Provided by the Springer Nature SharedIt content-sharing initiative, Rendiconti Lincei. Lees, J. P. et al. This effect is accounted for using simulation (Extended Data Figs. Energy Phys. Rev. J. A weighted least-squares method is then employed to find the precise vertex position. (Left, with log y-scale) the bremsstrahlung correction to the momentum of the electron is applied, resulting in a tail to the right. D 88, 072012 (2013). Individual groups or members have received support from ARC and ARDC (Australia); AvH Foundation (Germany); EPLANET, Marie Skodowska-Curie Actions and ERC (European Union); A*MIDEX, ANR, Labex P2IO and OCEVU, and Rgion Auvergne-Rhne-Alpes (France); Key Research Program of Frontier Sciences of CAS, CAS PIFI, CAS CCEPP, Fundamental Research Funds for the Central Universities, and Sci. Bay,V. Bellee,F. Blanc,S. A. Bouchiba,S. Celani,S. Cholak,M. De Cian,S. Ek-In,L. Ferreira Lopes,E. Graverini,G. Haefeli,D. Hill,V. S. Kirsebom,V. Macko,M. Marinangeli,T. Nakada,T. Nanut,T. D. Nguyen,C. Nguyen-Mau,G. Pietrzyk,F. Redi,A. Measurement of \({{{\mathcal{R}}}}(D)\) and \({{{\mathcal{R}}}}({D}^{* })\) with a semileptonic tagging method. Belyaev, I. et al. The effect on RK is at the 1% level. Measurements of the S-wave fraction in B0K++ decays and the B0K*(892)0+ differential branching fraction. A. Conf. For illustration, the expected distribution of signal candidates with true q2 outside the interval [1.1,6.0]GeV2/c4 is shown as a grey dashed and dotted line. The experiment is designed to study decays of particles containing a beauty quark, a fundamental particle that has roughly four times the mass of the proton. 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. Rev. Alok, A. K., Dighe, A., Gangal, S. & Kumar, D. Continuing search for new physics in bs decays: two operators at a time. Rev. The fit projection is superimposed, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend. Rev. 2016, 47 (2016); erratum 2017, 142 (2017). High. The relative fraction of partially reconstructed background in each trigger category is also shared across the different data-taking periods. High Energy Phys. Hint of lepton flavour non-universality in B meson decays. Explore our virtual experience Thank you for visiting nature.com. C 79, 719 (2019). The value of q2 is calculated using only the lepton momenta, without imposing any constraint on the m(K++) mass. 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. 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). LHCb collaboration. Phys. The EvtGen particle decay simulation package. 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. Energy Phys. Allison, J. 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. J. Phys. provides an independent validation of the double-ratio analysis procedure and further tests the control of the efficiencies. B 753, 424448 (2016). Test of lepton universality in beauty-quark decays, arXiv:2103.1176 . 109, 101802 (2012). Altmannshofer, W. & Straub, D. M. New physics in BK*? 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. Measurement of angular asymmetries in the decays BK*+. The ratio of branching fractions, RH (refs. The theory predicts that the different charged leptons, the electron, muon and tau, have identical electroweak interaction strengths. Assuming that the deviations observed are genuine mis-modelling of the efficiencies, rather than statistical fluctuations, a total shift of RK at a level less than 0.001 would be expected due to these effects. The measurement made by the LHCb team compares two types of decays of beauty quarks. Martnez Santos, D. & Dupertuis, F. Mass distributions marginalized over per-event errors. High Energy Phys. LHCb topological trigger reoptimization. s 199, 86101 (2016). Aubert, B. et al. Phys. Lett. J. Phys. Theor. The results indicate that particles are not behaving in the way they should. 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. 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Aaltonen, T. et al. Eur. 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. J. Instrum. Confirmation of any effect beyond the SM will clearly require independent evidence from a wide range of sources. Phys. 331, 032047 (2011). Rev. These differences arise due to the significant bremsstrahlung radiation emitted by the electrons and the different detector subsystems that are used to identify electron and muon candidates (Methods). Measurement of the branching ratio of \({B}^{0}\to \ \ {D}^{(*)}{\tau }^{-}{\overline{\nu }}_{\tau }\) relative to \(\overline{B}\to \ \ {D}^{(*)}{\ell }^{-}{\overline{\nu }}_{\ell }\) decays with hadronic tagging at Belle. J. D 69, 074020 (2004). The LHCb collaboration et al. The vertical dashed line indicates the SM