Probing the neutrino mass matrix in next-generation neutrino oscillation experiments
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NEUTRINO PHYSICS AND ASTROPHYSICS (Elementary Particles and Fields. Experiment)
Probing the Neutrino Mass Matrix in Next-Generation Neutrino Oscillation Experiments* S. Choubey** Rudolf Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford, OXI 3NP UK Received October 13, 2005
Abstract—We review the current status of the neutrino mass and mixing parameters needed to reconstruct the neutrino mass matrix. A comparative study of the precision in the measurement of oscillation parameters expected from the next-generation solar, atmospheric, reactor- and accelerator-based neutrino experiments is presented. We discuss the potential of 0νββ experiments in determining the neutrino mass hierarchy and the importance of a better θ12 measurement for it. PACS numbers : 14.60.Pq, 95.85.Ry DOI: 10.1134/S1063778806110184
1. INTRODUCTION The last few years have provided us with conclusive proof of the existence of oscillations and hence mass and mixing in the neutrino sector. While the atmospheric neutrino data from Super-Kamiokande (SK) and the accelerator data from the K2K have confirmed oscillations in the νμ −ντ sector with bestfit Δm231 = 2.1 × 10−3 eV2 and sin2 (2θ23 ) = 1 [1], the combined data from the solar neutrino experiments and the latest spectacular results from the KamLAND reactor experiment can be explained only νe ) with best-fit Δm221 = 8.0 × by oscillations of νe (¯ 10−5 eV2 and sin2 θ12 = 0.31 [2]. Thus, having established the existence of neutrino mass and mixing, these results have proclaimed a new era in neutrino physics, where the emphasis has shifted from unveiling the reasons for solar/atmospheric neutrino deficit to making increasingly precise measurements of neutrino oscillation parameters, a prerequisite for any progress in our understanding of the origin of the patterns of solar and atmospheric neutrino mass and mixing. In the present article, we discuss the possibilities of high-precision measurement of the solar and atmospheric neutrino oscillation parameters with future data from solar, reactor, atmospheric, and longbaseline neutrino experiments. We expound the possibility of measuring the deviation of θ23 from maximality using earth matter effects in atmospheric neutrinos. Finally, we study the feasibility of using 0νββ ∗ **
The text was submitted by the author in English. E-mail: [email protected]
experiments to determine the neutrino mass hierarchy and point out the necessity for better sin2 θ12 measurements for accomplishing it. 2. SOLAR NEUTRINO OSCILLATION PARAMETERS
2.1. Bounds from Current Solar and Reactor Experiments We present in the table from [3] the 3σ allowed range of Δm221 and sin2 θ12 that we have from the current available solar and reactor neutrino data. We also show the corresponding “spread”: prmmax − prmmin × 100. (1) spread = prmmax + prmmin Sensitivity of KamLAND to the shape and hence distortion of the reactor ν¯e induced positron spectrum gives the experiment a tremendous ability to constrain Δm221 . However, we can see from the table that
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