EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
CERN-EP-2016-070 LHCb-PAPER-2015-060 March 24, 2016Observation of Λ
0
b
→ ψ(2S)pK
−
and
Λ
0
b
→ J/ψ π
+
π
−
pK
−
decays and a
measurement of the Λ
0
b
baryon mass
The LHCb collaboration†
Abstract
The decays Λ0b→ ψ(2S)pK− and Λ0b→ J/ψ π+π−pK− are observed in a data sample
corresponding to an integrated luminosity of 3 fb−1, collected in proton-proton colli-sions at 7 and 8 TeV centre-of-mass energies by the LHCb detector. The ψ(2S) mesons are reconstructed through the decay modes ψ(2S) → µ+µ− and ψ(2S) → J/ψ π+π−. The branching fractions relative to that of Λ0b→ J/ψ pK− are measured to be
B(Λ0 b→ ψ(2S)pK−) B(Λ0 b→ J/ψ pK−) = (20.70 ± 0.76 ± 0.46 ± 0.37) × 10−2, B(Λ0 b→ J/ψ π+π−pK−) B(Λ0 b→ J/ψ pK−) = (20.86 ± 0.96 ± 1.34) × 10−2,
where the first uncertainties are statistical, the second are systematic and the third is related to the knowledge of J/ψ and ψ(2S) branching fractions. The mass of the Λ0b baryon is measured to be
M (Λ0b) = 5619.65 ± 0.17 ± 0.17 MeV/c2, where the uncertainties are statistical and systematic.
Published in JHEP 1605 (2016) 132
c
CERN on behalf of the LHCb collaboration, licence CC-BY-4.0.
†Authors are listed at the end of this paper.
1
Introduction
The Λ0
b baryon is the isospin singlet ground state of a bottom quark and two light
quarks. The rich phenomenology associated with decays of bottom baryons allows many measurements of masses, lifetimes and branching fractions, which test the theoretical understanding of weak decays of heavy hadrons in the framework of heavy quark effective theory (HQET) and the underlying QCD physics [1]. At the Tevatron, properties of the Λ0
b baryon, such as mass and lifetime, have been measured using two-body modes,
specifically Λ0
b→ J/ψ Λ0 and Λ0b → Λ+cπ
− decays [2–4].1 The high production rate of
b quarks at the Large Hadron Collider (LHC), along with the excellent momentum and mass resolution and the hadron identification capabilities of the LHCb detector, open up a host of multibody and Cabibbo-suppressed decay channels of Λ0
b baryons, e.g. the
de-cays Λ0b → D0pK−, Λ0 b → Λ + cK− [5], Λ0b → Λ + cD−, Λ0b → Λ + cD−s [6] and Λ0b → J/ψ pπ − [7].
The high signal yield of the Λ0
b → J/ψ pK
− decay [8] allowed the precise measurement of
the Λ0
b lifetime [9, 10]. The recent analysis of this decay mode uncovered a double resonant
structure in the J/ψ p system consistent with two pentaquark states [11]. LHCb has also measured several B meson decays into final states with charmonia [12–17]. The first observation of Λ0
b decays to excited charmonium, the Λ0b → ψ(2S)Λ0 decay, has been
presented by the ATLAS collaboration [18]. An experimental investigation of other similar multibody decays of the Λ0
b baryon should lead to deeper insights into QCD.
In this paper, the first observations of the decays Λ0
b→ ψ(2S)pK
− and
Λ0b→ J/ψ π+π−pK− are reported, where ψ(2S) mesons are reconstructed in the final
states µ+µ− and J/ψ π+π−. The ratios of the branching fractions of these decays to that
of the normalization decay Λ0
b→ J/ψ pK −, Rψ(2S) ≡ B(Λ 0 b→ ψ(2S)pK −) B(Λ0 b→ J/ψ pK−) , (1) RJ/ψ π+π− ≡ B(Λ 0 b→ J/ψ π+π −pK−) B(Λ0 b→ J/ψ pK−) , (2)
are measured. In measuring the branching fraction of Λ0
b→ J/ψ π+π
−pK− decays,
con-tributions via intermediate resonances, such as Λ0b→ ψ(2S)pK−, are implicitly included.
The low energy release in these decays allows a precise determination of the Λ0
b mass with
a small systematic uncertainty.
This study is based on a data sample corresponding to an integrated luminosity of 3 fb−1, collected with the LHCb detector in pp collisions at centre-of-mass energies √
s = 7 and 8 TeV.
2
Detector and simulation
The LHCb detector [19,20] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b 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 polarity of the dipole magnet is reversed periodically throughout data-taking. The tracking system provides a measurement of the momentum, p, of charged particles with a relative uncertainty 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 of (15 + 29/pT) µm, where pT is the component of the momentum transverse
to the beam, in GeV/c [21]. Large samples of B+ → J/ψ K+ and J/ψ → µ+µ− decays,
collected concurrently with the data set, were used to calibrate the momentum scale of the spectrometer to a precision of 0.03 % [22].
Different types of charged hadrons are distinguished using information from two ring-imaging Cherenkov detectors (RICH). Photons, electrons and hadrons are identified by a calorimeter system consisting of scintillating-pad and preshower detectors, an electromag-netic calorimeter and a hadronic calorimeter. Muons are identified by a system composed of alternating layers of iron and multiwire proportional chambers.
The trigger [23] comprises two stages. Events are first required to pass the hardware trigger, which selects muon candidates with pT > 1.48 (1.76) GeV/c or pairs of opposite-sign
muon candidates with a requirement that the product of the muon transverse momenta is larger than 1.7 (2.6) GeV2/c2 for data collected at √s = 7 (8) TeV. The subsequent
software trigger is composed of two stages, the first of which performs a partial event reconstruction, while full event reconstruction is done at the second stage. At the first stage of the software trigger the invariant mass of well-reconstructed pairs of oppositely charged muons forming a good-quality two-track vertex is required to exceed 2.7 GeV/c2, and the two-track vertex is required to be significantly displaced from all PVs.
The analysis technique reported below has been validated using simulated events. The pp collisions are generated using Pythia [24] with a specific LHCb configuration [25]. Decays of hadronic particles are described by EvtGen [26], in which final-state radiation is generated using Photos [27]. The interaction of the generated particles with the detector, and its response, are implemented using the Geant4 toolkit [28] as described in Ref. [29].
3
Event selection
The decays Λ0 b→ ψ(2S)pK −, Λ0 b→ J/ψ π+π −pK− and Λ0 b→ J/ψ pK − are reconstructedusing decay modes ψ(2S) → µ+µ−, ψ(2S) → J/ψ π+π− and J/ψ → µ+µ−. Common se-lection criteria, based on those used in Refs. [16, 30], are used for all channels, except for those related to the selection of two additional pions in the Λ0
b→ J/ψ π+π
−pK− and
Λ0b → ψ(2S)[→ J/ψ π+π−]pK− channels.
Muon, proton, kaon and pion candidates are selected from well-reconstructed tracks within the acceptance of the spectrometer that are identified using information from the RICH, calorimeter and muon detectors [31, 32]. Muons, protons, kaons and pions
are required to have a transverse momentum larger than 550, 800, 500 and 200 MeV/c, respectively. To allow good particle identification, kaons and pions are required to have a momentum between 3.2 GeV/c and 150 GeV/c whilst protons must have a momentum between 10 GeV/c and 150 GeV/c. To reduce combinatorial background involving tracks from the primary pp interaction vertices, only tracks that exceed a minimum impact parameter χ2 with respect to every PV are used. The impact parameter χ2 is defined as
the difference between the χ2 of the PV reconstructed with and without the considered particle.
Pairs of oppositely-charged muons originating from a common vertex are combined to form J/ψ → µ+µ− or ψ(2S) → µ+µ− candidates. The resulting dimuon candidates are required to have an invariant mass between −5σ and +3σ around the known J/ψ or ψ(2S) masses [33], where σ is the mass resolution. An asymmetric mass interval is chosen to include part of the low-mass tail due to final-state radiation.
