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A Search for Single Photon Events in Neutrino Interactions

Abstract : We present a search for neutrino-induced events containing a single, exclusive photon using data from the NOMAD experiment at the CERN SPS where the average energy of the neutrino flux is $\simeq 25$ GeV. The search is motivated by an excess of electron-like events in the 200--475 MeV energy region as reported by the MiniBOONE experiment. In NOMAD, photons are identified via their conversion to $e^+e^-$ in an active target embedded in a magnetic field. The background to the single photon signal is dominated by the asymmetric decay of neutral pions produced either in a coherent neutrino-nucleus interaction, or in a neutrino-nucleon neutral current deep inelastic scattering, or in an interaction occurring outside the fiducial volume. All three backgrounds are determined {\it in situ} using control data samples prior to opening the 'signal-box'. In the signal region, we observe {\bf 155} events with a predicted background of {\bf 129.2 $\pm$ 8.5 $\pm$ 3.3}. We interpret this as null evidence for excess of single photon events, and set a limit. Assuming that the hypothetical single photon has a momentum distribution similar to that of a photon from the coherent $\pi^0$ decay, the measurement yields an upper limit on single photon events, {\boldmath $< 4.0 \times 10^{-4}$} per \nm\ charged current event. Narrowing the search to events where the photon is approximately collinear with the incident neutrino, we observe {\bf 78} events with a predicted background of {\bf 76.6 $\pm$ 4.9 $\pm$ 1.9} yielding a more stringent upper limit, {\boldmath $< 1.6 \times 10^{-4}$} per \nm\ charged current event.
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Contributor : Claudine Bombar <>
Submitted on : Tuesday, March 6, 2012 - 5:36:43 PM
Last modification on : Thursday, September 17, 2020 - 12:30:09 PM

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C. T. Kullenberg, G. Bassompierre, J.M. Gaillard, M. Gouanère, J.P. Mendiburu, et al.. A Search for Single Photon Events in Neutrino Interactions. Physics Letters B, Elsevier, 2012, 706, pp.268-275. ⟨10.1016/j.physletb.2011.11.049⟩. ⟨in2p3-00676950⟩



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