Determination of the quark coupling strength | V ub | using baryonic decays
LHCb collaboration, R. Aaij, B. Adeva, M. Adinolfi, A. Affolder, Z. Ajaltouni, S. Akar, J. Albrecht, F. Alessio, M. Alexander, S. Ali, G. Alkhazov, P. Alvarez Cartelle, A.A. Alves Jr, S. Amato, S. Amerio, Y. Amhis, L. An, L. Anderlini, J. Anderson, M. Andreotti, J.E. Andrews, R.B. Appleby, O. Aquines Gutierrez, F. Archilli, A. Artamonov, M. Artuso, E. Aslanides, G. Auriemma, M. Baalouch, S. Bachmann, J.J. Back, A. Badalov, C. Baesso, W. Baldini, R.J. Barlow, C. Barschel, S. Barsuk, W. Barter, V. Batozskaya, V. Battista, A. Bay, L. Beaucourt, J. Beddow, F. Bedeschi, I. Bediaga, L.J. Bel, I. Belyaev, E. Ben-Haim, G. Bencivenni, S. Benson, J. Benton, A. Berezhnoy, R. Bernet, A. Bertolin, M.-O. Bettler, M. van Beuzekom, A. Bien, S. Bifani, T. Bird, A. Birnkraut, A. Bizzeti, T. Blake, F. Blanc, J. Blouw, S. Blusk, V. Bocci, A. Bondar, N. Bondar, W. Bonivento, S. Borghi, M. Borsato, T.J.V. Bowcock, E. Bowen, C. Bozzi, S. Braun, D. Brett, M. Britsch, T. Britton, J. Brodzicka, N.H. Brook, A. Bursche, J. Buytaert, S. Cadeddu, R. Calabrese, M. Calvi, M. Calvo Gomez, P. Campana, D. Campora Perez, L. Capriotti, A. Carbone, G. Carboni, R. Cardinale, A. Cardini, P. Carniti, L. Carson, K. Carvalho Akiba, R. Casanova Mohr, G. Casse, L. Cassina, et al. (612 additional authors not shown)
EEUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
CERN-PH-EP-2015-084LHCb-PAPER-2015-01327 July, 2015
Determination of the quark couplingstrength | V ub | using baryonic decays The LHCb collaboration † Abstract
In the Standard Model of particle physics, the strength of the couplings of the b quark tothe u and c quarks, | V ub | and | V cb | , are governed by the coupling of the quarks to the Higgsboson. Using data from the LHCb experiment at the Large Hadron Collider, the probabilityfor the Λ b baryon to decay into the pµ − ν µ final state relative to the Λ + c µ − ν µ final state ismeasured. Combined with theoretical calculations of the strong interaction and a previouslymeasured value of | V cb | , the first | V ub | measurement to use a baryonic decay is performed.This measurement is consistent with previous determinations of | V ub | using B meson decaysto specific final states and confirms the existing incompatibility with those using an inclusivesample of final states. Published in Nature Physics c (cid:13) CERN on behalf of the LHCb collaboration, licence CC-BY-4.0. † Authors are listed at the end of this paper. a r X i v : . [ h e p - e x ] J u l in the Standard Model (SM) of particle physics,the decay of one quark to another by the emis-sion of a virtual W boson is described by the 3 × V ub , which describes thetransition of a b quark to a u quark.The magnitude of V ub can be measuredvia the semileptonic quark-level transition b → u(cid:96) − ν (cid:96) . Semileptonic decays are used tominimise the uncertainties arising from the in-teraction of the strong force, described by quan-tum chromodynamics (QCD), between the final-state quarks. For the measurement of the mag-nitude of V ub , as opposed to measurements ofthe phase, all decays of the b quark, and theequivalent b quark, can be considered together.There are two complementary methods to per-form the measurement. From an experimentalpoint of view, the simplest is to measure thebranching fraction (probability to decay to agiven final state) of a specific (exclusive) decay.An example is the decay of a B ( bd ) mesonto the final state π + (cid:96) − ν , where the influenceof the strong interaction on the decay, encom-passed by a B → π + form factor, is predictedby non-perturbative techniques such as latticeQCD (LQCD) [5] or QCD sum rules [6]. Theworld average from Ref. [7] for this method, us-ing the decays B → π + (cid:96) − ν and B − → π (cid:96) − ν ,is | V ub | = (3 . ± . × − , where themost precise experimental inputs come from theBaBar [8, 9] and Belle [10, 11] experiments. The uncertainty is dominated by the LQCD calcula-tions, which have recently been updated [12, 13]and result in larger values of V ub than the averagegiven in Ref. [7]. The alternative method is tomeasure the differential decay rate in an inclusiveway over all possible B meson decays contain-ing the b → u(cid:96) − ν quark level transition. Thisresults in | V ub | = (4 . ± . +0 . − . ) × − [14],where the first uncertainty arises from the ex-perimental measurement and the second fromtheoretical calculations. The discrepancy be-tween the exclusive and inclusive | V ub | determi-nations is approximately three standard devi-ations and has been a long-standing puzzle inflavour physics. Several explanations have beenproposed, such as the presence of a right-handed(vector plus axial-vector) coupling as an exten-sion of the SM beyond the left-handed (vectorminus axial-vector) W coupling [15–18]. A simi-lar discrepancy also exists between exclusive andinclusive measurements of | V cb | (the coupling ofthe b quark to the c quark) [14].This