Jessica A. Dunmore, University of Hartford / University of Washington

Title: Background Neutron Sources to the Neutral-Current Signal in SNO

Authors: J.A. Dunmore (University of Hartford); R.G.H. Robertson (University of Washington)

Abstract: The primary purpose of the Sudbury Neutrino Observatory (SNO) is to gain insight to the "Solar Neutrino Problem," which arises from the puzzling fact that previous neutrino detection experiments have detected fewer neutrinos than predicted by the Standard Solar Model (SSM).  To detect these neutrinos, which are emitted by fusion reactions in the sun, the SNO is filled with ultrapure heavy water.  Neutrinos react with  the deuterium in heavy water through two different reactions.  The charged current reaction: n_e + d  -->  p + p + e-   emits a relativistic electron which is observed through the detection of Cerenkov radiation by photomultiplier tubes.  The neutral-current reaction:  n_x + d  -->  n + p + n_x  may also be observed with the photomultiplier tubes as the free neutron emitted is captured by a deuterium nucleus, emitting a Cerenkov radiation-producing gamma ray.  The SNO detector is unique because it will be able to detect all three flavors of neutrinos through the neutral-current reaction, whereas former detectors were able to detect electron neutrinos only.   The Sudbury Neutrino Observatory will also utilize He-3 filled neutral-current detectors (NCDs) that detect these free neutrons through the reaction:  He-3 + n --> H-3 + p.  The NCDs allow distinction to be made between events caused by the charged-current and neutral-current reactions.  Both reactions produce Cerenkov light, detectable by the PMTs, but these events are not distinguishable.  The NCDs only detect neutral-current events;  and, thus, a neutral-current to charged-current ratio may be determined.  This ratio may give convincing evidence for neutrino oscillations (the MSW effect).