Journal of High Energy Physics (Mar 2021)

Test of lepton flavor universality and search for lepton flavor violation in B → Kℓℓ decays

  • The BELLE collaboration,
  • S. Choudhury,
  • S. Sandilya,
  • K. Trabelsi,
  • A. Giri,
  • H. Aihara,
  • S. Al Said,
  • D. M. Asner,
  • H. Atmacan,
  • V. Aulchenko,
  • T. Aushev,
  • R. Ayad,
  • V. Babu,
  • S. Bahinipati,
  • P. Behera,
  • C. Beleño,
  • K. Belous,
  • J. Bennett,
  • F. Bernlochner,
  • M. Bessner,
  • V. Bhardwaj,
  • T. Bilka,
  • J. Biswal,
  • G. Bonvicini,
  • A. Bozek,
  • M. Bračko,
  • T. E. Browder,
  • M. Campajola,
  • D. Červenkov,
  • M.-C. Chang,
  • P. Chang,
  • V. Chekelian,
  • A. Chen,
  • B. G. Cheon,
  • K. Chilikin,
  • K. Cho,
  • S.-K. Choi,
  • Y. Choi,
  • D. Cinabro,
  • S. Cunliffe,
  • N. Dash,
  • G. De Nardo,
  • R. Dhamija,
  • F. Di Capua,
  • J. Dingfelder,
  • Z. Doležal,
  • T. V. Dong,
  • D. Dossett,
  • S. Dubey,
  • S. Eidelman,
  • D. Epifanov,
  • T. Ferber,
  • D. Ferlewicz,
  • B. G. Fulsom,
  • R. Garg,
  • V. Gaur,
  • N. Gabyshev,
  • A. Garmash,
  • P. Goldenzweig,
  • B. Golob,
  • D. Greenwald,
  • C. Hadjivasiliou,
  • O. Hartbrich,
  • H. Hayashii,
  • M. T. Hedges,
  • M. Hernandez Villanueva,
  • T. Higuchi,
  • W.-S. Hou,
  • C.-L. Hsu,
  • T. Iijima,
  • K. Inami,
  • A. Ishikawa,
  • R. Itoh,
  • M. Iwasaki,
  • Y. Iwasaki,
  • W. W. Jacobs,
  • E.-J. Jang,
  • H. B. Jeon,
  • S. Jia,
  • Y. Jin,
  • C. W. Joo,
  • K. K. Joo,
  • J. Kahn,
  • A. B. Kaliyar,
  • K. H. Kang,
  • G. Karyan,
  • H. Kichimi,
  • C. Kiesling,
  • B. H. Kim,
  • D. Y. Kim,
  • K.-H. Kim,
  • K. T. Kim,
  • S. H. Kim,
  • Y.-K. Kim,
  • K. Kinoshita,
  • P. Kodyš,
  • S. Korpar,
  • D. Kotchetkov,
  • P. Križan,
  • R. Kroeger,
  • P. Krokovny,
  • T. Kuhr,
  • R. Kulasiri,
  • R. Kumar,
  • K. Kumara,
  • A. Kuzmin,
  • Y.-J. Kwon,
  • K. Lalwani,
  • S. C. Lee,
  • P. Lewis,
  • C. H. Li,
  • L. K. Li,
  • Y. B. Li,
  • L. Li Gioi,
  • J. Libby,
  • K. Lieret,
  • Z. Liptak,
  • D. Liventsev,
  • T. Luo,
  • M. Masuda,
  • T. Matsuda,
  • D. Matvienko,
  • M. Merola,
  • K. Miyabayashi,
  • R. Mizuk,
  • G. B. Mohanty,
  • S. Mohanty,
  • T. J. Moon,
  • T. Mori,
  • I. Nakamura,
  • K. R. Nakamura,
  • M. Nakao,
  • Z. Natkaniec,
  • A. Natochii,
  • L. Nayak,
  • M. Nayak,
  • M. Niiyama,
  • N. K. Nisar,
  • S. Nishida,
  • K. Ogawa,
  • H. Ono,
  • Y. Onuki,
  • P. Oskin,
  • P. Pakhlov,
  • G. Pakhlova,
  • S. Pardi,
  • H. Park,
  • S.-H. Park,
  • S. Patra,
  • S. Paul,
  • T. K. Pedlar,
  • R. Pestotnik,
  • L. E. Piilonen,
  • T. Podobnik,
  • V. Popov,
  • E. Prencipe,
  • M. T. Prim,
  • A. Rabusov,
  • A. Rostomyan,
  • N. Rout,
  • M. Rozanska,
  • G. Russo,
  • D. Sahoo,
  • Y. Sakai,
  • L. Santelj,
  • T. Sanuki,
  • V. Savinov,
  • G. Schnell,
  • J. Schueler,
  • C. Schwanda,
  • A. J. Schwartz,
  • Y. Seino,
  • K. Senyo,
  • M. E. Sevior,
  • M. Shapkin,
  • V. Shebalin,
  • J.-G. Shiu,
  • B. Shwartz,
  • F. Simon,
  • A. Sokolov,
  • E. Solovieva,
  • S. Stanič,
  • M. Starič,
  • Z. S. Stottler,
  • T. Sumiyoshi,
  • W. Sutcliffe,
  • M. Takizawa,
  • U. Tamponi,
  • K. Tanida,
  • F. Tenchini,
  • M. Uchida,
  • S. Uehara,
  • T. Uglov,
  • Y. Unno,
  • S. Uno,
  • P. Urquijo,
  • Y. Ushiroda,
  • R. Van Tonder,
  • G. Varner,
  • K. E. Varvell,
  • A. Vinokurova,
  • V. Vorobyev,
  • E. Waheed,
  • C. H. Wang,
  • E. Wang,
  • M.-Z. Wang,
  • P. Wang,
  • M. Watanabe,
  • S. Watanuki,
  • S. Wehle,
  • J. Wiechczynski,
  • E. Won,
  • X. Xu,
  • B. D. Yabsley,
  • W. Yan,
  • S. B. Yang,
  • H. Ye,
  • J. Yelton,
  • J. H. Yin,
  • C. Z. Yuan,
  • Y. Yusa,
  • Z. P. Zhang,
  • V. Zhilich,
  • V. Zhukova

