1998/04/05 by The NOMAD Collaboration, J. Altegoer, P. Astier +99 · 1 citation
Physics and Astronomy · #Dark Matter and Cosmic Phenomena #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #hep-ex
paper · pdf · doi:10.1016/s0370-2693(98)00402-x
published as Phys.Lett.B428:197-205,1998 · 15 pages, LaTex, 6 eps figures included, submitted to Physics Letters B
arxiv created 1998/04/05 · openalex publication_date 1998/05/01 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
A search was made for a new light gauge boson X which might be produced in π0→γ+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→π0 conversion in the external Coulomb field of a nucleus. With 1.45×1018 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±2.8 background events from standard neutrino processes. A new 90 %C.L. upper limit on the branching ratio Br(π0→γ+X)< (3.3 to 1.9)×10−5 for X masses ranging from 0 to 120 MeV/c2 is obtained.