Search for Lepton-Universality Violation in B+ → K+l+l− Decays
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ISSN: 0031-9007
E-ISSN: 1079-7114
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American Physical Society
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Abstract
A measurement of the ratio of branching fractions of the decays 𝐵+ →𝐾+𝜇+𝜇− and 𝐵+ →𝐾+𝑒+𝑒− is presented. The proton-proton collision data used correspond to an integrated luminosity of 5.0 fb−1 recorded with the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. For the dilepton mass-squared range 1.1<𝑞2<6.0 GeV2/𝑐4 the ratio of branching fractions is measured to be 𝑅𝐾 =0.846+0.060−0.054+0.016−0.014, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of 𝑅𝐾 to date and is compatible with the standard model at the level of 2.5 standard deviations.
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R. Aaij et al. Phys. Rev. Lett. 122, 191801
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https://doi.org/10.1103/PhysRevLett.122.191801Sponsors
We acknowledge support from CERN and from the national agencies: CAPES, CNPq, FAPERJ, and FINEP (Brazil); MOST and NSFC (China); CNRS/ IN2P3 (France); BMBF, DFG, and MPG (Germany); INFN (Italy); NWO (Netherlands); MNiSW and NCN (Poland); MEN/IFA (Romania); MSHE (Russia); MinECo (Spain); SNSF and SER (Switzerland); NASU (Ukraine); STFC (United Kingdom); and NSF (USA). We acknowledge the computing resources that are provided by CERN, IN2P3 (France), KIT and DESY (Germany), INFN (Italy), SURF (Netherlands), PIC (Spain), GridPP (United Kingdom), RRCKI and Yandex LLC (Russia), CSCS (Switzerland), IFIN-HH (Romania), CBPF (Brazil), PL-GRID (Poland), and OSC (USA). We are indebted to the communities behind the multiple open-source software packages on which we depend. Individual groups or members have received support from AvH Foundation (Germany); m(K+e+e−) [MeV/c2] 5000 5500 6000 Candidates / (24 MeV/c2) 0 20 40 60 80 100 Data Total fit Total RK = 1 B+→ K+e+e− B+→ J/ψ (e+e−)K+ Part. Reco. Combinatorial LHCb m(K+μ+μ−) [MeV/c2] 5200 5300 5400 5500 5600 Candidates / (7 MeV/c2) 0 50 100 150 200 250 300 350 Data Total fit Total RK = 1 B+→ K+μ +μ − Combinatorial LHCb J/ψ (K+e+e−) [MeV/c2] m 5200 5400 5600 Candidates / (12 MeV/c2) 0 10 20 30 40 50 60 70 80 90 100 ×103 Data Total fit B+→ J/ψ (e+e−)K+ B+→ J/ψ (e+e−)π + Part. Reco. Combinatorial LHCb J/ψ (K+μ+μ−) [MeV/c2] m 5200 5300 5400 5500 5600 Candidates / (4 MeV/c2) 0 20 40 60 80 100 120 140 160 180 200 220 ×103 Data Total fit B+→ J/ψ (μ +μ −)K+ B+→ J/ψ (μ +μ −)π + Combinatorial LHCb FIG. 2. Fits to the mðJ=ψÞðKþlþl−Þ invariant mass distribution for (left) electron and (right) muon candidates for (top) nonresonant and (bottom) resonant decays. For the electron (muon) nonresonant plots, the red-dotted line shows the distribution that would be expected from the observed number of Bþ → Kþμþμ− (Bþ → Kþeþe−) decays and RK ¼ 1. PHYSICAL REVIEW LETTERS 122, 191801 (2019) EPLANET, Marie Skłodowska-Curie Actions, and ERC (European Union); ANR, Labex P2IO, and OCEVU, and R´egion Auvergne-Rhône-Alpes (France); Key Research Program of Frontier Sciences of CAS, CAS PIFI, and the Thousand Talents Program (China); RFBR, RSF, and Yandex LLC (Russia); GVA, XuntaGal, and GENCAT (Spain); the Royal Society and the Leverhulme Trust (United Kingdom); Laboratory Directed Research and Development program of LANL (USA).
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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