Measurement of B^{0}_{s} and D^{-}_{s} meson lifetimes
LHCb collaboration, R. Aaij, B. Adeva, M. Adinolfi, 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. Andreassi, M. Andreotti, J.E. Andrews, R.B. Appleby, F. Archilli, P. d'Argent, J. Arnau Romeu, A. Artamonov, M. Artuso, E. Aslanides, G. Auriemma, M. Baalouch, I. Babuschkin, S. Bachmann, J.J. Back, A. Badalov, C. Baesso, S. Baker, V. Balagura, W. Baldini, A. Baranov, R.J. Barlow, C. Barschel, S. Barsuk, W. Barter, F. Baryshnikov, M. Baszczyk, V. Batozskaya, B. Batsukh, V. Battista, A. Bay, L. Beaucourt, J. Beddow, F. Bedeschi, I. Bediaga, A. Beiter, L.J. Bel, V. Bellee, N. Belloli, K. Belous, I. Belyaev, E. Ben-Haim, G. Bencivenni, S. Benson, S. Beranek, A. Berezhnoy, R. Bernet, A. Bertolin, C. Betancourt, F. Betti, M.-O. Bettler, M. van Beuzekom, Ia. Bezshyiko, S. Bifani, P. Billoir, A. Birnkraut, A. Bitadze, A. Bizzeti, T. Blake, F. Blanc, J. Blouw, S. Blusk, V. Bocci, T. Boettcher, A. Bondar, N. Bondar, W. Bonivento, I. Bordyuzhin, A. Borgheresi, S. Borghi, M. Borisyak, M. Borsato, F. Bossu, M. Boubdir, T.J.V. Bowcock, E. Bowen, C. Bozzi, S. Braun, T. Britton, J. Brodzicka, E. Buchanan, C. Burr, et al. (678 additional authors not shown)
aa r X i v : . [ h e p - e x ] S e p EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
CERN-EP-2017-070LHCb-PAPER-2017-004September, 8, 2017
Measurement of B s and D − s mesonlifetimes The LHCb collaboration † Abstract
We report on a measurement of the flavor-specific B s lifetime and of the D − s lifetimeusing proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collectedby the LHCb experiment and corresponding to 3.0 fb − of integrated luminosity.Approximately 407 000 B s → D ( ∗ ) − s µ + ν µ decays are partially reconstructed in the K + K − π − µ + final state. The B s and D − s natural widths are determined using, as areference, kinematically similar B → D ( ∗ ) − µ + ν µ decays reconstructed in the samefinal state. The resulting differences between widths of B s and B mesons andof D − s and D − mesons are ∆ Γ ( B ) = − . ± . ± . − and ∆ Γ ( D ) = 1 . ± . ± . − , respectively. Combinedwith the known B and D − lifetimes, these yield the flavor-specific B s lifetime, τ fs B s = 1 . ± .
013 (stat) ± .
010 (syst) ± .
004 ( τ B ) ps and the D − s lifetime, τ D − s =0 . ± . ± . ± . τ D ) ps. The last uncertainties originatefrom the limited knowledge of the B and D − lifetimes. The results improve uponcurrent determinations. Published in Phys. Rev. Lett. 119, 101801 (2017). c (cid:13) CERN on behalf of the LHCb collaboration, licence CC-BY-4.0. † Authors are listed at the end of this paper. iomparisons of precise measurements and predictions associated with quark-flavor dy-namics probe the existence of unknown particles at energies much higher than those di-rectly accessible at particle colliders. The precision of the predictions is often limited bythe strong-interaction theory at low energies, where calculations are intractable. Predic-tive power is recovered by resorting to effective models such as heavy-quark expansion [1]which rely on an expansion of the quantum chromodynamics corrections in powers of1 /m , where m is the mass of the heavy quark in a bound system of a heavy quark anda light quark. These predictions are validated and refined using lifetime measurementsof heavy hadrons. Hence, improved lifetime measurements ultimately enhance the reachin searches for non-standard-model physics. Currently, more precise measurements areparticularly important as predictions of the lifetime ratio between B s and B mesonsshow a 2.5 standard-deviation discrepancy from measurements.Measurements of the “flavor-specific” B s meson lifetime, τ fs B s , have additional rele-vance. This empirical quantity is a function of the natural widths of the two mass eigen-states resulting from B s – B s oscillations, and therefore allows an indirect determinationof the width difference that can be compared with direct determinations in tests for non-standard-model physics [2]. The lifetime τ fs B s is measured with a single-exponential fit tothe distribution of decay time in final states to which only one of B s and B s mesons candecay [3]. The current best determination, τ fs B s = 1 . ± . ± . B s → D − s π + decays, has similarstatistical and systematic uncertainties. Semileptonic B s decays, owing to larger sig-nal yields than in hadronic decays, offer richer potential for precise τ fs B s measurements.However, neutrinos and low-momentum neutral final-state particles prevent the full re-construction of such decays. This introduces systematic limitations associated with poorknowledge of backgrounds and difficulties in obtaining the decay time from the observeddecay-length distribution. Indeed, the result τ fs B s = 1 . ± .
010 (stat) ± .