Candidate Λ0
b baryons are formed from J/ψ pK
−, ψ(2S)pK− and J/ψ π+π−pK−
combi-nations. Each candidate is associated with the PV with respect to which it has the smallest impact parameter significance. The Λ0b mass resolution is improved by employing a kine-matic fit [34] that constrains the mass of the J/ψ candidate to its known value and requires the momentum of the Λ0
b candidate to point back to the PV. A requirement on the quality
of this fit is applied to further suppress combinatorial background. Finally, the measured decay time of the Λ0
b candidate, calculated with respect to the associated primary vertex,
is required to be between 0.5 and 6.7 ps. The lower limit is used to suppress background from particles coming from the PV while the upper limit removes poorly reconstructed candidates.
To suppress cross-feed from decays of the B0
s meson into J/ψ K
−K+, ψ(2S)K−K+ and
J/ψ π+π−K−K+ final states, with the positively-charged kaon misidentified as a proton, a veto on the Λ0
b candidate mass, recalculated with a kaon mass hypothesis for the proton,
is applied. Any candidate with a recalculated mass consistent with the nominal B0 s mass
is rejected. A similar veto is applied to suppress cross-feed from decays of B0 mesons into J/ψ K−π+, ψ(2S)K−π+ and J/ψ π−π+π+K− decays with the positively-charged pion
misidentified as a proton.
4
Measurement of branching fractions
4.1
Signal yields and efficiencies
The mass distributions for selected Λ0b→ ψ(2S)[→ µ+µ
−]pK− candidates and candidates
for the normalization channel Λ0b→ J/ψ pK− are shown in Fig. 1. Signal yields are
deter-mined using unbinned extended maximum likelihood fits to these distributions. The signal is modelled with a modified Gaussian function with power-law tails on both sides [35, 36], where the tail parameters are fixed from simulation and the mass resolution parameter is allowed to vary. The background is modelled with an exponential function multiplied by a first-order polynomial. The resolution parameters obtained from the fits are found to be
5.6 5.65 0 50 100 150 5.6 5.65 0 1000 2000 3000 Candidates/(2 Me V /c 2 ) Candidates/(1 Me V /c 2 ) m(J/ψ pK−) m(ψ(2S)[→ µ+µ−]pK−) [ GeV/c2] [ GeV/c2] LHCb LHCb
Figure 1: Mass distributions of selected (left) Λ0b→ ψ(2S)[→ µ+µ−]pK− and
(right) Λ0b→ J/ψ pK− candidates. The total fit function (solid red), the Λ0
b signal
contri-bution (dotted magenta) and the combinatorial background (dashed blue) are shown. The error bars show 68% Poissonian confidence intervals.
3.82 ± 0.17 MeV/c2 for the channel Λ0
b→ ψ(2S)[→ µ+µ
−]pK− and 6.12 ± 0.05 MeV/c2 for
Λ0
b→ J/ψ pK
−, in good agreement with expectations from simulation.
The mass distribution for selected Λ0b→ J/ψ π+π−pK− candidates is shown in
Fig. 2(left), along with the result of an unbinned extended maximum likelihood fit using the model described above. The mass resolution parameter obtained from the fit is 4.72 ± 0.23 MeV/c2. The mass distribution of the J/ψ π+π− system from signal Λ0
b→ J/ψ π+π
−pK− decays is presented in Fig. 2(right) in the region
3.67 < m(J/ψ π+π−) < 3.7 GeV/c2.
The background subtraction is performed with the sPlot technique [37] us-ing the J/ψ π+π−pK− mass as the discriminating variable. The signal yield of
Λ0
b→ ψ(2S)[→ J/ψ π+π
−]pK− decays is determined using an unbinned extended
maxi-mum likelihood fit to the J/ψ π+π− invariant mass distribution. The ψ(2S) component is modelled with a modified Gaussian function with power-law tails on both sides, where the tail parameters are fixed from simulation. The nonresonant component is taken to be constant. The mass resolution parameter obtained from the fit is 2.29 ± 0.17 MeV/c2. The signal yields are summarized in Table 1.
5.6 5.65 0 50 100 150 Candidates/(2 Me V /c 2 ) m(J/ψ π+π−pK−) 3.67 3.68 3.69 3.7 0 20 40 Candidates/(1 Me V /c 2 ) m(J/ψ π+π−) [ GeV/c2] [ GeV/c2] LHCb LHCb
Figure 2: (left) Mass distribution of selected Λ0b→ J/ψ π+π−pK−candidates. (right)
Background-subtracted J/ψ π+π− mass distribution for that mode. The total fit function and the signal contributions are shown by solid red and dotted magenta lines, respectively. The combinatorial background in the left plot and nonresonant contribution in the right plot are shown by dashed blue lines.
Table 1: Signal yields of Λ0b decay channels. Uncertainties are statistical only.
Channel N (Λ0 b) Λ0b→ J/ψ pK− 28 834 ± 204 Λ0 b→ ψ(2S)[→ µ+µ −]pK− 665 ± 28 Λ0 b→ ψ(2S)[→ J/ψ π+π −]pK− 231 ± 17 Λ0b→ J/ψ π+π−pK− 793 ± 36 decay modes, Rψ(2S) ψ(2S)→µ+µ− = Nψ(2S)→µ+µ− NJ/ψ × ε Λ0 b J/ψ εΛ 0 b ψ(2S)→µ+µ− × B(J/ψ → µ +µ−) B(ψ(2S) → µ+µ−), Rψ(2S) ψ(2S)→J/ψ π+π− = Nψ(2S)→J/ψ π+π− NJ/ψ × ε Λ0 b J/ψ εΛ 0 b ψ(2S)→J/ψ π+π− × 1 B(ψ(2S) → J/ψ π+π−), (3)
and the ratio RJ/ψ π+π−
, defined in Eq. 2, is measured as
RJ/ψ π+π− = NJ/ψ π+π− NJ/ψ × ε Λ0 b J/ψ εΛ0b J/ψ π+π− , (4)
Table 2: Ratios of efficiencies. The uncertainties reflect the limited size of the simulation sample. Value εΛ0b J/ψ/ε Λ0 b ψ(2S)→µ+µ− 1.188 ± 0.006 εΛ 0 b J/ψ/ε Λ0 b ψ(2S)→J/ψ π+π− 8.84 ± 0.05 εΛ0b J/ψ/ε Λ0 b J/ψ π+π− 7.59 ± 0.04
where NX represents the observed signal yield and ε Λ0
b
X denotes the efficiency for the
de-cay Λ0b → XpK−. The ratio B(J/ψ → µ +µ−)
B(ψ(2S) → µ+µ−) is taken to be equal to the more precisely
measured ratio of dielectron branching fractions, B(J/ψ → e
+e−)
B(ψ(2S) → e+e−) = 7.57 ± 0.17 [33].
For the ψ(2S) → J/ψ π+π− branching fraction the world average (34.46 ± 0.30)% [33] is taken.
The efficiency is defined as the product of the geometric acceptance and the detection, reconstruction, selection and trigger efficiencies. The efficiencies for hadron identification as functions of kinematic parameters and event multiplicity are determined from data using calibration samples of low-background decays: D∗+ → D0π+followed by D0 → K−π−
for kaons and pions, and Λ0 → pπ− and Λ+
c → pK−π+ for protons [31]. The remaining
efficiencies are determined using simulation. In the simulation of Λ0
b→ J/ψ pK
− decays, the model established in Ref. [11] that
includes pentaquark contributions is used, while in the simulation of the other decay modes the events are generated uniformly in phase space. The simulation is corrected to reproduce the transverse momentum and rapidity distributions of the Λ0
bbaryons observed in data [8]
and to account for small discrepancies between data and simulation in the reconstruction of charged tracks [38]. The ratios of efficiencies to those in the Λ0b→ J/ψ pK− channel are
presented in Table 2.
4.2
Systematic uncertainties
Most systematic uncertainties cancel in the measurements of the ratios of branching fractions, notably those related to the reconstruction, identification and trigger efficiencies of the J/ψ → µ+µ−and ψ(2S) → µ+µ−candidates [12], due to the similarity of the muon and dimuon spectra for these modes. The remaining systematic uncertainties are summarized in Table 3 and discussed below.
