Single Pi Zero Production In Neutrino Interactions PDF Download

The production of single, highly forward [pi]0 mesons by NC coherent neutrino-nucleus interactions ([nu][mu] + N → [nu][mu] + N + [pi]0) is a process which probes fundamental aspects of the weak interaction. This reaction may also pose as a limiting background for long baseline searches for [nu][mu] → [nu]e oscillations if the neutrino mixing angle [theta]13 is very small. The high-statistics sample of neutrino interactions recorded by the MINOS Near Detector provides an opportunity to measure the cross section of this coherent reaction on a relatively large-A nucleus at an average Ev = 4.9 GeV. A major challenge for this measurement is the isolation of forward-going electromagnetic (EM) showers produced by the relatively rare coherent NC([pi]0) process amidst an abundant rate of incoherently produced EM showers. The backgrounds arise from single [pi]0 dominated NC events and also from quasi-elastic-like CC scattering of electron neutrinos. In this Thesis the theory of coherent interactions is summarized, and previous measurements of the coherent NC([pi]0) cross section are reviewed. Then, methods for selecting a sample of coherent NC([pi]0) like events, extracting the coherent NC([pi]0) event rate from that sample, estimating the analysis uncertainties, and calculating a cross section, are presented. A signal for neutrino-induced NC([pi]0) production is observed in the relevant kinematic regime as an excess of events of three standard deviations above background. The reaction cross sections, averaged over an energy window of 2.5 ≤ Ev ≤ 9.0 GeV is determined to be (31.6±10.5) x 10-40 cm2/nucleus. The result is the first evidence obtained for neutrino-nucleus coherent NC([pi]0) scattering on iron, and is the first measurement on an average nuclear target above A = 30. The cross section measurement is in agreement with NEUGEN3 implementation of the model by Rein and Sehgal which is motived by the PCAC hypothesis.