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Register a new userStatistical Significance of CP Violation in Long Baseline Neutrino Experiments
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The p-value or statistical significance of a CP conservation null hypothesis test is determined from counting electron neutrino and antineutrino appearance oscillation events. The statistical estimates include cases with background events and different data sample sizes, graphical plots to interpret results and methods to combine p-values from different experiments. These estimates are useful for optimizing the search for CP violation with different amounts of neutrino and antineutrino beam running, comparing results from different experiments and for simple cross checks of more elaborate statistical estimates that use likelihood fitting of neutrino parameters.
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The results obtained by several experiments on atmospheric neutrino oscillations are summarized and discussed. Then the results obtained by different long baseline neutrino experiments are considered. Finally conclusions and perspectives are made.
When neutrino masses arise from the exchange of neutral heavy leptons, as in most seesaw schemes, the effective lepton mixing matrix $N$ describing neutrino propagation is non-unitary, hence neutrinos are not exactly orthonormal. New CP violation phases appear in $N$ that could be confused with the standard phase $delta_{text{CP}}$ characterizing the three neutrino paradigm. We study the potential of the long-baseline neutrino experiment DUNE in probing CP violation induced by the standard CP phase in the presence of non-unitarity. In order to accomplish this we develop our previous formalism, so as to take into account the neutrino interactions with the medium, important in long baseline experiments such as DUNE. We find that the expected CP sensitivity of DUNE is somewhat degraded with respect to that characterizing the standard unitary case. However the effect is weaker than might have been expected thanks mainly to the wide neutrino beam. We also investigate the sensitivity of DUNE to the parameters characterizing non-unitarity. In this case we find that there is no improvement expected with respect to the current situation, unless the near detector setup is revamped.
We perform realistic simulations of the current and future long baseline experiments such as T2K, NO$ u$A, DUNE and T2HK in order to determine their ultimate potential in probing neutrino oscillation parameters. We quantify the potential of these experiments to underpin the octant of the atmospheric angle $theta_{23}$ as well as the value and sign of the CP phase $delta_{CP}$.
Future neutrino-oscillation experiments are expected to bring definite answers to the questions of neutrino-mass hierarchy and violation of charge-parity symmetry in the lepton sector. To realize this ambitious program it is necessary to ensure a significant reduction of uncertainties, particularly those related to neutrino-energy reconstruction. In this paper, we discuss different sources of systematic uncertainties, paying special attention to those arising from nuclear effects and detector response. By analyzing nuclear effects we show the importance of developing accurate theoretical models, capable to provide quantitative description of neutrino cross sections, together with the relevance of their implementation in Monte Carlo generators and extensive testing against lepton-scattering data. We also point out the fundamental role of efforts aiming to determine detector responses in test-beam exposures.
Environmental decoherence of oscillating neutrinos of strength $Gamma = (2.3 pm 1.1) times 10^{-23}$ GeV can explain how maximal $theta_{23}$ mixing observed at 295 km by T2K appears to be non-maximal at longer baselines. As shown recently by R. Oliveira, the MSW matter effect for neutrinos is altered by decoherence: In normal (inverted) mass hierarchy, a resonant enhancement of $ u_{mu} (bar{ u}_{mu}) rightarrow u_{e} (bar{ u}_{e})$ occurs for $6 < E_{ u} < 20$ GeV. Thus decoherence at the rated strength may be detectable as an excess of charged-current $ u_{e}$ events in the full $ u_{mu}$ exposures of MINOS+ and OPERA.
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