Alternative parametrizations for the signal and background are used to estimate the systematic uncertainties related to the fit model. A modified Novosibirsk function [39], an Apolonios function [40], an asymmetric variant of the Apolonios function and the Stu-dent’s t-distribution are used for the Λ0bsignal shape, and an exponential function multiplied
Table 3: Systematic uncertainties (in %) on the ratios of branching fractions Rψ(2S)and RJ/ψ π+π−. Source Rψ(2S) ψ(2S)→µ+µ− R ψ(2S) ψ(2S)→J/ψ π+π− R J/ψ π+π− Fit model 0.8 3.0 3.5 Cross-feed 0.8 0.9 0.9 Efficiency calculation: Λ0 b decay model 0.3 0.8 0.8
Reconstruction of additional pions:
Hadron interaction – 2 × 2.0 2 × 2.0
Track efficiency correction – 3.2 2.7
Hadron identification 0.1 0.1 0.2
Trigger 1.1 1.1 1.1
Selection criteria 0.6 0.9 0.2
Simulation sample size 1.0 1.6 1.7
Sum in quadrature 2.0 6.4 6.4
by a second-order polynomial is used for the background. The ratio of event yields is remeasured with the cross-check models, and the maximum deviation with respect to the nominal value is assigned as a systematic uncertainty.
The uncertainty associated with the B0s and B0 cross-feed is estimated by varying the widths of the rejected regions and recomputing the signal yields, taking into account the changes in efficiencies. As an additional cross-check, a veto is applied also on possible contributions from Λ0b → J/ψ pK+, Λ0
b → ψ(2S)pK
+and Λ0
b → J/ψ π
+π−pK+decays where
the positive kaon is misidentified as a proton and the antiproton is misidentified as a negative kaon. The maximum of the observed differences from the nominal values is assigned as the corresponding systematic uncertainty.
The remaining systematic uncertainties are associated with the efficiency determina-tion. The systematic uncertainty related to the decay model for Λ0
b → ψ(2S)pK − and
Λ0b → J/ψ π+π−pK− decays is estimated using the simulated samples, corrected to
repro-duce the invariant mass of the pK− and ψ(2S)p or J/ψ π+π−p systems observed in data. The largest change in efficiency is taken as the corresponding systematic uncertainty.
The decay modes Λ0b→ J/ψ π+π−pK− and Λ0
b→ ψ(2S)[→ J/ψ π
+π−]pK− have two
additional pions to reconstruct compared to the reference mode Λ0b→ J/ψ pK− . The un-certainty associated with the reconstruction of these additional low-pT tracks has two
independent contributions. First, the uncertainties in the amount and distribution of ma-terial in the detector result in an uncertainty of 2.0% per additional final-state pion due to the modelling of hadron interactions [38]. Second, the small difference in the track finding efficiency between data and simulation is corrected using a data-driven technique [38]. The uncertainties in the correction factors are propagated to the efficiency ratios by means of pseudoexperiments. This results in a systematic uncertainty of 3.2% for the ratio
Rψ(2S)
ψ(2S)→J/ψ π+π− and 2.7% for the ratio R
J/ψ π+π−
.
The systematic uncertainties related to the hadron identification efficiency, 0.1 (0.2)% for Rψ(2S)(RJ/ψ π+π−
) ratios, reflect the limited sizes of the calibration samples, and are propagated to the ratios Rψ(2S) and RJ/ψ π+π− by means of pseudoexperiments.
The trigger efficiency for events with J/ψ → µ+µ− and ψ(2S) → µ+µ− produced in beauty hadron decays is studied in data. A systematic uncertainty of 1.1% is assigned based on a comparison between data and simulation of the ratio of trigger efficiencies for high-yield samples of B+→ J/ψ K+ and B+ → ψ(2S)K+ decays [12].
Another source of uncertainty is the potential disagreement between data and simulation in the estimation of efficiencies, due to effects not considered above. This is studied by varying the selection criteria in ranges that lead to as much as ±20% change in the measured signal yields. The stability is tested by comparing the efficiency-corrected yields within these variations. The largest deviations range between 0.2% and 0.9% and are taken as systematic uncertainties.
Finally, a systematic uncertainty due to the limited size of the simulation sample is assigned. With all the systematic uncertainties added in quadrature, the total is 2.0% for the ratio Rψ(2S)
ψ(2S)→µ+µ−, 6.4% for the ratio R
ψ(2S)
ψ(2S)→J/ψ π+π− and 6.4% for
the ratio RJ/ψ π+π−.
4.3
Results
Using Eq. 3 and the ratios of yields and efficiencies determined above, the ratio Rψ(2S) is measured for each ψ(2S) decay mode separately:
Rψ(2S) ψ(2S)→µ+µ− = (20.74 ± 0.88 ± 0.41 ± 0.47) × 10 −2 , Rψ(2S) ψ(2S)→J/ψ π+π− = (20.55 ± 1.52 ± 1.32 ± 0.18) × 10 −2 , (5)
where the first uncertainty is statistical, the second is systematic and the third is re-lated to the uncertainties on the dielectron J/ψ and ψ(2S) branching fractions and the ψ(2S) → J/ψ π+π− branching fraction. The average of the ratios in Eq. 5 is
Rψ(2S) = (20.70 ± 0.76 ± 0.46 ± 0.37) × 10−2. (6)
In this average the systematic uncertainties related to the normalization channel, Λ0
b→ J/ψ pK
−, and the trigger efficiency are considered to be 100% correlated while
other systematic uncertainties are treated as uncorrelated. The ratio of the branching fractions of Λ0
b→ J/ψ π+π −pK− and Λ0 b→ J/ψ pK − is found to be RJ/ψ π+π− = (20.86 ± 0.96 ± 1.34) × 10−2, (7)
where contributions via intermediate resonances are included. The absolute branching fractions Λ0b→ ψ(2S)pK− and Λ0
b→ J/ψ π
+π−pK−are derived
using the branching fraction B(Λ0b→ J/ψ pK−) = (3.04 ± 0.04 ± 0.06 ± 0.33+0.43−0.27) × 10−4,
fraction of the decay B0 → J/ψ K∗(892)0 and the fourth is due to the knowledge of the ratio of fragmentation fractions fΛ0
b/fd. They are found to be
B(Λ0 b→ ψ(2S)pK − ) = (6.29 ± 0.23 ± 0.14+1.14−0.90) × 10−5, B(Λ0 b→ J/ψ π +π− pK−) = (6.34 ± 0.29 ± 0.41+1.15−0.91) × 10−5, (8) where the third uncertainty comes from the uncertainties in the branching fractions of Λ0
b→ J/ψ pK
−, ψ(2S) → J/ψ π+π−, ψ(2S) → e+e− and J/ψ → e+e− decays.
From the two separate measurements of the ratio Rψ(2S) via different decay modes of the ψ(2S) meson (Eq. 5), the ratio of the ψ(2S) → µ+µ−and ψ(2S) → J/ψ π+π−branching
fractions is calculated as B(ψ(2S) → µ+µ−) B(ψ(2S) → J/ψ π+π−) = Nψ(2S)→µ+µ− Nψ(2S)→J/ψ π+π− ×ε Λ0 b ψ(2S)→J/ψ π+π− εΛ0b ψ(2S)→µ+µ− × B(J/ψ → µ+µ−) = (2.30 ± 0.20 ± 0.12 ± 0.01) × 10−2, (9) where the third uncertainty is related to the uncertainty of the known branching fraction B(J/ψ → µ+µ−) = (5.961 ± 0.033)% [33]. This result is in agreement with the world
average of (2.29 ± 0.25) × 10−2 [33] based on results of the E672/E706 [41] and BaBar [42] collaborations, and has similar precision.
