A measurement of coherent neutral pion production in neutrino neutral current interactions in the NOMAD experiment

We present a study of exclusive neutral pion production in neutrino-nucleus Neutral Current interactions using data from the NOMAD experiment at the CERN SPS. The data correspond to 1.44×106 muon-neutrino Charged Current interactions in the energy range 2.5⩽E⩽300 GeV. Neutrino events with only one visible π0 in the final state are expected to result from two Neutral Current processes: coherent π0 production, ν+A→ν+A+π0 and single π0 production in neutrino-nucleon scattering. The signature of coherent π0 production is an emergent π0 almost collinear with the incident neutrino while π0's produced in neutrino-nucleon deep inelastic scattering have larger transverse momenta. In this analysis all relevant backgrounds to the coherent π0 production signal are measured using data themselves. Having determined the backgrounds, and using the Rein-Sehgal model for the coherent π0 production to compute the detection efficiency, we obtain 4630±522(stat)±426(syst) corrected coherent-π0 events with E⩾0.5 GeV. We measure σ(νA→νAπ0)=[72.6±8.1(stat)±6.9(syst)]×10-40 cm2/nucleus. This is the most precise measurement of the coherent π0 production to date.