University of Groningen
Updated measurement of decay-time-dependent CP asymmetries in D0 → K+K− and D0 → π
+ π − decays
Onderwater, C. J. G.; van Veghel, M.; LHCb Collaboration
Published in: Physical Review D DOI:
10.1103/PhysRevD.101.012005
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Onderwater, C. J. G., van Veghel, M., & LHCb Collaboration (2020). Updated measurement of decay-time-dependent CP asymmetries in D0 → K+K− and D0 → π + π − decays. Physical Review D, 101(1), [012005]. https://doi.org/10.1103/PhysRevD.101.012005
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Updated measurement of decay-time-dependent CP asymmetries
in D
0→ K
+K
−and D
0→ π
+π
−decays
R. Aaijet al.* (LHCb Collaboration)
(Received 3 November 2019; published 13 January 2020)
A search for decay-time-dependent charge-parity (CP) asymmetry in D0→ KþK− and D0→ πþπ− decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of5.4 fb−1. TheD0 mesons are required to originate from semileptonic decays of b hadrons, such that the charge of the muon identifies the flavor of the neutralD meson at production. The asymmetries in the effective decay widths of D0 and ¯D0 mesons are determined to be AΓðKþK−Þ ¼ ð−4.3 3.6 0.5Þ × 10−4 and AΓðπþπ−Þ ¼ ð2.2 7.0 0.8Þ × 10−4, where the uncertainties are statistical and systematic, respectively. The results are consistent withCP symmetry and, when combined with previous LHCb results, yield AΓðKþK−Þ ¼ ð−4.4 2.3 0.6Þ × 10−4 andAΓðπþπ−Þ ¼ ð2.5 4.3 0.7Þ × 10−4.
DOI:10.1103/PhysRevD.101.012005
I. INTRODUCTION
Charge-parity (CP) violation is one of the key ingre-dients that are needed to generate the asymmetry between matter and antimatter observed in the Universe [1]. The Standard Model (SM) of particle physics, where all known CP-violating processes arise from the irreducible phase of the Cabibbo-Kobayashi-Maskawa matrix [2,3], is, how-ever, unable to explain the observed asymmetry[4,5]. New dynamics that lead to a significant enhancement of CP-violating processes are required, making searches forCP violation a powerful probe for physics beyond the SM. Although CP violation has been experimentally observed in the down-type quark sector with measurements ofK and B mesons[6–10], no indication of new dynamics has been reported yet. Only recently hasCP violation been observed in the decay of charmed mesons[11]. The limited precision of the SM predictions, together with the limited amount of experimental information available [12], is, however, not yet sufficient to establish whether the observed signal could be explained by the SM[13–18]. Additional searches for CP violation in the charm sector, and particularly for more suppressed and yet-to-be-observed signs of CP-violating effects induced byD0- ¯D0mixing, have unique potential to probe for the existence of beyond-the-SM dynamics, which couple preferentially to up-type quarks [19–24].
This paper reports a search for CP violation in D0- ¯D0 mixing, or in the interference between mixing and decay, through the measurement of the asymmetry between the effective decay widths, ˆΓ, of mesons initially produced as D0 and ¯D0 and decaying into the CP-even final states f ¼ KþK−, πþπ−:
AΓðfÞ ≡ ˆΓðD
0→ fÞ − ˆΓð ¯D0→ fÞ
ˆΓðD0→ fÞ þ ˆΓð ¯D0→ fÞ: ð1Þ Several measurements of the parameterAΓðfÞ have been performed by the BABAR[25], CDF[26], Belle[27], and LHCb [28–30] Collaborations, leading to the current world-average value of ð−3.2 2.6Þ × 10−4 [12], when neglecting differences between theD0→ KþK−andD0→ πþπ− decays.1
The achieved sensitivity is still 1 order of magnitude larger than the theoretical predictions of AΓ≈ 3 × 10−5[31]. This paper updates the LHCb measurements of Refs.[28–30] using the data sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV during 2016–2018, and corresponding to an integrated luminosity of5.4 fb−1. The analysis is performed usingD0 mesons originating from semileptonic decays ofb hadrons, where the b-hadron candidates are only partially recon-structed. The charge of the muon identifies (“tags”) the flavor of theD0meson at its production. The samples are dominated by B− → D0μ−X and ¯B0→ D0μ−X decays,
*Full author list given at the end of the article.
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1Throughout the paper, the inclusion of the charge-conjugate decay mode is implied unless otherwise stated.
whereX denotes any set of final-state particles that are not reconstructed.
