000004245 001__ 4245
000004245 005__ 20240421134925.0
000004245 037__ $$aBELLE2-UTHESIS-2024-001
000004245 041__ $$aeng
000004245 100__ $$aArina Katscho
000004245 245__ $$aSelection of τ → Kππντ Decays for Data from the Belle II Experiment
000004245 260__ $$aGarching$$bMax Planck Institute for Physics$$c2024
000004245 300__ $$a80
000004245 500__ $$aPresented on 17 04 2024
000004245 502__ $$aBSc$$bGarching, Technical University of Munich$$c2024
000004245 520__ $$aWe develop the event selection of τ ∓ → K∓π∓π±ντ for data from the Belle II electron-positron collider experiment at SuperKEKB, Japan. The aim is that the event selection will be used for further spectroscopy analysis. We tested two event selection approaches to achieve a highly pure τ ∓ → K∓π∓π±ντ selection sample. In the first approach we trained Boosted Decision Trees (BDT) based on the previous preselection with a 3x1 prong topology, i.e. one τ decays to three charged final states particles (3-prong) and the other τ to one charged final state particle (1-prong). To this end, we tuned the hyperparameters of the BDT for an optimal event selection performance. Considering future acceptance corrections, we also tested a second event selection approach where we applied manual cuts on the particle identification (PID) variables and combined them with a BDT that was trained with the remaining variables. Performance comparison showed the first approach achieves significantly higher performance of 80% purity for 6.7% signal efficiency. We also studied acceptance effects and remaining background kinematics in the selected sample. The background is composed of various decays, mainly τ -decays to other hadrons. Noteworthy, the acceptance is not strongly modulated despite the restrictive selection.
000004245 700__ $$aStephan Paul$$edir.
000004245 700__ $$aStefan Wallner $$edir.
000004245 8560_ $$fakatscho@mpp.mpg.de
000004245 8564_ $$uhttps://docs.belle2.org/record/4245/files/BELLE2-UTHESIS-2024-001.pdf
000004245 980__ $$aTHESIS