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The KARMEN Time Anomaly, Search for a Neutral Particle of Mass 33.9 MeV in Pion Decay

M. Daum¹, M. Janousch², P.-R. Kettle¹,
J. Koglin^1,3, D. Pocanic³, J. Schottmüller¹,
C. Wigger¹, D. Wyler⁴, Z. G. Zhao⁵

¹PSI, Paul-Scherrer-Institut, CH-5232 Villigen-PSI, Switzerland
²IPP, Institut für Teilchenphysik der ETHZ, CH-5232 Villigen-PSI, Switzerland
³Physics Department, University of Virginia, Charlottesville, Virginia 22901,USA.
⁴Physik-Institut der Universität Zürich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
⁵Institute of High Energy Physics, Chinese Academy of Science, Beijing 100039, The People's Republic of China

Abstract:

We have searched for the rare pion-decay p⁺ ® m⁺ X where X is a neutral particle of mass 33.9 MeV, a process suggested by the KARMEN Collaboration to explain an anomaly seen in their time spectrum of neutrino induced reactions. By measuring the muon momentum spectrum of charged pions decaying in flight, we were able to place an upper limit on the branching fraction h of such decays, at the level of h < 2.7 · 10^-8 with a 95% confidence level.

Created by J. Koglin on October-15-1999.