B Aaij, R. 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. This gives. ADS Altmannshofer, W. & Straub, D. M. New physics in BK*? 0 Pseudo-experiments are also used to assess the degree of bias originating from the fitting procedure. Extended Data Table 2 Yields of the nonresonant and resonant decay modes. Correlations between different categories of selected events and data-taking periods are taken into account in these constraints. Phys. High Energy Phys. Aaij, R. et al. J. In addition, a 0.2% systematic uncertainty is assigned for the potential contribution from partially reconstructed decays with two additional pions. Calculation of the SM predictions for the branching fractions of B+K++ and B+K+e+e decays is complicated by the strong nuclear force that binds together the quarks into hadrons, as described by quantum chromodynamics (QCD). For RK the LHCb measurements are in the range 1.1Test of lepton universality in beauty-quark decays - Nature The y-axis in each figure shows the number of candidates in an interval of the indicated width. The Standard Model predicts that this occurs via electroweak bosons and the W + and Z 0 particles. D 68, 094016 (2003). The likelihood is non-Gaussian in the region RK>0.95 due to the comparatively low yield of B+K+e+e events. A challenge to lepton universality in B-meson decays | Nature Phys. Eur. These uncertainties are propagated to an uncertainty on RK using predictions from the FLAVIO software package7 but give rise to a negligible effect. Phys. 12, 104 (2020). The theory predicts that the different charged leptons, the electron, muon and tau . The pT of the final state particles, the vertex-fit 2 and the significance of the flight distance have the most discriminating power. Since the J/+ branching fractions are known to respect lepton universality to within 0.4% (refs. The B + hadron contains a beauty antiquark, b, and the K + a strange antiquark, s, such that at the quark level the decay involves a b s transition . Lett. Measurement of the ratio of branching fractions \({{{\mathcal{B}}}}({B}_{c}^{+}\to J/\psi {\tau }^{+}{\nu }_{\tau })/{{{\mathcal{B}}}}{{{\mathcal{B}}}}({B}_{c}^{+}\to J/\psi {\mu }^{+}{\nu }_{\mu })\). 2020, 40 (2020). 82,83,84,85,86,87,88. explanations of this apparent violation of lepton universality for decays . The majority of the sources of systematic uncertainty affect the relative efficiencies between non-resonant and resonant decays. 2017, 112 (2017). What our students say. J. 11, and only the main analysis steps are reviewed here. In both cases, for both signal and background, the efficiency of the BDT selection has negligible dependence on m(K++) and q2 in the regions used to determine the event yields. Test of lepton universality in beauty-quark decays. The analysis technique used to obtain the results presented in this paper is essentially identical to that used to obtain the previous LHCb RK measurement, described in ref. Lees, J. P. et al. Phys. Such a modification can be realized in new physics models with an additional heavy neutral boson or with leptoquarks. Sjstrand, T., Mrenna, S. & Skands, P. A brief introduction to PYTHIA 8.1. The standard model (SM) of particle physics provides precise predictions for the properties and interactions of fundamental particles, which have been confirmed by numerous experiments since the inception of the model in the 1960s. Lepton avour universality tests in electroweak penguin decays at LHCb Such studies can help to explain the matter-antimatter asymmetryof the Universe. Uncertainties on the data points are statistical only and represent one standard deviation, calculated assuming Poisson-distributed entries. To accommodate possible lepton universality violation in these partially reconstructed processes, which are underpinned by the same \(\overline{b}\to \overline{s}\) quark-level transitions as those of interest, the overall yield of such decays is left to vary freely in the fit. Bobeth, C., Chrzaszcz, M., van Dyk, D. & Virto, J. Part. Simulated events are weighted to correct for the imperfect modelling using control channels. Provided by the Springer Nature SharedIt content-sharing initiative, Rendiconti Lincei. This is the most precise measurement of this ratio to date and is compatible with the SM prediction with a P value of 0.10%. The rJ/ ratio is therefore also computed as a function of different kinematic variables. The ATLAS and CMS experiments may also be able to contribute73,74. High Energy Phys. Observables studied include rare meson decays, flavor oscillations of neutral mesons, rare lepton decays, and dipole moments. Methods A 506, 250303 (2003). The value of q2 is calculated using only the lepton momenta, without imposing any constraint on the m(K++) mass. Further tests give good compatibility for subsamples of the data corresponding to different trigger categories and magnet polarities. The latter also tend to accumulate around specific values of m(K++). Improved lepton universality measurements show agreement with the Davidson, N., Przedzinski, T. & Was, Z. 