New limits on exotic two-body decay of orthopositronium

S. Orito, K. Yoshimura, T. Haga, M. Minowa, M. Tsuchiaki

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)


Motivated by the recently reported discrepancy between measured and theoretical values for the orthopositronium lifetime, we have searched for exotic decay of orthopositronium into plus a long-lived neutral particle X, in the hitherto unexplored mass region of mx below 100 keV. Our negative result provides new upper limits of 6.4×10-5 to 7.6×10-6 on the branching ratio of such decay. Consequently we exclude the hypothesis of Samuel, i.e., that a new pseudoscalar particle with mass less than 5.7 keV is responsible for the discrepancy of the orthopositronium lifetime.

Original languageEnglish
Pages (from-to)597-600
Number of pages4
JournalPhysical Review Letters
Issue number6
Publication statusPublished - 1989
Externally publishedYes

ASJC Scopus subject areas

  • General Physics and Astronomy


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