021 (syst) ps [5],based on a B s → D ( ∗ ) − s µ + ν µ X sample from the D0 collaboration, is limited by the sys-tematic uncertainty. Throughout this Letter, the symbol X identifies any decay product,other than neutrinos, not included in the candidate reconstruction, and the inclusion ofcharge-conjugate processes is implied.In this Letter, we use a novel approach that suppresses the above limitations andachieves a precise measurement of the flavor-specific B s meson lifetime. The lifetime isdetermined from the variation in the B s signal yield as a function of decay time, relativeto that of B decays that are reconstructed in the same final state and whose lifetimeis precisely known. The use of kinematically similar B decays as a reference allows thereduction of the uncertainties from partial reconstruction and lifetime-biasing selectioncriteria. The analysis also yields a significantly improved determination of the D − s lifetimeover the current best result, τ D − s = 0 . ± . ± . − . We use a sample of approximately 407 000 B s → D ∗− s µ + ν µ and B s → D − s µ + ν µ “signal” decays, and a sample of approximately 108 000 B → D ∗− µ + ν µ and B → D − µ + ν µ “reference” decays. The D candidates are reconstructed as combinations of K + , K − , and π − candidates originating from a common vertex, displaced from any proton-proton interaction vertex. The B s ) candidates, K + K − π − µ + , are formed by D candidates1ssociated with muon candidates originating from another common displaced vertex. Wecollectively refer to the signal and reference decays as B s → [ K + K − π − ] D ( ∗ ) − s µ + ν µ and B → [ K + K − π − ] D ( ∗ ) − µ + ν µ , respectively. A fit to the ratio of event yields between thesignal and reference decays as a function of B s ) decay time, t , determines ∆ Γ ( B ) ≡ /τ fs B s − Γ d , where Γ d is the known natural width of the B meson. A similar fit performedas a function of the D − ( s ) decay time determines the decay-width difference between D − s and D − mesons, ∆ Γ ( D ). Event yields are determined by fitting the “corrected-mass”distribution of the candidates, m corr = p ⊥ ,Dµ + q m Dµ + p ⊥ ,Dµ [7]. This is determinedfrom the invariant mass of the D − ( s ) µ + pair, m Dµ , and the component of its momentumperpendicular to the B s ) flight direction, p ⊥ ,Dµ , to compensate for the average momentumof unreconstructed decay products. The flight direction is the line connecting the B s ) production and decay vertices; the decay time t = m B Lk/p Dµ uses the known B s ) mass, m B [8], the measured B s ) decay length, L , and the momentum of the D − ( s ) µ + pair, p Dµ .The scale factor k corrects p Dµ for the average momentum fraction carried by decayproducts excluded from the reconstruction [9, 10]. The effects of decay-time acceptancesand resolutions, determined from simulation, are included.The LHCb detector is a single-arm forward spectrometer equipped with pre-cise charged-particle vertexing and tracking detectors, hadron-identification detectors,calorimeters, and muon detectors, optimized for the study of bottom- and charm-hadrondecays [11,12]. Simulation [13,14] is used to identify all relevant sources of bottom-hadrondecays, model the mass distributions, and correct for the effects of incomplete kinematicreconstructions, relative decay-time acceptances, and decay-time resolutions. The un-known details of the B s decay dynamics are modeled in the simulation through empiricalform-factor parameters [15], assuming values inspired by the known B form factors [2].We assess the impact of these assumptions on the systematic uncertainties.The online selection requires a muon candidate, with transverse momentum exceed-ing 1.5–1.8 GeV /c , associated with one, two, or three charged particles, all with originsdisplaced from the proton-proton interaction points [16]. In the offline reconstruction,the muon is combined with charged particles consistent with the topology and kinemat-ics of signal B s → [ K + K − π − ] D ( ∗ ) − s µ + ν µ and reference B → [ K + K − π − ] D ( ∗ ) − µ + ν µ decays.The range of K + K − π − mass is restricted around the known values of the D − ( s ) mesonmasses such that cross-contamination between signal and reference samples is smallerthan 0.1%, as estimated from simulation. We also reconstruct “same-sign” K + K − π − µ − candidates, formed by charm and muon candidates with same-sign charge, to model com-binatorial background from accidental D − ( s ) µ + associations. The event selection is opti-mized toward suppressing the background under the charm signals and making same-signcandidates a reliable model for the combinatorial background: track- and vertex-quality,vertex-displacement, transverse-momentum, and particle-identification criteria are cho-sen to minimize shape and yield differences between same-sign and signal candidates inthe m Dµ > . /c region, where genuine bottom-hadron decays are kinematicallyexcluded and combinatorial background dominates. Mass vetoes suppress backgroundfrom misreconstructed decays such as B s → ψ ( ′ ) ( → µ + µ − ) φ ( → K + K − ) decays where amuon is misidentified as a pion, Λ b → Λ + c ( → pK − π + ) µ − ¯ ν µ X decays where the proton ismisidentified as a kaon or a pion, and B s ) → D − ( s ) π + decays where the pion is misidenti-fied as a muon. Significant contributions arise from decays of a bottom hadron into pairs2f charm hadrons, one peaking at the D − ( s ) mass and the other decaying semileptonically,or into single charm hadrons and other particles. Such decays include B s ) → D ( ∗ ) − ( s ) D +( s ) , B + → D ( ∗ ) D ( ∗ ) + , B + → D − µ + ν µ X , B + → D ( ∗ ) − s K + µ + ν µ X , B → D ( ∗ ) − s K µ + ν µ X , B s → D D − s K + , B s → D − D + s K , Λ b → Λ + c D ( ∗ ) − s X , and Λ b → D + s Λµ − ¯ ν µ X decays.We suppress these backgrounds with a threshold, linearly dependent on m corr , appliedto the D − ( s ) momentum component perpendicular to the B s ) flight direction. Finally, a t > . D − ( s ) proper decay time renders the signal- and reference-decay acceptances as functions of decay time more similar, with little signal loss.A total of approximately 