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

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(${\mu }^{\mathrm{-}}$ +Ti→$e^{\mathrm{-}}$+Ti)<4.6×1 $0^{\mathrm{-}12}$ [90% confidence level (C.L.)] relative to ordinary muon capture was obtained. For the process ${\mu }^{\mathrm{-}}$+Ti→$e^{+}$+Ca no events were observed for positron momenta p>96 MeV/c leading to an upper limit on the partial branching ratio relative to ordinary muon capture ${\Gamma }_{p>96\mathrm{}}$(${\mu }^{\mathrm{-}}$+Ti→$e^{+}$ +Ca)/Γ(${\mu }^{\mathrm{-}}$+Ti→capture) <9×${10}^{\mathrm{-}12}$ (90% C.L.). With the assumption of a giant-resonance-excitation model the integrated limit would be Γ(${\mathrm{\mu }}^{\mathrm{-}}$+Ti→$e^{+}$+Ca)/Γ(${\mu }^{\mathrm{-}}$ +Ti→capture)<1.7×${10}^{\mathrm{-}10}$ (90% C.L.).