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. 11,12, the P value is computed by integrating the posterior probability density function for RK, having folded in the theory uncertainty on the SM prediction, for RK values larger than the SM expectation. 178, 852867 (2008). Test of lepton universality in beauty-quark decays. LHCb collaboration. Test of lepton universality in beauty-quark decays Lett. Eur. 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. A comparison with previous measurements is shown in Fig. In particular, in the RK ratio, the denominator is affected by larger statistical uncertainties than the numerator, owing to the larger number of non-resonant muonic signal candidates. The Belle II physics book. 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. 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. 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. Part. Khodjamirian, A. A B+ meson, consisting of \(\overline{b}\) and uquarks, decays into a K+, containing \(\overline{s}\) and uquarks, and two charged leptons, +. Program of Guangzhou (China); RFBR, RSF and Yandex LLC (Russia); GVA, XuntaGal and GENCAT (Spain); the Leverhulme Trust, the Royal Society and UKRI (United Kingdom). 2018, 47 (2018). D 96, 093006 (2017). So far, LHCb has collected 260 billion bottom-quark antiquark pairs in experimental runs using protons with 7 and 8 tera-electron-volt (TeV) center-of-mass energies. This is the most precise measurement of this quantity to date and, given the large (\({{{\mathcal{O}}}}(10 \%)\)) theoretical uncertainty on the predictions7,66, is consistent with the SM. (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. Charpentier,G. Ciezarek,M. Clemencic,J. Closier,V. Coco,P. Collins,T. Colombo,G. Corti,B. Couturier,C. DAmbrosio,P. dArgent,H. Dijkstra,L. Dufour,P. Durante,T. Evans,M. Fo,M. Ferro-Luzzi,R. Forty,M. Frank,C. Frei,W. Funk,S. Gambetta,C. Gaspar,C. Giugliano,E. L. Gkougkousis,E. Govorkova,L. A. Granado Cardoso,T. Gys,C. Haen,J. Haimberger,C. Hasse,M. Hatch,A. M. Hennequin,R. Jacobsson,S. Jakobsen,D. Johnson,B. Jost,N. Jurik,M. Karacson,F. Keizer,R. D. Krawczyk,D. Lacarrere,R. Lindner,B. Malecki,C. Marin Benito,L. Martinazzoli,R. Matev,Z. Mathe,M. Mazurek,M. Mikhasenko,M. Milovanovic,D. S. Mitzel,F. Muheim,M. Mulder,D. Mller,P. Muzzetto,N. Neufeld,P. R. Pais,A. Pearce,M. Pepe Altarelli,M. Petric,F. Pisani,S. Ponce,D. Popov,L. Promberger,P. Roloff,T. Ruf,M. Salomoni,H. Schindler,B. Schmidt,A. Schopper,R. Schwemmer,P. Seyfert,F. Stagni,S. Stahl,M. Szymanski,F. Teubert,E. Thomas,N. Tuning,A. Valassi,C. Vzquez Sierra,K. Wyllie&O. Zenaiev, School of Physics and Astronomy, University of Glasgow, Glasgow, UK, M. Alexander,D. Bobulska,G. Coombs,L. Douglas,L. Eklund,D. A. Friday,I. Longstaff,M. Petric,G. Sarpis,M. Schiller,F. J. P. Soler&P. Spradlin, ICCUB, Universitat de Barcelona, Barcelona, Spain, A. Alfonso Albero,A. Camboni,J. M. Fernandez-tenllado Arribas,P. Garcia Moreno,L. Garrido,P. Gironella Gironell,S. Gomez Fernandez,E. Graugs,J. Mauricio&D. Sanchez Gonzalo, Department of Physics and Astronomy, University of Manchester, Manchester, UK, Z. Aliouche,R. J. Barlow,A. Bitadze,S. Borghi,J. L. Cobbledick,A. Davis,O. A. Rodriguez Lopez, Universitt Bonn Helmholtz-Institut fr Strahlen und Kernphysik, Bonn, Germany, Hanoi University of Science, Hanoi, Vietnam, P.N. The classifier includes the following variables: the pT of the B+, K+ and dilepton candidates, and the minimum and maximum pT of the leptons; the B+, dilepton and K+\({\chi }_{{{{\rm{IP}}}}}^{2}\) with respect to the associated PV, where \({\chi }_{{{{\rm{IP}}}}}^{2}\) is defined as the difference in the vertex-fit 2 of the PV reconstructed with and without the considered particle; the minimum and maximum \({\chi }_{{{{\rm{IP}}}}}^{2}\) of the leptons; the B+ vertex-fit quality; the statistical significance of the B+ flight distance; and the angle between the B+ candidate momentum vector and the direction between the associated PV and the B+ decay vertex. Handling of the generation of primary events in Gauss, the LHCb simulation framework. 