Update on atmospheric neutrinos

Abstract

We discuss the impact of recent experimental results on the determination of atmospheric neutrino oscillation parameters. We use all published results on atmospheric neutrinos, including the preliminary large statistics data of Super-Kamiokande. We reanalyze the data in terms of both vμ → vτ and vμ → ve channels using new improved calculations of the atmospheric neutrino flux. We compare the sensitivity attained in atmospheric neutrino experiments with those of accelerator and reactor neutrino oscillation searches, including the recent CHOOZ experiment. We briefly comment on the implications of atmospheric neutrino data in relation to future searches for neutrino oscillations with long baselines, such as the K2K, MINOS, ICARUS, and NOE experiments.

MC is obtained by folding a prediction for the atmospheric neutrino flux with the properties of every individual detector through a Monte Carlo ~MC! procedure. Apart from studying the impact of the new data, our motivation for the present reanalysis of atmospheric neutrino data is theoretical. In this regard, we first of all include the results of a recent calculation of the atmospheric neutrino fluxes as a function of zenith angles @11#, including the muon polarization effect @12#. Moreover, we develop an independent procedure for the comparison of results from different experiments. We demonstrate that our theoretical calculation of the energy distribution of the event rates is in good agreement with the MC expectations. The comparison of the experimental results presented below thus reflects the significance of the atmospheric neutrino anomaly and provides evidence for neutrino oscillations. In this paper we analyze the impact of recent experimental results on atmospheric neutrinos from Super-Kamiokande and Soudan2 on the determinations of atmospheric neutrino