The paper is structured as follows: the analysis strategy is described in Sec. II; the LHCb detector is sketched in Sec. III; Sec. IV details the criteria used to select the signal and control samples; Sec. V describes the fit method, and its validation using D0→ K−πþ decays; the determination of the systematic uncertainties is outlined in Sec. VI, before concluding with the presentation of the final results in Sec.VII.
II. ANALYSIS STRATEGY
Due to the weak interactions, the mass eigenstates of neutral charm mesons, D1 and D2, are a superposition of the flavor states, D0 and ¯D0: jD1;2i ≡ pjD0i qj ¯D0i, where q and p are complex coefficients satisfying jpj2þ jqj2¼ 1. Hence, an originally produced D0 meson can oscillate as a function of time into a ¯D0meson, and vice versa, before decaying. In the limit of CP symmetry, q equals p and the oscillations are characterized by only two dimensionless parameters, x ≡ ðm1− m2Þc2=Γ and y ≡ ðΓ1− Γ2Þ=2Γ, where m1ð2Þ and Γ1ð2Þ are the mass and decay width of the CP-even (odd) eigenstate D1ð2Þ, respectively, and Γ ≡ ðΓ1þ Γ2Þ=2 is the average decay width[32]. The values ofx and y have been measured to be of the order of 1% or smaller[12]. In the presence ofCP violation, the mixing rates for mesons produced asD0and ¯D0 differ, further enriching the phenomenology. As an example, indicating withAf( ¯Af) the decay amplitude of a D0 ( ¯D0) meson into the final state f, three different manifestations of CP violation can be measured: (i) CP violation in the decay ifAdirCPðfÞ ≡ ðjAfj2− j ¯Afj2Þ=ðjAfj2þ j ¯Afj2Þ differs from zero, (ii) CP violation in mixing if jq=pj differs from unity, and (iii)CP violation in the interference between mixing and decay if ϕf≡ arg½ðq ¯AfÞ=ðpAfÞ differs from zero. The latter two can be accessed by measuring the decay-time-dependent CP asymmetry ACPðD0→ f; tÞ ¼ΓðD
0ðtÞ → fÞ − Γð ¯D0ðtÞ → fÞ ΓðD0ðtÞ → fÞ þ Γð ¯D0ðtÞ → fÞ: ð2Þ In the limit of small mixing parameters, Eq. (2) can be approximated as a linear function of decay time[33,34],
ACPðD0→ f; tÞ ≈ AdirCPðfÞ − AΓðfÞτt; ð3Þ whereτ ¼ 1=Γ is the average lifetime of neutral D mesons. The coefficient AΓðfÞ is related to the mixing and CP-violation parameters by [35]
AΓðfÞ ≈ −xϕfþ yðjq=pj − 1Þ − yAdirCPðfÞ: ð4Þ Contrarily to the measurement reported in Ref.[11], which is sensitive toAdir
CPðKþK−Þ − AdirCPðπþπ−Þ, AΓðfÞ is mostly
sensitive toCP violation in mixing or in the interference between mixing and decay, because the term yAdir
CPðfÞ ≤ 10−5 [12] can be neglected at the current level of exper-imental precision. Moreover, neglecting theOð10−3Þ differ-ence between the weak phases of the decay amplitudes to the CP-even final states KþK− and πþπ−, ϕf≈ ϕ ≡ argðq=pÞ becomes universal and AΓindependent off[22]. Experimentally, the partial rate asymmetry of Eq. (2)
cannot be measured directly because of charge-asymmetric detection efficiencies and asymmetric production rates of D0and ¯D0mesons from semileptonicb-hadron decays in proton-proton collisions. Instead, the “raw” asymmetry between theD0and ¯D0mesons yields,
ArawðD0→ fÞ
¼Nð ¯B → D0ð→ fÞμ−XÞ − NðB → ¯D0ð→ fÞμþXÞ Nð ¯B → D0ð→ fÞμ−XÞ þ NðB → ¯D0ð→ fÞμþXÞ; ð5Þ is measured as a function of decay time. Neglecting higher-order terms in the involved asymmetries, which are at most Oð1%Þ, the raw asymmetry can be approximated as ArawðD0→ f;tÞ ≈ ACPðD0→ f;tÞ þ ADðμÞþ APðDÞ; ð6Þ whereADðμÞ and APðDÞ are the nuisance asymmetries due to the detection efficiency of the tagging muon and to the production rates of the neutralD mesons, respectively. The parameterAΓ corresponds to the slope of the decay-time-dependent raw asymmetry only if AD and AP are inde-pendent of decay time. In this analysis, a possible time dependence of AD and AP is considered as a source of systematic uncertainty. The analysis procedure is validated on data using a control sample of Cabibbo-favoredD0→ K−πþdecays, whose size exceeds that of theD0→ KþK− andD0→ πþπ−signal modes by approximately 1 order of magnitude, and where measured asymmetries can be attributed solely to instrumental effects because no CP violation is expected. To avoid potential experimenter’s bias, the measured values of AΓðKþK−Þ and AΓðπþπ−Þ remained unknown during the development of the analysis and were examined only after the analysis procedure and the evaluation of the systematic uncertainties were finalized.
