The dominant such background for the non-resonant and resonant modes comes from partially reconstructed B(0,+)K+(,0)e+e and B(0,+)J/(e+e)K+(,0) decays, respectively, where the pion is not included in the B+ candidate. In the remainder of this paper, the notation B+K++ is used to denote only decays with 1.1\) as a function of pT. High. & Rusov, A. V. BsK and B(s)(K)+ decays at large recoil and CKM matrix elements. The extent of the dark, medium and light blue regions shows the values allowed for RK at 1, 3 and 5 levels. The raw data in all of the figures of this paper, and additional supplementary material, can be downloaded from https://cds.cern.ch/record/2758740, where no access codes are required. D 93, 014028 (2016). Correlations between different categories of selected events and data-taking periods are taken into account in these constraints. The distribution of this ratio as a function of the angle between the leptons and the minimum pT of the leptons is shown in Extended Data Fig. The analogous ratio has also been measured for \({\Lambda }_{b}^{0}\) decays with H=pK and is compatible with unity at the level of one standard deviation23. and JavaScript. 2). Ciuchini, M. et al. Methods A 506, 250303 (2003). Test of lepton universality in beauty-quark decays LHCb Collaboration Roel Aaij( NIKHEF, Amsterdam Show All(961) Mar 22, 2021 25 pages Published in: Nature Phys.18(2022)3,277-282 Published: Mar 15, 2022 e-Print: 2103.11769[hep-ex] DOI: 10.1038/s41567-021-01478-8 Report number: LHCb-PAPER-2021-004, CERN-EP-2021-042 Experiments: CERN-LHC-LHCb The resulting variations are typically at the permille level and hence well within the estimated systematic uncertainty on RK. & Virto, J. The resonant yields are determined from separate fits to the mass, mJ/(K++), formed by kinematically constraining the dilepton system to the known J/ mass2 and thereby improving the mass resolution. 126, 161802 (2021). MathSciNet If confirmed by future measurements, this violation of lepton universality would imply physics beyond the standard model, such as a new fundamental interaction between quarks and leptons. High. 12, 040 (2007). Serra, N., Silva Coutinho, R. & van Dyk, D. Measuring the breaking of lepton flavor universality in BK*+. The calibrated simulation is used subsequently to obtain the m(K++) mass shape and relative fractions of these background components. High Energy Phys. The results presented today focus on lepton flavour universality, but the LHCb experiment also studies matter-antimatter differences. CMS collaboration Angular analysis of the decay B0K*0+ from pp collisions at \(\sqrt{s}=8\) TeV. Rev. 120, 121801 (2018). Bobeth, C., Chrzaszcz, M., van Dyk, D. & Virto, J. Test of lepton universality in beauty-quark decays, arXiv:2103.1176 . Yields of the nonresonant and resonant decay modes obtained from the fits to the data. Nature 546, 227 . 2015, 115 (2015); erratum 2018, 145 (2018). One method to search for new physics is to compare measurements of the properties of hadron decays, where hadrons are bound states of quarks, with their SM predictions. Phys. These fractions are observed to agree well with those observed in resonant events selected from the data. Lane,A. Lupato,T. H. Mcgrath,A. McNab,B. Mitreska,D. Murray,Y. Pan,C. Parkes,F. Reiss,N. Skidmore,P. Svihra,S. Taneja,D. J. High. Distribution of the invariant mass m(K+e+e) for B+K+e+e candidates. The distributions are all normalised to unity. D 95, 035029 (2017). This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton-proton collision data collected with . Measurement of the lepton polarization and R(D*) in the decay \(\overline{B}\to {D}^{* }{\tau }^{-}{\overline{\nu }}_{\tau }\) with one-prong hadronic decays at Belle. High Energy Phys. 2014, 125 (2014). A. Bertolin. Conf. In the SM description of such processes, these virtual particles include the electroweak force carriers, the , W and Z0 bosons, and the top quark (Fig. Jger, S. & Martin Camalich, J. J. J. High Energy Phys. Eur. In addition, a 0.2% systematic uncertainty is assigned for the potential contribution from partially reconstructed decays with two additional pions. The Standard Model of particle physics predicts that particles called beauty quarks, which are measured in the LHCb experiment, should decay into either muons or electrons in equal measure. {6\ }_{-\ 1.4}^{+\ 1.5}\ \pm 1.3)\times 1{0}^{-9}\ {c}^{4}\,{{{{\rm{GeV}}}}}^{-2}\ .\end{array}$$, \(\overline{b}\to \overline{s}{\ell }^{+}{\ell }^{-}\), \(\overline{b}\to \overline{s}{\tau }^{+}{\tau }^{-}\), \(B\to {H}_{c}(\to {K}^{+}{\ell }^{-}{\overline{\nu }}_{\ell }X){\ell }^{+}{\nu }_{\ell }Y\), $$\begin{array}{rcl}{R}_{K}&=&\frac{N({B}^{+}\to {K}^{+}{\mu }^{+}{\mu }^{-})}{\varepsilon ({B}^{+}\to {K}^{+}{\mu }^{+}{\mu }^{-})}\cdot \frac{\varepsilon ({B}^{+}\to {K}^{+}{e}^{+}{e}^{-})}{N({B}^{+}\to {K}^{+}{e}^{+}{e}^{-})}\\ &&\times \frac{\varepsilon ({B}^{+}\to J/\psi (\to {\mu }^{+}{\mu }^{-}){K}^{+})}{N({B}^{+}\to J/\psi (\to {\mu }^{+}{\mu }^{-}){K}^{+})}\cdot \frac{N({B}^{+}\to J/\psi (\to {e}^{+}{e}^{-}){K}^{+})}{\varepsilon ({B}^{+}\to J/\psi (\to {e}^{+}{e}^{-}){K}^{+})}\ ,\end{array}$$, \(\overline{B}\to \overline{K}{{{{\rm{\ell }}}}}^{+}{{{{\rm{\ell }}}}}^{-}\), \({\Lambda }_{b}^{0}\to p{K}^{-}{\ell }^{+}{\ell }^{-}\), \({B}_{d}^{0}\to {K}^{* }{\mu }^{+}{\mu }^{-}\), \({B}_{s}^{0}\to \phi {\mu }^{+}{\mu }^{-}\), \({\Lambda }_{b}^{0}\to \Lambda {\mu }^{+}{\mu }^{-}\), \({B}_{s}^{0}\to \ \ \phi {\mu }^{+}{\mu }^{-}\), \(\overline{B}\to \ \ {D}^{(*)}{\tau }^{-}{\overline{\nu }}_{\tau }\), \({{{\mathcal{B}}}}({B}_{c}^{+}\to J/\psi {\tau }^{+}{\nu }_{\tau })/{{{\mathcal{B}}}}{{{\mathcal{B}}}}({B}_{c}^{+}\to J/\psi {\mu }^{+}{\nu }_{\mu })\), \({\overline{B}}^{0}\to {D}^{* +}{\tau }^{-}{\overline{\nu }}_{\tau }\), \({\overline{B}}^{0}\to {D}^{* +}{\ell }^{-}{\overline{\nu }}_{\ell }\), \({{{\mathcal{B}}}}({\overline{B}}^{0}\to {D}^{* +}{\tau }^{-}{\overline{\nu }}_{\tau })/{{{\mathcal{B}}}}({\overline{B}}^{0}\to {D}^{* +}{\mu }^{-}{\overline{\nu }}_{\mu })\), \({B}^{0}\to \ \ {D}^{(*)}{\tau }^{-}{\overline{\nu }}_{\tau }\), \(\overline{B}\to \ \ {D}^{(*)}{\ell }^{-}{\overline{\nu }}_{\ell }\), \(\overline{B}\to {D}^{* }{\tau }^{-}{\overline{\nu }}_{\tau }\), \({{{\mathcal{B}}}}[\psi (3686)\to \ \ {\pi }^{+}{\pi }^{-}J/\psi ]\), \({{{\mathcal{B}}}}[J/\psi \to \ \ {\ell }^{+}{\ell }^{-}]\), \({B}_{s}^{0}\to {\tau }^{+}{\tau }^{-}\), https://doi.org/10.1038/s41567-021-01478-8. Phys. Eur. Lett. The mass distributions are shown in Extended Data Fig. Test of lepton universality in beauty-quark decays. Right: a possible new physics contribution to the decay with a hypothetical leptoquark (LQ) which, unlike the electroweak bosons, could have different interaction strengths with the different types of leptons. Internet Explorer). Test of lepton universality using B 0 K S0 l + l - and B + K* + l + l - decays. The y axis in each panel shows the number of candidates in an interval of the indicated width. The effect on RK is at the 1% level. Martin, B. R., and Shaw, G. (2017). The Large Hadron Collider (LHC) is the worlds highest-energy particle accelerator and is situated approximately 100m underground, close to Geneva, Switzerland. Alok, A. K., Dighe, A., Gangal, S. & Kumar, D. Continuing search for new physics in bs decays: two operators at a time. Test of lepton universality in beauty-quark decays . Even