Simulation Studies for the KLEVER Small-Angle Calorimeter

The Standard Model of particle physics attempts to describe all observable particles and forces, excluding gravity. There are also many fundamentally conserved quantities under the SM, such as charge, lepton flavour, and baryon number. The Standard Model can be used to calculate branching ratios, or the probability of one decay happening out of all possible decays for a particle. The branching ratio for the KL → π0νν ̄ decay is predicted to be BR(KL → π0νν ̄) = (3.4 ± 0.6) × 10−11 [1] and is extremely suppressed under the Standard Model, making this a prime candidate for potentially observing physics beyond the Standard Model. BR(KL → π0νν ̄) has never been experimentally measured. Discovering evidence of and measuring phenomena beyond the Standard Model could help to understand the potential flavour structure of new physics, and would help solve many open questions, such as the hierarchy problem, matter- antimatter asymmetry, and the origin and nature of dark matter. This paper focuses on simulating and testing the effectiveness of a lead fluoride-based small- angle calorimeter in catching photons escaping from the beam hole of KLEVER, an experiment aiming to measure BR(KL → π0νν ̄) to ∼20% accuracy. By catching these photons, the SAC will differentiate KL → π0π0 decays (BR = 8.64 × 10−4) from the decay of interest. First, fast- simulation of the entire KLEVER detector was used to obtain the needed inefficiencies for the SAC. Then, a detailed simulation of the SAC was constructed to confirm its opacity to photons and transparency to hadrons and test its reached inefficiencies. Finally, future work focuses on integrating detector readout and oriented crystals into the Geant4 simulation, testing the SAC with a more non-idealized KL beam, and testing different configurations of the SAC. As a rough approximation, the SAC currently reaches the needed inefficiencies, though the SAC efficiency will be decreased by a factor of ∼10 once the full readout chain is simulated, which may be compensated in part by increases from detector design improvements.