III. DETECTOR
The LHCb detector [36,37] is a single-arm forward spectrometer covering the pseudorapidity range2 < η < 5, designed for the study of particles containingb or c quarks. The detector includes a high-precision tracking system consisting of a silicon-strip vertex detector surrounding the pp interaction region, a large-area silicon-strip detector located upstream of a dipole magnet with a bending power of about 4 Tm, and three stations of silicon-strip detectors and straw drift tubes placed downstream of the magnet.
The tracking system provides a measurement of the momentum, p, of charged particles with relative uncer-tainty that varies from 0.5% at low momentum to 1.0% at 200 GeV=c. The minimum distance of a track to a primary vertex (PV), the impact parameter, is measured with a resolution ofð15 þ 29=pTÞ μm, where pTis the component of the momentum transverse to the beam, in GeV=c. Different types of charged hadrons are distinguished using information from two ring-imaging Cherenkov detectors. Photons, electrons, and hadrons are identified by a calorim-eter system consisting of scintillating-pad and preshower detectors, an electromagnetic and a hadronic calorimeter. Muons are identified by a system composed of alternating layers of iron and multiwire proportional chambers. The magnetic-field polarity is reversed periodically during data taking to mitigate the differences of reconstruction efficien-cies of particles with opposite charges.
The on-line event selection is performed by a trigger, which consists of a hardware stage followed by a two-level software stage. In between the two software stages, an alignment and calibration of the detector is performed in near real time [38]. The same alignment and calibration information is propagated to the off-line reconstruction, ensuring consistent and high-quality particle identification information between the trigger and off-line software. The identical performance of the on-line and off-line recon-structions offers the opportunity to perform physics analy-ses directly using candidates reconstructed in the trigger
[39,40], which the present analysis exploits. IV. SELECTION
The selection criteria are mainly inherited from the measurement of the difference between the decay-time-integrated CP asymmetries in D0→ KþK− and D0→ πþπ− decays[11], which uses the same sample of proton-proton collisions. Signal candidates are first required to pass the hardware trigger, which selects events containing at least one charged particle with high transverse momen-tum that leaves a track in the muon system. At the first stage of the software trigger, events are selected if they contain at least one track having large transverse momentum and being incompatible with originating from any PV, or if any two-track combination forming a secondary vertex passes a multivariate classifier. If a particle is identified as a muon, a lower pT threshold is applied. At the second stage of the software trigger, the full event reconstruction is performed, and requirements on kinematic, topological, and particle-identification criteria are placed on the signal candidates. A D0 candidate is formed by combining two well-reconstructed, oppositely charged tracks such that they are consistent with originating from a common vertex. The D0 candidate must satisfy requirements on the vertex quality and has to be well separated from all PVs in the event. At the next step, theD0candidate is combined with a muon to form aB candidate. Only candidates where the D0
meson decays downstream along the beam axis with respect to theB candidate are further considered. The B candidate must have a visible mass,mðD0μÞ, and a corrected mass, mcorrðBÞ, consistent with a signal decay. The corrected mass is computed as mcorrðBÞ ≡pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffim2ðD0μÞ þ p2⊥ðD0μÞþ p⊥ðD0μÞ, where p⊥ðD0μÞ is the momentum of the D0μ system transverse to the B flight direction, to partially correct for the unreconstructed particles in the decay of theB hadron.