article describes a measurement of theratio of branching fractions of the Λ b ( bud )baryon into the p(cid:96) − ν and Λ + c (cid:96) − ν final states.This is performed using proton-proton collisiondata from the LHCb detector, corresponding to2.0 fb − of integrated luminosity collected at acentre-of-mass energy of 8 TeV. The b → u tran-sition, Λ b → pµ − ν µ , has not been considered be-fore as Λ b baryons are not produced at an e + e − B -factory; however, at the LHC, they consti-tute around 20% of the b -hadrons produced [19].These measurements together with recent LQCDcalculations [20] allow for the determination of | V ub | / | V cb | according to | V ub | | V cb | = B ( Λ b → pµ − ν µ ) B ( Λ b → Λ + c µ − ν µ ) R FF (1)where B denotes the branching fraction and R FF is a ratio of the relevant form factors, calcu-lated using LQCD. This is then converted into ameasurement of | V ub | using the existing measure-1ents of | V cb | obtained from exclusive decays.The normalisation to the Λ b → Λ + c µ − ν µ decaycancels many experimental uncertainties, includ-ing the uncertainty on the total production rateof Λ b baryons. At the LHC, the number of signalcandidates is large, allowing the optimisation ofthe event selection and the analysis approach tominimise systematic effects.The LHCb detector [21, 22] is one of the fourmajor detectors at the Large Hadron Collider.It is instrumented in a cone around the protonbeam axis, covering the angles between 10 and250 mrad, where most b -hadron decays producedin proton-proton collisions occur. The detectorincludes a high-precision tracking system witha dipole magnet, providing a measurement ofmomentum and impact parameter (IP), definedfor charged particles as the minimum distance ofa track to a primary proton-proton interactionvertex (PV). Different types of charged particlesare distinguished using information from tworing-imaging Cherenkov detectors, a calorime-ter and a muon system. Simulated samples ofspecific signal and background decay modes of b hadrons are used at many stages throughoutthe analysis. These simulated events model theexperimental conditions in full detail, includingthe proton-proton collision, the decay of the par-ticles, and the response of the detector. Thesoftware used is described in Refs. [23–29].Candidates of the signal modes are requiredto pass a trigger system [30] which reduces inreal-time the rate of recorded collisions (events)from the 40 MHz read-out clock of the LHC toaround 4 kHz. For this analysis, the trigger re-quires a muon with a large momentum transverseto the beam axis that at the same time formsa good vertex with another track in the event.This vertex should be displaced from the PVs inthe event. The identification efficiency for thesehigh momentum muons is 98%.In the selection of the final states, stringentparticle identification (PID) requirements are applied to the proton. These criteria are accom-panied by a requirement that its momentum isgreater than 15 GeV /c as the PID performance ismost effective for protons above the momentumthreshold to produce Cherenkov light. The pµ − vertex fit is required to be of good quality, whichreduces background from most of the b → cµ − ν µ decays as the resulting ground state charmedhadrons have significant lifetime.To reconstruct Λ b → ( Λ + c → pK − π + ) µ − ν µ candidates, two additional tracks, positivelyidentified as a pion and kaon, are combinedwith the proton to form a Λ + c → pK − π + can-didate. These are reconstructed from the same pµ − vertex as the Λ b → pµ − ν µ signal to min-imise systematic uncertainties. As the lifetimeof the Λ + c is short compared to other weaklydecaying charm hadrons, the requirement hasan acceptable efficiency.There is a large background from b -hadrondecays with additional charged tracks in the de-cay products, as illustrated in Fig. 1. To reducethis background, a multivariate machine learningalgorithm (a boosted decision tree, BDT [31,32])is employed to determine the compatibility ofeach track from a charged particle in the eventto originate from the same vertex as the signalcandidate. This isolation BDT includes vari-ables such as the change in vertex quality ifthe track is combined with the signal vertex,as well as kinematic and IP information of thetrack that is tested. For the BDT, the train-ing sample of well isolated tracks consists ofall tracks apart from the signal decay productsin a sample of simulated Λ b → pµ − ν µ events.The training sample of non-isolated tracks con-sists of the tracks from charged particles inthe decay products X in a sample of simulated Λ b → ( Λ + c → pX ) µ − ν µ events. The BDT se-lection removes 90% of background with addi-tional charged particles from the signal vertexwhile it retains more than 80% of signal. Thesame isolation requirement is placed on both the2 V X ¯b ⇤ µ ¯ ⌫ µ p PV X ¯b ⇤ µ ¯ ⌫ µ p⇤ + c Figure 1:
Diagram illustrating the topol-ogy for the (top) signal and (bottom) back-ground decays.
