Heidelberg 2022 – scientific programme

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T: Fachverband Teilchenphysik

T 103: Neutrino Physics without Accelerators 8

T 103.1: Talk

Thursday, March 24, 2022, 16:15–16:30, T-H35

First directional detection of sub-MeV solar neutrinos in Borexino — •Johann Martyn for the Borexino collaboration — Johannes Gutenberg-Universität Mainz

Borexino is a 280 t liquid scintillator detector at the Laboratori Nazionali del Gran Sasso (LNGS), Italy. Its main goal is the precision spectroscopy of solar neutrinos down to energies of 0.19 MeV and for this task it features an unprecedented high radio-purity and a high light yield of ∼10000 scintillation photons per 1 MeV deposited energy.
In this talk we present the first measurement of sub-MeV solar neutrinos around the ⁷Be edge, using their associated Cherenkov photons in a liquid scintillation detector. In Borexino electrons with E>0.16 MeV produce Cherenkov photons but the ratio of Cherenkov photons from the neutrino scattered electrons is estimated to be <0.5% for all PMT hits, so a typical reconstruction of the event direction is not possible. Therefore we look instead at the so called "Correlated and Integrated Directionality" (CID), where the known position of the Sun is correlated with the photon hit direction, given by the reconstructed event vertex, and integrated over all selected events. In this way it is possible to measure an angular distribution that shows the statistical contribution of Cherenkov photons from the neutrino recoil electrons. The number of solar neutrinos is then inferred from the measured angle distribution with probability density functions produced by the Geant4-based Borexino Monte Carlo simulation. This work is supported by the Cluster of Excellence No. 2118 PRISMA+, funded by the German Research Foundation (DFG).