5
Measurement of Λ
0bbaryon mass
The low energy release in Λ0
b→ ψ(2S)pK
− and Λ0
b→ J/ψ π+π
−pK− decays
al-lows the Λ0b mass to be determined with a small systematic uncertainty. The mass is measured using four decay channels: Λ0
b→ ψ(2S)[→ µ+µ −]pK−, Λ0 b→ ψ(2S)[→ J/ψ π+π −]pK−, Λ0 b→ J/ψ π+π −pK− and Λ0 b→ J/ψ pK
−. The mass
dis-tributions for the Λ0b→ ψ(2S)[→ µ+µ−]pK− and Λ0
b→ J/ψ pK− channels are shown in
Fig. 1. In the Λ0
b→ ψ(2S)[→ J/ψ π+π
−]pK− channel, the J/ψ π+π− system is constrained
to the nominal ψ(2S) mass [33] to improve the precision. In the Λ0
b→ J/ψ π+π −pK−
channel, to avoid overlap with the Λ0b→ ψ(2S)[→ J/ψ π+π−]pK− channel the ψ(2S) region
is vetoed, i.e. the mass of the J/ψ π+π− combination is required to be outside the range
3670 < m(J/ψ π+π−) < 3700 MeV/c2. The mass distributions for these two samples, along
with the result of an unbinned extended maximum likelihood fit using the model described in Sect. 4.1, are shown in Fig. 3.
The systematic uncertainties on the measurement of the Λ0
b baryon mass for all four
channels are listed in Table 4. The precision of the absolute momentum scale calibration of 0.03% is the dominant source of uncertainty [22, 43]. This uncertainty is proportional to the energy release in the decay and is minimal for the processes with a ψ(2S) in the final state. A further uncertainty is related to the energy loss in the material of the tracking system [44], which is known with an accuracy of 10% [45]. This effect is estimated by varying the energy loss correction in the reconstruction by 10% and taking the observed
5.6 5.65 0 20 40 Candidates/(2 Me V /c 2 ) m(ψ(2S)pK−) 5.6 5.65 0 50 100 Candidates/(2 Me V /c 2 ) m(J/ψ π+π−pK−) [ GeV/c2] [ GeV/c2] LHCb LHCb
Figure 3: (left) Mass distribution of selected Λ0b→ ψ(2S)[→ J/ψ π+π−]pK− candidates with
an additional constraint for the ψ(2S) mass [33]. (right) Mass distribution of selected Λ0b→ J/ψ π+π−pK− candidates with a requirement of the J/ψ π+π− combination mass to be
outside the range 3670 < m(J/ψ π+π−) < 3700 MeV/c2. The total fit function (solid red), the Λ0b signal contribution (dotted magenta) and the combinatorial background (dashed blue) are shown.
Table 4: Systematic uncertainties (in MeV/c2) on the Λ0b mass using the de-cay modes Λ0b→ J/ψ pK−, Λ0
b→ ψ(2S)[→ µ+µ−]pK−, Λ0b→ ψ(2S)[→ J/ψ π+π−]pK− and
Λ0b→ J/ψ π+π−pK− with the J/ψ π+π− mass outside the ψ(2S) region.
J/ψ ψ(2S) → µ+µ− ψ(2S) → J/ψ π+π− J/ψ π+π−,
ψ(2S)
Momentum scale 0.34 0.19 0.15 0.26
Energy loss correction 0.03 0.02 0.06 0.07
Fit model 0.04 0.03 0.08 0.05
Sum in quadrature 0.34 0.19 0.18 0.27
mass shift as an uncertainty. The uncertainty due to the fit model is estimated using the same set of cross-check models for the signal and background parameterization as considered in Sect. 4, with the maximum deviation in the mass assigned as a systematic uncertainty. The uncertainties on the masses of the J/ψ and ψ(2S) mesons [33] are small and are therefore neglected.
As a cross-check, the data sample is divided into four parts, for data collected at√s = 7 and 8 TeV and with different magnet polarities. The measured masses are consistent among these subsamples, and therefore no systematic uncertainty is assigned. To check the effect of the selection criteria (see Sect. 3), the high-yield Λ0
b→ J/ψ pK
− decay channel is used.
No sizeable dependence of the mass on the selection criteria is observed and no additional uncertainty is assigned.
Table 5: Measured Λ0b mass in different decay channels. The first uncertainty is statistical and the second is systematic.
Channel M (Λ0b) [ MeV/c2] Λ0 b→ J/ψ pK − 5619.62 ± 0.04 ± 0.34 Λ0 b→ ψ(2S)[→ µ+µ −]pK− 5619.84 ± 0.18 ± 0.19 Λ0 b→ ψ(2S)[→ J/ψ π+π −]pK− 5619.38 ± 0.33 ± 0.18 Λ0 b→ J/ψ π+π −pK− excluding ψ(2S) 5619.08 ± 0.30 ± 0.27
The results from the four decay channels are presented in Table 5. To combine them, correlations must be taken into account. The statistical uncertainties and those related to the fit procedure are treated as uncorrelated while those due to the momentum scale and energy loss correction are considered to be fully correlated. The combined value of the Λ0
b mass is
M (Λ0b) = 5619.65 ± 0.17 ± 0.17 MeV/c2, (10) where the first uncertainty is statistical and the second systematic. The χ2/ndf calculated
for the individual measurements with respect to the combined value is 3.0/3. This is the most precise measurement of any b-hadron mass reported to date.
Previous direct measurements of the Λ0
b mass by LHCb were made using the
de-cay Λ0b → J/ψ Λ0 [22, 44] and are statistically independent of the results of this study.
The combination obtained here is consistent with, and more precise than, the results of these earlier studies. The LHCb results are combined, taking the statistical uncertainties and those related to the fit procedure to be uncorrelated and those due to the energy loss correction to be fully correlated. The uncertainty due to the momentum scale in Ref. [22] is also taken to be fully correlated, whereas in Ref. [44] a different alignment and calibration procedure was used and so the corresponding uncertainty is considered to be uncorrelated with the other measurements. The result of the combination is dominated by the measurements of this analysis and is
M (Λ0b) = 5619.65 ± 0.16 ± 0.14 MeV/c2, (11) where the uncertainties are statistical and systematic. The χ2/ndf calculated for the
individual measurements with respect to the combined value is 3.4/5. The measured mass is in agreement with, but more precise than, the results of the ATLAS [46] and CDF [4] collaborations.
From the value of the Λ0
b mass in Eq. 11 and a precise measurement of the mass
difference between the Λ0b and B0 hadrons reported in Ref. [6], the mass of the B0 meson is calculated to be
where the correlation of 41% between the LHCb measurements of the Λ0b mass and the Λ0
b–B0mass splitting has been taken into account. This is in agreement with the current
world average of 5279.61 ± 0.16 MeV/c2 [33].
6
Results and summary
The Λ0
b→ ψ(2S)pK
− and Λ0
b→ J/ψ π+π
−pK− decay modes are observed using a
sam-ple of pp collisions at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb−1. With results from the channels ψ(2S) → µ+µ− and ψ(2S) → J/ψ π+π− combined, the ratio of branching fractions is measured:
Rψ(2S) = B(Λ 0 b→ ψ(2S)pK −) B(Λ0 b→ J/ψ pK−) = (20.70 ± 0.76 ± 0.46 ± 0.37) × 10−2,
where the first uncertainty is statistical, the second is systematic and the third is related to the uncertainties of the known dielectron J/ψ and ψ(2S) branching fractions and of the branching fraction of the ψ(2S) → J/ψ π+π− decay. The ratio of branching fractions for Λ0 b→ J/ψ π+π −pK− and Λ0 b→ J/ψ pK − is RJ/ψ π+π− = B(Λ 0 b→ J/ψ π+π−pK−) B(Λ0 b→ J/ψ pK−) = (20.86 ± 0.96 ± 1.34) × 10−2,
where the first uncertainty is statistical, the second is systematic and contributions via intermediate resonances are included.
From measurements of the ratio Rψ(2S)via two different decay modes of the ψ(2S) meson
it is determined that
B(ψ(2S) → µ+µ−)
B(ψ(2S) → J/ψ π+π−) = (2.30 ± 0.20 ± 0.12 ± 0.01) × 10 −2
,
where the first uncertainty is statistical, the second is systematic and the third is related to the uncertainty on B(J/ψ → µ+µ−). This is the most precise direct measurement of
this ratio to date. Using Λ0 b→ ψ(2S)pK −, Λ0 b→ J/ψ π+π −pK− and Λ0 b→ J/ψ pK
− decays, the mass of
the Λ0
b baryon is measured to be
M (Λ0b) = 5619.65 ± 0.17 ± 0.17 MeV/c2,
where the first uncertainty is statistical and the second is systematic. Combining this result with previous LHCb measurements that used the channel Λ0b → J/ψ Λ0 [22, 44] gives
M (Λ0b) = 5619.65 ± 0.16 ± 0.14 MeV/c2, (13) where the first uncertainty is statistical and the second is systematic. This is the most precise determination of the mass of any b hadron to date.
