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Bayesian evidence for non-zero θ 13 and CP-violation in neutrino oscillations

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Abstract

We present the Bayesian method for evaluating the evidence for a non-zero value of the leptonic mixing angle θ 13 and CP-violation in neutrino oscillation experiments. This is an application of the well-established method of Bayesian model selection, of which we give a concise and pedagogical overview. When comparing the hypothesis θ 13 = 0 with hypotheses where θ 13 > 0 using global data but excluding the recent reactor measurements, we obtain only a weak preference for a non-zero θ 13, even though the significance is over 3σ. We then add the reactor measurements one by one and show how the evidence for θ 13 > 0 quickly increases. When including the Double Chooz, Daya Bay, and RENO data, the evidence becomes overwhelming with a posterior probability of the hypothesis θ 13 = 0 below 10−11. Owing to the small amount of information on the CP-phase δ, very similar evidences are obtained for the CP-conserving and CP-violating hypotheses. Hence, there is, not unexpectedly, neither evidence for nor against leptonic CP-violation. However, when future experiments aiming to search for CP-violation have started taking data, this question will be of great importance and the method described here can be used as an important complement to standard analyses.

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  1. Department of Theoretical Physics, School of Engineering Sciences, KTH Royal Institute of Technology - AlbaNova University Center, Roslagstullsbacken 21, 106 91, Stockholm, Sweden

    Johannes Bergström

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Bergström, J. Bayesian evidence for non-zero θ 13 and CP-violation in neutrino oscillations. J. High Energ. Phys. 2012, 163 (2012). https://doi.org/10.1007/JHEP08(2012)163

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