The Λ b baryon travels about 1 cmon average before decaying; its flight direction isindicated in the diagram. In the Λ b → pµ − ν µ signalcase, the only other particles present are typicallyreconstructed far away from the signal, which areshown as grey arrows. For the background from Λ + c decays, there are particles which are reconstructedin close proximity to the signal and which are indi-cated as dotted arrows. Λ b → pµ − ν µ and Λ b → ( Λ + c → pK − π + ) µ − ν µ decay candidates, where the pion and kaon areignored in the calculation of the BDT responsefor the Λ b → ( Λ + c → pK − π + ) µ − ν µ case.The Λ b mass is reconstructed using the so-called corrected mass [33], defined as m corr = (cid:113) m hµ + p ⊥ + p ⊥ , where m hµ is the visible mass of the hµ pair and p ⊥ is the momentum of the hµ pair transverse to the Λ b flight direction, where h representseither the proton or Λ + c candidate. The flightdirection is measured using the PV and Λ b vertexpositions. The uncertainties on the PV andthe Λ b vertex are estimated for each candidateand propagated to the uncertainty on m corr ; thedominant contribution is from the uncertaintyin the Λ b vertex.Candidates with an uncertainty of less than100 MeV /c on the corrected mass are selectedfor the Λ b → pµ − ν µ decay. This selects only 23%of the signal; however, the separation betweensignal and background for these candidates issignificantly improved and the selection thus re-duces the dependence on background modelling.The LQCD form-factors that are required tocalculate | V ub | are most precise in the kinematicregion where q , the invariant mass squared ofthe muon and the neutrino in the decay, is high.The neutrino is not reconstructed, but q canstill be determined using the Λ b flight directionand the Λ b mass, but only up to a two-foldambiguity. The correct solution has a resolu-tion of about 1 GeV /c , while the wrong solu-tion has a resolution of 4 GeV /c . To avoidinfluence on the measurement by the large un-certainty in form factors at low q , both so-lutions are required to exceed 15 GeV /c forthe Λ b → pµ − ν µ decay and 7 GeV /c for the Λ b → ( Λ + c → pK − π + ) µ − ν µ decay. Simulationshows that only 2% of Λ b → pµ − ν µ decays and5% of Λ b → Λ + c µ − ν µ decays with q values belowthe cut values pass the selection requirements.The effect of this can be seen in Fig. 2, where theefficiency for signal below 15 GeV /c is reducedsignificantly if requirements are applied on bothsolutions. It is also possible that both solutionsare imaginary due to the limited detector resolu-tion. Candidates of this type are rejected. Theoverall q selection has an efficiency of 38% for Λ b → pµ − ν µ and 39% for Λ b → Λ + c µ − ν µ decaysin their respective high- q regions.The mass distributions of the signal candi-3 c / [GeV q s e l ec ti on e ff i c i e n c y [ % ] q LHCb simulationboth solutionsone solution
Figure 2:
Illustrating the method used to re-duce the number of selected events from the q region where lattice QCD has high uncer-tainties. The efficiency of simulated Λ b → pµ − ν µ candidates as a function of q . For the case whereone q solution is required to be above 15 GeV /c (marked by the vertical line), there is still significantefficiency for signal below this value, whereas, whenboth solutions have this requirement, only a smallamount of signal below 15 GeV /c is selected. dates for the two decays are shown in Fig. 3. Thesignal yields are determined from separate χ fits to the m corr distributions of the Λ b → pµ − ν µ and Λ b → ( Λ + c → pK − π + ) µ − ν µ candidates. Theshapes of the signal and background componentsare modelled using simulation, where the un-certainties coming from the finite size of thesimulated samples are propagated in the fits.The yields of all background components areallowed to vary within uncertainties obtained asdescribed below.For the fit to the m corr distribution of the Λ b → pµ − ν µ candidates, many sources of back-ground are accounted for. The largest ofthese is the cross-feed from Λ b → Λ + c µ − ν µ decays, where the Λ + c decays into a pro-ton and other particles that are not recon-structed. The amount of background arising ] c mass [MeV/ - m p Corrected ) c C a nd i d a t e s / ( M e V / CombinatorialMis-identified n - m p D n - m c + L n - m c+ L n - m N n - m p LHCb ** ] c mass [MeV/ - m + p - pK Corrected ) c C a nd i d a t e s / ( M e V / n - m c+ L n - m *+c L Combinatorial
LHCb
Figure 3:
Corrected mass fit used for de-termining signal yields.
Fits are made to(top) Λ b → pµ − ν µ and (bottom) Λ b → ( Λ + c → pK − π + ) µ − ν µ candidates. The statistical uncer-tainties arising from the finite size of the simulationsamples used to model the mass shapes are indi-cated by open boxes while the data are representedby the black points. The statistical uncertainty onthe data points is smaller than the marker size used.The different signal and background componentsappear in the same order in the fits and the legends.There are no data above the nominal Λ b mass dueto the removal of unphysical q solutions. from these decay modes is estimated by fullyreconstructing two Λ + c decays in the data. Thebackground where the additional particles in-clude charged particles originating directly from4he Λ + c decay is estimated by reconstructing Λ b → ( Λ + c → pK − π + ) µ − ν µ decays, whereas thebackground where only neutral particles comedirectly from the Λ + c decay is estimated byreconstructing Λ b → ( Λ + c → pK S ) µ − ν µ decays.These two background categories are separatedbecause the isolation BDT significantly reducesthe charged component but has no effect onthe neutral case. For the rest of the Λ + c de-cay modes, the relative branching fraction be-tween the decay and either the Λ + c → pK − π + or Λ + c → pK S decay modes, as appropriate, istaken from Ref. [14]. For some neutral decaymodes, where only the corresponding mode withcharged decay particles is measured, assump-tions based on isospin