The B+J/(+)K+ events selected from the data have also been used to demonstrate control of the electron track reconstruction efficiency at the percent level90. 12, 040 (2007). Yields of the nonresonant and resonant decay modes obtained from the fits to the data. Eur. Phys. Confirmation of any effect beyond the SM will clearly require independent evidence from a wide range of sources. The LHCb collaboration et al. For each of the classifiers, a requirement is placed on the output variable to maximize the predicted significance of the non-resonant signal yield. The value of rJ/ is measured to be 0.9810.020. Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands, R. Aaij,J. S. Butter,K. Carvalho Akiba,S. Ferreres Sole,E. Gabriel,R. E. Geertsema,L. M. Greeven,K. Heijhoff,W. Hulsbergen,D. Hynds,E. Jans,S. Klaver,P. Koppenburg,I. Kostiuk,H. S. Kuindersma,M. Lucio Martinez,V. Lukashenko,A. Mauri,M. Merk,A. Pellegrino,C. Sanchez Gras,M. Schubiger,A. Snoch,N. Tuning,A. Usachov,M. van Beuzekom&M. Veronesi, Physik-Institut, Universitt Zrich, Zrich, Switzerland, C. Abelln Beteta,M. Atzeni,R. Bernet,C. Betancourt,Ia. High. To suppress background, each final-state particle is required to have sizeable pT and to be inconsistent with coming from a PV. High Energy Phys. The orange shaded area corresponds to B+K+e+e candidates with true q2 (\({q}_{{{{\rm{t}}}}rue}^{2}\)) outside the [1.1,6.0] GeV 2/c4 interval. Precision measurements of \({{{\mathcal{B}}}}[\psi (3686)\to \ \ {\pi }^{+}{\pi }^{-}J/\psi ]\) and \({{{\mathcal{B}}}}[J/\psi \to \ \ {\ell }^{+}{\ell }^{-}]\). Lyon, J., & Zwicky, R. Resonances gone topsy turvythe charm of QCD or new physics in bs+? universality in B-meson decays. ISSN 1745-2481 (online) Uncertainties on the data points are statistical only and represent one standard deviation. Classification and Regression Trees (Wadsworth, 1984). Energy Phys. Eur. provides an independent validation of the double-ratio analysis procedure and further tests the control of the efficiencies. Altmannshofer, W., Niehoff, C., Stangl, P. & Straub, D. M. Status of the BK*+ anomaly after Moriond 2017. The LHCb collaboration et al. High Energy Phys. Lett. Rev. Test of lepton flavour universality in beauty-quark decays The resulting variations are typically at the permille level and hence well within the estimated systematic uncertainty on RK. Lepton universality is the idea that all three types of charged lepton particles - electrons, muons and taus - interact in the same way with other particles. A weighted least-squares method is then employed to find the precise vertex position. Phys. To avoid unconscious bias, the analysis procedure was developed and the cross-checks described below performed before the result for RK was examined. Phys. Article The LHCbdetector at the LHC. The electron and muon veto cuts differ given the relative helicity suppression of ++ decays. 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. 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. 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. LHCb explores the beauty of lepton universality - phys.org 2017, 36 (2017). The LHCb collaboration et al. Eur. 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. 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. Lett. Test of the universality of and lepton couplings in W-boson decays with the ATLAS detector, A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery, Search for charged-lepton-flavour violation in Z-boson decays with the ATLAS detector, Evidence for intrinsic charm quarks in the proton, Precise determination of the J. For the non-resonant muon mode and for each of the three different trigger categories of the non-resonant electron mode, a single BDT classifier is trained for the 7 and 8TeV data, and an additional classifier is trained for the 13TeV data. High. Test of lepton universality with B0K*0+ decays. Nucl. Beauty quarks don't exist in large numbers in the world around as they are incredibly short-lived surviving on average for just a trillionth of a second before transforming or decaying into other particles. Rev. The veto requirements retain 97% of B+K++ and 95% of B+K+e+e decays passing all other selection requirements. The signal mass shapes of the electron modes are described with the sum of three distributions, which model whether the ECAL energy deposit from a bremsstrahlung photon was added to both, either or neither of the e candidates. Internet Explorer). This is the most precise measurement to date and is consistent with the SM expectation, 1.000.01 (refs. This causes misidentification backgrounds to populate a range of K masses but only a peak in the Ke mass. An uncertainty comparable to that from the modelling of the signal and background components is induced by the limited sizes of calibration samples. Comput. The double ratio of branching fractions, R(2S), defined by. Ciuchini, M. et al. 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. Phys. Breiman, L., Friedman, J. H., Olshen, R. A., & Stone C. J. The fit projections for the m(K++) and mJ/(K++) distributions are shown in Fig. Test of lepton universality in beauty-quark decays - arXiv Vanity 3). D 88, 072012 (2013). 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. Serra, N., Silva Coutinho, R. & van Dyk, D. Measuring the breaking of lepton flavor universality in BK*+. Article Aad, G. et al. Measurements from Run 1 of decays of beauty hadrons at the LHCb experiment, in addition to earlier results from the B-facto - Beauty quarks test lepton universality A series of measurements from LHCb and B-factory experiments have tested whether the interactions of charged leptons agree with the Standard Model. Phys. Bremsstrahlung photons can be added to none, either or both of the final-state e+ and e candidates. Predictions for lepton flavor universality violation in rare B decays in models with gauged LL. Energy Phys. Beating the hold-out: bounds for K-fold and progressive cross-validation. decays of heavy quarks. Background from decays with a photon converted into an e+e pair are also negligible due to the q2 selection. For the electron mode, this requirement is illustrated in Extended Data Fig. 124, 161803 (2020). 