DOI
https://doi.org/10.1007/JHEP03(2021)105
Journal volume & issue
Vol. 2021, no. 3
pp. 1 – 24

Abstract

Read online

Abstract We present measurements of the branching fractions for the decays B → Kμ + μ − and B → Ke + e − , and their ratio (R K ), using a data sample of 711 fb −1 that contains 772 × 106 B B ¯ $$ B\overline{B} $$ events. The data were collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. The ratio R K is measured in five bins of dilepton invariant-mass-squared (q 2): q 2 ∈ (0.1, 4.0), (4.00, 8.12), (1.0, 6.0), (10.2, 12.8) and (> 14.18) GeV2 /c 4, along with the whole q 2 region. The R K value for q 2 ∈ (1.0, 6.0) GeV2 /c 4 is 1.03 − 0.24 + 0.28 $$ {1.03}_{-0.24}^{+0.28} $$ ± 0.01. The first and second uncertainties listed are statistical and systematic, respectively. All results for R K are consistent with Standard Model predictions. We also measure CP-averaged isospin asymmetries in the same q 2 bins. The results are consistent with a null asymmetry, with the largest difference of 2.6 standard deviations occurring for the q 2 ∈ (1.0, 6.0) GeV2 /c 4 bin in the mode with muon final states. The measured differential branching fractions, d ℬ $$ d\mathrm{\mathcal{B}} $$ /dq 2, are consistent with theoretical predictions for charged B decays, while the corresponding values are below the expectations for neutral B decays. We have also searched for lepton-flavor-violating B → Kμ ± e ∓ decays and set 90% confidence-level upper limits on the branching fraction in the range of 10 −8 for B + → K + μ ± e ∓, and B 0 → K 0 μ ± e ∓ modes.

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