In the off-line selection, trigger signals are associated with reconstructed particles. Particle-identification criteria and requirements on mðD0μÞ and mcorrðBÞ are tightened with respect to the on-line selection. The mass of the D0 candidate is required to be in the ranges ½1825; 1925 MeV=c2, ½1820; 1939 MeV=c2, and ½1780; 1940 MeV=c2 for D0→ KþK−, D0→ πþπ−, and D0→ K−πþdecays, respectively, to reduce the amount of background decays with misidentified final-state particles to a negligible level. The reconstructed decay time is computed from the distance, L, between the measured D0 and B decay vertices and from the D0 momentum, pðD0Þ, as t ¼ m
D0L=½pðD0Þc, where mD0is the knownD0
mass [32]. AllD0 candidates with a reconstructed decay time that is either negative or exceeds 10 times the D0 lifetime are discarded. Mass vetoes suppress background from misreconstructedB decays to final states involving a charmonium resonance, such as B−→ ψð0Þð→ μþμ−Þh− withh ¼ π or K, where a muon is misidentified as a pion or kaon and is used in the D0 final state. Tag muons reconstructed in regions of phase space with large instru-mental asymmetries, due to muons of one charge either being bent out of the detector acceptance or deflected into the LHC beam pipe, are vetoed. The fraction of signal candidates removed by this requirement is 10%. In addi-tion, forD0→ K−πþ decays, candidates with kaon pT< 800 MeV=c are removed to reduce instrumental asymme-try between the detection of negatively and positively charged kaons. Since these requirements do not reduce the background to a sufficiently low level forD0→ KþK− andD0→ πþπ−decays, a dedicated boosted decision tree (BDT) is trained to isolate the signal candidates from background made of accidental combinations of charged particles (“combinatorial background”). The variables used in the BDT to discriminate signal from combinatorial background are the fit quality of theD0and the B decay vertices, the D0 flight distance, the D0 impact parameter with respect to the closest PV, the transverse momenta of the D0 decay products, the significance of the distance between theD0andB decay vertices, and the visible and corrected masses of theB-hadron candidate. The BDT is trained using D0→ K−πþ decays as signal proxies and candidates from theD0mass sidebands of the signal decay modes as background. The optimal requirement on the BDT discriminant is chosen by maximizing the figure of
merit S=pffiffiffiffiffiffiffiffiffiffiffiffiffiS þ B in a range corresponding to approxi-mately 3 times the mass resolution around the D0 mass, where S and B denote the signal and background yields, respectively. If an event contains more than one candidate after the full selection, one is chosen at random. The fraction of candidates removed by this requirement is 0.4%. The mass distributions of the selected signal- and control-decay candidates are shown in Fig.1. Details about the fit model are given in the next section. Approximately 9 × 106, 3 × 106, and 76 × 106 signal D0→ KþK−, D0→ πþπ−, and D0→ K−πþ decays, respectively, are
reconstructed over a smooth background dominated by accidental combinations of charged particles.
V. FIT METHOD
The samples of selectedD0→ KþK−,D0→ πþπ−, and D0→ K−πþ candidates are split into 20 approximately equally populated subsets (“bins”) of decay time in the range½0; 10τ. In each decay-time bin, the raw asymmetry Araw is determined by a simultaneous binnedχ2 fit to the mðD0Þ distributions of the D0 and ¯D0 candidates, split according to the muon tag. The total signal yields and asymmetries are treated as shared floating parameters of the fit. The fits include two components: signal and combina-torial background. The signal is described with a sum of a Gaussian and a Johnson’s SU distribution [41], with parameters determined from a fit to the decay-time-integrated mass spectra. To account for the observed dependence of the signal mass shape on decay time, the means and widths of the signal distributions are left free to float individually for each decay-time bin. The mass shape is assumed to be the same for D0 and ¯D0 candidates for charge-symmetric final states of the signal modes, and allowed to differ forD0→ K−πþ and ¯D0→ Kþπ− candi-dates. The combinatorial background is described by a linear function, with a slope that floats independently in each decay-time bin and is allowed to differ between D0 and ¯D0 candidates.
