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Search for the decay B_S → η^\prime K_S at Belle

Pang, Tong (2021) Search for the decay B_S → η^\prime K_S at Belle. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Abstract

I report the results of the first search for the decay Bs to Eta' Ks. The results are obtained using a 121.4 fb^−1 data sample that contains (16.60 ± 2.68) × 10^6 Bs mesons collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric energy e+ e- collider. I use Monte Carlo simulation to optimize the selection criteria and use the package RooKSFW to maximize the discovery potential for the signal process. An unbinned maximum likelihood fit is performed to obtain the number of signal and background events. No signal is observed, and I report a 90% confidence level upper limit on the branching fraction of the decay Bs to Eta' Ks to be 8.16 × 10^−6 . The theoretical predictions for the branching fraction of this decay are in the range between 0.7 × 10^−6 and 4.5 × 10^−6 . I also report a 90% confidence level upper limit on the product of fs, bs bsbar hadronization factor in Υ(5S) decays, and the branching fraction, i.e. fs × B(Bs to eta' Ks), to be 1.64 × 10^−6.
I also report my studies of a new neural network I developed using the machine learning library PyTorch to improve the sensitivity of rare decay searches at Belle. Compared with machine learning tools developed by the Belle collaboration, such as RooKSFW and NeuroBayes, my neural network rejects about 50% more background for the same signal efficiency, however, it exhibits a bias making backgrounds to partially resemble the signal.


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Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Pang, Tongtop16@pitt.edutop160000-0003-1204-0846
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairSavinov, Vladimirvladimirsavinov@gmail.com
Committee MemberHan, Taothan@pitt.edu
Committee MemberMueller, James A.mueller@pitt.edu
Committee MemberBriere, Roy A.rbriere@andrew.cmu.edu
Committee MemberMong, Rogerrmong@pitt.edu
Date: 18 December 2021
Date Type: Publication
Defense Date: 18 November 2021
Approval Date: 24 October 2024
Submission Date: 8 January 2022
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 129
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Charmless B decay, Upsilon(5S)
Date Deposited: 24 Oct 2024 15:36
Last Modified: 18 Dec 2024 19:31
URI: http://d-scholarship.pitt.edu/id/eprint/42164

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