though the non-resonant and resonant samples are mutually exclusive as a function of q2, there is significant overlap between them in the quantities on which the efficiency depends, such as the laboratory-frame momenta of the final-state particles or the opening angle between the two leptons. These ratios have been determined to be 2.12.5 standard deviations below their respective SM expectations3,4,5,6,7,16,17,18,19,20,21,22. In the muon case, K[] combinations with mass smaller than \(m_{D^0}\) are rejected. Article Huber, P. J. in Robust Estimation of a Location Parameter (eds Kotz S. & Johnson N. L.) 492518 (Springer, 1992). In the measurement of the rJ/ ratio, the systematic uncertainty is dominated by the imperfect modelling of the B+ production kinematics and the modelling of selection requirements, which have a negligible impact on the RK measurement. & Atwood, D. Rate difference between bs+ and bse+e in supersymmetry with large tan . Phys. Lett. The measurement made by the LHCb team compares two types of decays of beauty quarks. Phys. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The k-folding technique is used in the training and testing81. Phys. We are indebted to the communities behind the multiple open-source software packages on which we depend. Sifting through proton . 178, 852867 (2008). CERN https://cds.cern.ch/record/2636441 (2019). Instrum. J. High. This causes misidentification backgrounds to populate a range of K masses but only a peak in the Ke mass. J. Altmannshofer, W. & Yavin, I. Phys. Aaij, R. et al. They involve the transformation of a beauty quark into a strange quark (bs), a process that is highly suppressed in the SM and can be affected by the existence of new particles. Energy Phys. Measurement of the ratio of branching fractions \({{{\mathcal{B}}}}({B}_{c}^{+}\to J/\psi {\tau }^{+}{\nu }_{\tau })/{{{\mathcal{B}}}}{{{\mathcal{B}}}}({B}_{c}^{+}\to J/\psi {\mu }^{+}{\nu }_{\mu })\). J. Phys. Hurth, T., Mahmoudi, F. & Neshatpour, S. Implications of the new LHCb angular analysis of BK*+: hadronic effects or new physics? The PVs are reconstructed by searching for space points where an accumulation of track trajectories is observed. An unbinned extended maximum-likelihood fit is made to the m(K+e+e) and m(K++) distributions of non-resonant candidates. 4. Blum, A., Kalai, A. However, it is clear that the model is incomplete. The value of q2 is calculated using only the lepton momenta, without imposing any constraint on the m(K++) mass. To suppress background, each final-state particle is required to have sizeable pT and to be inconsistent with coming from a PV. Wei J.-T. et al. This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton-proton collision data collected with the LHCb detector at CERN's Large Hadron Collider. Rev. Davidson, N., Przedzinski, T. & Was, Z. oscillation frequency, Probing CP symmetry and weak phases with entangled double-strange baryons, Polarization and entanglement in baryonantibaryon pair production in electronpositron annihilation, The Higgs boson implications and prospects for future discoveries, http://opendata.cern.ch/record/410/files/LHCb-Data-Policy.pdf, https://www.hepdata.net/record/ins1852846?version=1. (Right) the bin definition in this two-dimensional space together with the distribution for B+K+e+e (B+J/(e+e)K+) decays depicted as red (blue) contours. Rev. High Energy Phys. New physics in bs+ confronts new data on lepton universality. White&G. 