Search for invisible decay of orthopositronium

T. Mitsui, R. Fujimoto, Y. Ishisaki, Y. Ueda, Y. Yamazaki, S. Asai, S. Orito

Research output: Contribution to journalArticlepeer-review

24 Citations (Scopus)


Orthopositronium (o-Ps) decay or conversion into ''invisible'' final states is searched for by measuring the energy deposited in a hermetic photon detector for each positron produced from β+ decay of Na22 and stopped by an aerogel target. No invisible event is detected for a total of 108 stopping positrons, thereby giving an upper limit of 2.8×10-6 on the o-Ps branching ratio, which is 200 times more stringent than previous limits. This experiment excludes an invisible decay as the origin of the reported discrepancy on o-Ps lifetime, provides a limit of ε<1.5×10-8 on the photon-mirror-photon mixing, and rules out millicharged particles lighter than 500 keV.

Original languageEnglish
Pages (from-to)2265-2268
Number of pages4
JournalPhysical review letters
Issue number15
Publication statusPublished - 1993
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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