Measurement of the Cross Section for Elastic Scattering of Electron Neutrinos on Electrons.

Abstract

In this dissertation, we measure the cross section for the elastic scattering of electron neutrinos on electrons. We use data from the LSND experiment which is located at the Los Alamos Neutron Scattering Center at Los Alamos National Laboratory, New Mexico. The neutrino beam is produced when an 800 MeV proton beam from a linear accelerator is incident on a target located 29.8 m from the detector. The LSND veto system allows us to reject charged cosmic-ray particles entering the detector with high efficiency. The detector consists of 180 tons of mineral oil, to which a small quantity of scintillator is added. This combination enables us to detect both Cerenkov and scintillation light produced by highly relativistic charged particles. For the neutrino-electron elastic scattering process, we detect the recoil electron and require it to be scattered along the direction of the incident neutrino. This requirement has a large acceptance for the elastic scattering events while at the same time it reduces the background due to other processes. We obtain 133 +/- 22 events for the nee-→nee - process and measure a cross section, sigma = [11.6 +/- 1.9( stat.) +/- 1.4(syst.)] x Ene (MeV) x 10-45cm2, for this reaction. The average energy of the nue beam at LSND is 31.7 MeV. A feature of this reaction is that it can proceed through either charged current or neutral current interactions. The standard model of electroweak interactions predicts a destructive interference between these two channels which leads to a reduction in the cross section from its value had there been no interference. We measure the strength of this destructive interference, I = -0.88 +/- 0.22(stat .) +/- 0.11(syst.), and compare it to a value of I = -1.08 predicted by the standard model of electroweak interactions.