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Uncertainties on the data points are statistical only and represent one standard deviation, calculated assuming Poisson-distributed entries. Energy Phys. The LHCb simulation application, Gauss: design, evolution and experience. Phys. Capdevila, B., Descotes-Genon, S., Matias, J. No significant trend is observed in either rJ/ distribution. Phys. Again, no significant trend is seen. The only exception to this is due to the Higgs field, since the leptonHiggs interaction strength gives rise to the differing lepton masses m>m>me. Measurements of the S-wave fraction in B0K++ decays and the B0K*(892)0+ differential branching fraction. The hierarchical effect needed to explain the existing \(\overline{b}\to \overline{s}{\ell }^{+}{\ell }^{-}\) and \(\overline{b}\to \overline{c}{\ell }^{+}{\nu }_{\ell }\) data, with the largest effects observed in tau modes, then muon modes and little or no effects in electron modes, suggests that studies of \(\overline{b}\to \overline{s}{\tau }^{+}{\tau }^{-}\) transitions are also of great interest69,70. Phys. This resolution scaling changes the migration of candidates into the q2 region of interest by less than 1%. B Phys. Ghosh, D., Nardecchia, M. & Renner, S. A. In this paper, a measurement of the RK ratio is presented based on protonproton collision data collected with the LHCb detector at the CERNs Large Hadron Collider (Methods). ISSN 1745-2473 (print). refers to partially reconstructed B hadron decays. Rev. Phys. B. Zonneveld, Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania, L. Cojocariu,A. Ene,L. Giubega,A. Grecu,F. Maciuc,V. 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Pugatch, School of Physics, University College Dublin, Dublin, Ireland, A. M. Donohoe,L. Mcconnell,R. McNulty,N. V. Raab&C. B. Lees, J. P. et al. These two processes are separated by applying a requirement on q2. Test of lepton-flavor universality in BK*+ decays at Belle. Nucl. Rev. The departure of the profile likelihood shown in Extended Data Fig. Lepton Flavour Universality can be studied in two classes of B meson decays in which a beauty b quark can be transformed into either a strange quark (bs) or into a charm quark (bc). The CMS collaboration Measurement of angular parameters from the decay B0K*0+ in proton-proton collisions at \(\sqrt{s}=\) 8 TeV. Similarly, the differing q2 resolution between data and simulation, which alters estimates of the q2 migration, has negligible impact on the result. The relative fraction of partially reconstructed background in each trigger category is also shared across the different data-taking periods. Extended Data Fig. The value of RK is a fit parameter, which is related to the signal yields and efficiencies according to. Rev. Aaij, R. et al. Energy Phys. Combining the uncertainties gives \({R}_{K}=0.84{6}_{-\ 0.041}^{+\ 0.044}\). Instrum. Tension with the SM is also seen in the combination of several ratios that test lepton universality in \(\overline{b}\to \overline{c}{\ell }^{+}{\nu }_{\ell }\) transitions55,56,57,58,59,60,61,62,63. LHCb collaboration LHCb detector performance. Phys. J. This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton-proton collision data collected with the LHCb detector . Measurement of CP-averaged observables in the B0K*0+ decay. 53, 270278 (2006). LHCb collaboration. The LHCb experiment75,76 is instrumented in the region covering the polar angles between 10 and 250mrad around the proton beam axis, in which the products from B hadron decays can be efficiently captured and identified. Differential branching fractions and isospin asymmetries of BK(*)+ decays. As detailed below, percent-level control of the efficiencies is verified with a direct comparison of the B+J/(e+e)K+ and B+J/(+)K+ branching fractions in the ratio. The determination of the rJ/ ratio requires control of the relative selection efficiencies for the resonant electron and muon modes and does not therefore benefit from the cancellation of systematic effects in the double ratio used to measure RK. D 96 (2017) 095010 [ arXiv:1704.06659] [ INSPIRE ]. The significance of this discrepancy is 3.1standard deviations, giving evidence for the violation of lepton universality in these decays. J. Instrum. 