The raw asymmetry measured in decay-time bini is fit by minimizing the least squares with respect to the linear function Arawð0Þ − AΓhtii=τ. The decay-time-independent terms of Eqs. (3) and (6) are incorporated into a single parameter, Arawð0Þ, that is determined by the fit together with AΓ. The average decay time in each bin i, htii, is computed using the decay-time distribution of background-subtractedD0candidates. Statistically consistent values are found for the control and signal modes. TheD0lifetimeτ is set to its known value [32]. Using large samples of simulated experiments, it is verified that the analysis procedure leads to unbiased estimates of the fit parameters and of their uncertainties. Figure2shows the projection of the decay-time-dependent fit to the D0→ K−πþ control
1840 1860 1880 1900 ] 2 c [MeV/ ) − K + m(K 0 50 100 150 200 250 300 3 10 × 2c
Candidates per 0.45 MeV/
TeV LHCb 13 − K + K → 0 D Data Fit Comb. backg. (a) 1850 1900 ] 2 c [MeV/ ) − π + π m( 0 10 20 30 40 50 60 70 80 90 100 3 10 × 2c
Candidates per 0.6 MeV/
TeV LHCb 13 − π + π → 0 D Data Fit Comb. backg. (b) 1800 1850 1900 ] 2 c [MeV/ ) + π − m(K 0 0.5 1 1.5 2 2.5 3 3.5 6 10 × 2c
Candidates per 0.8 MeV/
TeV LHCb 13 + π − K → 0 D Data Fit Comb. backg. (c)
FIG. 1. Mass distributions of (a)D0→ KþK−, (b)D0→ πþπ−, and (c)D0→ K−πþcandidates with fit projections overlaid.
10 4 2 0 τ t/ 1.5 − 1.4 − 1.3 − 1.2 − 1.1 − 1 − 0.9 − 0.8 − 0.7 − 0.6 − 0.5 − ) [%]t ( raw A TeV LHCb 13 + π − K → 0 D Data Fit
FIG. 2. Raw asymmetry as a function of decay time with fit projection overlaid forD0→ K−πþsignal candidates.
sample. Here AΓ is measured to be ð1.6 1.2Þ × 10−4, where the uncertainty is statistical only. The measured value is consistent with zero as expected, confirming the validity of the assumption of decay-time-independent nuisance asymmetries. InD0→ K−πþ decays, due to their charge-asymmetric final states, detection asymmetries are more pronounced compared to the signal modes, where these asymmetries are only caused by the muons used to tag the flavor of the D0 mesons.
VI. SYSTEMATIC UNCERTAINTIES
The systematic uncertainty is dominated by the follow-ing contributions: the impact of decay-time acceptance and resolution, the effect of neglected background from combi-nations of realD0candidates with unrelated muons (which might lead to a wrong identification of the neutralD-meson flavor), and the impact of the assumed parametrization of the signal and background mass shapes. These effects are studied using large samples of pseudoexperiments, where the above sources of systematic biases are simulated.
The average decay-time resolution is estimated to be 127 fs using simulated decays. In the generation of the pseudoexperiments, the resolution is increased by 10% to account for differences between data and simulation. The decay-time acceptance is estimated from data by comparing the background-subtracted decay-time distributions of D0→ K−πþ candidates with an exponential function con-voluted with the decay-time resolution. Different sets of pseudoexperiments, simulating the effect of decay-time acceptance and resolution, are generated with values ofAΓ in the range ½−30; 30 × 10−4. Each pseudoexperiment is then fit with the default analysis approach, and the differ-ence between the measured and the input values of AΓ is used to determine the systematic bias. As the bias is found to depend linearly on the true value ofAΓ, the largest bias observed within the 68% confidence-level interval of the current world average [12] is taken as the systematic uncertainty. This amounts to 0.3 × 10−4 (0.4 × 10−4) for D0→ KþK− (D0→ πþπ−) decays.
The probability to wrongly associate unrelated muons with the D0 candidates is estimated using the yields of “wrong-sign” D0ð→ K−πþÞμþ and ¯D0ð→ Kþπ−Þμ− can-didates in data, which are corrected for the rate of doubly Cabibbo-suppressed decays and decays due to flavor oscillation using the measurements reported in Ref. [42]. Mistag probabilities between 1% at low decay times and 3% at high decay times are observed. Also, in this case, the bias observed in pseudoexperiments depends linearly on the true value of AΓ. Following the same strategy as discussed above, a systematic uncertainty of 0.3 × 10−4 (0.6 × 10−4) is assigned for D0→ KþK− (D0→ πþπ−) decays.
To estimate any potential bias due to the specific choice of the mass model used in the fits that determine the raw
asymmetries, samples of pseudoexperiments are generated using alternative signal and background models that describe the data equally well. The observed bias is independent of the input AΓ and results in an additional systematic uncertainty of0.3 × 10−4for both signal decay channels.
Uncertainties on htii=τ arising from relative misalign-ments of subdetectors and from the uncertainty on the input value of theD0lifetime[32]give negligible contributions. Furthermore, unexpected biases due to a possible decay-time dependence of the nuisance asymmetries and due to the selection procedure are investigated using the D0→ K−πþ control sample and/or by measuring A
Γ in disjoint subsamples split by magnetic-field polarity, year of data taking, and kinematic variables of theB hadron, D0meson, and muon candidates. No unexpected variations are observed, and no additional systematic uncertainties are assigned.
