ISSN:
1434-601X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract We have found a possible example of the rare decayσ + →nΜ + Ν, which violatesδS=δQ. The positive decay track of theσ + comes to rest in the hydrogen bubble chamber and decays into ane +. This track has all the characteristics of a stoppingΜ +. The decay neutron fortuitously scatters twice, producing two recoil protons. The only other possible interpretation of the event isσ +→nγ(π + →Μ + Ν), where theπ + →Μ + Ν decay produces no deflection (θ〈0.1 rad) and no significant change in curvature. Using thep-wave radiative decay predictions ofBarshay et al. we calculate that the integrated branching ratio for such “accidental” events isγ(σ + →nγ(π + →Μ stop + Ν))/γ(σ + →nπ +)=1.6×10−6. Most of the contribution to this “accidental” branching ratio comes from radiative decays where theπ + mesons have ranges less than 1 mm (p π〈20 MeV/c). If one excludes thoseΜ's with ranges less than 1.2 cm the above “accidental” branching ratio becomes 5.5×10−7. With this figure we estimate that we should have seen 6.5×10−2 events of this type thusfar in our experiment. The neutron momentum does not help in deciding between the two hypotheses. We therefore assign a confidence level of 7% for the radiative hypothesis. For the leptonic hypothesis we obtain an estimate of the branching ratio,γ(σ + →nΜ + Ν)/γ(σ + →nπ +)=5×10−5. If one further accepts theσ + →nπ + Ν event reported byBarbaro-Galtieri et al. and theσ + →ne + Ν event reported byNauenberg et al., one obtains theδS=−δQ leptonic branching ratio [γ(σ + →nΜ + Ν)+γ(σ + →ne + Ν)]/γ(σ + →nπ +)=(4±3)×10−5.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01325596
