# 17th International Conference on Topics in Astroparticle and Underground Physics (TAUP 2021)

26 August 2021 to 3 September 2021

## Directional measurement in Borexino: Calibration of Cherenkov photons in a liquid scintillator detector using gamma sources

30 Aug 2021, 18:00
1h 30m
Poster Neutrino physics and astrophysics

### Speaker

Sindhujha Kumaran (IKP-2 Forschungszentrum Jülich and RWTH Aachen University)

### Description

Borexino is a 280-ton liquid scintillator detector located at the Laboratori Nazionali del Gran Sasso (LNGS), Italy. The main goal of Borexino is to measure solar neutrinos via elastic scattering off electrons in the liquid scintillator. The electrons are then detected by the photo-multiplier tubes via isotropically emitted scintillation photons. However, in the first few nanoseconds after a neutrino interaction, Cherenkov photons (< 1% of all detected photons) are also produced in the scintillator for electrons with kinetic energy ≥ 0.16 MeV. It is possible to obtain the $^{7}$Be solar neutrino rate in Borexino, purely based on the direction of the detected Cherenkov photons with respect to the Sun’s position. The major systematic effect for this analysis arises from the lack of a dedicated calibration for the effective refractive index of Cherenkov photons in the liquid scintillator. Therefore, in Borexino, we obtain this through gamma calibration sources namely, $^{40}$K and $^{54}$Mn. A group velocity correction estimated through the gamma sources is then used for the solar neutrino analysis. This poster will discuss the analysis strategy and methods used for this calibration, and provide motivation for a dedicated Cherenkov calibration in next-generation liquid scintillator detectors.

### Primary authors

Sindhujha Kumaran (IKP-2 Forschungszentrum Jülich and RWTH Aachen University) Mr. Johann Martyn (Johannes Gutenberg-Universität Mainz)

### Presentation Materials

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