We searched for an exotic decay of orthopositronium into a single photon and a short-lived neutral boson ø0 in hitherto unexplored mass region below 300 keV/c2. A high-resolution measurement of the associated photon energy spectrum was carried out with a germanium detector to discriminate the expected sharp peak of this decay from the broader peak of the pick-off annihilations. No evidence of such decay was observed, resulting in the upper-limits on the branching ratio of 3.0×10-4 (mΦ0<500 keV/c2). This clearly rules out the possibility of this exotic decay mode explaining the reported discrepancy in the orthopositronium decay rate.
|Number of pages
|Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
|Published - 1994 Mar 3