prediction. J. & Virto, J. Rev. J. J. J. Exp. 4. Sjstrand, T., Mrenna, S. & Skands, P. PYTHIA 6.4 physics and manual. Wang, Y. 3,4,5,6,7), at the level of 0.10% (3.1 standard deviations), giving evidence for the violation of lepton universality in these decays. Only potentially interesting events, selected using real-time event filters referred to as triggers, are recorded. The profile likelihood is given in Methods. CMS collaboration Angular analysis of the decay B0K*0+ from pp collisions at \(\sqrt{s}=8\) TeV. Test of lepton universality using B+K++ decays. The standard model of particle physics currently provides our best description of fundamental particles and their interactions. Extensions to the SM that aim to address many of its shortfalls predict new virtual particles that could contribute to \(\overline{b}\to \overline{s}\) transitions (Fig. 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. 120, 121801 (2018). Background from decays with a photon converted into an e+e pair are also negligible due to the q2 selection. Lett. We thank our colleagues in the CERN accelerator departments for the excellent performance of the LHC, and the technical and administrative staff at the LHCb institutes. 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. Phys. This is the most precise measurement to date and is consistent with the SM expectation, 1.000.01 (refs. Lett. Systematic uncertainties affecting the determination of the signal yield are assessed using pseudo-experiments generated with variations of the fit model. To obtain Bainbridge, R. on behalf of the CMS collaboration Recording and reconstructing 10 billion unbiased b hadron decays in CMS. An example distribution, with rJ/ determined as a function of B+ momentum component transverse to the beam direction, pT, is shown in Fig. The quoted uncertainty is the combination of statistical and systematic effects. Uncertainties on the data points are statistical only and represent one standard deviation. This is known as lepton universality. Isidori, G., Nabeebaccus, S. & Zwicky, R. QED corrections in \(\overline{B}\to \overline{K}{{{{\rm{\ell }}}}}^{+}{{{{\rm{\ell }}}}}^{-}\) at the double-differential level. High Energy Phys. Phys. Each top (antitop) quark decays almost immediately into a bottom b ( b) quark and a W+ ( W -) boson, and we have reexamined those events in which one of the W bosons decays into a charged. 118, 031802 (2017). 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. D 2, 12851292 (1970). Energy Phys. 9,10), is defined in the dilepton mass-squared range \({q}_{\min }^{2} < {q}^{2} < {q}_{\max }^{2}\) as. Geant4 developments and applications, IEEE Trans. Lett. All contributing authors, as listed at the end of the manuscript, have contributed to the publication, being variously involved in the design and construction of the detector, writing software, calibrating sub-systems, operating the detector, acquiring data and analysing the processed data. There are excellent prospects for all of the above and further measurements with the much larger samples that will be collected with the upgraded LHCb detector from 2022 and, in the longer term, with the LHCb Upgrade II71. Analogous background sources with a misidentified particle are reduced by applying a similar veto, but with the lepton mass hypothesis changed to that of a pion (denoted []). 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. Test of lepton universality in beauty-quark decays. The 1.9% uncertainty on the B+J/K+ branching fraction2 gives rise to the dominant systematic uncertainty. Phys. Particle Physics (4th ed. Instrum. Test of lepton universality using B 0 K S 0 l + l- and B + K* + l + l- decays.. Today at the CERN seminar and at the Rencontres de Blois the LHCb Collaboration presented new tests of lepton universality, one of the basic principles of the Standard Model (SM) of particle physics. Blum, A., Kalai, A. In the electron minimum pT spectra, the structure at 2800 MeV/c is related to the trigger threshold. The correlation is evaluated using a bootstrapping method to recompute the yields and efficiencies many times with different subsets of the data. In the software trigger, the tracks of the final-state particles are required to form a displaced vertex with good fit quality. The standard model of particle physics currently provides our best description of fundamental particles and their interactions. Back,T. Blake,A. Brossa Gonzalo,M. F. Cicala,C. M. Costa Sobral,L. M. Garcia Martin,T. Gershon,R. J. Rev. 