Probing tau neutrino appearance with ORCA and determination of the leptonic CP-phase with Super-ORCA

点击翻译按钮获取中文摘要

Neutrino physics is entering an era of precision measurements. Some of the most important questions of neutrino physics are the ordering of neutrino mass eigenstates, tests of the unitarity of the mixing matrix of the well established 3-flavour model and the determination of the CP-violating leptonic Dirac phase.ORCA (Oscillation Research with Cosmics in the Abyss) is a megaton-sized water-Cherenkov detector currently under construction in the Mediterranean Sea that will precisely measure the energy and zenith angle dependent oscillation probabilities of atmospheric neutrinos in the energy range from 3 to 50 GeV. This experiment will allow to determine the neutrino mass ordering within a few years of data taking and provide a high statistics measurement of the rate of tau neutrino appearance in the detector.This grant application pursues 2 main goals.Firstly, we will participate in the data taking and analysis of the first construction phase of the ORCA detector with 7 detection units (phase-1). Based on our earlier developments of event reconstruction algorithms for ORCA, we will develop the necessary tools to detect tau neutrinos as an excess of cascade-like events in ORCA phase-1 and with the full phase-2 detector with 115 detection units. This will allow us to measure with high significance and precision possible deviations from the flux normalization given by the 3-flavour model and thus provide an important test of the unitarity assumption for the mixing matrix.The second goal is to investigate the feasibility of determining the leptonic CP-phase using atmospheric neutrinos and a megaton-sized water-Cherenkov detector in the Mediterranean Sea. We want to investigate if a more densly instrumented detector - called Super-ORCA - will allow to measure the rapid oscillations of muon and electron neutrinos and the size of a possible CP-phase induced phase shift below 2 GeV. To this end, we will optimize the detector geometry together with newly developed reconstruction algorithms. The optimization will focus on the sensitivity to detect a deviation of the CP-phase from zero.Furthermore, we will determine the event and detector intrinsic limitations on the attainable resolutions of reconstruction algorithms which will provide an important guideline for the event reconstruction development and detector optimization. Finally, we will study how the systematic uncertainties in our knowledge of the atmospheric neutrino flux and of the cross sections of neutrino interactions with the nucleon and the nucleus limit the attainable sensitivity.