468 000 (141 000) signal (reference) candidates, formed bycombining K + K − π − candidates in the D − s ( D − ) signal range with µ + candidates, sat-isfy the selection. Figure 1 shows the relevant mass distributions. The enhancementsof the signal and reference distributions over the corresponding same-sign distributionsfor m Dµ < . /c are due to bottom-hadron decays. The absence of candidates at m Dµ ≈ . /c results from the B s ) → D − ( s ) π + veto. The two peaks in the K + K − π − distributions of same-sign candidates are due to genuine charm decays accidentally com-bined with muon candidates. Along with B s → [ K + K − π − ] D ( ∗ ) − s µ + ν µ decays, many B s decays potentially useful for the lifetime measurement contribute signal candidates,including decays into D ∗∗ ( s ) ( → D ( ∗ ) − s X ) µ + ν µ , D − s τ + ( → µ + ν µ ¯ ν τ ) ν τ , D ∗− s ( → D − s X ) τ + ( → µ + ν µ ¯ ν τ ) ν τ , and D ∗∗ s ( → D ( ∗ ) − s X ) τ + ( → µ + ν µ ¯ ν τ ) ν τ final states. Similarly, along with the B → [ K + K − π − ] D ( ∗ ) − µ + ν µ decays, potential reference candidates come from B decaysinto D ∗∗ ( → D ( ∗ ) − X ) µ + ν µ , D − τ + ( → µ + ν µ ¯ ν τ ) ν τ , D ∗− ( → D − X ) τ + ( → µ + ν µ ¯ ν τ ) ν τ , and D ∗∗ ( → D ( ∗ ) − X ) τ + ( → µ + ν µ ¯ ν τ ) ν τ final states. However, we restrict the signal (reference)decays solely to the B s → [ K + K − π − ] D ( ∗ ) − s µ + ν µ ( B → [ K + K − π − ] D ( ∗ ) − µ + ν µ ) channelsbecause they contribute 95% (91%) of the inclusive K + K − π − µ + yield from semileptonic B ( B s ) decays and require smaller and better-known k -factor corrections to relate theobserved decay times to their true values.A reliable understanding of the sample composition is essential for unbiased lifetimeresults. An unbiased determination from simulation of the acceptances and mass dis-tributions as functions of decay time requires that the simulated sample mirrors thedata composition. We therefore weight the composition of the simulated samples ac-cording to the results of a least-squares fit to the m corr distributions in data, shown inFig. 2. In the B s sample, such a global composition-fit includes the two signal compo-nents, B s → [ K + K − π − ] D − s µ + ν µ and B s → [ K + K − π − ] D ∗− s µ + ν µ ; a combinatorial compo-nent; and two physics backgrounds. The physics backgrounds are formed by groupingtogether contributions with similar corrected-mass distributions, determined from sim-ulation. They are divided into contributions at lower values of corrected mass ( B → D ( ∗ ) − D ( ∗ ) + s , B + → D ( ∗ ) D ( ∗ ) + s , and D ∗∗ ( → D ( ∗ ) − s X ) µ + ν µ ) and at higher corrected-mass val-ues ( B + → D ( ∗ ) − s K + µ + ν µ X , B → D ( ∗ ) − s K µ + ν µ X , and B s → D − s τ + ( → µ + ν µ ¯ ν τ ) ν τ X ).The distributions of all components are modeled empirically from simulation, except forthe combinatorial component, which is modeled using same-sign data. Contributionsexpected to be smaller than 0.5% are neglected. The effect of this approximation andof possible variations of the relative proportions within each fit category are treated ascontributions to the systematic uncertainties. The fit p -value is 62.1% and the frac-tions of each component are determined with absolute statistical uncertainties in the Here and in the following, the symbol D ∗∗ ( s ) identifies collectively higher orbital excitations of D − ( s ) mesons. B LHCb
DataSame-sign candidates0 s B ] c [GeV/ µ D m c C a nd i d a t e s p e r M e V / ] c mass [GeV/ − π − K + K c C a nd i d a t e s p e r M e V / Figure 1: Distributions of Dµ mass for (top panel) reference candidates, formed by combining D − → K + K − π − candidates with µ + candidates, and (bottom panel) signal candidates formedby D − s → K + K − π − candidates combined with µ + candidates. The inset shows the K + K − π − -mass distribution with vertical lines enclosing the D − ( D − s ) candidates used to form the reference(signal) candidates. The dark-filled histograms show same-sign candidate distributions. range 0.13%–0.91%. A simpler composition fit is used for the B sample. Signal andcombinatorial components are chosen similarly to the B s case; the contributions from B → D ∗∗− ( → D ( ∗ ) − X ) µ + ν µ and B + → D − µ + ν µ X decays have sufficiently similar dis-tributions to be merged into a single physics-background component. The results of thecorrected-mass fit of the reference sample also offer a validation of the approach, sincethe composition of this sample is known precisely from other experiments. The largestdiscrepancy observed among the individual fractional contributions is 1.3 statistical stan-dard deviations.The composition fit is sufficient for the determination of ∆ Γ ( D ), where no k -factorcorrections are needed since the final state is fully reconstructed. We determine ∆ Γ ( D )through a least-squares fit of the ratio of signal B s and reference B yields as a functionof the charm-meson decay time in the range 0.1–4.0 ps. The yields of signal B s → [ K + K − π − ] D ( ∗ ) − s µ + ν µ and reference B → [ K + K − π − ] D ( ∗ ) − µ + ν µ decays are determined ineach of 20 decay-time bins with a m corr fit similar to the global composition-fit. Thetwo signal and the two physics-background contributions are each merged into a singlecomponent according to the total proportions determined by the global fit and theirdecay-time dependence as determined from simulation. The fit includes the decay-timeresolution and the ratio between signal and reference decay-time acceptances, which isdetermined from simulation to be uniform within 1%. The fit is shown in the top panelof Fig. 3; it has 34% p -value and determines ∆ Γ ( D ) = 1 . ± . − .4 × LHCb B × Data µ ν + µ −) s ( D → s ( B µ ν + µ − * ) s ( D → s ( B Physics backg.Comb. backg.Fit s B ] c [GeV/ corr m c C a nd i d a t e s p e r M e V / × Figure 2: Corrected-mass distributions for (top panel) reference B → [ K + K − π − ] D ( ∗ ) − µ + ν µ and(bottom panel) signal B s → [ K + K − π − ] D ( ∗ ) − s µ + ν µ candidates satisfying the selection. Resultsof the global composition-fit are overlaid. In the B s fit projection, the