1/10/2024 0 Comments Sudbury neutrino observatory![]() ![]() This was determined using two methods: with a neutron calibration source mixed into the heavy water and with a calibrated Monte Carlo simulation. Converting the number of neutrons detected by the NCDs into a number of NC interactions required a knowledge of the neutron detection efficiency. This thesis presents results from the third phase of the experiment in which an array of 3He proportional counters, called Neutral Current Detectors (NCDs), were deployed in the heavy water to detect neutrons produced in NC interactions of neutrinos with deuterium. ![]() The experiment has demonstrated that neutrinos change flavour and that the total neutrino flux is consistent with the prediction of solar models. New experiments that will start in 1996 will test–independent of solar models–the inference that physics beyond the standard electroweak model is required to resolve the solar neutrino problem.The Sudbury Neutrino Observatory (SNO) was a heavy water ˘ Cerenkov detector that had the unique ability to measure both the total active flux of solar neutrino, using a neutral current (NC) interaction, and the flux of electron neutrinos, using a charged current (CC) interaction. The results of the two gallium solar neutrino experiments strengthen the conclusion that new physics is required and help determine a relatively small allowed region for the MSW neutrino parameters. The boundary conditions that the solar model luminosity equals the current observed photon luminosity and that the solar model must be consistent with helioseismological measurements are two of the strongest reasons that the predictions of the standard solar model are robust. Monte Carlo studies with 1000 implementations of the standard solar model indicate that the chlorine and the Kamiokande experiments cannot be reconciled unless new weak interaction physics changes the shape of the 8 neutrino energy spectrum. A direct comparison of the chlorine and the Kamiokande experiments, both of which are sensitive to 8 neutrinos, suggests that the discrepancy between theory and observations depends upon neutrino energy, in conflict with standard expectations. If standard electroweak theory is correct, the energy spectrum for 8 neutrinos created in the solar interior must be the same (to one part in 10 5) as the known laboratory 8 neutrino energy spectrum. However, the measured rate for each of the four solar neutrino experiments differs significantly (by factors of 2.0 to 3.5) from the corresponding theoretical prediction that is based upon the standard solar model and the simplest version of the standard electroweak theory (zero-neutrino masses, no flavor mixing). The results of these experiments confirm the hypothesis that the energy source for solar luminosity is hydrogen fusion. Four solar neutrino experiments are currently taking data. Other frequently-discussed weak interaction solutions to the solar neutrino problem are also not expected to change significantly the line profile. 1 The characteristic modulation of the 7Be line shape that would be caused by either vacuum neutrino oscillations or by matter-enhanced (MSW) neutrino oscillations is shown to be small. The energy profile of the 7Be neutrino line should be taken into account in calculations of vacuum neutrino oscillations and of the absorption cross section for 7 Be solar neutrinos incident on 7 Li nuclei. The effective temperature of the high-energy exponential tail is 15 × 106 K. The line shape is asymmetric: on the low-energy side, the line shape is Gaussian with a half-width at half-maximum of 0.6 keV and on the high-energy side, the line shape is exponential with a half-width at halfmaximum of 1.1 keV. The energy profile of the 7Be line is derived analytically and is evaluated numerically. Therefore, a measurement of the energy shift is a measurement of the central temperature distribution of the sun. The energy shift is approximately equal to the average temperature of the solar core, computed by integrating the temperature over the solar interior with a weighting factor equal to the locally-produced 7Be neutrino emission. This energy shift is calculated to be 1.29 keV (to an accuracy of a few percent) for the dominant ground-state to ground-state transition. A precise test of the theory of stellar evolution can be performed by measuring the average difference in energy between the neutrino line produced by 7Be electron capture in the solar interior and the corresponding neutrino line produced in a terrestrial laboratory.
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