A Study of Charged Current Single Charged Pion Productions on Carbon in a Few-GeV Neutrino Beam

Abstract

Understanding single charged pion production via neutrino-nucleus charged current interaction in the neutrino energy region of a few GeV is essential for future neutrino oscillation experiments since this process is a dominant background for vμ → vx oscillation measurements. There are two contributions to this process: single pion production via baryonic resonance (vμN → μ- Nπ+) and coherent pion production interacting with the entire nucleus (vμA → μ- Aπ+), where N is nucleon in the nucleus and A is the nucleus. The purpose of the study presented in this thesis is a precise measurement of charged current single charged pion productions, resonant and coherent pion productions, with a good final state separation in the neutrino energy region of a few GeV. In this thesis, we focus on the study of charged current coherent pion production from muon neutrinos scattering on carbon, vμ 12C → μ-12Cπ+, in the SciBooNE experiment. This is motivated by the fact that without measuring this component first, the precise determination of resonant pion production cross section can not be achieved since the contribution of coherent pion production in the region of small muon scattering angle is not small. Furthermore, the coherent process is particularly interesting because it is deeply rooted in fundamental physics via Adler's partially conserved axial-vector current theorem. We took data from June 2007 until August 2008, in both the neutrino and antineutrino beam. In total, 2.52 x 1020 protons on target were collected. We have performed a search for charged current coherent pion production by using SciBooNE's full neutrino data set, corresponding to 0.99 x 1020 protons on target. No evidence for coherent pion production is observed. We set 90% confidence level upper limits on the cross section ratio of charged current coherent pion production to the total charged current cross section at 0.67 x 10-2 at mean neutrino energy 1.1 GeV and 1.36 x 10-2 at mean neutrino energy 2.2 GeV. We reveal that the Rein-Sehgal model widely used in neutrino oscillation experiments breaks down at the neutrino energy region of a few GeV. This creates active controversies on the model of coherent pion production, and the understanding of coherent pion production is being progressed. In addition, future prospects of measurements of charged current single charged pion production in SciBooNE are discussed.