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. However, a bremsstrahlung photon emitted upstream of the magnet will deposit energy in a different part of the ECAL than the electron, which is deflected in the magnetic field. Phys. J. C77, 377 (2017). Measurement of CP-averaged observables in the B0K*0+ decay. where N(X) indicates the yield of decay mode X and (X) is the efficiency for selecting decay mode X. Article In addition to the LHCb result, the measurements by the BaBar15 and Belle13 collaborations, which combine B+K++ and \({B}^{0}\to {K}_{{{{\rm{S}}}}}^{0}{\ell }^{+}{\ell }^{-}\) decays, are also shown. Phys. High Energy Phys. J. Phys. 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. Agostinelli, S. et al. The Standard Model predicts that this occurs via electroweak bosons and the W + and Z 0 particles. LHCb collaboration et al. The efficiency of the non-resonant B+K+e+e decay therefore needs to be known only relative to that of the resonant B+J/(e+e)K+ decay, rather than relative to the B+K++ decay. C 82, 7 (2022). Geng, L.-S. et al. J. The theory predicts that the different charged leptons, the electron, muon and tau . Phys. Ratio between the likelihood value (L) and that found by the fit (\({L}_{\max }\)) as a function of RK. Phys. The Standard Model of particle physics currently provides our best description of fundamental particles and their interactions. 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. 10, 075 (2016). Gligorov, V. V. & Williams, M. Efficient, reliable and fast high-level triggering using a bonsai boosted decision tree. 2017, 112 (2017). Pion electronic decay and lepton universality License CC BY 4.0 Authors: Dinko Pocanic Abstract In common with a number of simple processes involving elementary particles, charged pion decays. 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 Aaij, R. et al. 3 Resonant candidates invariant mass distributions. Capdevila, B., Descotes-Genon, S., Matias, J. J. Search for lepton-universality violation in B+K++ decays. High Energy Phys. Fan,Y. Gan,G. Gong,C. Gu,F. Jiang,Y. Kang,X. Liu,Y. Luo,H. Mu,Z. Ren,J. Wang,M. Wang,Z. Wang,L. Xu,D. Yang,Z. Yang,M. Zeng,L. Zhang&X. Zhu, School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK, P. E. L. Clarke,R. Currie,S. Eisenhardt,S. Gambetta,K. Gizdov,S. E. Mitchell,F. Muheim,M. Needham,S. Petrucci,G. Robertson,M. R. J. Williams&J. Electrons are identified by matching tracks to particle showers in the electromagnetic calorimeter (ECAL) and using the ratio of the energy detected in the ECAL to the momentum measured by the tracking system. The y axis in each panel shows the number of candidates in an interval of the indicated width. 2014, 133 (2014). The 3,85070 B+K++ decay candidates that are observed are used to compute the B+K++ branching fraction as a function of q2. Energy Phys. Conversely, lepton universality is an accidental symmetry of the SM, which is not a consequence of any axiom of the theory. High Energy Phys. Today at the Rencontres de Moriond EW conference, the LHCb Collaboration presented an updated measurement of the ratio R K, an important test of a principle of the Standard Model of particle physics known as " lepton universality ", which states that the Standard Model treats the three charged leptons (electrons, muons and . An angular analysis of the electron mode, where SM-like behaviour might be expected in the light of the present results and those from \(\overline{b}\to \overline{s}{\mu }^{+}{\mu }^{-}\) decays, would allow the formation of ratios between observable quantities other than branching fractions, enabling further precise tests of lepton universality16,18,31,67,68. J. Other experiments should also be able to determine RH ratios, with the Belle II experiment in particular expected to have competitive sensitivity72. J. Uncertainties on the data points are the combination of statistical and systematic and represent one standard deviation. The theory predicts that the different charged leptons, the electron, muon and tau, have . Rev. volume18,pages 277282 (2022)Cite this article. Lepton avour universality tests in electroweak penguin decays at LHCbSebastian Schmitt 1. 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. The theory predicts that the di erent charged leptons, the electron, muon and tau, have identical electroweak interaction strengths. The red line indicates the prediction from the SM. J. Instrum. The particles are required to originate from a common vertex, displaced from the protonproton interaction point, with good vertex-fit quality. Previous measurements have shown that a wide range of particle decays are consistent with this principle of lepton universality. and JavaScript. The bias is found to be 1% of the statistical precision and thus negligible with respect to other sources of systematic uncertainty. Previous measurements have shown a wide range of particle decays are consistent with this principle of lepton