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Matter Effects in Atmospheric Neutrino Oscillations

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 Added by ul
 Publication date 1992
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and research's language is English




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The Kamiokande II and IMB data on contained events induced by atmospheric neutrinos exhibit too low a ratio of muons to electrons, which has been interpreted as a possible indication of neutrino oscillations. At the same time, the recent data on upward--going muons in underground detectors have shown no evidence for neutrino oscillations, strongly limiting the allowed region of oscillation parameter space. In this paper we confront different types of neutrino oscillation hypotheses with the experimental results. The matter effects in $ u_mu leftrightarrow u_e$ and in $ u_mu leftrightarrow u_{sterile}$ oscillations are discussed and shown to affect significantly the upward--going muons.



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We study neutrino oscillations in a medium of dark matter which generalizes the standard matter effect. A general formula is derived to describe the effect of various mediums and their mediators to neutrinos. Neutrinos and anti-neutrinos receive opposite contributions from asymmetric distribution of (dark) matter and anti-matter, and thus it could appear in precision measurement of neutrino or anti-neutrino oscillations. Furthermore, the standard neutrino oscillation can occur from the symmetric dark matter effect even for massless neutrinos.
Following similar approaches in the past, the Schrodinger equation for three neutrino propagation in matter of constant density is solved analytically by two successive diagonalizations of 2x2 matrices. The final result for the oscillation probabilities is obtained directly in the conventional parametric form as in the vacuum but with explicit simple modification of two mixing angles ($theta_{12}$ and $theta_{13}$) and mass eigenvalues.
Atmospheric neutrinos travel very long distances through earth matter. It is expected that the matter effects lead to significant changes in the neutrino survival and oscillation probabilities. Initial analysis of atmospheric neutrino data by the Super- Kamiokande collaboration is done using the vacuum oscillation hypothesis, which provided a good fit to the data. In this work, we did a study to differentiate the effects of vacuum oscillations and matter modified oscillations in the atmospheric neutrino data. We find that magnetized iron detector, ICAL at INO, can make a 3 sigma discrimination between vacuum oscillations and matter oscillations, for both normal and inverted hierarchies, in ten years.
The main goal of the IceCube Deep Core Array is to search for neutrinos of astrophysical origins. Atmospheric neutrinos are commonly considered as a background for these searches. We show here that cascade measurements in the Ice Cube Deep Core Array can provide strong evidence for tau neutrino appearance in atmospheric neutrino oscillations. A careful study of these tau neutrinos is crucial, since they constitute an irreducible background for astrophysical neutrino detection.
Following similar approaches in the past, the Schrodinger equation for three neutrino propagation in matter of constant density is solved analytically by two successive diagonalizations of 2x2 matrices. The final result for the oscillation probabilities is obtained directly in the conventional parametric form as in the vacuum but with explicit simple modification of two mixing angles ($theta_{12}$ and $theta_{13}$) and mass eigenvalues.
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