Acknowledgements
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); NSFC (China); CNRS/IN2P3 (France); BMBF, DFG and MPG (Germany); INFN (Italy); FOM and NWO (The Nether-lands); MNiSW and NCN (Poland); MEN/IFA (Romania); MinES and FANO (Russia); MinECo (Spain); SNSF and SER (Switzerland); NASU (Ukraine); STFC (United King-dom); NSF (USA). We acknowledge the computing resources that are provided by CERN, IN2P3 (France), KIT and DESY (Germany), INFN (Italy), SURF (The Nether-lands), 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 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 Yandex LLC (Russia), GVA, XuntaGal and GENCAT (Spain), Herchel Smith Fund, The Royal Society, Royal Commission for the Exhibition of 1851 and the Leverhulme Trust (United Kingdom).
References
[1] M. Neubert, Heavy quark symmetry, Phys. Rept. 245 (1994) 259, arXiv:hep-ph/9306320; A. V. Manohar and M. B. Wise, Heavy quark physics, Camb. Monogr. Part. Phys. Nucl. Phys. Cosmol. 10 (2000) 1.
[2] CDF collaboration, A. Abulencia et al., Measurement of σ(Λ0b)/σ( ¯B0) × B(Λ0b → Λ+
cπ
−)/B( ¯B0 → D+π−) in pp collisions at √s = 1.96 TeV , Phys. Rev. Lett. 98
(2007) 122002, arXiv:hep-ex/0601003.
[3] D0 collaboration, V. M. Abazov et al., Measurement of the production fraction times branching fraction f (b → Λ0
b) · B(Λ0b → J/ψ Λ), Phys. Rev. D84 (2011) 031102,
arXiv:1105.0690.
[4] CDF collaboration, T. Aaltonen et al., Mass and lifetime measurements of bottom and charm baryons in pp collisions at √s = 1.96 TeV , Phys. Rev. D89 (2014) 072014, arXiv:1403.8126.
[5] LHCb collaboration, R. Aaij et al., Study of beauty baryon decays to D0ph− and Λ+ch− final states, Phys. Rev. D89 (2014) 032001, arXiv:1311.4823.
[6] LHCb collaboration, R. Aaij et al., Study of beauty hadron decays into pairs of charm hadrons, Phys. Rev. Lett. 112 (2014) 202001, arXiv:1403.3606.
[7] LHCb collaboration, R. Aaij et al., Observation of the Λ0b → J/ψ pπ− decay, JHEP
07 (2014) 103, arXiv:1406.0755.
[8] LHCb collaboration, R. Aaij et al., Study of the productions of Λ0
b and ¯B0 hadrons in
pp collisions and first measurement of the Λ0b → J/ψ pK− branching fraction, Chin.
Phys. C 40 (2015) 011001, arXiv:1509.00292.
[9] LHCb collaboration, R. Aaij et al., Precision measurement of the ratio of the Λ0 b to
B0 lifetimes, Phys. Lett. B734 (2014) 122, arXiv:1402.6242.
[10] LHCb collaboration, R. Aaij et al., Precision measurement of the mass and lifetime of the Ξ−b baryon, Phys. Rev. Lett. 113 (2014) 242002, arXiv:1409.8568.
[11] LHCb collaboration, R. Aaij et al., Observation of J/ψ p resonances consistent with pentaquark states in Λ0
b → J/ψ pK
− decays, Phys. Rev. Lett. 115 (2015) 072001,
arXiv:1507.03414.
[12] LHCb collaboration, R. Aaij et al., Measurement of relative branching fractions of B decays to ψ(2S) and J/ψ mesons, Eur. Phys. J. C72 (2012) 2118, arXiv:1205.0918. [13] LHCb collaboration, R. Aaij et al., Observations of B0
s → ψ(2S)η and
B0(s)→ ψ(2S)π+π− decays, Nucl. Phys. B871 (2013) 403 , arXiv:1302.6354.
[14] LHCb collaboration, R. Aaij et al., Observation of B0s → χc1φ decay and study of
B0 → χ
c1,2K∗0 decays, Nucl. Phys. B874 (2013) 663, arXiv:1305.6511.
[15] LHCb collaboration, R. Aaij et al., Measurement of B+
c production at
√
s = 8 TeV , Phys. Rev. Lett. 114 (2014) 132001, arXiv:1411.2943.
[16] LHCb collaboration, R. Aaij et al., Study of η–η0 mixing from measurement of B0(s)→ J/ψ η(0) decay rates, JHEP 01 (2015) 024, arXiv:1411.0943.
[17] LHCb collaboration, R. Aaij et al., Measurement of the branching fraction ra-tio B(B+c → ψ(2S)π+)/B(B+
c → J/ψ π+), Phys. Rev. D92 (2015) 057007,
arXiv:1507.03516.
[18] ATLAS collaboration, G. Aad et al., Measurement of the branching ratio Γ(Λ0b → ψ(2S)Λ)/Γ(Λ0
b→ J/ψ Λ) with the ATLAS detector, Phys. Lett. B751 (2015)
63, arXiv:1507.08202.
[19] LHCb collaboration, A. A. Alves Jr. et al., The LHCb detector at the LHC, JINST 3 (2008) S08005.
[20] LHCb collaboration, R. Aaij et al., LHCb detector performance, Int. J. Mod. Phys. A30 (2015) 1530022, arXiv:1412.6352.
[21] R. Aaij et al., Performance of the LHCb Vertex Locator, JINST 9 (2014) P09007, arXiv:1405.7808.
[22] LHCb collaboration, R. Aaij et al., Measurements of the Λ0b, Ξ−b, and Ω−b baryon masses, Phys. Rev. Lett. 110 (2013) 182001, arXiv:1302.1072.
[23] R. Aaij et al., The LHCb trigger and its performance in 2011, JINST 8 (2013) P04022, arXiv:1211.3055.
[24] T. Sj¨ostrand, S. Mrenna, and P. Skands, PYTHIA 6.4 physics and manual, JHEP 05 (2006) 026, arXiv:hep-ph/0603175; T. Sj¨ostrand, S. Mrenna, and P. Skands, A brief introduction to PYTHIA 8.1, Comput. Phys. Commun. 178 (2008) 852, arXiv:0710.3820.
[25] I. Belyaev et al., Handling of the generation of primary events in Gauss, the LHCb simulation framework, J. Phys. Conf. Ser. 331 (2011) 032047.
[26] D. J. Lange, The EvtGen particle decay simulation package, Nucl. Instrum. Meth. A462 (2001) 152.
[27] P. Golonka and Z. Was, PHOTOS Monte Carlo: A precision tool for QED corrections in Z and W decays, Eur. Phys. J. C45 (2006) 97, arXiv:hep-ph/0506026.
[28] Geant4 collaboration, J. Allison et al., Geant4 developments and applications, IEEE Trans. Nucl. Sci. 53 (2006) 270; Geant4 collaboration, S. Agostinelli et al., Geant4: A simulation toolkit, Nucl. Instrum. Meth. A506 (2003) 250.
[29] M. Clemencic et al., The LHCb simulation application, Gauss: Design, evolution and experience, J. Phys. Conf. Ser. 331 (2011) 032023.
[30] LHCb collaboration, R. Aaij et al., Evidence for the decay B+
c → J/ψ 3π+2π
−, JHEP
05 (2014) 148, arXiv:1404.0287.
[31] M. Adinolfi et al., Performance of the LHCb RICH detector at the LHC, Eur. Phys. J. C73 (2013) 2431, arXiv:1211.6759.
[32] F. Archilli et al., Performance of the muon identification at LHCb, JINST 8 (2013) P10020, arXiv:1306.0249.
[33] Particle Data Group, K. A. Olive et al., Review of particle physics, Chin. Phys. C38 (2014) 090001, and 2015 update.