symmetry are used. Inthese decays, an uncertainty corresponding to100% of the branching fraction is allowed forin the fit. Background from Λ b → D pµ − ν µ decays is constrained in a similar way to the Λ + c charged decay modes, with the normalisa-tion done relative to Λ b → D ( → K − π + ) pµ − ν µ decays reconstructed in the data.Any background with a Λ + c baryon mayalso arise from decays of the type Λ b → ( Λ ∗ + c → Λ + c ππ ) µ − ν µ , where Λ ∗ + c represents the Λ c (2595) + or Λ c (2625) + resonances as well asnon-resonant contributions. The proportionsbetween the Λ b → ( Λ ∗ + c → Λ + c ππ ) µ − ν µ and the Λ b → Λ + c µ − ν µ backgrounds are determined fromthe fit to the Λ b → ( Λ + c → pK − π + ) µ − ν µ m corr distribution and then used in the Λ b → pµ − ν µ fit. The decays Λ b → N ∗ µ − ν µ , where the N ∗ baryon decays into a proton and other non-reconstructed particles, are very similar to thesignal decay and have poorly known branch-ing fractions. The N ∗ resonance represents anyof the states N (1440), N (1520), N (1535) or N (1770). None of the Λ b → N ∗ µ − ν µ decayshave been observed and the m corr shape of thesedecays is obtained using simulation samples gen-erated according to the quark-model prediction of the form factors and branching fractions [34].A 100% uncertainty is allowed for in the branch-ing fractions of these decays.Background where a pion or kaon is mis-identified as a proton originates from varioussources and is measured by using a special dataset where no PID is applied to the proton can-didate. Finally, an estimate of combinatorialbackground, where the proton and muon origi-nate from different decays, is obtained from adata set where the proton and muon have thesame charge. The amount and shape of thisbackground are in good agreement between thesame-sign and opposite-sign pµ samples for cor-rected masses above 6 GeV /c .For the Λ b → ( Λ + c → pK − π + ) µ − ν µ yield,the reconstructed pK − π + mass is studied to de-termine the level of combinatorial background.The Λ + c signal shape is modelled using a Gaus-sian function with an asymmetric power-law tail,and the background is modelled as an exponen-tial function. Within a selected signal region of30 MeV /c from the known Λ + c mass the combi-natorial background is 2% of the signal yield.Subsequently, a fit is performed to the m corr distribution for Λ b → ( Λ + c → pK − π + ) µ − ν µ candidates, as shown in Fig. 3, which is usedto discriminate between Λ b → Λ + c µ − ν µ and Λ b → ( Λ ∗ + c → Λ + c ππ ) µ − ν µ decays.The Λ b → pµ − ν µ and Λ b → ( Λ + c → pK − π + ) µ − ν µ yields are 17,687 ±
733 and34,255 ± Λ b → pµ − ν µ .The Λ b → pµ − ν µ branching fraction is mea-sured relative to the Λ b → ( Λ + c → pK − π + ) µ − ν µ branching fraction. The relative efficiencies forreconstruction, trigger and final event selectionare obtained from simulated events, with severalcorrections applied to improve the agreementbetween the data and the simulation. Thesecorrect for differences between data and simu-lation in the detector response and differencesin the Λ b kinematic properties for the selected5 b → pµ − ν µ and Λ b → ( Λ + c → pK − π + ) µ − ν µ candidates. The ratio of efficiencies is 3 . ± . Λ + c → pK − π + branching fraction, which is taken fromRef. [35]. This is followed by the uncertaintyon the trigger response, which is due to thestatistical uncertainty of the calibration sam-ple. Other contributions come from the track-ing efficiency, which is due to possible differ-ences between the data and simulation in theprobability of interactions with the materialof the detector for the kaon and pion in the Λ b → ( Λ + c → pK − π + ) µ − ν µ decay. Another sys-tematic uncertainty is assigned due to the lim-ited knowledge of the momentum distributionfor the Λ + c → pK − π + decay products. Uncer-tainties related to the background compositionare included in the statistical uncertainty forthe signal yield through the use of nuisance pa-rameters in the fit. The exception to this is theuncertainty on the Λ b → N ∗ µ − ν µ mass shapesdue to the limited knowledge of the form factorsand widths of each state, which is estimated bygenerating pseudoexperiments and assessing theimpact on the signal yield.Smaller uncertainties are assigned for thefollowing effects: the uncertainty in the Λ b life-time; differences in data and simulation in theisolation BDT response; differences in the rel-ative efficiency and q migration due to formfactor uncertainties for both signal and normali-sation channels; corrections to the Λ b kinematicproperties; the disagreement in the q migra-tion between data and simulation; and the finitesize of the PID calibration samples. The to-tal fractional systematic uncertainty is +7 . − . %,where the individual uncertainties are added inquadrature. The small impact of the form factoruncertainties means that the measured ratio of Table 1:
Summary of systematic uncertainties.
The table shows the relative systematic uncertaintyon the ratio of the Λ b → pµ − ν µ and Λ b → Λ + c µ − ν µ branching fractions broken into its individual con-tributions. The total is obtained by adding them inquadrature. Uncertainties on the background levelsare not listed here as they are incorporated into thefits. Source Relative uncertainty (%) B ( Λ + c → pK + π − ) +4 . − . Trigger 3.2Tracking 3.0 Λ + c selection efficiency 3.0 Λ b → N ∗ µ − ν µ shapes 2.3 Λ b lifetime 1.5Isolation 1.4Form factor 1.0 Λ b kinematics 0.5 q migration 0.4PID 0.2Total +7 . − . branching fractions can safely be considered in-dependent of the theoretical input at the currentlevel of precision.From the ratio of yields and their determinedefficiencies, the ratio of branching fractions of Λ b → pµ − ν µ to Λ b → Λ + c µ − ν µ in the selected q regions is B ( Λ b → pµ − ν µ ) q >
15 GeV /c B ( Λ b → Λ + c µ − ν µ ) q > /c =(1 . ± . ± . × − , where the first uncertainty is statistical andthe second is systematic. Using Eq. 1 with R FF = 0 . ± .
