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arXiv · hep-ex/9804003

Search for a new gauge boson in $π^{0}$ decays

The NOMAD Collaboration·J. Altegoer et al
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Abstract

A search was made for a new light gauge boson $X$ which might be produced in $π^{0}\toγ+ X$ decay from neutral pions generated by 450-GeV protons in the CERN SPS neutrino target. The X's would penetrate the downstream shielding and be observed in the NOMAD detector via the Primakoff effect, in the process of $X \toπ^{0}$ conversion in the external Coulomb field of a nucleus. With $1.45\times10^{18}$ protons on target, 20 candidate events with energy between 8 and 140 GeV were found from the analysis of neutrino data. This number is in agreement with the expectation of 18.1$\pm$2.8 background events from standard neutrino processes. A new 90% C.L. upper limit on the branching ratio $Br(π^{0}\toγ+ X)< (3.3 to 1.9) \times10^{-5}$ for $X$ masses ranging from 0 to 120 MeV/c^2 is obtained.

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The NOMAD Collaboration, J. Altegoer et al. 1998-04-05. Search for a new gauge boson in $π^{0}$ decays. https://doi.org/10.1016/s0370-2693(98)00402-x

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