24, 01025 (2020). For decays with H=K+ and H=K*0 such ratios, denoted by RK and RK*0, respectively, have previously been measured by the Large Hadron Collider beauty (LHCb)11,12, Belle13,14 and BaBar15 collaborations. When compared with the 20% shift that these corrections induce in the measurement of rJ/, this demonstrates the robustness of the double-ratio method in suppressing systematic biases that affect the resonant and non-resonant decay modes similarly. Khodjamirian, A. The Belle collaboration et al. Reassessing the discovery potential of the B + K + + l + +l - decays in the large-recoil region: SM challenges and BSM opportunities, Physical Review D93: 014028. arXiv:1412.3183. The detector includes a high-precision tracking system with a dipole magnet, providing measurements of momentum and impact parameter (IP), defined for charged particles as the minimum distance of a track to a primary protonproton interaction vertex (PV). Provided by the Springer Nature SharedIt content-sharing initiative, Rendiconti Lincei. Lange, D. J. J. The B+ hadron contains a beauty antiquark, \(\overline{b}\), and the K+ a strange antiquark, \(\overline{s}\), such that at the quark level the decay involves a \(\overline{b}\to \overline{s}\) transition. Ghez,J. F. Marchand,M.-N. Minard,B. Pietrzyk,B. Quintana,M. Reboud&S. TJampens, Center for High Energy Physics, Tsinghua University, Beijing, China, C. Chen,J. The measurements are of processes in which a beauty meson transforms into a strange meson with . J. For the non-resonant B+K+e+e decays, the systematic uncertainties are dominated by the modelling of the signal and background components used in the fit. This uncertainty includes both statistical and systematic effects, where the latter dominate. decays of heavy quarks. Aaij, R. et al. PHOTOS interface in C++: technical and physics documentation. Caria, G. et al. The large interaction strengths preclude predictions of QCD effects with the perturbation techniques used to compute the electroweak force amplitudes, and only approximate calculations are currently possible. To obtain https://doi.org/10.1038/s41567-021-01478-8, DOI: https://doi.org/10.1038/s41567-021-01478-8. Jan 2019; PHYS REV LETT; High Energy Phys. Hirose, S. et al. High. Savoie Mont Blanc, CNRS, IN2P3-LAPP, Annecy, France, M. Chefdeville,D. Decamp,A. G. Downes,Ph. EOS version 0.3.3. A comparison with previous measurements is shown in Fig. The latest LHCb result is the first test of lepton universality made using the decays of beauty baryonsthree-quark particles containing at least one beauty quark. The fit projections for the m(K++) and mJ/(K++) distributions are shown in Fig. The uncertainties on parameters used in the simulation model of the signal decays affect the q2 distribution and hence the selection efficiency. Altmannshofer, W. & Straub, D. M. New physics in BK*? 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Confirmation of any effect beyond the SM will clearly require independent evidence from a wide range of sources. De Aguiar Francisco,S. De Capua,D. Dutta,C. Fitzpatrick,E. Gersabeck,M. Gersabeck,L. Grillo,M. Hilton,G. Lafferty,J. J. B 781, 517541 (2018). Phys. Differential branching fraction and angular analysis of the decay B0K+I+in the \({K}_{0,2}^{* }{(1430)}^{0}\) region.
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