07, computed in Ref. [20] forthe restricted q regions, the measurement | V ub || V cb | = 0 . ± . ± . , is obtained. The first uncertainty arises fromthe experimental measurement and the second is6ue to the uncertainty in the LQCD prediction.Finally, using the world average | V cb | = (39 . ± . × − measured using exclusive decays [14], | V ub | is measured as | V ub | = (3 . ± . ± . ± . × − , where the first uncertainty is due to the exper-imental measurement, the second arises fromthe uncertainty in the LQCD prediction andthe third from the normalisation to | V cb | . Asthe measurement of | V ub | / | V cb | already dependson LQCD calculations of the form factors itmakes sense to normalise to the | V cb | exclusiveworld average and not include the inclusive | V cb | measurements. The experimental uncertainty isdominated by systematic effects, most of whichwill be improved with additional data by a reduc-tion of the statistical uncertainty of the controlsamples.The measured ratio of branching frac-tions can be extrapolated to the full q re-gion using | V cb | and the form factor pre-dictions [20], resulting in a measurement of B ( Λ b → pµ − ν µ ) = (4 . ± . × − , where theuncertainty is dominated by knowledge of theform factors at low q .The determination of | V ub | from the mea-sured ratio of branching fractions depends onthe size of a possible right-handed coupling [36].This can clearly be seen in Fig. 4, which showsthe experimental constraints on the left-handedcoupling, | V L ub | and the fractional right-handedcoupling added to the SM, (cid:15) R , for different mea-surements. The LHCb result presented here iscompared to the world averages of the inclusiveand exclusive measurements. Unlike the case forthe pion in B → π + (cid:96) − ν and B − → π (cid:96) − ν de-cays, the spin of the proton is non-zero, allowingan axial-vector current, which gives a differentsensitivity to (cid:15) R . The overlap of the bands fromthe previous measurements suggested a signifi-cant right-handed coupling but the inclusion ofthe LHCb | V ub | measurement does not support R e · | L ub | V - - inclusive n l pfi B (LHCb) nm p fi b L combined Figure 4:
Experimental constraints on theleft-handed coupling, | V L ub | and the fractionalright-handed coupling, (cid:15) R . While the overlapof the 68% confidence level bands for the inclu-sive [14] and exclusive [7] world averages of pastmeasurements suggested a right handed couplingof significant magnitude, the inclusion of the LHCb | V ub | measurement does not support this. that.In summary, a measurement of the ratio of | V ub | to | V cb | is performed using the exclusivedecay modes Λ b → pµ − ν µ and Λ b → Λ + c µ − ν µ .Using a previously measured value of | V cb | , | V ub | is determined precisely. The | V ub | measurementis in agreement with the exclusively measuredworld average from Ref. [7], but disagrees withthe inclusive measurement [14] at a significancelevel of 3.5 standard deviations. The measure-ment will have a significant impact on the globalfits to the parameters of the CKM matrix.7 cknowledgements This article is dedicated to the memory of our dear friend and colleague, Till Moritz Karbach,who died following a climbing accident on 9th April 2015. Moritz contributed much to the physicsanalysis presented in this article. Within LHCb he was active in many areas; he convened theanalysis group on beauty to open charm decays, he was deputy project leader for the LHCbOuter Tracker detector and he served the experiment as a shift leader. Moritz was a highlypromising young physicist and we miss him greatly. We thank Stefan Meinel for a productivecollaboration regarding form factor predictions of the Λ b → pµ − ν µ and Λ b → Λ + c µ − ν µ decays,Winston Roberts for discussions regarding the Λ b → N ∗ µ − ν µ decays and Florian Bernlochnerfor help in understanding the impact of right-handed currents. We express our gratitude to ourcolleagues in the CERN accelerator departments for the excellent performance of the LHC. Wethank the technical and administrative staff at the LHCb institutes. We acknowledge supportfrom CERN and from the national agencies: CAPES, CNPq, FAPERJ and FINEP (Brazil); NSFC(China); CNRS/IN2P3 (France); BMBF, DFG, HGF and MPG (Germany); INFN (Italy); FOMand NWO (The Netherlands); MNiSW and NCN (Poland); MEN/IFA (Romania); MinES andFANO (Russia); MinECo (Spain); SNSF and SER (Switzerland); NASU (Ukraine); STFC (UnitedKingdom); NSF (USA). The Tier1 computing centres are supported by IN2P3 (France), KIT andBMBF (Germany), INFN (Italy), NWO and SURF (The Netherlands), PIC (Spain), GridPP(United Kingdom). We are indebted to the communities behind the multiple open source softwarepackages on which we depend. We are also thankful for the computing resources and the accessto software R&D tools provided by Yandex LLC (Russia). Individual groups or members havereceived support from EPLANET, Marie Sk(cid:32)lodowska-Curie Actions and ERC (European Union),Conseil g´en´eral de Haute-Savoie, Labex ENIGMASS and OCEVU, R´egion Auvergne (France),RFBR (Russia), XuntaGal and GENCAT (Spain), Royal Society and Royal Commission for theExhibition of 1851 (United Kingdom). 