A<sc>bstract</sc> We present the result of a search for the charged-lepton-flavor violating decayτ−→μ−μ+μ−using a 424 fb−1sample of data recorded by the Belle II experiment at the SuperKEKBe+e−collider. The selection ofe+e−→τ+τ−events is based on an inclusive reconstruction of the non-signal tau decay, and on a boosted decision tree to suppress background. We observe one signal candidate, which is compatible with the expectation from background processes. We set a 90% confidence level upper limit of 1.9×10−8on the branching fraction of theτ−→ μ−μ+μ−decay, which is the most stringent bound to date.
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Estimation of combinatoric background in seaquest using an event-mixing method
Abstract All experiments observing dilepton pairs (e.g.e+e-, μ+μ-) must confront the existence of acombinatoricbackground caused by the combining of tracks not arising from the same physics vertex. Some method must be devised to calculate and remove this background. In this document we describe a particular event-mixing method relying on many of the unique aspects of the SeaQuest spectrometer and data. The method described here calculates the combinatoric background with correct normalization; i.e., there is no need to assign a floating normalization factor that is then determined in a subsequent fitting procedure. Numerous tests are applied to demonstrate the reliability of the method.
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- PAR ID:
- 10511514
- Publisher / Repository:
- https://iopscience.iop.org/
- Date Published:
- Journal Name:
- Journal of Instrumentation
- Volume:
- 18
- Issue:
- 10
- ISSN:
- 1748-0221
- Page Range / eLocation ID:
- P10032
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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