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Search for the Hypothetical pi -> mu x Decay

R. Bilger·H. Clement·A. Denig·K. Fohl·P. Hautle·W. Kluge·J. A. Konter·G. Kurz·S. Mango·D. Schapler·F. Schonleber·U. Siodlaczek·B. van den Brandt·G. J. Wagner·R. Wieser
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Abstract

The KARMEN collaboration has reported the possible observation of a hitherto unknown neutral and weakly interacting particle x, which is produced in the decay pi -> mu + x with a mass m(x) = 33.9 MeV. We have searched for this hypothetical decay branch by studying muons from pion decay in flight with the LEPS spectrometer at the piE3 channel at PSI and find branching ratios BR(pi- to mu- anti-x) < 4e-7 and BR(pi+ to mu+ x) < 7e-8 (95\% C.L.). Together with the limit BR > 2e-8 derived in a recent theoretical paper our result would leave only a narrow region for the existence of x if it is a heavy neutrino.

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R. Bilger, H. Clement, A. Denig, K. Fohl, P. Hautle, W. Kluge, J. A. Konter, G. Kurz, S. Mango, D. Schapler, F. Schonleber, U. Siodlaczek, B. van den Brandt, G. J. Wagner, R. Wieser. 1995-08-18. Search for the Hypothetical pi -> mu x Decay. https://doi.org/10.1016/0370-2693(95)01232-f

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