Poster Summary: Event Reconstruction in the KM3NeT/ORCA Detector
(by Jannik Hofestädt) KM3NeT/ORCA is a megaton-scale underwater Cherenkov detector optimised for the neutrino mass hierarchy determination by measuring the energy- and zenith-angle-dependent oscillation pattern of atmospheric few-GeV neutrinos. Event reconstruction is a key task and substantial for the mass hierarchy sensitivity.
The poster illustrates the reconstruction strategy for shower-like events (mostly nu_e CC), presents the achieved energy and direction resolutions, and compares them to intrinsic resolution limits. In addition, the separation capacity between track-like (mostly nu_mu CC) and shower-like events are briefly discussed.
The shower reconstruction is designed to find the electron direction in nu_e CC events. Figure 1 shows the expected number of detected photons as a function of the angle with respect to the outgoing electron. With higher Bjorken y (interaction inelasticity) the Cherenkov peak of the electron at 42deg becomes fainter, while the number of expected photons in the off-peak region increases. This makes an estimation of Bjorken y in shower-like events feasible.
Due to the large scattering length in deep-sea water the light emission characteristics are conserved over sufficiently large distances, so that information from a large detector volume (large lever arm) can contribute to event reconstruction, resulting in good direction and energy resolutions. The direction resolution is limited by the neutrino-electron scattering angle. Figure 2 shows the neutrino energy resolution for nu_e CC events. About 25% is achieved at 10GeV, and about 20% for a subset of fully contained events. The latter is close to the accuracy limit imposed by intrinsic fluctuations in the Cherenkov light yield.