[34] W. D. Hulsbergen, Decay chain fitting with a Kalman filter, Nucl. Instrum. Meth. A552 (2005) 566, arXiv:physics/0503191.
[35] T. Skwarnicki, A study of the radiative cascade transitions between the Υ0 and Υ resonances, PhD thesis, Institute of Nuclear Physics, Krakow, 1986, DESY-F31-86-02. [36] LHCb collaboration, R. Aaij et al., Observation of J/ψ -pair production in pp collisions
[37] M. Pivk and F. R. Le Diberder, sPlot: A statistical tool to unfold data distributions, Nucl. Instrum. Meth. A555 (2005) 356, arXiv:physics/0402083.
[38] LHCb collaboration, R. Aaij et al., Measurement of the track reconstruction efficiency at LHCb, JINST 10 (2015) P02007, arXiv:1408.1251.
[39] BaBar collaboration, J. P. Lees et al., Branching fraction measurements of the col-or-suppressed decays ¯B0 → D(∗)0π0, D(∗)0η, D(∗)0ω, and D(∗)0η0 and measurement of
the polarization in the decay ¯B0 → D∗0ω, Phys. Rev. D84 (2011) 112007, Erratum
ibid. D87 (2013) 039901, arXiv:1107.5751.
[40] D. Martinez Santos and F. Dupertuis, Mass distributions marginalized over per-event errors, Nucl. Instrum. Meth. A764 (2014) 150, arXiv:1312.5000.
[41] E672 and E706 collaborations, A. Gribushin et al., Production of J/ψ and ψ(2S) mesons in π−Be collisions at 515 GeV/c, Phys. Rev. D53 (1996) 4723 FERMILAB-PUB-95-298-E.
[42] BaBar collaboration, B. Aubert et al., Measurement of the branching frac-tions for ψ(2S) → e+e− and ψ(2S) → µ+µ−, Phys. Rev. D65 (2002) 031101, arXiv:hep-ex/0109004.
[43] LHCb collaboration, R. Aaij et al., Precision measurement of D meson mass differ-ences, JHEP 06 (2013) 065, arXiv:1304.6865.
[44] LHCb collaboration, R. Aaij et al., Measurement of b-hadron masses, Phys. Lett. B708 (2012) 241, arXiv:1112.4896.
[45] LHCb collaboration, R. Aaij et al., Prompt K0S production in pp collisions at √s = 0.9 TeV , Phys. Lett. B693 (2010) 69, arXiv:1008.3105.
[46] ATLAS collaboration, G. Aad et al., Measurement of the Λ0
b lifetime and mass in the
LHCb collaboration
R. Aaij39, C. Abell´an Beteta41, B. Adeva38, M. Adinolfi47, A. Affolder53, Z. Ajaltouni5, S. Akar6, J. Albrecht10, F. Alessio39, M. Alexander52, S. Ali42, G. Alkhazov31, P. Alvarez Cartelle54, A.A. Alves Jr58, S. Amato2, S. Amerio23, Y. Amhis7, L. An3,40, L. Anderlini18, G. Andreassi40, M. Andreotti17,g, J.E. Andrews59, R.B. Appleby55, O. Aquines Gutierrez11, F. Archilli39,
P. d’Argent12, A. Artamonov36, M. Artuso60, E. Aslanides6, G. Auriemma26,n, M. Baalouch5, S. Bachmann12, J.J. Back49, A. Badalov37, C. Baesso61, W. Baldini17,39, R.J. Barlow55,
C. Barschel39, S. Barsuk7, W. Barter39, V. Batozskaya29, V. Battista40, A. Bay40, L. Beaucourt4,
J. Beddow52, F. Bedeschi24, I. Bediaga1, L.J. Bel42, V. Bellee40, N. Belloli21,k, I. Belyaev32, E. Ben-Haim8, G. Bencivenni19, S. Benson39, J. Benton47, A. Berezhnoy33, R. Bernet41,
A. Bertolin23, F. Betti15, M.-O. Bettler39, M. van Beuzekom42, S. Bifani46, P. Billoir8, T. Bird55,
A. Birnkraut10, A. Bizzeti18,i, T. Blake49, F. Blanc40, J. Blouw11, S. Blusk60, V. Bocci26, A. Bondar35, N. Bondar31,39, W. Bonivento16, A. Borgheresi21,k, S. Borghi55, M. Borisyak67, M. Borsato38, T.J.V. Bowcock53, E. Bowen41, C. Bozzi17,39, S. Braun12, M. Britsch12,
T. Britton60, J. Brodzicka55, N.H. Brook47, E. Buchanan47, C. Burr55, A. Bursche2,
J. Buytaert39, S. Cadeddu16, R. Calabrese17,g, M. Calvi21,k, M. Calvo Gomez37,p, P. Campana19, D. Campora Perez39, L. Capriotti55, A. Carbone15,e, G. Carboni25,l, R. Cardinale20,j,
A. Cardini16, P. Carniti21,k, L. Carson51, K. Carvalho Akiba2, G. Casse53, L. Cassina21,k, L. Castillo Garcia40, M. Cattaneo39, Ch. Cauet10, G. Cavallero20, R. Cenci24,t, M. Charles8, Ph. Charpentier39, G. Chatzikonstantinidis46, M. Chefdeville4, S. Chen55, S.-F. Cheung56, N. Chiapolini41, M. Chrzaszcz41,27, X. Cid Vidal39, G. Ciezarek42, P.E.L. Clarke51,
M. Clemencic39, H.V. Cliff48, J. Closier39, V. Coco39, J. Cogan6, E. Cogneras5, V. Cogoni16,f, L. Cojocariu30, G. Collazuol23,r, P. Collins39, A. Comerma-Montells12, A. Contu39, A. Cook47, M. Coombes47, S. Coquereau8, G. Corti39, M. Corvo17,g, B. Couturier39, G.A. Cowan51, D.C. Craik51, A. Crocombe49, M. Cruz Torres61, S. Cunliffe54, R. Currie54, C. D’Ambrosio39, E. Dall’Occo42, J. Dalseno47, P.N.Y. David42, A. Davis58, O. De Aguiar Francisco2,
K. De Bruyn6, S. De Capua55, M. De Cian12, J.M. De Miranda1, L. De Paula2, P. De Simone19, C.-T. Dean52, D. Decamp4, M. Deckenhoff10, L. Del Buono8, N. D´el´eage4, M. Demmer10, D. Derkach67, O. Deschamps5, F. Dettori39, B. Dey22, A. Di Canto39, F. Di Ruscio25, H. Dijkstra39, S. Donleavy53, F. Dordei39, M. Dorigo40, A. Dosil Su´arez38, A. Dovbnya44, K. Dreimanis53, L. Dufour42, G. Dujany55, K. Dungs39, P. Durante39, R. Dzhelyadin36, A. Dziurda27, A. Dzyuba31, S. Easo50,39, U. Egede54, V. Egorychev32, S. Eidelman35, S. Eisenhardt51, U. Eitschberger10, R. Ekelhof10, L. Eklund52, I. El Rifai5, Ch. Elsasser41, S. Ely60, S. Esen12, H.M. Evans48, T. Evans56, A. Falabella15, C. F¨arber39, N. Farley46, S. Farry53, R. Fay53, D. Fazzini21,k, D. Ferguson51, V. Fernandez Albor38, F. Ferrari15, F. Ferreira Rodrigues1, M. Ferro-Luzzi39, S. Filippov34, M. Fiore17,39,g, M. Fiorini17,g, M. Firlej28, C. Fitzpatrick40, T. Fiutowski28, F. Fleuret7,b, K. Fohl39, M. Fontana16, F. Fontanelli20,j, D. C. Forshaw60, R. Forty39, M. Frank39, C. Frei39, M. Frosini18, J. Fu22, E. Furfaro25,l, A. Gallas Torreira38, D. Galli15,e, S. Gallorini23, S. Gambetta51, M. Gandelman2, P. Gandini56, Y. Gao3, J. Garc´ıa Pardi˜nas38, J. Garra Tico48, L. Garrido37, D. Gascon37, C. Gaspar39, L. Gavardi10, G. Gazzoni5, D. Gerick12, E. Gersabeck12, M. Gersabeck55, T. Gershon49, Ph. Ghez4, S. Gian`ı40, V. Gibson48, O.G. Girard40, L. Giubega30,
V.V. Gligorov39, C. G¨obel61, D. Golubkov32, A. Golutvin54,39, A. Gomes1,a, C. Gotti21,k, M. Grabalosa G´andara5, R. Graciani Diaz37, L.A. Granado Cardoso39, E. Graug´es37,
E. Gushchin34, Yu. Guz36,39, T. Gys39, T. Hadavizadeh56, C. Hadjivasiliou60, G. Haefeli40, C. Haen39, S.C. Haines48, S. Hall54, B. Hamilton59, X. Han12, S. Hansmann-Menzemer12, N. Harnew56, S.T. Harnew47, J. Harrison55, J. He39, T. Head40, V. Heijne42, A. Heister9,