lower- and higher-mass background components described in the text are displayed as a single, merged “physicsbackground” component. The measurement of ∆ Γ ( B ) requires an acceptance correction for the differences be-tween signal and reference decays and the k -factor correction. The acceptance correctionaccounts for the difference in decay-time-dependent efficiency due to the combined ef-fect of the difference between D − and D − s lifetimes and the online requirements on thespatial separation between D − ( s ) and B s ) decay vertices: we apply to the B s sample aper-candidate weight, w i ≡ exp[∆ Γ ( D ) t ( D − s )], based on the ∆ Γ ( D ) result and the D − s decay time, such that the D − s and D − decay-time distributions become consistent. The k -factor correction is a candidate-specific correction, where the average missing momen-tum in a simulated sample is used to correct the reconstructed momentum in data. The k -factor dependence on the kinematic properties of each candidate is included througha dependence on m Dµ , k ( m Dµ ) = h p Dµ /p true i , where p true indicates the true momentumof the B s ) meson. The equalization of the compositions of simulated and experimentaldata samples ensures that the k -factor distribution specific to each of the four signal andreference decays is unbiased. We determine ∆ Γ ( B ) with the same fit of m corr used tomeasure ∆ Γ ( D ) but where the ratios of signal and reference yields are determined asfunctions of the B s ) decay time. The decay-time smearing due to the k -factor spreadis included in the fit. After the D − s lifetime weighting, the decay-time acceptances ofsimulated signal and reference modes are consistent, with a p -value of 83%, and are notincluded in the fit. The fit is shown in the middle panel of Fig. 3; the resulting widthdifference is ∆ Γ ( B ) = − . ± . − , with 91% p -value.5 decay time [ps] ) s ( − D ) B / s B ( R LHCbDataFit decay time [ps] ) s (0 B ) B / s B ( R decay time [ps] B ) π KK B / ππ K B ( R Figure 3: Ratio between acceptance-corrected yields of signal B s → [ K + K − π − ] D ( ∗ ) − s µ + ν µ andreference B → [ K + K − π − ] D ( ∗ ) − µ + ν µ decay yields as a function of (top panel) charm-meson and(middle panel) bottom-meson decay time. The bottom panel shows the ratio between acceptance-corrected B decay yields in the [ K + π − π − ] D ( ∗ ) − µ + ν µ and [ K + K − π − ] D ( ∗ ) − µ + ν µ channels as afunction of B decay time. Fit results are overlaid. Relevant for the results is only the slopeof the ratios as a function of decay time; absolute ratios, which depend on the decay yields,weighting, and efficiencies, are irrelevant. To check against biases due to differing acceptances and kinematic properties, theanalysis is validated with a null test. We repeat the width-difference determination byusing the same reference B → [ K + K − π − ] D ( ∗ ) − µ + ν µ sample and replacing the signaldecays with 2.1 million B → [ K + π − π − ] D ( ∗ ) − µ + ν µ decays, where the D − is reconstructedin the K + π − π − final state (Fig. 3, bottom panel). Differing momentum and vertex-displacement selection criteria induce up to 10% differences between acceptances as afunction of D − decay time and up to 25% variations as a function of B decay time.Acceptance ratios are therefore included in the fit. The p -values are 21% for the B fitand 33% for the D − fit. The resulting width differences, ∆ Γ ( D ) = ( − ± × − ps − and ∆ Γ ( B ) = ( − . ± . × − ps − , are consistent with zero.We assess independent systematic uncertainties due to (i) potential fit biases; (ii) as-sumptions on the components contributing to the sample and their mass distributions;(iii) assumptions on the signal decay model, e.g., choice of B s → D ∗− s form factors; (iv) un-certainties on the decay-time acceptances; (v) uncertainties on the decay-time resolution;(vi) contamination from B s candidates produced in B + c decays; and (vii) mismodeling oftransverse-momentum ( p T ) differences between B and B s mesons. We evaluate each con-tribution by including the relevant effect in the model and repeating the whole analysison ensembles of simulated experiments that mirror the data. For the ∆ Γ ( D ) result, the6ystematic uncertainty is dominated by a 0.0049 ps − contribution due to the decay-timeacceptance, and a 0.0039 ps − contribution due to the decay-time resolution. A smallercontribution of 0.0018 ps − arises from possible mismodeling of p T differences in B and B s production. For the ∆ Γ ( B ) result, a 0.0028 ps − uncertainty from mismodeling of p T differences between B and B s mesons and a 0.0025 ps − contribution from the B s decay model dominate. Smaller contributions arise from B + c feed-down (0.0010 ps − ),residual fit biases (0.0009 ps − ), sample composition (0.0005 ps − ), and decay-time accep-tance and resolution (0.0004 ps − each). The uncertainties associated with the limitedsize of simulated samples are included in the fit χ and contribute up to 20% of thestatistical uncertainties. The uncertainty in the decay length has negligible impact. Con-sistency checks based on repeating the measurement independently on subsamples chosenaccording to data-taking time, online-selection criteria, charged-particle and vertex mul-tiplicities, momentum of the K + K − π − µ + system, and whether only the D − s µ + ν µ or the D ∗− s µ + ν µ channel is considered as signal, all yield results compatible with statistical fluc-tuations.In summary, we report world-leading measurements of B s and D − s meson lifetimesusing a novel method. We reconstruct B s → D ∗− s µ + ν µ and B s → D − s µ + ν µ decays fromproton-proton collision data collected by the LHCb experiment and corresponding to3.0 fb − of integrated luminosity. We use B → D ∗− µ + ν µ and B → D − µ + ν µ decaysreconstructed in the same final state as a reference to suppress systematic uncertainties.The resulting width differences are ∆ Γ ( B ) = − . ± . ± . − and ∆ Γ ( D ) = 1 . ± . ± . − . Their correlation is negligible.Using the known values of the B [8, 17] and D − lifetimes [8, 18], we determine the flavor-specific B s lifetime, τ fs B s = 1 . ± .
