Measurement of the νe and total 8B solar neutrino fluxes with the Sudbury Neutrino Observatory phase-III data set

This paper details the solar neutrino analysis of the 385.17-day phase-III data set acquired by the Sudbury Neutrino Observatory (SNO). An array of 3He proportional counters was installed in the heavy-water target to measure precisely the rate of neutrino-deuteron neutral-current interactions. This technique to determine the total active 8B solar neutrino flux was largely independent of the methods employed in previous phases. The total flux of active neutrinos was measured to be 5.54-0.31+0.33(stat.)-0.34+0.36(syst.)×106 cm-2 s-1, consistent with previous measurements and standard solar models. A global analysis of solar and reactor neutrino mixing parameters yielded the best-fit values of Δm2=7.59-0.21+0.19×10 -5eV2 and θ=34.4-1.2+1.3degrees

"3He neutral current detectors for the Sudbury Neutrino Observatory

Current solar neutrino experiments indicate the possibility of neutrino oscillations. These flavour oscillations can be confirmed or refuted by the Sudbury Neutrino Observatory (SNO), a 1,000 tonne heavy water Cerenkov detector presently under construction. This detector will measure the "8B #nu#_e flux and energy spectrum via a pure charge current reaction, and independently the "8B total #nu# flux via a pure neutral current reaction. The experiment is thus self-normalizing and does not rely on the predictions of solar models to search for neutrino oscillations. The default method suggested for observing the neutron produced in the neutral current reaction proposed by the SNO collaboration is to dope the heavy water with "3"5Cl in the form of dissolved salt and observe the #gamma# shower produced by neutron capture. Presented here is an alternative method for observing the neutral current neutron by using "3He proportional counters, distributed throughout the detector. The total length of detectors will approach half a mile. The pulse shape analysis techniques developed through the course of this thesis are used to differentiate the neutron signal from the inherent #alpha# backgrounds present in the walls of the detector and also as a method of assaying the radiopurity of the counters. As proof of principle, experiments have been running at the Waste Isolation Pilot Plant in Carlsbad, New Mexico, using prototype detectors. The results of these experiments show that the use of "3He proportional counters inside the SNO detector is feasible and will not cause an appreciable increase in backgrounds. In addition, discrete neutral current detectors have the particular advantage over the default method of being able to identify neutral current events on an event by event basis. (author)Available from British Library Document Supply Centre-DSC:D211131 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Low-background 3He Proportional Counters for Use in the Sudbury Neutrino Observatory

Current solar neutrino detectors measure a considerably lower flux of electron-flavor neutrinos than predicted by solar models. This could be an indication of neutrino oscillations, which would provide direct evidence that neutrinos have mass. The Sudbury Neutrino Observatory (SNO) was designed to detect all flavors of neutrinos, and will provide a rigorous test of this theory. The SNO detector's heavy water target gives it the unique ability to detect all non-sterile neutrino flavors via the neutral-current (NC) break-up of the deuteron. This NC interaction liberates a neutron which may be detected with an array of discrete 3He proportional counters. The strict radioactivity requirements imposed by the need for low backgrounds dictate the use of ultra-pure materials and processes in building these counters. Additionally, they must survive in the heavy water environment for several years. The design, construction, and testing of these unique counters are described. © 1999 IEEE

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 flux of solar neutrinos in the Sudbury Neutrino Observatory (SNO). Data in the third phase of the SNO experiment were collected between November 2004 and 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 filled 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 filled 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