A summary of the relevant systematic uncertainties is given in Table I. The total systematic uncertainty is obtained by summing in quadrature the individual compo-nents and amounts to 0.5 × 10−4 and 0.8 × 10−4 for AΓðKþK−Þ and AΓðπþπ−Þ, respectively.
VII. RESULTS AND CONCLUSIONS
A search for decay-time-dependent CP violation in D0→ KþK− andD0→ πþπ− decays is performed using proton-proton collision data recorded with the LHCb detector at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 5.4 fb−1. TheD0mesons are required to originate from semileptonic b-hadron decays, such that the charge of the muon identifies the flavor of the neutralD meson at the moment of its production. The parameterAΓis determined from a fit to the asymmetry betweenD0and ¯D0yields as a function of decay time. The projections of the fits for bothD0→ KþK− andD0→ πþπ− samples are shown in Fig.3. The results are
AΓðKþK−Þ ¼ ð−4.3 3.6 0.5Þ × 10−4; AΓðπþπ−Þ ¼ ð2.2 7.0 0.8Þ × 10−4;
TABLE I. Summary of the dominant contributions to the systematic uncertainty onAΓðKþK−Þ and AΓðπþπ−Þ.
Source of uncertainty AΓðKþK−Þ [10−4] AΓðπþπ−Þ [10−4] Decay-time resolution and acceptance 0.3 0.4 Mistag probability 0.3 0.6 Mass-fit model 0.3 0.3 Total 0.5 0.8
where the uncertainties are statistical and systematic, respectively.
The measured values are combined with previous LHCb measurements based on data corresponding to 3 fb−1 collected at center-of-mass energies of 7 and 8 TeV, and where the neutral D mesons originate either from semi-leptonicb-hadron decays[28]or from promptly produced Dþð2010Þ mesons [29], with which they are consistent. The combination accounts for correlations in the systematic uncertainties and yields
AΓðKþK−Þ ¼ ð−4.4 2.3 0.6Þ × 10−4; AΓðπþπ−Þ ¼ ð2.5 4.3 0.7Þ × 10−4:
AssumingAΓ to be universal, the above two results can be averaged to yield AΓ¼ ð−2.9 2.0 0.6Þ × 10−4. The results do not show any indication of CP violation in charm mixing or in the interference between mixing and decay.
ACKNOWLEDGMENTS
We express our gratitude to our colleagues in the CERN accelerator departments for the excellent performance of the LHC. We thank the technical and administrative staff at the LHCb institutes. We acknowledge support from CERN and from the national agencies: CAPES, CNPq, FAPERJ, and FINEP (Brazil); MOST and NSFC (China); CNRS/ IN2P3 (France); BMBF, DFG, and MPG (Germany); INFN (Italy); NWO (Netherlands); MNiSW and NCN (Poland); MEN/IFA (Romania); MSHE (Russia); MinECo (Spain); SNSF and SER (Switzerland); NASU (Ukraine); STFC (United Kingdom); DOE NP and NSF (USA). We acknowledge the computing resources that are provided by CERN, IN2P3 (France), KIT and DESY (Germany), INFN (Italy), SURF (Netherlands), PIC (Spain), GridPP (United Kingdom), RRCKI and Yandex LLC (Russia), CSCS (Switzerland), IFIN-HH (Romania), CBPF (Brazil), PL-GRID (Poland) and OSC (USA). We are indebted to the communities behind the multiple open-source software packages on which we depend. Individual groups or
members have received support from the AvH
Foundation (Germany); EPLANET, Marie Sk łodowska-Curie Actions, and ERC (European Union); ANR, Labex P2IO and OCEVU, and R´egion Auvergne-Rhône-Alpes (France); Key Research Program of Frontier Sciences of CAS, CAS PIFI, and the Thousand Talents Program (China); RFBR, RSF and Yandex LLC (Russia); GVA, XuntaGal and GENCAT (Spain); the Royal Society and the Leverhulme Trust (United Kingdom).
