T.D. Steiger

New limit on the D coefficient in polarized neutron decay

We describe an experiment that has set new limits on the time reversal invariance violating D coefficient in neutron beta-decay. The emiT experiment measured the angular correlation J . p_e x p_p using an octagonal symmetry that optimizes electron-proton coincidence rates. The result is D=[-0.6+/-1.2(stat)+/-0.5(syst)]x10^(-3). This improves constraints on the phase of g_A/g_V and limits contributions to T violation due to leptoquarks. This paper presents details of the experiment, data analysis, and the investigation of systematic effects.

An array of low-background 3He proportional counters for the Sudbury Neutrino Observatory

An array of Neutral-Current Detectors (NCDs) has been built in order to make a unique measurement of the total active ux of solar neutrinos in the Sudbury Neutrino Observatory (SNO). Data in the third phase of the SNO experiment were collected between November 2004 and November 2006, after the NCD array was added to improve the neutral-current sensitivity of the SNO detector. This array consisted of 36 strings of proportional counters lled with a mixture of 3He and CF4 gas capable of detecting the neutrons liberated by the neutrino-deuteron neutral current reaction in the D2O, and four strings lled with a mixture of 4He and CF4 gas for background measurements. The proportional counter diameter is 5 cm. The total deployed array length was 398 m. The SNO NCD array is the lowest-radioactivity large array of proportional counters ever produced. This article describes the design, construction, deployment, and characterization of the NCD array, discusses the electronics and data acquisition system, and considers event signatures and backgrounds.

High-voltage microdischarge in ultra-low background /sup 3/He proportional counters

This paper discusses the phenomenon of surface microdischarge induced by high voltage, and techniques for the reduction and discrimination of such breakdowns in ultralow background proportional counters. An array of ultra-low background /sup 3/He-filled proportional counters will measure the neutral-current interaction rate of all active neutrino species in the Sudbury Neutrino Observatory. The sensitivity of these neutral current detectors and their stringent background criteria make it essential to minimize all spurious pulses including signals induced by high voltage. Such pulses can originate from microscopic surface discharges in the various proportional counter components. Studies have shown that this discharge effect occurs mainly at interfaces and in microscopic voids between dielectric surfaces, on contaminated surfaces, and on surfaces with imperfections. Because of its occurrence in various materials and environments, microdischarge is a concern for all low-background detectors that operate under high voltage.

Background studies for the neutral current detector array in the Sudbury Neutrino Observatory

Abstract An array of 3 He-filled proportional counters will be used in the Sudbury Neutrino Observatory to measure the neutral-current interaction of neutrinos and deuterium. We describe the backgrounds to this detection method.