013 (stat) ± .
010 (syst) ± .
004 ( τ B ) ps, and the D − s lifetime, τ D − s = 0 . ± . ± . ± . τ D ) ps; the last uncertaintiesare due to the limited knowledge of the B and D − lifetime, respectively. The results areconsistent with, and significantly more precise than the current values [4–6]. They mightoffer improved insight into the interplay between strong and weak interactions in thedynamics of heavy mesons and sharpen the reach of current and future indirect searchesfor non-standard-model physics. Acknowledgments
We thank Alexander Lenz for useful discussions. We express our gratitude to our col-leagues in the CERN accelerator departments for the excellent performance of the LHC.We thank the technical and administrative staff at the LHCb institutes. We acknowl-edge support from CERN and from the national agencies: CAPES, CNPq, FAPERJ andFINEP (Brazil); MOST and NSFC (China); CNRS/IN2P3 (France); BMBF, DFG andMPG (Germany); INFN (Italy); NWO (The Netherlands); MNiSW and NCN (Poland);MEN/IFA (Romania); MinES and FASO (Russia); MinECo (Spain); SNSF and SER(Switzerland); NASU (Ukraine); STFC (United Kingdom); NSF (USA). We acknowledgethe computing resources that are provided by CERN, IN2P3 (France), KIT and DESY(Germany), INFN (Italy), SURF (The Netherlands), PIC (Spain), GridPP (United King-dom), RRCKI and Yandex LLC (Russia), CSCS (Switzerland), IFIN-HH (Romania),CBPF (Brazil), PL-GRID (Poland) and OSC (USA). We are indebted to the communi-ties behind the multiple open source software packages on which we depend. Individual7roups or members have received support from AvH Foundation (Germany), EPLANET,Marie Sk lodowska-Curie Actions and ERC (European Union), Conseil G´en´eral de Haute-Savoie, Labex ENIGMASS and OCEVU, R´egion Auvergne (France), RFBR and YandexLLC (Russia), GVA, XuntaGal and GENCAT (Spain), Herchel Smith Fund, The RoyalSociety, Royal Commission for the Exhibition of 1851 and the Leverhulme Trust (UnitedKingdom).
References [1] For a recent review, see A. Lenz,
Lifetimes and HQE , arXiv:1405.3601 and refer-ences therein.[2] Heavy Flavor Averaging Group, Y. Amhis et al. , Averages of b -hadron, c -hadron,and τ -lepton properties as of summer 2016 , arXiv:1612.07233 , updated results andplots available at .[3] K. Hartkorn and H. G. Moser, A new method of measuring ∆(Γ) / Γ in the B s - B s system , Eur. Phys. J. C8 (1999) 381.[4] LHCb collaboration, R. Aaij et al. , Measurement of the B s meson lifetime in D + s π − decays , Phys. Rev. Lett. (2014) 172001, arXiv:1407.5873 .[5] D0 collaboration, V. M. Abazov et al. , Measurement of the B s lifetime in theflavor-specific decay channel B s → D − s µ + νX , Phys. Rev. Lett. (2015) 062001, arXiv:1410.1568 .[6] FOCUS collaboration, J. M. Link et al. , A measurement of the D + s lifetime ,Phys. Rev. Lett. (2005) 052003, arXiv:hep-ex/0504056 .[7] Fermilab E653 collaboration, K. Kodama et al. , Measurement of the relative branch-ing fraction Γ( D → Kµν ) / Γ( D → µX ), Phys. Rev. Lett. (1991) 1819.[8] Particle Data Group, C. Patrignani et al. , Review of particle physics ,Chin. Phys.
C40 (2016) 100001.[9] CDF collaboration, A. Abulencia et al. , Observation of B s - B s oscillations ,Phys. Rev. Lett. (2006) 242003, arXiv:hep-ex/0609040 .[10] N. T. Leonardo, Analysis of B s flavor oscillations at CDF , PhD thesis, FERMILAB-THESIS-2006-18, (2006).[11] LHCb collaboration, A. A. Alves Jr. et al. , The LHCb detector at the LHC ,JINST (2008) S08005.[12] LHCb collaboration, R. Aaij et al. , LHCb detector performance ,Int. J. Mod. Phys.