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A. Vollhardt,46D. Vom Bruch,9A. Vorobyev,34V. Vorobyev,40,xN. Voropaev,34 J. A. de Vries,28C. Vázquez Sierra,28 R. Waldi,71J. Walsh,25J. Wang,4 J. Wang,3 J. Wang,68M. Wang,3 Y. Wang,69Z. Wang,46D. R. Ward,51H. M. Wark,56
N. K. Watson,49D. Websdale,57A. Weiden,46C. Weisser,60B. D. C. Westhenry,50 D. J. White,58M. Whitehead,10 D. Wiedner,11G. Wilkinson,59 M. Wilkinson,63 I. Williams,51M. R. J. Williams,58M. Williams,60 T. Williams,49 F. F. Wilson,53M. Winn,8 W. Wislicki,32M. Witek,30G. Wormser,8 S. A. Wotton,51H. Wu,63K. Wyllie,44Z. Xiang,66
D. Xiao,69Y. Xie,69 H. Xing,67A. Xu,3 L. Xu,3 M. Xu,69Q. Xu,66Z. Xu,3 Z. Xu,5Z. Yang,3 Z. Yang,62Y. Yao,63 L. E. Yeomans,56H. Yin,69J. Yu,69,aaX. Yuan,63O. Yushchenko,41K. A. Zarebski,49M. Zavertyaev,12,c M. Zdybal,30 M. Zeng,3D. Zhang,69L. Zhang,3S. Zhang,3W. C. Zhang,3,zY. Zhang,44A. Zhelezov,13Y. Zheng,66X. Zhou,66Y. Zhou,66
X. Zhu,3V. Zhukov,10,36J. B. Zonneveld,54 and S. Zucchelli16,e (LHCb Collaboration)
1
Centro Brasileiro de Pesquisas Físicas (CBPF), Rio de Janeiro, Brazil 2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
3
Center for High Energy Physics, Tsinghua University, Beijing, China 4Institute Of High Energy Physics (IHEP), Beijing, China 5
Universit´e Grenoble Alpes, Universit´e Savoie Mont Blanc, CNRS, IN2P3-LAPP, Annecy, France 6Universit´e Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
7
Aix Marseille Universit´e, CNRS/IN2P3, CPPM, Marseille, France 8LAL, Universit´e Paris-Sud, CNRS/IN2P3, Universit´e Paris-Saclay, Orsay, France 9
LPNHE, Sorbonne Universit´e, Paris Diderot Sorbonne Paris Cit´e, CNRS/IN2P3, Paris, France 10I. Physikalisches Institut, RWTH Aachen University, Aachen, Germany
11
Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany 12Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany 13
Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany 14School of Physics, University College Dublin, Dublin, Ireland
15
INFN Sezione di Bari, Bari, Italy 16INFN Sezione di Bologna, Bologna, Italy
17
INFN Sezione di Ferrara, Ferrara, Italy 18INFN Sezione di Firenze, Firenze, Italy 19
INFN Laboratori Nazionali di Frascati, Frascati, Italy 20INFN Sezione di Genova, Genova, Italy 21
INFN Sezione di Milano-Bicocca, Milano, Italy 22INFN Sezione di Milano, Milano, Italy 23
INFN Sezione di Cagliari, Monserrato, Italy 24INFN Sezione di Padova, Padova, Italy
25
INFN Sezione di Pisa, Pisa, Italy 26INFN Sezione di Roma Tor Vergata, Roma, Italy 27
INFN Sezione di Roma La Sapienza, Roma, Italy
28Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands 29
Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, Netherlands 30Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Kraków, Poland
31
AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science, Kraków, Poland
32
National Center for Nuclear Research (NCBJ), Warsaw, Poland
33Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania 34
Petersburg Nuclear Physics Institute NRC Kurchatov Institute (PNPI NRC KI), Gatchina, Russia 35Institute of Theoretical and Experimental Physics NRC Kurchatov Institute (ITEP NRC KI),
Moscow, Russia
36Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia 37
Institute for Nuclear Research of the Russian Academy of Sciences (INR RAS), Moscow, Russia 38Yandex School of Data Analysis, Moscow, Russia
39
National Research University Higher School of Economics, Moscow, Russia 40Budker Institute of Nuclear Physics (SB RAS), Novosibirsk, Russia 41
Institute for High Energy Physics NRC Kurchatov Institute (IHEP NRC KI), Protvino, Russia 42ICCUB, Universitat de Barcelona, Barcelona, Spain
43
Instituto Galego de Física de Altas Enerxías (IGFAE), Universidade de Santiago de Compostela, Santiago de Compostela, Spain
44European Organization for Nuclear Research (CERN), Geneva, Switzerland 45
Institute of Physics, Ecole Polytechnique F´ed´erale de Lausanne (EPFL), Lausanne, Switzerland 46Physik-Institut, Universität Zürich, Zürich, Switzerland
47
NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine 48Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine
49
University of Birmingham, Birmingham, United Kingdom
50H. H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom 51
Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom 52Department of Physics, University of Warwick, Coventry, United Kingdom