08, 098 (2016). This gives. Candidate B+K++ decays are found by combining the reconstructed trajectory (track) of a particle identified as a charged kaon, together with the tracks from a pair of well-reconstructed oppositely charged particles identified as either electrons or muons. Sign up for the Nature Briefing newsletter what matters in science, free to your inbox daily. D 73, 092001 (2006). High Energy Phys. J. Mod. Test of lepton universality in beauty-quark decays. The proportion of signal candidates that migrate in and out of the q2 region of interest is on the order of 10%. The value of RK is found to be consistent in subsets of the data divided on the basis of data-taking period, different selection categories and magnet polarity (Methods). Phys. Test of lepton universality in beauty-quark decays Standard Model of particle physics currently predicts that the different charged leptons, the electron, muon and tau, have identical electroweak interaction strengths. ISSN 1745-2473 (print). The y-axis in each figure shows the number of candidates in an interval of the indicated width. Sjstrand, T., Mrenna, S. & Skands, P. A brief introduction to PYTHIA 8.1. Zenodo https://doi.org/10.5281/zenodo.4586379 (2021). Rev. Recent evidence of a possible fifth force of nature Measurement of the branching ratio of \({\overline{B}}^{0}\to {D}^{* +}{\tau }^{-}{\overline{\nu }}_{\tau }\) relative to \({\overline{B}}^{0}\to {D}^{* +}{\ell }^{-}{\overline{\nu }}_{\ell }\) decays with a semileptonic tagging method. Rev. J. EPJ Web Conf. https://doi.org/10.1038/s41567-021-01478-8, DOI: https://doi.org/10.1038/s41567-021-01478-8. J. Phys. Particle Data Group et al. Extended Data Fig. Conf. Khodjamirian, A., Mannel, T., Pivovarov, A. Measurable quantities can be predicted precisely in the decays of a charged beauty hadron, B+, into a charged kaon, K+, and two charged leptons, +. http://creativecommons.org/licenses/by/4.0/, Heavy flavour physics and CP violation at LHCb: A ten-year review, New UTfit analysis of the unitarity triangle in the CabibboKobayashiMaskawa scheme, Hint of crack in standard model vanishes in LHC data, How the revamped Large Hadron Collider will hunt for new physics. Test of lepton universality with B0K*0+ decays. Given the scale of the corrections required, comparison of rJ/ with unity is a stringent cross-check of the experimental procedure. 126, 161801 (2021). The decay process involves the conversion of a beauty quark into a strange quark with the production of an electron and antielectron or a muon and antimuon. 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. Google Scholar. To obtain The correlation is evaluated using a bootstrapping method to recompute the yields and efficiencies many times with different subsets of the data. 12, 040 (2007). Phys. 2016, 104 (2016). For the electron modes, in addition to combinatorial background, other specific background decays contribute significantly in the signal region. For the resonant modes, the results from independent fits to each period/category are shown. Eur. The LHCb collaboration et al. Has a new particle called a 'leptoquark' been spotted at CERN? Lett. Khodjamirian, A., Mannel, T. & Wang, Y.-M. BK+ decay at large hadronic recoil. 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 region to the left of the vertical dashed line is rejected. The theory predicts that the different charged leptons, the electron, muon and tau . Angular analysis of the B0K*0+ decay using 3fb1 of integrated luminosity. The rJ/ ratio is therefore also computed as a function of different kinematic variables. Lange, D. J. Chat with our students. A test statistic is constructed that is based on the likelihood ratio between two hypotheses with common (null) or different (test) RK values for the part of the sample analysed previously (7, 8 and part of the 13TeV data) and for the new portion of the 13TeV data. The mass-shape parameters are derived from the calibrated simulation. The decays involve the transformation of a beauty quark into a strange quark (bs) plus a lepton pair ( + - or e + e - ), a process that is highly suppressed in the Standard Model but which could be affected by the existence of new particles, whose masses could be too high to be produced directly at the Large Hadron Collider. Measurements of the angular distributions in the decays BK(*)+ at CDF. 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. These two processes are separated by applying a requirement on q2. & Atwood, D. Rate difference between bs+ and bse+e in supersymmetry with large tan . Phys. The standard model of particle physics currently provides our best description of fundamental particles and their interactions. Rev. We investigate the phenomenology of an ALP with flavor-changing couplings, and present a comprehensive analysis of quark and lepton flavor-changing observables within a general ALP effective field theory. The latter also tend to accumulate around specific values of m(K++). Bainbridge, R. on behalf of the CMS collaboration Recording and reconstructing 10 billion unbiased b hadron decays in CMS. 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. Energy Phys. & Langford J. High. 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. Likhomanenko, T. et al. To avoid unconscious bias, the analysis procedure was developed and the cross-checks described below performed before the result for RK was examined. where the first uncertainty is statistical and the second systematic. 