 and 60 candidates for electron neutrino and antineutrino interactions, respectively, have been analyzed in the heavy liquid bubble chamber Gargamelle exposed to the CERN PS neutrino beam. Evidence for scaling has been found for these interactions, with slopes of the cross sections in good agreement with those obtained for muon neutrino and antineutrino events in the same chamber. No evidence appears for oscillations of neutrinos or antineutrinos, which would induce in the present experiment an excess of electron or positron events. The corresponding limits are given as functions of the mixing parameter, for the finite mass Majorana neutrinos. The possibility of a multiplicative law for the lepton number has also been investigated. A search for isolated electron-positron pairs revealed no excess in the forward direction, in contradiction to the expectation for muonic neutrino and antineutrino decays. The corresponding limits on the c.m. half lifetimes are given.

On the lifetime of the 3ΛH ypernucleus

The mean lifetime of the 3ΛH hypernucleus has been estimated in nuclear emulsion using the (π−+1H+2H) decays both at rest and in flight. The result, τ(3ΛH) = (1.28−0.26+0.35) · 10−10sec, is significantly lower than another recent experimental value [5] and the theoretical predictions. A possible explanation of the discrepancy with the theoretical predictions is briefly discussed.

Branching ratios for the π− mesonic decays of the hypernuclei Λ3H and Λ4H

Results are presented concerning the experimental determination, with large statistics, of the branching ratios for the π− mesonic decay of the hypernuclei Λ3H and Λ4H. The spin assignments J(Λ3H) = 12and J(Λ4H) = 0 are confirmed.

The non-mesonic decay of helium hypernuclei

Abstract The analysis is reported of a sample of hypernuclei decaying non-mesonically with the emission of one or two charged particles which were obtained from K − meson captures at rest in nuclear emulsion. Making use of the decay parameters established for the 4 Λ He hypernucleus from observations in a helium bubble chamber, a value of Q − , the ratio of non-mesonic to π − mesonic decays, for λ 5 He together with the rates of certain decay modes have been determined.

Neutral pion production by weak neutral currents in neutrino and antineutrino reactions

Abstract A study is presented of single πo production in neutrino and antineutrino interactions in Gargamelle filled with freon CF3Br. Limits on the neutral to charged current cross-section ratios R v =σ(v N →v N ′π o )/2 σ(v N → μ - N ′π o ) and R ν = σ( ν N → ν N ′π o )/2 σ( ν N → ω + N ′π o ) are found to be 0.10 ν and 0.26 ν at 68% confidence level.

SEARCH FOR STRANGENESS CHANGING NEUTRAL CURRENTS INDUCED BY NEUTRINOS IN GARGAMELLE

Abstract A sample of 9930 neutrino neutral current interactions has been examined for single strange particle production. No signal in the channels ν N → νγ X and ν N → ν | gS 0 X, where X means non-strange hadrons, has been found. This yields an upper limit of 5.4 × 10 −3 to a 90% confidence level on the ratio [( ν → νΓ X) + ( ν → νΣ 0 X)]/[ ν → ν + anything]

A determination of the binding energy of the Λ13C hypernucleus

Abstract From the observation of 11 examples of the π − mesonic decay of Λ 13 C the binding energy of this hypernucleus is found to be 11.39 ± 0.15 MeV.

The question of the existence of a particle-stable Λ6Li hypernucleus

The recent reported evidence for the existence of the Λ6Li hypernucleus is questioned. No example of the (π−1H1H4He) decay mode of this hypernucleus was found in a sample of 7000 mesonically decaying hypernuclei.

The π+ mesonic decays of light hypernuclei

Twenty examples of π+ mesonic decays of light hypernuclei have been found together with 7000 π− mesonic decays. The ratio R4 of π+ mesonic decays for the gL4 He hypernucleus has been computed from the results of this work and those of a previous experiment [1] and is found to lie between the values 5.4 ± 1.5%1.7% and 6.9 ± 1.8%2.1%. The π+ mesonic decays of other species of hypernuclei are briefly discussed.