53
STFC Rutherford Appleton Laboratory, Didcot, United Kingdom
54School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 55
School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 56Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom
57
Imperial College London, London, United Kingdom
58Department of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 59
Department of Physics, University of Oxford, Oxford, United Kingdom 60Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
61
University of Cincinnati, Cincinnati, Ohio, USA 62University of Maryland, College Park, Maryland, USA
63
Syracuse University, Syracuse, New York, USA
64Laboratory of Mathematical and Subatomic Physics, Constantine, Algeria [associated with Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil]
65Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil [associated with Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil]
66University of Chinese Academy of Sciences, Beijing, China
[associated with Center for High Energy Physics, Tsinghua University, Beijing, China] 67South China Normal University, Guangzhou, China (associated with Center for High Energy Physics,
Tsinghua University, Beijing, China)
68School of Physics and Technology, Wuhan University, Wuhan, China (associated with Center for High Energy Physics, Tsinghua University, Beijing, China) 69Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China (associated with Center for High Energy Physics, Tsinghua University, Beijing, China)
70Departamento de Fisica, Universidad Nacional de Colombia, Bogota, Colombia (associated with LPNHE, Sorbonne Universit´e, Paris Diderot Sorbonne Paris Cit´e,
CNRS/IN2P3, Paris, France) 71
Institut für Physik, Universität Rostock, Rostock, Germany (associated with Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany)
72
Van Swinderen Institute, University of Groningen, Groningen, Netherlands (associated with Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands)
73
National Research Centre Kurchatov Institute, Moscow, Russia
[associated with Institute of Theoretical and Experimental Physics NRC Kurchatov Institute (ITEP NRC KI), Moscow, Russia]
74National University of Science and Technology“MISIS,” Moscow, Russia [associated with Institute of Theoretical and Experimental Physics NRC Kurchatov Institute
(ITEP NRC KI), Moscow, Russia] 75
National Research Tomsk Polytechnic University, Tomsk, Russia
[associated with Institute of Theoretical and Experimental Physics NRC Kurchatov Institute (ITEP NRC KI), Moscow, Russia]
76Instituto de Fisica Corpuscular, Centro Mixto Universidad de Valencia - CSIC, Valencia, Spain (associated with ICCUB, Universitat de Barcelona, Barcelona, Spain)
77University of Michigan, Ann Arbor, Michigan, USA (associated with Syracuse University, Syracuse, New York, USA) 78Los Alamos National Laboratory (LANL), Los Alamos, New Mexico, USA
(associated with Syracuse University, Syracuse, New York, USA)
†Deceased. a
Universidade Federal do Triângulo Mineiro (UFTM), Uberaba-MG, Brazil.
bLaboratoire Leprince-Ringuet, Palaiseau, France. c
P. N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia.
eUniversit`a di Bologna, Bologna, Italy. f
Universit`a di Cagliari, Cagliari, Italy.
gUniversit`a di Ferrara, Ferrara, Italy. h
Universit`a di Genova, Genova, Italy.
iUniversit`a di Milano Bicocca, Milano, Italy. j
Universit`a di Roma Tor Vergata, Roma, Italy.
kUniversit`a di Roma La Sapienza, Roma, Italy. l
AGH - University of Science and Technology, Faculty of Computer Science, Electronics and Telecommunications, Kraków, Poland.
mLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain. n
Hanoi University of Science, Hanoi, Vietnam.
oUniversit`a di Padova, Padova, Italy. p
Universit`a di Pisa, Pisa, Italy.
qUniversit`a degli Studi di Milano, Milano, Italy. r
Universit`a di Urbino, Urbino, Italy.
sUniversit`a della Basilicata, Potenza, Italy. t
Scuola Normale Superiore, Pisa, Italy.
uUniversit`a di Modena e Reggio Emilia, Modena, Italy. v
Universit`a di Siena, Siena, Italy.
wMSU - Iligan Institute of Technology (MSU-IIT), Iligan, Philippines. x
Novosibirsk State University, Novosibirsk, Russia.
ySezione INFN di Trieste, Trieste, Italy. z
School of Physics and Information Technology, Shaanxi Normal University (SNNU), Xi’an, China.