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. Distribution of the invariant mass m(K++) for nonresonant candidates in the (left) sample previously analysed11 and (right) the new data sample. Aaltonen, T. et al. High Energy Phys. 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. The particle identification performance is calibrated using data, where the species of particles in the final state can be unambiguously determined purely on the basis of the kinematics. Such studies can help to explain the matter-antimatter asymmetryof the Universe. {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. Test of lepton universality in beauty-quark decays - CERN Document Server 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. The systematic uncertainty (Methods) from the choice of signal and background mass-shape models in the fits is estimated by fitting pseudo-experiments with alternative models that still describe the data well. J. Previous measurements have shown a wide range of particle decays are consistent with this principle of lepton universality. & Maiani, L. Weak interactions with leptonhadron symmetry. 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. After the application of the selection requirements, the resonant and non-resonant decays are clearly visible in the mass distributions (Fig. J. 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. (2016). You are using a browser version with limited support for CSS. where the first uncertainty is statistical and the second systematic. Flavor probes of axion-like particles | SpringerLink This symmetry is called lepton avour universality (LFU) and is established in for example /0! For the resonant modes, the results from independent fits to each period/category are shown. 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. Allison, J. et al. Electroweak Penguin Decays at LHCb - ResearchGate Test of lepton universality in beauty-quark decays (Journal Article D 88, 032007 (2013). To take into account the correlation between the selection efficiencies, the m(K+e+e) and m(K++) distributions of non-resonant candidates in each of the different trigger categories and data-taking periods are fitted simultaneously, with a common value of RK. 1, left). B 753, 424448 (2016). This resolution scaling changes the migration of candidates into the q2 region of interest by less than 1%. 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. 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. To obtain A breaking of lepton universality would require an extension of the gauge structure of the SM that gives rise to the known fundamental forces. J. The ratio of branching fractions, RH (refs. 113, 151601 (2014). Phys. The likelihood is non-Gaussian in the region RK>0.95 due to the comparatively low yield of B+K+e+e events. The distributions are all normalised to unity. Lett. Rev. Martnez Santos, D. & Dupertuis, F. Mass distributions marginalized over per-event errors. An example distribution, with rJ/ determined as a function of B+ momentum component transverse to the beam direction, pT, is shown in Fig. D 69, 074020 (2004). LHCb collaboration. The first decay involves the electron and the second the muon, another elementary particle similar to the electron but approximately 200 times heavier. & Virto, J. . 4. s According to the Standard Model of particle physics, particles such as beauty quarks should decay into either muons or electrons in equal measure. D 97, 072013 (2018). 331, 032047 (2011). Energy Phys. Extended Data Table 1 Nonresonant and resonant mode. Conf. Rev. 2020, 40 (2020). In the latter two decays, the kaon is misidentified as a lepton and the lepton (of the same electric charge) as a kaon. Test of lepton universality in beauty-quark decays Eur. Jan 2019; PHYS REV LETT; Conversely, the non-resonant distributions show the projections from the simultaneous fit across data-taking periods and trigger categories that is used to obtain RK. Bainbridge, R. on behalf of the CMS collaboration Recording and reconstructing 10 billion unbiased b hadron decays in CMS. Test of lepton universality in beauty-quark decays - Nature What our students say. Beauty quarks test lepton universality - CERN Courier Correlations in the systematic uncertainties between different trigger categories and run periods are taken into account. These two processes are separated by applying a requirement on q2. D 97, 012004 (2018). Lett. The theory predicts that the di erent charged leptons, the electron, muon and tau, have identical electroweak interaction strengths. B-decay discrepancies after Moriond 2019. Phys. Quantum field theory allows such a process to be mediated by virtual particles that can have a physical mass larger than the energy available in the interaction. PDF Beauty quarks test lepton universality - cds.cern.ch This is known as lepton universality. In addition, the likelihood profile shown in Extended Data Fig. Measurement of branching fractions and rate asymmetries in the rare decays BK(*)+. Rev. Other sources of systematic uncertainty, such as the calibration of B+ production kinematics, the trigger calibration and the determination of the particle identification efficiencies, contribute at the few-permille or permille level, depending strongly on the data-taking period and the trigger category. Likhomanenko, T. et al. Lett. Phys. CERN https://cds.cern.ch/record/2636441 (2019). The LHCb trigger system has a hardware stage, based on information from the calorimeter and muon systems, followed by a software stage that uses all the information from the detector, including the tracking, to make the final selection of events to be recorded for subsequent analysis.