K. Hennessy53, P. Henrard5, L. Henry8, J.A. Hernando Morata38, E. van Herwijnen39, M. Heß65, A. Hicheur2, D. Hill56, M. Hoballah5, C. Hombach55, L. Hongming40, W. Hulsbergen42,
T. Humair54, M. Hushchyn67, N. Hussain56, D. Hutchcroft53, M. Idzik28, P. Ilten57,
R. Jacobsson39, A. Jaeger12, J. Jalocha56, E. Jans42, A. Jawahery59, M. John56, D. Johnson39, C.R. Jones48, C. Joram39, B. Jost39, N. Jurik60, S. Kandybei44, W. Kanso6, M. Karacson39, T.M. Karbach39,†, S. Karodia52, M. Kecke12, M. Kelsey60, I.R. Kenyon46, M. Kenzie39, T. Ketel43, E. Khairullin67, B. Khanji21,39,k, C. Khurewathanakul40, T. Kirn9, S. Klaver55, K. Klimaszewski29, O. Kochebina7, M. Kolpin12, I. Komarov40, R.F. Koopman43,
P. Koppenburg42,39, M. Kozeiha5, L. Kravchuk34, K. Kreplin12, M. Kreps49, P. Krokovny35, F. Kruse10, W. Krzemien29, W. Kucewicz27,o, M. Kucharczyk27, V. Kudryavtsev35, A. K. Kuonen40, K. Kurek29, T. Kvaratskheliya32, D. Lacarrere39, G. Lafferty55,39, A. Lai16, D. Lambert51, G. Lanfranchi19, C. Langenbruch49, B. Langhans39, T. Latham49, C. Lazzeroni46, R. Le Gac6, J. van Leerdam42, J.-P. Lees4, R. Lef`evre5, A. Leflat33,39, J. Lefran¸cois7,
E. Lemos Cid38, O. Leroy6, T. Lesiak27, B. Leverington12, Y. Li7, T. Likhomanenko67,66, M. Liles53, R. Lindner39, C. Linn39, F. Lionetto41, B. Liu16, X. Liu3, D. Loh49, I. Longstaff52, J.H. Lopes2, D. Lucchesi23,r, M. Lucio Martinez38, H. Luo51, A. Lupato23, E. Luppi17,g,
O. Lupton56, N. Lusardi22, A. Lusiani24, F. Machefert7, F. Maciuc30, O. Maev31, K. Maguire55, S. Malde56, A. Malinin66, G. Manca7, G. Mancinelli6, P. Manning60, A. Mapelli39, J. Maratas5, J.F. Marchand4, U. Marconi15, C. Marin Benito37, P. Marino24,39,t, J. Marks12, G. Martellotti26, M. Martin6, M. Martinelli40, D. Martinez Santos38, F. Martinez Vidal68, D. Martins Tostes2, L.M. Massacrier7, A. Massafferri1, R. Matev39, A. Mathad49, Z. Mathe39, C. Matteuzzi21, A. Mauri41, B. Maurin40, A. Mazurov46, M. McCann54, J. McCarthy46, A. McNab55, R. McNulty13, B. Meadows58, F. Meier10, M. Meissner12, D. Melnychuk29, M. Merk42,
A Merli22,u, E Michielin23, D.A. Milanes64, M.-N. Minard4, D.S. Mitzel12, J. Molina Rodriguez61, I.A. Monroy64, S. Monteil5, M. Morandin23, P. Morawski28, A. Mord`a6, M.J. Morello24,t, J. Moron28, A.B. Morris51, R. Mountain60, F. Muheim51, D. M¨uller55, J. M¨uller10, K. M¨uller41, V. M¨uller10, M. Mussini15, B. Muster40, P. Naik47, T. Nakada40, R. Nandakumar50, A. Nandi56, I. Nasteva2, M. Needham51, N. Neri22, S. Neubert12, N. Neufeld39, M. Neuner12, A.D. Nguyen40,
C. Nguyen-Mau40,q, V. Niess5, S. Nieswand9, R. Niet10, N. Nikitin33, T. Nikodem12, A. Novoselov36, D.P. O’Hanlon49, A. Oblakowska-Mucha28, V. Obraztsov36, S. Ogilvy52, O. Okhrimenko45, R. Oldeman16,48,f, C.J.G. Onderwater69, B. Osorio Rodrigues1,
J.M. Otalora Goicochea2, A. Otto39, P. Owen54, A. Oyanguren68, A. Palano14,d, F. Palombo22,u, M. Palutan19, J. Panman39, A. Papanestis50, M. Pappagallo52, L.L. Pappalardo17,g,
C. Pappenheimer58, W. Parker59, C. Parkes55, G. Passaleva18, G.D. Patel53, M. Patel54,
C. Patrignani20,j, A. Pearce55,50, A. Pellegrino42, G. Penso26,m, M. Pepe Altarelli39, S. Perazzini15,e, P. Perret5, L. Pescatore46, K. Petridis47, A. Petrolini20,j, M. Petruzzo22, E. Picatoste Olloqui37, B. Pietrzyk4, M. Pikies27, D. Pinci26, A. Pistone20, A. Piucci12,
S. Playfer51, M. Plo Casasus38, T. Poikela39, F. Polci8, A. Poluektov49,35, I. Polyakov32,
E. Polycarpo2, A. Popov36, D. Popov11,39, B. Popovici30, C. Potterat2, E. Price47, J.D. Price53, J. Prisciandaro38, A. Pritchard53, C. Prouve47, V. Pugatch45, A. Puig Navarro40, G. Punzi24,s, W. Qian56, R. Quagliani7,47, B. Rachwal27, J.H. Rademacker47, M. Rama24, M. Ramos Pernas38, M.S. Rangel2, I. Raniuk44, G. Raven43, F. Redi54, S. Reichert55, A.C. dos Reis1, V. Renaudin7, S. Ricciardi50, S. Richards47, M. Rihl39, K. Rinnert53,39, V. Rives Molina37, P. Robbe7,39,
A.B. Rodrigues1, E. Rodrigues55, J.A. Rodriguez Lopez64, P. Rodriguez Perez55,
A. Rogozhnikov67, S. Roiser39, V. Romanovsky36, A. Romero Vidal38, J. W. Ronayne13, M. Rotondo23, T. Ruf39, P. Ruiz Valls68, J.J. Saborido Silva38, N. Sagidova31, B. Saitta16,f,
V. Salustino Guimaraes2, C. Sanchez Mayordomo68, B. Sanmartin Sedes38, R. Santacesaria26, C. Santamarina Rios38, M. Santimaria19, E. Santovetti25,l, A. Sarti19,m, C. Satriano26,n, A. Satta25, D.M. Saunders47, D. Savrina32,33, S. Schael9, M. Schiller39, H. Schindler39,
M. Schlupp10, M. Schmelling11, T. Schmelzer10, B. Schmidt39, O. Schneider40, A. Schopper39, M. Schubiger40, M.-H. Schune7, R. Schwemmer39, B. Sciascia19, A. Sciubba26,m,
A. Semennikov32, A. Sergi46, N. Serra41, J. Serrano6, L. Sestini23, P. Seyfert21, M. Shapkin36, I. Shapoval17,44,g, Y. Shcheglov31, T. Shears53, L. Shekhtman35, V. Shevchenko66, A. Shires10, B.G. Siddi17, R. Silva Coutinho41, L. Silva de Oliveira2, G. Simi23,s, M. Sirendi48,
N. Skidmore47, T. Skwarnicki60, E. Smith54, I.T. Smith51, J. Smith48, M. Smith55, H. Snoek42, M.D. Sokoloff58,39, F.J.P. Soler52, F. Soomro40, D. Souza47, B. Souza De Paula2, B. Spaan10, P. Spradlin52, S. Sridharan39, F. Stagni39, M. Stahl12, S. Stahl39, S. Stefkova54, O. Steinkamp41, O. Stenyakin36, S. Stevenson56, S. Stoica30, S. Stone60, B. Storaci41, S. Stracka24,t,
M. Straticiuc30, U. Straumann41, L. Sun58, W. Sutcliffe54, K. Swientek28, S. Swientek10, V. Syropoulos43, M. Szczekowski29, T. Szumlak28, S. T’Jampens4, A. Tayduganov6,
T. Tekampe10, G. Tellarini17,g, F. Teubert39, C. Thomas56, E. Thomas39, J. van Tilburg42, V. Tisserand4, M. Tobin40, J. Todd58, S. Tolk43, L. Tomassetti17,g, D. Tonelli39,
S. Topp-Joergensen56, E. Tournefier4, S. Tourneur40, K. Trabelsi40, M. Traill52, M.T. Tran40, M. Tresch41, A. Trisovic39, A. Tsaregorodtsev6, P. Tsopelas42, N. Tuning42,39, A. Ukleja29, A. Ustyuzhanin67,66, U. Uwer12, C. Vacca16,39,f, V. Vagnoni15, G. Valenti15, A. Vallier7,
R. Vazquez Gomez19, P. Vazquez Regueiro38, C. V´azquez Sierra38, S. Vecchi17, M. van Veghel42, J.J. Velthuis47, M. Veltri18,h, G. Veneziano40, M. Vesterinen12, B. Viaud7, D. Vieira2,
M. Vieites Diaz38, X. Vilasis-Cardona37,p, V. Volkov33, A. Vollhardt41, D. Voong47,
