Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Richard L. Imlay

Abstract

This document describes the results of a neutrino oscillation experiment in the channel $\bar\nu\sb{\mu} \to \ \bar\nu\sb{\rm e}$ and measurements of neutrino-carbon cross sections. This is an accelerator based experiment performed using $\nu\sb{\rm e}, \ \bar\nu\sb{\mu}$ and $\nu\sb{\mu}$ neutrinos from the LAMPF A-6 beam stop. The $\bar\nu\sb{\mu}$ were used to look for neutrino oscillations and the $\mu\sb{\rm e}$ were used to measure the neutrino-carbon cross sections. The main features of the detector are its large mass of liquid scintillator (180 tons of mineral oil with 0.03 g/l b-PBD added), recording of history before and after a prompt event, good particle identification and an active cosmic-ray anticoincidence shield. The detector is located 29.8 m from the neutrino source. The 1220 photomultiplier tubes on the inside of the tank provide 25% photocathode coverage with uniform spacing. If $\bar\nu\sb{\mu}$ oscillates into $\bar\nu\sb{\rm e}$, the positron from the reaction $\bar\nu\sb{\rm e}$p $\to$ e$\sp+$n followed by a 2.2 MeV gamma ray is the event signature for oscillations. There is no significant $\bar\nu\sb{\rm e}$ production at the beam stop. An analysis of data taken in 1994 yields 7 events consistent with neutrino oscillations with an estimated background of 1.1 events. If we interpret these events as arising from neutrino oscillations the 90% confidence level upper limit of the oscillation probability is 10.3 $\times$ 10$\sp{-3}$ and the 90% confidence level lower limit is 3.4 $\times$ 10$\sp{-3}$. In a separate analysis, 283 $\pm$ 27 $\sp{12}$C($\nu\sb{\rm e},$e$\sp-)\sp{12}$N$\sb{\rm g.s.}$ events with subsequent $\sp{12}$N($\beta\sp+)\sp{12}$C were observed. The measured total cross section is (9.0 $\pm$ 0.8(stat.) $\pm$ 0.8(syst.)) $\times$ 10$\sp{-42}$ cm$\sp2$. Also 138 $\pm$ 43 events were observed for the reaction $\nu\sbsp{\rm e}{12}$C $\to \ \sp{12}$ N*e$\sp-$ and the resulting cross section is (5.0 $\pm$ 1.6(stat.) $\pm$ 0.5(syst.)) $\times$ 10$\sp{-42}$ cm$\sp2$. The ratio of the exclusive events to inclusive events is 0.67 $\pm$ 0.08(stat.) $\pm$ 0.06(syst.). These cross sections are in good agreement with theoretical calculations and other experimental measurements.

Pages

262

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