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  • Search for the Hypothetical pi -> mu x Decay
    Bilger, R; Clement, H; Denig, A; Fohl, K; Hautle, P; Kluge, W; Konter, J A; Kurz, G; Mango, S; Schapler, D; Schonleber, F; Siodlaczek, U; van den Brandt, B; Wagner, G J; Wieser, R

    arXiv.org, 08/1995
    Paper

    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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