Limit on an exotic three-body decay of orthopositronium

T. Mitsui; K. Maki; S. Asai; Y. Ishisaki; R. Fujimoto; N. Muramoto; T. Sato; Y. Ueda; Y. Yamazaki; S. Orito

doi:10.1209/epl/i1996-00307-8

All issues

Volume 33 / No 2 (January II 1996)

Europhys. Lett., 33 2 (1996) 111-116

Abstract

Issue		Europhys. Lett. Volume 33, Number 2, January II 1996


Page(s)		111 - 116
Section		The physics of elementary particles and fields
DOI		https://doi.org/10.1209/epl/i1996-00307-8
Published online		01 September 2002

Europhys. Lett., 33 (2), pp. 111-116 (1996)

Limit on an exotic three-body decay of orthopositronium

T. Mitsui, K. Maki, S. Asai, Y. Ishisaki, R. Fujimoto, N. Muramoto, T. Sato, Y. Ueda, Y. Yamazaki and S. Orito

Department of Physics, Faculty of Science, University of Tokyo, Tokyo 113, Japan

Received: 18 September 1995
Accepted: 27 November 1995

Abstract

An exotic annihilation of ${\rm e}^{+}{\rm e}^{-}$ at rest into a single γ and a weakly interacting neutral vector boson ${\rm V}^0$ was searched for by measuring the related γ energy under the condition that no additional γ was detected by a hermetic detector. No evidence of such an annihilation was observed, resulting in the upper limits on the branching ratio of $4.2 \times 10^{-6}$ ( $m_{{\rm V}^0} < 200$ keV/c²) and $2.1 \times 10^{-5}$ ( $m_{{\rm V}^0} < 2m_{\rm e} = 1022$ keV/c²). These upper limits were converted to those on the branching ratio of an exotic three-body decay ( $\gamma\gamma{\rm V}^0$ ) of orthopositronium (o-Ps), i.e. $6.2 \times 10^{-6}$ ( $m_{{\rm V}^0}< 200$ keV/c²) and $1.7 \times 10^{-5}$ ( $m_{{\rm V}^0}< 2m_{\rm e}$ ). As a result, this mode was definitely excluded as the source of the reported discrepancy in the o-Ps decay rate.

PACS: 14.80.-j – Properties of specific particles: Other particles (including hypothetical) / 36.10.Dr – Positronium, muonium, muonic atoms and molecules / 12.20.Fv – Experimental tests

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