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. Placinta&M. Straticiuc, L. Congedo,M. De Serio,R. A. Fini,A. Palano,M. Pappagallo,A. Pastore&S. Simone, L. Congedo,M. De Serio,M. Pappagallo&S. Simone, Los Alamos National Laboratory (LANL), Los Alamos, NM, USA, J. Crkovsk,C. L. Da Silva,C. T. Dean,J. M. Durham,E. Epple&G. J. Kunde, Van Swinderen Institute, University of Groningen, Groningen, Netherlands, K. De Bruyn,C. J. G. Onderwater&M. van Veghel, Universiteit Maastricht, Maastricht, Netherlands, Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Krakw, Poland, A. Dendek,M. Firlej,T. Fiutowski,M. Idzik,P. Kopciewicz,W. Krupa,O. Madejczyk,M. W. Majewski,J. Moron,A. Oblakowska-Mucha,B. Rachwal,J. Ryzka,K. Swientek&T. Szumlak, F. Dettori,C. Giugliano,G. Manca,R. Oldeman&B. Saitta, Eotvos Lorand University, Budapest, Hungary, Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine, V. Dobishuk,S. Koliiev,I. Kostiuk,O. Kot&V. 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. In the fits to non-resonant B+K+e+e candidates, the mass shape of the background from B+J/(e+e)K+ decays with an emitted photon that is not reconstructed is also taken from simulation and, adjusting for the relevant selection efficiency, its yield is constrained to the value from the fit to the resonant mode within its uncertainty. No significant trend is observed in the differential determination of rJ/ as a function of any considered variable. This symmetry is called lepton avour universality (LFU) and is established in for example /0! 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. Previous measurements have shown that a wide range of particle decays are consistent with this principle of lepton universality. Wei J.-T. et al. Capdevila, B., Descotes-Genon, S., Matias, J. As a result, the different lepton types should be created equally often in particle transformations, or "decays", once differences in their mass are accounted for. The fit projections for the m(K++) and mJ/(K++) distributions are shown in Fig. Distribution of the invariant mass m(K+e+e) for B+K+e+e candidates. Similarly, the differing q2 resolution between data and simulation, which alters estimates of the q2 migration, has negligible impact on the result. Whenever B+J/(+)K+ events are used to correct the simulation, the correlations between calibration and measurement samples are taken into account in the results and cross-checks presented in this paper. Rev. D 95, 035029 (2017). 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. where the first uncertainty is statistical and the second systematic. 118, 251802 (2017). Measurement of branching fractions and rate asymmetries in the rare decays BK(*)+. Lett. The measurement made by the LHCb team compares two types of decays of beauty quarks. For the RK measurement, candidate events are required to have passed a hardware trigger algorithm that selects either a high-pT muon, or an electron, hadron or photon with high transverse energy deposited in the calorimeters. 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. The corresponding significance in terms of standard deviations is computed using the inverse Gaussian cumulative distribution function for a one-sided conversion. J. C 79, 719 (2019). 2014, 133 (2014). The data were recorded during 2011, 2012 and 20152018 with centre-of-mass energy of the collisions of 7, 8 and 13TeV and correspond to an integrated luminosity of 9fb1. Previous measurements have shown that a wide range of particle decays are consistent with this principle of lepton universality. 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. 178, 852867 (2008). Blum, A., Kalai, A. Lett. LHCb experiment - Wikipedia In the electron case, a 40MeV c2 window around the D0 mass is used to reject candidates where the veto is applied without the bremsstrahlung recovery, that is, on the basis of only the measured track momenta. Bainbridge, R. on behalf of the CMS collaboration Recording and reconstructing 10 billion unbiased b hadron decays in CMS. These two processes are separated by applying a requirement on q2. (Top) distributions of the reconstructed spectra of (left) the angle between the leptons, (+,), and (right) the minimum pT of the leptons for B+K++ and B+J/(+)K+ decays. The performance of the particle identification requirements is then evaluated from the proportion of events in these samples which fulfil the particle identification selection criteria. 12, 131 (2014). In addition to affecting the decay rates, new physics can also alter how the decay products are distributed in phase space. Phys. Savoie Mont Blanc, CNRS, IN2P3-LAPP, Annecy, France, M. Chefdeville,D. Decamp,A. G. Downes,Ph. The mass distributions are shown in Extended Data Fig. Handling of the generation of primary events in Gauss, the LHCb simulation framework. J. Sun, Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia, I. Belov,A. Berezhnoy,I. V. Gorelov,M. Korolev,A. Leflat,N. Nikitin,D. Savrina&V. Zhukov, Institute of Theoretical and Experimental Physics NRC Kurchatov Institute (ITEP NRC KI), Moscow, Russia, I. Belyaev,A. Danilina,V. Egorychev,D. Golubkov,P. Gorbounov,A. Konoplyannikov,T. Kvaratskheliya,V. Matiunin,T. Ovsiannikova,D. Pereima,D. Savrina,A. Semennikov&A. Smetkina, INFN Laboratori Nazionali di Frascati, Frascati, Italy, G. Bencivenni,L. Calero Diaz,S. Cali,P. Campana,P. Ciambrone,P. De Simone,P. Di Nezza,M. Giovannetti,G. Lanfranchi,G. Morello,M. Palutan,M. Poli Lener,M. Rotondo,M. Santimaria&B. Sciascia, LPNHE, Sorbonne Universit, Paris Diderot Sorbonne Paris Cit, CNRS/IN2P3, Paris, France, E. Ben-Haim,P. Billoir,L. Calefice,M. Charles,L. Del Buono,S. Esen,M. Fontana,V. V. Gligorov,T. Grammatico,F. Polci,R. Quagliani,D. Y. Tou,P. Vincent&S. G. 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