Definizione del protocollo di calibrazione per il calorimetro dell'esperimento FOOT

The goal of the FOOT experiment is the measurement of differential cross sections for the production of nuclear fragments in beam-target interactions using protons or Carbon ions impinging on 12C or C4H2 targets. FOOT relies on several detectors providing measurements of the main physical quantities of the fragments in order to perform their isotopic identification. The present work focuses on the commissioning of the FOOT calorimeter, made of 320 BGO crystals that provide the measurements of the kinetic energy of the fragments. The light produced in the crystal by ionization processes conveys to a Silicon Photo-Multiplier (SiPM) tile that converts the optical signal in an electronic signal, then processed by a readout board and sampled by a digitizer module. This work aims at calibrating the response of the calorimeter and defining the best calibration protocol. Indeed, even though the calorimeter crystals have similar response, they must be equalized in order to provide a correct energy reconstruction, keep the systematic uncertainty under the 1%. In June 2021, a data taking was performed at Centro Nazionale di Adroterapia Oncologica (CNAO), where 3 crystals have been tested with the aim of evaluating the inter-calibration factors. The response of a particular crystal was selected as reference and the factors have been evaluated by analyzing the response of the crystal by performing two different tests: a frontal scan, where the beam was fired at the front of the BGO crystal and a lateral scan, where the beam impinged on the long side of the crystal at different positions. By applying the inter-calibration factors to the response of the BGO crystals under study, a satisfying calibration can be achieved: the ratio of the calibrated response to the reference one is close to 1, thus both the calibration methods are reliable. Furthermore, a validation test has been pursued by positioning the three crystals side-by-side and firing them with proton or carbon ion beams. The sum of the calibrated response of the three crystals differs by less than 1% with the respect to the case in which the beam inmpinges on the front face of the reference crystal. Since the calibration must be performed on 320 BGO crystals, optimizing the procedureis crucial. In the last part of this work, several methods have been explored with the aim to minimize the data points recorded during the scans. Inter-calibration factors have been evaluated for different combinations of points of the scan and the results have been compared with the factors found using the complete data set