Calibration campaign of the Borexino detector for the search of sterile neutrinos with SOX

Abstract

The SOX (Short distance Oscillations with boreXino) experiment aims to investigate possible anomalous oscillatory behaviours in neutrinos, including the existence of sterile neutrinos, by exploiting the very low radioactive background of the Borexino detector. A calibration campaign is crucial to achieve a deeper understanding of the energy response and the spatial reconstruction accuracies of the detector. It will be performed with a suite of low-activity radioactive sources which will map the whole active volume, especially nearby the inner vessel. The calibration points at the border of the active zones will be extremely important to study the neutron detection efficiency. The calibration system, already used in Borexino Phase-I, allows the insertion of the sources without perturbing the radio-purity of the detector. The calibration campaign will take place a few months before the beginning of the SOX experiment. In this work, we describe in detail both the calibration hardware and the calibration strategy.