Searches for muon-electron and muon-positron conversion in titanium

Abstract

Searches have been performed for neutrinoless muon-electron conversion and muon-positron conversion using a time projection chamber. An upper limit on the branching ratio for the coherent reaction R(${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$ +Ti\ensuremath{\rightarrow}${e}^{\mathrm{\ensuremath{-}}}$+Ti)4.6\ifmmode\times\else\texttimes\fi{}1 ${0}^{\mathrm{\ensuremath{-}}12}$ [90% confidence level (C.L.)] relative to ordinary muon capture was obtained. For the process ${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$+Ti\ensuremath{\rightarrow}${e}^{+}$+Ca no events were observed for positron momenta p96 MeV/c leading to an upper limit on the partial branching ratio relative to ordinary muon capture ${\ensuremath{\Gamma}}_{p96}$(${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$+Ti\ensuremath{\rightarrow}${e}^{+}$ +Ca)/\ensuremath{\Gamma}(${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$+Ti\ensuremath{\rightarrow}capture) 9\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$ (90% C.L.). With the assumption of a giant-resonance-excitation model the integrated limit would be \ensuremath{\Gamma}(${\mathrm{\ensuremath{\mu}}}^{\mathrm{\ensuremath{-}}}$+Ti\ensuremath{\rightarrow}${e}^{+}$+Ca)/\ensuremath{\Gamma}(${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$ +Ti\ensuremath{\rightarrow}capture)1.7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ (90% C.L.).