A30 (2015) 1530022, arXiv:1412.6352 .[13] M. Clemencic et al. , The LHCb simulation application, Gauss: Design, evolutionand experience , J. Phys. Conf. Ser. (2011) 032023.814] I. Belyaev et al. , Handling of the generation of primary events in Gauss, the LHCbsimulation framework , J. Phys. Conf. Ser. (2011) 032047.[15] I. Caprini, L. Lellouch, and M. Neubert,
Dispersive bounds on the shape of B → D ( ∗ ) ℓ ¯ ν ℓ form factors , Nucl. Phys. B530 (1998) 153, arXiv:hep-ph/9712417 .[16] R. Aaij et al. , The LHCb trigger and its performance in 2011 ,JINST (2013) P04022, arXiv:1211.3055 .[17] LHCb collaboration, R. Aaij et al. , Measurements of the B + , B , B s meson and Λ b baryon lifetimes , JHEP (2014) 114, arXiv:1402.2554 .[18] FOCUS collaboration, J. M. Link et al. , New measurements of the D and D + life-times , Phys. Lett. B537 (2002) 192, arXiv:hep-ex/0203037 .9 HCb collaboration
R. Aaij , B. Adeva , M. Adinolfi , 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. Andreassi , M. Andreotti ,g ,J.E. Andrews , R.B. Appleby , F. Archilli , P. d’Argent , J. Arnau Romeu ,A. Artamonov , M. Artuso , E. Aslanides , G. Auriemma , M. Baalouch , I. Babuschkin ,S. Bachmann , J.J. Back , A. Badalov , C. Baesso , S. Baker , V. Balagura ,c ,W. Baldini , A. Baranov , R.J. Barlow , C. Barschel , S. Barsuk , W. Barter ,F. Baryshnikov , M. Baszczyk , V. Batozskaya , B. Batsukh , V. Battista , A. Bay ,L. Beaucourt , J. Beddow , F. Bedeschi , I. Bediaga , A. Beiter , L.J. Bel , V. Bellee ,N. Belloli ,i , K. Belous , I. Belyaev , E. Ben-Haim , G. Bencivenni , S. Benson ,S. Beranek , A. Berezhnoy , R. Bernet , A. Bertolin , C. Betancourt , F. Betti ,M.-O. Bettler , M. van Beuzekom , Ia. Bezshyiko , S. Bifani , P. Billoir , A. Birnkraut ,A. Bitadze , A. Bizzeti ,u , T. Blake , F. Blanc , J. Blouw , † , S. Blusk , V. Bocci ,T. Boettcher , A. Bondar ,w , N. Bondar , W. Bonivento , I. Bordyuzhin ,A. Borgheresi ,i , S. Borghi , M. Borisyak , M. Borsato , F. Bossu , M. Boubdir ,T.J.V. Bowcock , E. Bowen , C. Bozzi , , S. Braun , T. Britton , J. Brodzicka ,E. Buchanan , C. Burr , A. Bursche , J. Buytaert , S. Cadeddu , R. Calabrese ,g ,M. Calvi ,i , M. Calvo Gomez ,m , A. Camboni , P. Campana , D.H. Campora Perez ,L. Capriotti , A. Carbone ,e , G. Carboni ,j , R. Cardinale ,h , A. Cardini , P. Carniti ,i ,L. Carson , K. Carvalho Akiba , G. Casse , L. Cassina ,i , L. Castillo Garcia ,M. Cattaneo , G. Cavallero , R. Cenci ,t , D. Chamont , M. Charles , Ph. Charpentier ,G. Chatzikonstantinidis , M. Chefdeville , S. Chen , S.-F. Cheung , V. Chobanova ,M. Chrzaszcz , , A. Chubykin , X. Cid Vidal , G. Ciezarek , P.E.L. Clarke ,M. Clemencic , H.V. Cliff , J. Closier , V. Coco , J. Cogan , E. Cogneras , V. Cogoni ,f ,L. Cojocariu , P. Collins , A. Comerma-Montells , A. Contu , A. Cook , G. Coombs ,S. Coquereau , G. Corti , M. Corvo ,g , C.M. Costa Sobral , B. Couturier , G.A. Cowan ,D.C. Craik , A. Crocombe , M. Cruz Torres , S. Cunliffe , R. Currie , C. D’Ambrosio ,F. Da Cunha Marinho , E. Dall’Occo , J. Dalseno , P.N.Y. David , A. Davis ,K. De Bruyn , S. De Capua , M. De Cian , J.M. De Miranda , L. De Paula ,M. De Serio ,d , P. De Simone , C.T. Dean , D. Decamp , M. Deckenhoff , L. Del Buono ,H.-P. Dembinski , M. Demmer , A. Dendek , D. Derkach , O. Deschamps , F. Dettori ,B. Dey , A. Di Canto , P. Di Nezza , H. Dijkstra , F. Dordei , M. Dorigo ,A. Dosil Su´arez , A. Dovbnya , K. Dreimanis , L. Dufour , G. Dujany , K. Dungs ,P. Durante , R. Dzhelyadin , M. Dziewiecki , A. Dziurda , A. Dzyuba , N. D´el´eage ,S. Easo , M. Ebert , U. Egede , V. Egorychev , S. Eidelman ,w , S. Eisenhardt ,U. Eitschberger , R. Ekelhof , L. Eklund , S. Ely , S. Esen , H.M. Evans , T. Evans ,A. Falabella , N. Farley , S. Farry , R. Fay , D. Fazzini ,i , D. Ferguson , G. Fernandez ,A. Fernandez Prieto , F. Ferrari , F. Ferreira Rodrigues , M. Ferro-Luzzi , S. Filippov ,R.A. Fini , M. Fiore ,g , M. Fiorini ,g , M. Firlej , C. Fitzpatrick , T. Fiutowski ,F. Fleuret ,b , K. Fohl , M. Fontana , , F. Fontanelli ,h , D.C. Forshaw , R. Forty ,V. Franco Lima , M. Frank , C. Frei , J. Fu ,q , W. Funk , E. Furfaro ,j , C. F¨arber ,A. Gallas Torreira , D. Galli ,e , S. Gallorini , S. Gambetta , M. Gandelman , P. Gandini ,Y. Gao , L.M. Garcia Martin , J. Garc´ıa Pardi˜nas , J. Garra Tico , L. Garrido ,P.J. Garsed , D. Gascon , C. Gaspar , L. Gavardi , G. Gazzoni , D. Gerick ,E. Gersabeck , M. Gersabeck , T. Gershon , Ph. Ghez , S. Gian`ı , V. Gibson ,O.G. Girard , L. Giubega , K. Gizdov , V.V. Gligorov , D. Golubkov , A. Golutvin , ,A. Gomes ,a , I.V. Gorelov , C. Gotti ,i , E. Govorkova , R. Graciani Diaz ,L.A. Granado Cardoso , E. Graug´es , E. Graverini , G. Graziani , A. Grecu , R. Greim , . Griffith , L. Grillo , ,i , B.R. Gruberg Cazon , O. Gr¨unberg , E. Gushchin , Yu. Guz ,T. Gys , C. G¨obel , T. Hadavizadeh , C. Hadjivasiliou , G. Haefeli , C. Haen ,S.C. Haines , B. Hamilton , X. Han , S. Hansmann-Menzemer , N. Harnew ,S.T. Harnew , J. Harrison , M. Hatch , J. He , T. Head , A. Heister , K. Hennessy ,P. Henrard , L. Henry , E. van Herwijnen , M. Heß , A. Hicheur , D. Hill , C. Hombach ,H. Hopchev , Z.-C. Huard , W. Hulsbergen , T. Humair , M. Hushchyn , D. Hutchcroft ,M. Idzik , P. Ilten , R. Jacobsson , J. Jalocha , E. Jans , A. Jawahery , F. Jiang ,M. John , D. Johnson , C.R. Jones , C. Joram , B. Jost , N. Jurik , S. Kandybei ,M. Karacson , J.M. Kariuki , S. Karodia , M. Kecke , M. Kelsey , M. Kenzie ,T. Ketel , E. Khairullin , B. Khanji , C. Khurewathanakul , T. Kirn , S. Klaver ,K. Klimaszewski , T. Klimkovich , S. Koliiev , M. Kolpin , I. Komarov , R. Kopecna ,P. Koppenburg , A. Kosmyntseva , S. Kotriakhova , A. Kozachuk , M. Kozeiha ,L. Kravchuk , M. Kreps , P. Krokovny ,w , F. Kruse , W. Krzemien , W. Kucewicz ,l ,M. Kucharczyk , V. Kudryavtsev ,w , A.K. Kuonen , K. Kurek , T. Kvaratskheliya , ,D. Lacarrere , G. Lafferty , A. Lai , G. Lanfranchi , C. Langenbruch , T. Latham ,C. Lazzeroni , R. Le Gac , J. van Leerdam , A. Leflat , , J. Lefran¸cois , R. Lef`evre ,F. Lemaitre , E. Lemos Cid , O. Leroy , T. Lesiak , B. Leverington , T. Li , Y. Li ,Z. Li , T. Likhomanenko , , R. Lindner , F. Lionetto , X. Liu , D. Loh , I. Longstaff ,J.H. Lopes , D. Lucchesi ,o , M. Lucio Martinez , H. Luo , A. Lupato , E. Luppi ,g ,O. Lupton , A. Lusiani , X. Lyu , F. Machefert , F. Maciuc , O. Maev , K. Maguire ,S. Malde , A. Malinin , T. Maltsev , G. Manca ,f , G. Mancinelli , P. Manning ,J. Maratas ,v , J.F. Marchand , U. Marconi , C. Marin Benito , M. Marinangeli ,P. Marino ,t , J. Marks , G. Martellotti , M. Martin , M. Martinelli , D. Martinez Santos ,F. Martinez Vidal , D. Martins Tostes , L.M. Massacrier , A. Massafferri , R. Matev ,A. Mathad , Z. Mathe , C. Matteuzzi , A. Mauri , E. Maurice ,b , B. Maurin ,A. Mazurov , M. McCann , , A. McNab , R. McNulty , B. Meadows , F. Meier ,D. Melnychuk , M. Merk , A. Merli ,q , E. Michielin , D.A. Milanes , M.-N. Minard ,D.S. Mitzel , A. Mogini , J. Molina Rodriguez , I.A. Monroy , S. Monteil , M. Morandin ,M.J. Morello ,t , O. Morgunova , J. Moron , A.B. Morris , R. Mountain , F. Muheim ,M. Mulder , M. Mussini , D. M¨uller , J. M¨uller , K. M¨uller , V. M¨uller , P. Naik ,T. Nakada , R. Nandakumar , A. Nandi , I. Nasteva , M. Needham , N. Neri , ,S. Neubert , N. Neufeld , M. Neuner , T.D. Nguyen , C. Nguyen-Mau ,n , S. Nieswand ,R. Niet , N. Nikitin , T. Nikodem , A. Nogay , A. Novoselov , D.P. O’Hanlon ,A. Oblakowska-Mucha , V. Obraztsov , S. Ogilvy , R. Oldeman ,f , C.J.G. Onderwater ,A. Ossowska , J.M. Otalora Goicochea , P. Owen , A. Oyanguren , P.R. Pais ,A. Palano ,d , M. Palutan , , A. Papanestis , M. Pappagallo ,d , L.L. Pappalardo ,g ,C. Pappenheimer , W. Parker , C. Parkes , G. Passaleva , A. Pastore ,d , M. Patel ,C. Patrignani ,e , A. Pearce , A. Pellegrino , G. Penso , M. Pepe Altarelli , S. Perazzini ,P. Perret , L. Pescatore , K. Petridis , A. Petrolini ,h , A. Petrov , M. Petruzzo ,q ,E. Picatoste Olloqui , B. Pietrzyk , M. Pikies , D. Pinci , A. Pistone , A. Piucci ,V. Placinta , S. Playfer , M. Plo Casasus , T. Poikela , F. Polci , M Poli Lener ,A. Poluektov , , I. Polyakov , E. Polycarpo , G.J. Pomery , S. Ponce , A. Popov ,D. Popov , , B. Popovici , S. Poslavskii , C. Potterat , E. Price , J. Prisciandaro ,C. Prouve , V. Pugatch , A. Puig Navarro , G. Punzi ,p , C. Qian , W. Qian ,R. Quagliani , , B. Rachwal , J.H. Rademacker , M. Rama , M. Ramos Pernas ,M.S. Rangel , I. Raniuk , F. Ratnikov , G. Raven , F. Redi , S. Reichert , A.C. dos Reis ,C. Remon Alepuz , V. Renaudin , 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 , † , A. Rogozhnikov , S. Roiser , A. Rollings , V. Romanovskiy ,A. Romero Vidal , J.W. Ronayne , M. Rotondo , M.S. Rudolph , T. Ruf , P. Ruiz Valls , .J. Saborido Silva , E. Sadykhov , N. Sagidova , B. Saitta ,f , V. Salustino Guimaraes ,D. Sanchez Gonzalo , C. Sanchez Mayordomo , B. Sanmartin Sedes , R. Santacesaria ,C. Santamarina Rios , M. Santimaria , E. Santovetti ,j , A. Sarti ,k , C. Satriano ,s ,A. Satta , D.M. Saunders , D. Savrina , , S. Schael , M. Schellenberg , M. Schiller ,H. Schindler , M. Schlupp , M. Schmelling , T. Schmelzer , B. Schmidt , O. Schneider ,A. Schopper , H.F. Schreiner , K. Schubert , M. Schubiger , M.-H. Schune ,R. Schwemmer , B. Sciascia , A. Sciubba ,k , A. Semennikov , A. Sergi , N. Serra ,J. Serrano , L. Sestini , P. Seyfert , M. Shapkin , I. Shapoval , Y. Shcheglov ,T. Shears , L. Shekhtman ,w , V. Shevchenko , B.G. Siddi , , R. Silva Coutinho ,L. Silva de Oliveira , G. Simi ,o , S. Simone ,d , M. Sirendi , N. Skidmore , T. Skwarnicki ,E. Smith , I.T. Smith , J. Smith , M. Smith , l. Soares Lavra , M.D. Sokoloff ,F.J.P. Soler , B. Souza De Paula , B. Spaan , P. Spradlin , S. Sridharan , F. Stagni ,M. Stahl , S. Stahl , P. Stefko , S. Stefkova , O. Steinkamp , S. Stemmle ,O. Stenyakin , H. Stevens , S. Stoica , S. Stone , B. Storaci , S. Stracka ,p ,M.E. Stramaglia , M. Straticiuc , U. Straumann , L. Sun , W. Sutcliffe , K. Swientek ,V. Syropoulos , M. Szczekowski , T. Szumlak , S. T’Jampens , A. Tayduganov ,T. Tekampe , G. Tellarini ,g , F. Teubert , E. Thomas , J. van Tilburg , M.J. Tilley ,V. Tisserand , M. Tobin , S. Tolk , L. Tomassetti ,g , D. Tonelli , S. Topp-Joergensen ,F. Toriello , R. Tourinho Jadallah Aoude , E. Tournefier , S. Tourneur , K. Trabelsi ,M. Traill , M.T. Tran , M. Tresch , A. Trisovic , A. Tsaregorodtsev , P. Tsopelas ,A. Tully , N. Tuning , A. Ukleja , A. Ustyuzhanin , U. Uwer , C. Vacca ,f ,V. Vagnoni , , A. Valassi , S. Valat , G. Valenti , R. Vazquez Gomez ,P. Vazquez Regueiro , S. Vecchi , M. van Veghel , J.J. Velthuis , M. Veltri ,r ,G. Veneziano , A. Venkateswaran , T.A. Verlage , M. Vernet , M. Vesterinen ,J.V. Viana Barbosa , B. Viaud , D. Vieira , M. Vieites Diaz , H. Viemann ,X. Vilasis-Cardona ,m , M. Vitti , V. Volkov , A. Vollhardt , B. Voneki , A. Vorobyev ,V. Vorobyev ,w , C. Voß , J.A. de Vries , C. V´azquez Sierra , R. Waldi , C. Wallace ,R. Wallace , J. Walsh , J. Wang , D.R. Ward , H.M. Wark , N.K. Watson ,D. Websdale , A. Weiden , M. Whitehead , J. Wicht , G. Wilkinson , , M. Wilkinson ,M. Williams , M.P. Williams , M. Williams , T. Williams , F.F. Wilson , J. Wimberley ,M.A. Winn , J. Wishahi , W. Wislicki , M. Witek , G. Wormser , S.A. Wotton ,K. Wraight , K. Wyllie , Y. Xie , Z. Xing , Z. Xu , Z. Yang , Z Yang , Y. Yao ,H. Yin , J. Yu , X. Yuan ,w , O. Yushchenko , K.A. Zarebski , M. Zavertyaev ,c ,L. Zhang , Y. Zhang , A. Zhelezov , Y. Zheng , X. Zhu , V. Zhukov , S. Zucchelli . 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 I. Physikalisches Institut, RWTH Aachen University, Aachen, Germany 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 Yandex School of Data Analysis, Moscow, Russia Budker Institute of Nuclear Physics (SB RAS), Novosibirsk, Russia Institute for High Energy Physics (IHEP), Protvino, Russia ICCUB, Universitat de Barcelona, Barcelona, Spain Universidad de Santiago de Compostela, Santiago de Compostela, Spain European Organization for Nuclear Research (CERN), Geneva, Switzerland Institute of Physics, 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, TheNetherlands 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
University of Chinese Academy of Sciences, Beijing, China, associated to
School of Physics and Technology, Wuhan University, Wuhan, China, 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
Instituto de Fisica Corpuscular, Centro Mixto Universidad de Valencia - CSIC, Valencia, Spain,associated to