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. 108, 081807 (2012). In all fits, the combinatorial background is modelled with an exponential function with a freely varying yield and shape. Altmannshofer, W. & Yavin, I. Steven D. Bass, Albert De Roeck & Marumi Kado, Nature Physics The overall effect of these corrections on the measured value of RK is a relative shift of (+31)%. 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. Jger, S. and Martin, J. Aaij, R. et al. Phys. 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. Phys. C 79, 840 (2019). A distinctive feature of the SM is that the different leptons, electron (e), muon () and tau (\(\tau^{-}\)), have the same interaction strengths. 37), taking into account correlated systematic uncertainties. Simulated events are weighted to correct for the imperfect modelling using control channels. The muon BDT classifier has similar performance. Yields of the nonresonant and resonant decay modes obtained from the fits to the data. 12th Annual Conference on Computational Learning Theory, COLT 99 203208 (ACM, 1999). The LHCb collaboration et al. Rev. Linear (top) and logarithmic (bottom) scales are shown. In the meantime, to ensure continued support, we are displaying the site without styles 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. Tomassetti, INFN Sezione di Milano-Bicocca, Milano, Italy, M. Calvi,S. Capelli,P. Carniti,D. Fazzini,J. Garca Pardias,C. Gotti,M. Martinelli,C. Matteuzzi,S. Meloni&E. B. Shields, Universit di Milano Bicocca, Milano, Italy, M. Calvi,S. Capelli,P. Carniti,D. Fazzini,J. Garca Pardias,L. Martinazzoli,M. Martinelli,S. Meloni&E. B. Shields, DS4DS, La Salle, Universitat Ramon Llull, Barcelona, Spain, M. Calvo Gomez,A. Camboni,E. Golobardes,N. Valls Canudas&X. Vilasis-Cardona, University of Chinese Academy of Sciences, Beijing, China, A. F. Campoverde Quezada,Y. Phys. 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). Phys. This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on protonproton collision data collected with the LHCb detector at CERNs Large Hadron Collider. The measurements are of processes in which a beauty meson transforms into a strange meson with . Phys. Similarly, the differing q2 resolution between data and simulation, which alters estimates of the q2 migration, has negligible impact on the result. 2019, 89 (2019). In addition, rJ/ is computed in two-dimensional intervals of reconstructed quantities (Extended Data Fig. CERN https://cds.cern.ch/record/2636441 (2019). The shape of the B+J/+ background contribution is taken from simulation, but the size with respect to the B+J/K+ mode is constrained using the known ratio of the relevant branching fractions2,94 and efficiencies. Energy Phys. D 96 (2017) 095010 [ arXiv:1704.06659] [ INSPIRE ]. The fit projection is superimposed, with a black dotted line describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend. C 74, 2897 (2014); erratum 74, 3179 (2014). Uncertainties on the data points are statistical only and represent one standard deviation. ADS The value of q2 is calculated using only the lepton momenta, without imposing any constraint on the m(K++) mass. High. Beauty quarks test lepton universality - CERN Courier The double ratio of branching fractions, R(2S), defined by. The yields in the two B+K++ and two B+J/(+)K+ decay modes are determined by performing unbinned extended maximum-likelihood fits to these distributions (Methods). The techniques used to identify the different particles and to form B+ candidates are described in Methods. Rev. PDF Test of lepton universality in beauty-quark decays - DiVA portal 2015, 179 (2015). The four signal modes are modelled by multiple Gaussian functions with power-law tails on both sides of the peak91,92, although the differing detector response gives different shapes for the electron and muon modes. 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. Commun. Rev. In summary, in the dilepton mass-squared region 1.1\) as a function of these variables. The simulated data used in this analysis are produced using the software described in refs. In the remainder of this paper, the notation B+K++ is used to denote only decays with 1.1Physics - A Challenge to Lepton Universality Such decays are highly suppressed1, and the fraction of B+ hadrons that decay into this final state (the branching fraction, \({{{\mathcal{B}}}}\)) is on the order of 106 (ref. D 89, 074014 (2014). Phys. Flavor probes of axion-like particles | SpringerLink Wehle, S. et al. Previous measurements have shown that a wide range of particle decays are consistent with this principle of lepton universality.