8 eferences [1] N. Cabibbo, Unitary symmetry and leptonic decays , Phys. Rev. Lett. (1963) 531.[2] M. Kobayashi and T. Maskawa, CP violation in the renormalizable theory of weak interaction ,Prog. Theor. Phys. (1973) 652.[3] J. Charles et al. , Current status of the Standard Model CKM fit and constraints on ∆ F = 2 New Physics , arXiv:1501.05013 , updated results and plots available at http://ckmfitter.in2p3.fr/ .[4] UTfit collaboration, M. Bona et al. , The Unitarity Triangle fit in the Standard Model andhadronic parameters from lattice QCD: A reappraisal after the measurements of ∆ m s and BR ( B → τ ν τ ), JHEP (2006) 081, arXiv:hep-ph/0606167 , updated results and plotsavailable at .[5] H. J. Rothe, Lattice Gauge Theories: An Introduction; 4th ed. , World Scientific Lecture Notesin Physics, World Scientific, Singapore, 2012.[6] C. A. Dominguez,
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R. Aaij , B. Adeva , M. Adinolfi , A. Affolder , Z. Ajaltouni , S. Akar , J. Albrecht , F. Alessio ,M. Alexander , S. Ali , G. Alkhazov , P. Alvarez Cartelle , A.A. Alves Jr , S. Amato , S. Amerio ,Y. Amhis , L. An , L. Anderlini ,g , J. Anderson , M. Andreotti ,f , J.E. Andrews , R.B. Appleby ,O. Aquines Gutierrez , F. Archilli , A. Artamonov , M. Artuso , E. Aslanides , G. Auriemma ,n ,M. Baalouch , S. Bachmann , J.J. Back , A. Badalov , C. Baesso , W. Baldini , , R.J. Barlow ,C. Barschel , S. Barsuk , W. Barter , V. Batozskaya , V. Battista , A. Bay , L. Beaucourt ,J. Beddow , F. Bedeschi , I. Bediaga , L.J. Bel , I. Belyaev , E. Ben-Haim , G. Bencivenni ,S. Benson , J. Benton , A. Berezhnoy , R. Bernet , A. Bertolin , M.-O. Bettler ,M. van Beuzekom , A. Bien , S. Bifani , T. Bird , A. Birnkraut , A. Bizzeti ,i , T. Blake ,F. Blanc , J. Blouw , S. Blusk , V. Bocci , A. Bondar , N. Bondar , , W. Bonivento , S. Borghi ,M. Borsato , T.J.V. Bowcock , E. Bowen , C. Bozzi , S. Braun , D. Brett , M. Britsch ,T. Britton , J. Brodzicka , N.H. Brook , A. Bursche , J. Buytaert , S. Cadeddu , R. Calabrese ,f ,M. Calvi ,k , M. Calvo Gomez ,p , P. Campana , D. Campora Perez , L. Capriotti , A. Carbone ,d ,G. Carboni ,l , R. Cardinale ,j , A. Cardini , P. Carniti , L. Carson , K. Carvalho Akiba , ,R. Casanova Mohr , G. Casse , L. Cassina ,k , L. Castillo Garcia , M. Cattaneo , Ch. Cauet ,G. Cavallero , R. Cenci ,t , M. Charles , Ph. Charpentier , M. Chefdeville , S. Chen , S.-F. Cheung ,N. Chiapolini , M. Chrzaszcz , , X. Cid Vidal , G. Ciezarek , P.E.L. Clarke , M. Clemencic ,H.V. Cliff , J. Closier , V. Coco , J. Cogan , E. Cogneras , V. Cogoni ,e , L. Cojocariu ,G. Collazuol , P. Collins , A. Comerma-Montells , A. Contu , , A. Cook , M. Coombes ,S. Coquereau , G. Corti , M. Corvo ,f , B. Couturier , G.A. Cowan , D.C. Craik , A. Crocombe ,M. Cruz Torres , S. Cunliffe , R. Currie , C. D’Ambrosio , J. Dalseno , P.N.Y. David , A. Davis ,K. De Bruyn , S. De Capua , M. De Cian , J.M. De Miranda , L. De Paula , W. De Silva ,P. De Simone , C.-T. Dean , D. Decamp , M. Deckenhoff , L. Del Buono , N. D´el´eage , D. Derkach ,O. Deschamps , F. Dettori , B. Dey , A. Di Canto , F. Di Ruscio , H. Dijkstra , S. Donleavy ,F. Dordei , M. Dorigo , A. Dosil Su´arez , D. Dossett , A. Dovbnya , K. Dreimanis , L. Dufour ,G. Dujany , F. Dupertuis , P. Durante , R. Dzhelyadin , A. Dziurda , A. Dzyuba , S. Easo , ,U. Egede , V. Egorychev , S. Eidelman , S. Eisenhardt , U. Eitschberger , R. Ekelhof , L. Eklund ,I. El Rifai , Ch. Elsasser , S. Ely , S. Esen , H.M. Evans , T. Evans , A. Falabella , C. F¨arber ,C. Farinelli , N. Farley , S. Farry , R. Fay , D. Ferguson , V. Fernandez Albor , F. Ferrari ,F. Ferreira Rodrigues , M. Ferro-Luzzi , S. Filippov , M. Fiore , ,f , M. Fiorini ,f , M. Firlej ,C. Fitzpatrick , T. Fiutowski , P. Fol , M. Fontana , F. Fontanelli ,j , R. Forty , O. Francisco ,M. Frank , C. Frei , M. Frosini , J. Fu , E. Furfaro ,l , A. Gallas Torreira , D. Galli ,d ,S. Gallorini , , S. Gambetta ,j , M. Gandelman , P. Gandini , Y. Gao , J. Garc´ıa Pardi˜nas ,J. Garofoli , J. Garra Tico , L. Garrido , D. Gascon , C. Gaspar , U. Gastaldi , R. Gauld ,L. Gavardi , G. Gazzoni , A. Geraci ,v , D. Gerick , E. Gersabeck , M. Gersabeck , T. Gershon ,Ph. Ghez , A. Gianelle , S. Gian`ı , V. Gibson , L. Giubega , V.V. Gligorov , C. G¨obel ,D. Golubkov , A. Golutvin , , , A. Gomes ,a , C. Gotti ,k , M. Grabalosa G´andara ,R. Graciani Diaz , L.A. Granado Cardoso , E. Graug´es , E. Graverini , G. Graziani , A. Grecu ,E. Greening , S. Gregson , P. Griffith , L. Grillo , O. Gr¨unberg , B. Gui , E. Gushchin ,Yu. Guz , , T. Gys , C. Hadjivasiliou , G. Haefeli , C. Haen , S.C. Haines , S. Hall ,B. Hamilton , T. Hampson , X. Han , S. Hansmann-Menzemer , N. Harnew , S.T. Harnew ,J. Harrison , J. He , T. Head , V. Heijne , K. Hennessy , P. Henrard , L. Henry ,J.A. Hernando Morata , E. van Herwijnen , M. Heß , A. Hicheur , D. Hill , M. Hoballah ,C. Hombach , W. Hulsbergen , T. Humair , N. Hussain , D. Hutchcroft , D. Hynds , M. Idzik , . Ilten , R. Jacobsson , A. Jaeger , J. Jalocha , E. Jans , A. Jawahery , F. Jing , M. John ,D. Johnson , C.R. Jones , C. Joram , B. Jost , N. Jurik , S. Kandybei , W. Kanso , M. Karacson ,T.M. Karbach , S. Karodia , M. Kelsey , I.R. Kenyon , M. Kenzie , T. Ketel , B. Khanji , ,k ,C. Khurewathanakul , S. Klaver , K. Klimaszewski , O. Kochebina , M. Kolpin , I. Komarov ,R.F. Koopman , P. Koppenburg , , M. Korolev , L. Kravchuk , K. Kreplin , M. Kreps ,G. Krocker , P. Krokovny , F. Kruse , W. Kucewicz ,o , M. Kucharczyk , V. Kudryavtsev ,K. Kurek , T. Kvaratskheliya , V.N. La Thi , D. Lacarrere , G. Lafferty , A. Lai , D. Lambert ,R.W. Lambert , G. Lanfranchi , C. Langenbruch , B. Langhans , T. Latham , C. Lazzeroni ,R. Le Gac , J. van Leerdam , J.-P. Lees , R. Lef`evre , A. Leflat , J. Lefran¸cois , O. Leroy , T. Lesiak ,B. Leverington , Y. Li , T. Likhomanenko , , M. Liles , R. Lindner , C. Linn , F. Lionetto ,B. Liu , S. Lohn , I. Longstaff , J.H. Lopes , P. Lowdon , D. Lucchesi ,r , H. Luo , A. Lupato ,E. Luppi ,f , O. Lupton , F. Machefert , F. Maciuc , O. Maev , K. Maguire , S. Malde ,A. Malinin , G. Manca ,e , G. Mancinelli , P. Manning , A. Mapelli , J. Maratas , J.F. Marchand ,U. Marconi , C. Marin Benito , P. Marino , ,t , R. M¨arki , J. Marks , G. Martellotti ,M. Martinelli , D. Martinez Santos , F. Martinez Vidal , D. Martins Tostes , A. Massafferri ,R. Matev , A. Mathad , Z. Mathe , C. Matteuzzi , A. Mauri , B. Maurin , A. Mazurov ,M. McCann , J. McCarthy , A. McNab , R. McNulty , B. Meadows , F. Meier , M. Meissner ,M. Merk , D.A. Milanes , M.-N. Minard , D.S. Mitzel , J. Molina Rodriguez , S. Monteil ,M. Morandin , P. Morawski , A. Mord`a , M.J. Morello ,t , J. Moron , A.-B. Morris , R. Mountain ,F. Muheim , J. M¨uller , K. M¨uller , V. M¨uller , M. Mussini , B. Muster , P. Naik , T. Nakada ,R. Nandakumar , I. Nasteva , M. Needham , N. Neri , S. Neubert , N. Neufeld , M. Neuner ,A.D. Nguyen , T.D. Nguyen , C. Nguyen-Mau ,q , V. Niess , R. Niet , N. Nikitin , T. Nikodem ,D Ninci , A. Novoselov , D.P. O’Hanlon , A. Oblakowska-Mucha , V. Obraztsov , S. Ogilvy ,O. Okhrimenko , R. Oldeman ,e , C.J.G. Onderwater , B. Osorio Rodrigues , J.M. Otalora Goicochea ,A. Otto , P. Owen , A. Oyanguren , A. Palano ,c , F. Palombo ,u , M. Palutan , J. Panman ,A. Papanestis , M. Pappagallo , L.L. Pappalardo ,f , C. Parkes , G. Passaleva , G.D. Patel ,M. Patel , C. Patrignani ,j , A. Pearce , , A. Pellegrino , G. Penso ,m , M. Pepe Altarelli ,S. Perazzini ,d , P. Perret , L. Pescatore , K. Petridis , A. Petrolini ,j , M. Petruzzo ,E. Picatoste Olloqui , B. Pietrzyk , T. Pilaˇr , D. Pinci , A. Pistone , S. Playfer , M. Plo Casasus ,T. Poikela , F. Polci , A. Poluektov , , I. Polyakov , E. Polycarpo , A. Popov , D. Popov ,B. Popovici , C. Potterat , E. Price , J.D. Price , J. Prisciandaro , A. Pritchard , C. Prouve ,V. Pugatch , A. Puig Navarro , G. Punzi ,s , W. Qian , R. Quagliani , , B. Rachwal ,J.H. Rademacker , B. Rakotomiaramanana , M. Rama , M.S. Rangel , I. Raniuk , N. Rauschmayr ,G. Raven , F. Redi , S. Reichert , M.M. Reid , A.C. dos Reis , S. Ricciardi , S. Richards ,M. Rihl , K. Rinnert , V. Rives Molina , P. Robbe , , A.B. Rodrigues , E. Rodrigues ,J.A. Rodriguez Lopez , P. Rodriguez Perez , S. Roiser , V. Romanovsky , A. Romero Vidal ,M. Rotondo , J. Rouvinet , T. Ruf , H. Ruiz , P. Ruiz Valls , J.J. Saborido Silva , N. Sagidova ,P. Sail , B. Saitta ,e , V. Salustino Guimaraes , C. Sanchez Mayordomo , B. Sanmartin Sedes ,R. Santacesaria , C. Santamarina Rios , M. Santimaria , E. Santovetti ,l , A. Sarti ,m ,C. Satriano ,n , A. Satta , D.M. Saunders , D. Savrina , , M. Schiller , H. Schindler , M. Schlupp ,M. Schmelling , T. Schmelzer , B. Schmidt , O. Schneider , A. Schopper , M.