Medium Energy Elementary Particle Physics: Technical Progress Report, 11/1/86 Thru 5/28/87

摘要

We have searched for spontaneous conversion of muonium (M identical to mu sup + e sup - ) to antimuonium (anti M identical to mu sup - e sup + ) at LAMPF. When mu sup + of 10 MeV/c pass through an Al foil (0.2 mg/cm sup 2 ), M atoms with kinetic energies of 1 to 20 keV are formed by e sup - -capture. They pass a drift space of 342 cm, of which 206 cm is magnetically shielded to less than or equal to20 mG, and are stopped on a 1 mu m thick Bi target, which was evaporated onto a 2 mil mylar backing and coated with 75 A of MgO. The impact of M or anti M atoms on the target liberates about 5 secondary electrons each with kinetic energies of a few eV. These are electrostatically collected and guided onto a microchannel plate detector, using electric fields of about 100 V/cm. We have counted M at 1 to 20 keV with 50% efficiency using this 0.4 m sup 2 area active target. If an oscillation of M to anti M has occurred, stopping an anti M atom will entail formation of a Bi mu sup - atom and emission of its characteristic muonic x rays. The crystal box detector then detects the coincident L alpha and K alpha x rays at 4% efficiency. The anti M event signature was defined as a triple coincidence of a Bi mu sup - L alpha x ray, a K alpha x ray, and a count in the M(anti M) secondary emission counter. No statistically significant signal was seen and our preliminary data analysis yields an upper limit of G/sub M anti M/ less than or equal to 8 G/sub F/ (95% C.L.) on the coupling constant of a four-Fermion contact interaction. The current published limit is G/sub M anti M/ less than or equal to 20 G/sub F/. A conversion of M to anti M is forbidden in the standard model, since it would violate additive lepton flavor conservation. However, an alternative theory based on a lef-tright symmetric model allows the M implies anti M coupling at G/sub M anti M/ - 10 G/sub F/. 8 refs., 4 figs. (ERA citation 12:035971)