Jheng-Hao Su

2023
Graduate Institute of Applied Physics Taipei

Abstract: We can study K0L through K0L particle list reconstructed from ECL cluster or KLM cluster. Particle identification (PID) can help separate K0L from other particles, like γ, neutron, anti-neutron and other neutral particles. This thesis shows the establishment, method, performance and the comparison of K0L particle identification by using only ECL information in Belle II experiment. In this thesis, we use Fast Boosted Decision Tree (FastBDT) to get a trained multivariate analysis (MVA) method which can separate signal (K0L) and background (neutral particles excluding K0L). We present the results on the reconstruction of the B0 → J/ψ K0L decay, where J/ψ → μ+μ−. K0L mesons are reconstructed from the hadronic neutral clusters in the Electromagnetic Calorimeter (ECL). Using signal Monte Carlo (MC) with one millon events in Belle II, we have about 25% efficiency. In generic MC corresponding to a luminosity of 100/fb, we get 681 ± 71 candidates. Moreover, we use the Belle II experiment dataset corresponding to a luminosity of 189.049/fb collected in the asymmetric energy e+e− collider at SuperKEKB. We measure 1031±95 candidates with J/ψ → μ+μ− in total. We also compare the results above with the reconstruction of the B0 → J/ψ K0L decay, while K0L mesons are reconstructed from the hadronic neutral clusters in K0L and muons (KLM) subdetector. By the comparison of the result in ECL and KLM in whole region and signal region with signal MC and Data, we notice that the overlap of ECL and KLM is not large. This provides another way for K0L identification.

Note: Presented on 20 06 2023
Note: MSc