-H. Schune ,R. Schwemmer , B. Sciascia , A. Sciubba ,m , A. Semennikov , I. Sepp , N. Serra , J. Serrano ,L. Sestini , P. Seyfert , M. Shapkin , I. Shapoval , ,f , Y. Shcheglov , T. Shears , L. Shekhtman ,V. Shevchenko , A. Shires , R. Silva Coutinho , G. Simi , M. Sirendi , N. Skidmore , I. Skillicorn ,T. Skwarnicki , E. Smith , , E. Smith , J. Smith , M. Smith , H. Snoek , M.D. Sokoloff , ,F.J.P. Soler , F. Soomro , D. Souza , B. Souza De Paula , B. Spaan , P. Spradlin , S. Sridharan , . Stagni , M. Stahl , S. Stahl , O. Steinkamp , O. Stenyakin , F. Sterpka , S. Stevenson ,S. Stoica , S. Stone , B. Storaci , S. Stracka ,t , M. Straticiuc , U. Straumann , R. Stroili ,L. Sun , W. Sutcliffe , K. Swientek , S. Swientek , V. Syropoulos , M. Szczekowski ,P. Szczypka , , T. Szumlak , S. T’Jampens , T. Tekampe , M. Teklishyn , G. Tellarini ,f ,F. Teubert , C. Thomas , E. Thomas , J. van Tilburg , V. Tisserand , M. Tobin , J. Todd ,S. Tolk , L. Tomassetti ,f , D. Tonelli , S. Topp-Joergensen , N. Torr , E. Tournefier , S. Tourneur ,K. Trabelsi , M.T. Tran , M. Tresch , A. Trisovic , A. Tsaregorodtsev , P. Tsopelas , N. Tuning , ,A. Ukleja , A. Ustyuzhanin , , U. Uwer , C. Vacca ,e , V. Vagnoni , G. Valenti , A. Vallier ,R. Vazquez Gomez , P. Vazquez Regueiro , C. V´azquez Sierra , S. Vecchi , J.J. Velthuis ,M. Veltri ,h , G. Veneziano , M. Vesterinen , J.V. Viana Barbosa , B. Viaud , D. Vieira ,M. Vieites Diaz , X. Vilasis-Cardona ,p , A. Vollhardt , D. Volyanskyy , D. Voong , A. Vorobyev ,V. Vorobyev , C. Voß , J.A. de Vries , R. Waldi , C. Wallace , R. Wallace , J. Walsh ,S. Wandernoth , J. Wang , D.R. Ward , N.K. Watson , D. Websdale , A. Weiden ,M. Whitehead , D. Wiedner , G. Wilkinson , , M. Wilkinson , M. Williams , M.P. Williams ,M. Williams , F.F. Wilson , J. Wimberley , J. Wishahi , W. Wislicki , M. Witek , G. Wormser ,S.A. Wotton , S. Wright , K. Wyllie , Y. Xie , Z. Xu , Z. Yang , X. Yuan , O. Yushchenko ,M. Zangoli , M. Zavertyaev ,b , L. Zhang , Y. Zhang , A. Zhelezov , A. Zhokhov , L. Zhong . Centro Brasileiro de Pesquisas F´ısicas (CBPF), Rio de Janeiro, Brazil Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil Center for High Energy Physics, Tsinghua University, Beijing, China LAPP, Universit´e Savoie Mont-Blanc, CNRS/IN2P3, Annecy-Le-Vieux, France Clermont Universit´e, Universit´e Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France LAL, Universit´e Paris-Sud, CNRS/IN2P3, Orsay, France LPNHE, Universit´e Pierre et Marie Curie, Universit´e Paris Diderot, CNRS/IN2P3, Paris, France Fakult¨at Physik, Technische Universit¨at Dortmund, Dortmund, Germany Max-Planck-Institut f¨ur Kernphysik (MPIK), Heidelberg, Germany Physikalisches Institut, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg, Germany School of Physics, University College Dublin, Dublin, Ireland Sezione INFN di Bari, Bari, Italy Sezione INFN di Bologna, Bologna, Italy Sezione INFN di Cagliari, Cagliari, Italy Sezione INFN di Ferrara, Ferrara, Italy Sezione INFN di Firenze, Firenze, Italy Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy Sezione INFN di Genova, Genova, Italy Sezione INFN di Milano Bicocca, Milano, Italy Sezione INFN di Milano, Milano, Italy Sezione INFN di Padova, Padova, Italy Sezione INFN di Pisa, Pisa, Italy Sezione INFN di Roma Tor Vergata, Roma, Italy Sezione INFN di Roma La Sapienza, Roma, Italy Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Krak´ow, Poland AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science, Krak´ow, Poland National Center for Nuclear Research (NCBJ), Warsaw, Poland Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia Institute for High Energy Physics (IHEP), Protvino, Russia Universitat de Barcelona, Barcelona, Spain Universidad de Santiago de Compostela, Santiago de Compostela, Spain European Organization for Nuclear Research (CERN), Geneva, Switzerland Ecole Polytechnique F´ed´erale de Lausanne (EPFL), Lausanne, Switzerland Physik-Institut, Universit¨at Z¨urich, Z¨urich, Switzerland Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine University of Birmingham, Birmingham, United Kingdom H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom Department of Physics, University of Warwick, Coventry, United Kingdom STFC Rutherford Appleton Laboratory, Didcot, United Kingdom School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom Imperial College London, London, United Kingdom School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom Department of Physics, University of Oxford, Oxford, United Kingdom Massachusetts Institute of Technology, Cambridge, MA, United States University of Cincinnati, Cincinnati, OH, United States University of Maryland, College Park, MD, United States Syracuse University, Syracuse, NY, United States Pontif´ıcia Universidade Cat´olica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated to
Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China, associated to
Departamento de Fisica , Universidad Nacional de Colombia, Bogota, Colombia, associated to
Institut f¨ur Physik, Universit¨at Rostock, Rostock, Germany, associated to
National Research Centre Kurchatov Institute, Moscow, Russia, associated to
Yandex School of Data Analysis, Moscow, Russia, associated to
Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC, Valencia, Spain, associated to