Test beam studies of SpaCal prototype calorimeter module with tungsten absorber

The electromagnetic calorimeter, ECAL, is a sub-detector of the general-purpose flavor physics experiment, LHCb, operating at the LHC accelerator at the European Organization for Nuclear Research - CERN. Since one-third of heavy flavor decay products are $\pi_0$ mesons or other neutral particles decaying to photons in a wide energy range from a few $\text{GeV}$ to several 100 $\text{GeV}$, a high-performance electromagnetic calorimeter is essential in LHCb. A scintillating sampling calorimeter has been chosen as a good compromise between energy resolution, ability to detect compact electromagnetic showers, fast time response, and moderate price. In 2022, a significant upgrade to the LHCb ECAL system has been proposed, socalled Upgrade II, which includes the upgrade of other sub-detectors of the LHCb experiment. At Upgrade II conditions, the LHCb detector will take data at a much higher luminosity as of now, of up to 1.5×1034 cm$^{−2}$ s $^{−1}$. This puts new severe requirements on the calorimeter, in particular, the need for better granularity and time response of O(10) ps. As one of the candidates for the Upgrade II of the LHCb ECAL, a new type of Spaghetti Calorimeter (SpaCal) is being developed. In this thesis, I study the performance of a module-size SpaCal prototype with a tungsten absorber and plastic scintillating fibers through test beams at CERN and DESY and through simulation validations. The prototype achieves an energy resolution of ∼ 9.75%/$\sqrt{E}$ ⊕ 1.26% and a time resolution of ∼ 20 ps at 100 $\text{GeV}$. The time response is further studied, and I show it to be homogeneous over a large area within a calorimeter cell.