Evidence for 𝐵⁺ → 𝐾⁺ 𝜈⁢𝜈¯ decays

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hdl_143940.pdf (13.09 MB)
  (Published version)

Date

2024

Authors

Adachi, I.
Adamczyk, K.
Aggarwal, L.
Ahmed, H.
Aihara, H.
Akopov, N.
Aloisio, A.
Anh Ky, N.
Asner, D.M.
Atmacan, H.

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Journal article

Citation

Physical Review D (particles, fields, gravitation, and cosmology), 2024; 109(11):112006-1-112006-29

Statement of Responsibility

I. Adachi ... et al. (Belle II Collaboration)

Conference Name

DOI

10.1103/physrevd.109.112006

Abstract

We search for the rare decay 𝐵+ →𝐾+⁢𝜈⁢ ¯ 𝜈 in a 362  fb−1 sample of electron-positron collisions at the ϒ⁡(4⁢𝑆) resonance collected with the Belle II detector at the SuperKEKB collider. We use the inclusive properties of the accompanying 𝐵 meson in ϒ⁡(4⁢𝑆)→𝐵⁢ ¯ 𝐵 events to suppress background from other decays of the signal 𝐵 candidate and light-quark pair production. We validate the measurement with an auxiliary analysis based on a conventional hadronic reconstruction of the accompanying 𝐵 meson. For background suppression, we exploit distinct signal features using machine learning methods tuned with simulated data. The signal-reconstruction efficiency and background suppression are validated through various control channels. The branching fraction is extracted in a maximum likelihood fit. Our inclusive and hadronic analyses yield consistent results for the 𝐵+ →𝐾+⁢𝜈⁢ ¯ 𝜈 branching fraction of [2.7±0.5⁢(stat)±0.5⁢(syst)] ×10−5 and [1.1+0.9 −0.8⁢(stat)+0.8 −0.5⁢(syst)] ×10−5, respectively. Combining the results, we determine the branching fraction of the decay 𝐵+ →𝐾+⁢𝜈⁢ ¯ 𝜈 to be [2.3±0.5⁢(stat)+0.5 −0.4⁢(syst)] ×10−5, providing the first evidence for this decay at 3.5 standard deviations. The combined result is 2.7 standard deviations above the standard model expectation.

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Dissertation Note

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Published 6 June 2024

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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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http://purl.org/au-research/grants/arc/DP200101792
 http://purl.org/au-research/grants/arc/DP210101900
 http://purl.org/au-research/grants/arc/DP210102831
 http://purl.org/au-research/grants/arc/DE220100462
 http://purl.org/au-research/grants/arc/LE210100098
 http://purl.org/au-research/grants/arc/LE230100085

Published Version

http://dx.doi.org/10.1103/physrevd.109.112006

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Persistent link to this record

https://hdl.handle.net/2440/143940