Search

A detailed discussion is given of the analysis of recent data to obtain improved upper bounds on the couplings |Ue4|² and |Uμ4|² for a mainly sterile neutrino mass eigenstate ν4. Using the excellent agreement among the Ft values (products of kinematic rate factors times half-lives with radiative corrections included) for superallowed nuclear beta decays, an improved upper limit is derived for emission of a ν4. The agreement of the ratios of branching ratios Re/μ(π)=BR(π+→e+νe)/BR(π+→μ+νμ), Re/μ(K), Re/τ(Ds), Rμ/τ(Ds), and Re/τ(D), and the branching ratios BR(B+→e+νe) and BR(B+→μ+νμ) decays with predictions of the Standard Model is utilized to derive new constraints on ν4 emission covering the ν4 mass range from MeV to GeV. We also discuss constraints from peak search experiments probing for emission of a ν4 via lepton mixing, as well as constraints from pion beta decay, CKM unitarity, μ decay, leptonic τ decay, and other experimental inputs. [ABSTRACT FROM AUTHOR]

A detailed discussion is given of the analysis of recent data to obtain improved upper bounds on the couplings |Ue4|² and |Uμ4|² for a mainly sterile neutrino mass eigenstate ν4. Using the excellent agreement among the Ft values (products of kinematic rate factors times half-lives with radiative corrections included) for superallowed nuclear beta decays, an improved upper limit is derived for emission of a ν4. The agreement of the ratios of branching ratios Re/μ(π)=BR(π+→e+νe)/BR(π+→μ+νμ), Re/μ(K), Re/τ(Ds), Rμ/τ(Ds), and Re/τ(D), and the branching ratios BR(B+→e+νe) and BR(B+→μ+νμ) decays with predictions of the Standard Model is utilized to derive new constraints on ν4 emission covering the ν4 mass range from MeV to GeV. We also discuss constraints from peak search experiments probing for emission of a ν4 via lepton mixing, as well as constraints from pion beta decay, CKM unitarity, μ decay, leptonic τ decay, and other experimental inputs. [ABSTRACT FROM AUTHOR]

Improved upper bounds are presented on the coupling |Ue4|2 of an electron to a sterile neutrino ν4 from analyses of data on nuclear and particle decays, including superallowed nuclear beta decays, the ratios R(π)e/μ=BR(π+→e+νe)/BR(π+→μ+νμ), R(K)e/μ, R(Ds)e/τ, and B+e2 decay, covering the mass range from MeV to GeV. [ABSTRACT FROM AUTHOR]

Evidence of a heavy neutrino, νH, in the K+ → µ+ νH decays was sought using the E949 experimental data with an exposure of 1.70 × 1012 stopped kaons. With the major background from the radiative K+ → µ+νµγ decay understood and suppressed, upper limits (90% C.L.) on the neutrino mixing matrix element between the muon and heavy neutrinos, |UµH|², were set at the level of 10-7 to 10-9 for the heavy neutrino mass region 175 to 300 MeV/c². [ABSTRACT FROM AUTHOR]

The three body pion decays π+→l+νX(l=e,μ), where X is a weakly interacting neutral boson, were searched for using the full data set from the PIENU experiment. An improved limit on Γ(π+→e+νX)/Γ(π+→μ+νμ) in the mass range 0

Charged lepton flavor violating muon decay μ+ → e+XH, where XH is a massive neutral boson, was sought by searching for extra peaks in the muon decay μ+ → e+νν energy spectrum in the mXH mass region 47.8 - 95.1 MeV/c². No signal was found and 90% confidence level upper limits were set on the branching ratio Γ(μ+ → e+XH)/Γ(μ+ → e+νν) at the level of 10-5 for this region. [ABSTRACT FROM AUTHOR]

A search for massive neutrinos has been made in the decay π+→e+ν. No evidence was found for extra peaks in the positron energy spectrum indicative of pion decays involving massive neutrinos (π→e+νh). Upper limits (90% C.L.) on the neutrino mixing matrix element |Uei|2 in the neutrino mass region 60-135 MeV/c2 were set and are an order of magnitude improvement over previous results. [ABSTRACT FROM AUTHOR]