/ Experiment-HEP hep-ex/9804003

Search for a new gauge boson in pi0 decays

Altegoer, J. ; Astier, P. ; Autiero, D. ; Baldisseri, A. ; Baldo-Ceolin, M. ; Ballocchi, G. ; Banner, M. ; Basa, S. ; Bassompierre, G. ; Benslama, K. ; Besson, N. ; Bird, I. ; Blumenfeld, Barry J. ; Bobisut, F. ; Bouchez, J. ; Boyd, S. ; Bueno, A. ; Bunyatov, S. ; Camilleri, L. ; Cardini, A. ; Castera, A. ; Cattaneo, P.W. ; Cavasinni, V. ; Cervera-Villanueva, A. ; Collazuol, G.M.

Published in: Phys.Lett.
Year: 1998
Vol.: B428
Page No: 197-205
Pages: 15

Abstract: A search was made for a new light gauge boson $X$ which might be produced in $\pi^{0}\to\gamma + X$ 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 $X \to\pi^{0}$ 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 $Br(\pi^{0}\to\gamma + X)< (3.3 to 1.9) \times10^{-5}$ for $X$ masses ranging from 0 to 120 MeV/c^2 is obtained.

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