A Measurement of Coherent Neutral Pion Production in Neutrino Neutral Current Interactions in NOMAD

TL;DR

This paper reports the most precise measurement to date of coherent neutral pion production in neutrino neutral current interactions, using NOMAD data to analyze event signatures and backgrounds, and comparing results with theoretical models.

Contribution

First precise measurement of coherent neutral pion production in neutrino interactions using NOMAD data, with detailed background analysis and model comparison.

Findings

Measured cross section: (72.6 ± 8.1(stat) ± 6.9(syst)) × 10^{-40} cm^2/nucleus

Identified 4630 ± 522 coherent π^0 events after background subtraction

Validated the Rein-Sehgal model against experimental data

Abstract

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 $1.44 \times 10^6$ muon-neutrino Charged Current interactions in the energy range $2.5 \leq E_{\nu} \leq 300$ GeV. Neutrino events with only one visible $\pi^0$ in the final state are expected to result from two Neutral Current processes: coherent $\pi^0$ production, {\boldmath $\nu + {\cal A} \to \nu + {\cal A} + \pi^0$} and single $\pi^0$ production in neutrino-nucleon scattering. The signature of coherent $\pi^0$ production is an emergent $\pi^0$ almost collinear with the incident neutrino while $\pi^0$'s produced in neutrino-nucleon deep inelastic scattering have larger transverse momenta. In this analysis all relevant backgrounds to the coherent $\pi^0$ production signal are measured using data themselves. Having determined the backgrounds, and using the Rein-Sehgal model for the coherent $\pi^0$ production to compute the detection efficiency, we obtain {\boldmath $4630 \pm 522 (stat) \pm 426 (syst)$} corrected coherent-$\pi^0$ events with $E_{\pi^0} \geq 0.5$ GeV. We measure {\boldmath $\sigma (\nu {\cal A} \to \nu {\cal A} \pi^0) = [ 72.6 \pm 8.1(stat) \pm 6.9(syst) ] \times 10^{-40} cm^2/nucleus$}. This is the most precise measurement of the coherent $\pi^0$ production to date.