Status of the SNO experiment
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NEUTRINO PHYSICS AND ASTROPHYSICS (Elementary Particles and Fields. Experiment)
Status of the SNO Experiment* C. Kraus** (for the SNO Collaboration) Departement of Physics, Queen’s University, Kingston, Canada Received November 23, 2005
Abstract—The Sudbury Neutrino Observatory (SNO) is a 1-kt heavy water Cherenkov detector sensitive to the flavor content of the 8 B neutrinos originating in the Sun. The analysis of the second phase, in which salt (NaCl) was added to the heavy water in order to increase the cross section for neutrons and therefore enhance the sensitivity to solar neutrinos, is completed. Results from 391 d of data (June 2001 until September 2003) are summarized and constraints on the neutrino mixing parameters are given. The third phase of operation has started in which 3 He proportional counters have been deployed inside the D2 O. These neutral-current detectors will perform a systematically independent measurement of the Solar-neutrino flux on a event-by-event basis. SNO finishes data taking at the end of 2006 and the heavy water will be removed. A new experiment using liquid scintillator to measure the pep solar neutrinos and geoneutrinos is proposed and will be described briefly. PACS numbers : 95.55.Vj, 96.40.Tv DOI: 10.1134/S1063778806110020
1. INTRODUCTION
(CC), neutral-current (NC), and elastic-scattering (ES) reactions, which are written as follows:
Solar neutrino experiments over the past 30 years [1–6] have observed fewer neutrinos than predicted by solar models [7]. This was known as the solar neutrino problem. One possible explanation for the occurring effect is that neutrinos are able to transform from one flavor to another while they are traveling from their origin (the Sun) to the detector (on Earth). The Sudbury Neutrino Observatory (SNO) [8] was designed to measure the flavor content of the 8 B solar neutrino flux in order to test the model of neutrino flavor change. SNO is located in the Inco Ltd. Creighton mine near Sudbury (Ontario, Canada) 2 km underground, which corresponds to 6010 m w.e. The detector consists of a 12-m-diameter clear acrylic vessel (AV) filled with 1 kt of ultrapure heavy water (D2 O). The AV is surrounded by 9456 photomultiplier tubes (PMTs) mounted on a 17.8m-diameter stainless steel geodesic sphere (PSUP). The detector is immersed in ultrapure light water to provide shielding from radioactivity in both the rock wall of the cavity and the PMTs with their support structure. SNO detects neutrinos from 8 B decays in the Sun through three reactions which have different sensitivity to the flavor content: charged-current ∗ **
The text was submitted by the author in English. E-mail: [email protected]
CC : NC : ES :
νe + d → p + p + e− , νx + d → νx + p + n, νx + e− → νx + e− .
The CC reaction is sensitive only to electron neutrinos, while the NC reaction has sensitivity to any active flavor (νx , x = e, μ, τ ). The ES reaction is mainly sensitive to νe and by roughly a factor of 6 less; it also has some sensitivity to nonelectron flavors. The NC reaction in SNO all
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