universality. & Langford J. The measurements are of processes in which a beauty meson transforms into a strange meson with the emission of either an electron and a positron, or a muon and an antimuon. High. Uncertainties on the data points are statistical only and represent one standard deviation. The value of rJ/ is measured to be 0.9810.020. A consistent model-independent interpretation of all these data is possible via a modification of the \(\overline{b}\to \overline{s}\) coupling strength48,49,50,51,52,53,54. The weights are calculated by requiring that simulated B+J/(+)K+ events exhibit the same trigger performance as the control data. The electron and muon veto cuts differ given the relative helicity suppression of ++ decays. The expected values from simulated events are used to constrain the fraction of signal decays in each of these categories. Uncertainties on the data points are statistical only and represent one standard deviation, calculated assuming Poisson-distributed entries. Horgan, R. R., Liu, Z., Meinel, S. & Wingate, M. Calculation of B0K*0+ and \({B}_{s}^{0}\to \ \ \phi {\mu }^{+}{\mu }^{-}\) observables using form factors from lattice QCD. 06, 092 (2016). Phys. C 78, 451 (2018). 108, 081807 (2012). The BDT output is not strongly correlated with q2, and the same classifiers are used to select the respective resonant decays. Phys. Van Hulse, NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine, STFC Rutherford Appleton Laboratory, Didcot, UK, S. Easo,R. Nandakumar,A. Papanestis,S. Ricciardi&F. F. Wilson, School of Physics and Astronomy, Monash University, Melbourne, Victoria, Australia, Novosibirsk State University, Novosibirsk, Russia, S. Eidelman,P. Krokovny,V. Kudryavtsev,T. Maltsev,L. Shekhtman&V. Vorobyev, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden, School of Physics State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, China, Y. Gao,Y. Shang,Z. Shen,J. Wang,A. Xu,Z. Xu,S. Zhang&Y. Zhang, National Center for Nuclear Research (NCBJ), Warsaw, Poland, H. K. Giemza,K. Klimaszewski,W. Krzemien,D. Melnychuk,A. Szabelski,A. Ukleja&W. Wislicki, Universit di Roma Tor Vergata, Roma, Italy, Pontifcia Universidade Catlica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, Universidade Federal do Tringulo Mineiro (UFTM), Uberaba-MG, Brazil, Institute of Particle Physics, Central China Normal University, Wuhan, China, Q. Han,W. Hu,S. Li,Y. Wang,D. Xiao,Y. Xie,M. Xu,H. Yin&D. Zhang, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China, Instituto de Fisica Corpuscular, Centro Mixto Universidad de Valencia - CSIC, Valencia, Spain, L. Henry,B. K. Jashal,F. Martinez Vidal,A. Oyanguren,C. Remon Alepuz&J. Ruiz Vidal, Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, Netherlands, T. Ketel,H. S. Kuindersma,G. Raven&M. Senghi Soares, National Research Tomsk Polytechnic University, Tomsk, Russia, Faculty of Computer Science, Electronics and Telecommunications, AGH University of Science and Technology, Krakw, Poland, National Research Centre Kurchatov Institute, Moscow, Russia, Universit degli Studi di Milano, Milano, Italy, D. Marangotto,N. Neri&E. Spadaro Norella, MSUIligan Institute of Technology (MSU-IIT), Iligan, Philippines, INFN Sezione di Roma La Sapienza, Roma, Italy, G. Martellotti,D. Pinci,R. Santacesaria,A. Sarti&C. Satriano, Institut fr Physik, Universitt Rostock, Rostock, Germany, Departamento de Fisica, Universidad Nacional de Colombia, Bogota, Colombia, D. A. Milanes,I. Instrum. Lett. $$B_{\mathrm{s}}^0$$ Correlations in the systematic uncertainties between different trigger categories and run periods are taken into account. D 88, 032007 (2013). Beaujean, F., Bobeth, C. & van Dyk, D. Comprehensive Bayesian analysis of rare (semi)leptonic and radiative B decays. Simulated events are weighted to correct for the imperfect modelling using control channels. The residual contribution from such decays is considered as a source of systematic uncertainty. Geant4: a simulation toolkit. Descotes-Genon, S., Hofer, L., Matias, J. The yields observed in these four decay modes and the ratios of efficiencies determined from simulated events then enable an RK measurement with statistically dominated uncertainties. Angular analysis and differential branching fraction of the decay \({B}_{s}^{0}\to \phi {\mu }^{+}{\mu }^{-}\). Sun&Z. Yang, Guangdong Provencial Key Laboratory of Nuclear Science, Institute of Quantum Matter, South China Normal University, Guangzhou, China, Institute for Nuclear Research of the Russian Academy of Sciences (INR RAS), Moscow, Russia, A. Butkevich,S. Filippov,E. Gushchin,L. Kravchuk&S. Luchuk, R. Calabrese,M. Fiorini,P. Griffith,E. Luppi,L. Minzoni,L. L. Pappalardo,I. Slazyk&L. 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