A. Vorobyev31, V. Vorobyev35, C. Voß65, J.A. de Vries42, R. Waldi65, C. Wallace49, R. Wallace13, J. Walsh24, J. Wang60, D.R. Ward48, N.K. Watson46, D. Websdale54, A. Weiden41,
M. Whitehead39, J. Wicht49, G. Wilkinson56,39, M. Wilkinson60, M. Williams39,
M.P. Williams46, M. Williams57, T. Williams46, F.F. Wilson50, J. Wimberley59, J. Wishahi10, W. Wislicki29, M. Witek27, G. Wormser7, S.A. Wotton48, K. Wraight52, S. Wright48,
K. Wyllie39, Y. Xie63, Z. Xu40, Z. Yang3, H. Yin63, J. Yu63, X. Yuan35, O. Yushchenko36,
M. Zangoli15, M. Zavertyaev11,c, L. Zhang3, Y. Zhang3, A. Zhelezov12, Y. Zheng62, A. Zhokhov32, L. Zhong3, V. Zhukov9, S. Zucchelli15.
1Centro Brasileiro de Pesquisas F´ısicas (CBPF), Rio de Janeiro, Brazil 2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil 3Center for High Energy Physics, Tsinghua University, Beijing, China
4LAPP, Universit´e Savoie Mont-Blanc, CNRS/IN2P3, Annecy-Le-Vieux, France
5Clermont Universit´e, Universit´e Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France 6CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France
7LAL, Universit´e Paris-Sud, CNRS/IN2P3, Orsay, France
8LPNHE, Universit´e Pierre et Marie Curie, Universit´e Paris Diderot, CNRS/IN2P3, Paris, France 9I. Physikalisches Institut, RWTH Aachen University, Aachen, Germany
10Fakult¨at Physik, Technische Universit¨at Dortmund, Dortmund, Germany 11Max-Planck-Institut f¨ur Kernphysik (MPIK), Heidelberg, Germany
12Physikalisches Institut, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg, Germany 13School of Physics, University College Dublin, Dublin, Ireland
15Sezione INFN di Bologna, Bologna, Italy 16Sezione INFN di Cagliari, Cagliari, Italy 17Sezione INFN di Ferrara, Ferrara, Italy 18Sezione INFN di Firenze, Firenze, Italy
19Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy 20Sezione INFN di Genova, Genova, Italy
21Sezione INFN di Milano Bicocca, Milano, Italy 22Sezione INFN di Milano, Milano, Italy
23Sezione INFN di Padova, Padova, Italy 24Sezione INFN di Pisa, Pisa, Italy
25Sezione INFN di Roma Tor Vergata, Roma, Italy 26Sezione INFN di Roma La Sapienza, Roma, Italy
27Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Krak´ow, Poland 28AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science,
Krak´ow, Poland
29National Center for Nuclear Research (NCBJ), Warsaw, Poland
30Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania 31Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia
32Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia
33Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia
34Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia 35Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia 36Institute for High Energy Physics (IHEP), Protvino, Russia
37Universitat de Barcelona, Barcelona, Spain
38Universidad de Santiago de Compostela, Santiago de Compostela, Spain 39European Organization for Nuclear Research (CERN), Geneva, Switzerland 40Ecole Polytechnique F´ed´erale de Lausanne (EPFL), Lausanne, Switzerland 41Physik-Institut, Universit¨at Z¨urich, Z¨urich, Switzerland
42Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands
43Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The
Netherlands
44NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine
45Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine 46University of Birmingham, Birmingham, United Kingdom
47H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom 48Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom 49Department of Physics, University of Warwick, Coventry, United Kingdom 50STFC Rutherford Appleton Laboratory, Didcot, United Kingdom
51School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 52School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 53Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom 54Imperial College London, London, United Kingdom
55School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 56Department of Physics, University of Oxford, Oxford, United Kingdom
57Massachusetts Institute of Technology, Cambridge, MA, United States 58University of Cincinnati, Cincinnati, OH, United States
59University of Maryland, College Park, MD, United States 60Syracuse University, Syracuse, NY, United States
61Pontif´ıcia Universidade Cat´olica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated to 2 62University of Chinese Academy of Sciences, Beijing, China, associated to 3
63Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China, associated to3 64Departamento de Fisica , Universidad Nacional de Colombia, Bogota, Colombia, associated to8
65Institut f¨ur Physik, Universit¨at Rostock, Rostock, Germany, associated to12 66National Research Centre Kurchatov Institute, Moscow, Russia, associated to32 67Yandex School of Data Analysis, Moscow, Russia, associated to32
68Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC, Valencia, Spain, associated to37 69Van Swinderen Institute, University of Groningen, Groningen, The Netherlands, associated to42
aUniversidade Federal do Triˆangulo Mineiro (UFTM), Uberaba-MG, Brazil bLaboratoire Leprince-Ringuet, Palaiseau, France
cP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia dUniversit`a di Bari, Bari, Italy
eUniversit`a di Bologna, Bologna, Italy fUniversit`a di Cagliari, Cagliari, Italy gUniversit`a di Ferrara, Ferrara, Italy hUniversit`a di Urbino, Urbino, Italy
iUniversit`a di Modena e Reggio Emilia, Modena, Italy jUniversit`a di Genova, Genova, Italy
kUniversit`a di Milano Bicocca, Milano, Italy lUniversit`a di Roma Tor Vergata, Roma, Italy mUniversit`a di Roma La Sapienza, Roma, Italy nUniversit`a della Basilicata, Potenza, Italy
oAGH - University of Science and Technology, Faculty of Computer Science, Electronics and
Telecommunications, Krak´ow, Poland
pLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain qHanoi University of Science, Hanoi, Viet Nam
rUniversit`a di Padova, Padova, Italy sUniversit`a di Pisa, Pisa, Italy
tScuola Normale Superiore, Pisa, Italy
uUniversit`a degli Studi di Milano, Milano, Italy
![Figure 1: Mass distributions of selected (left) Λ 0 b → ψ(2S)[→ µ + µ − ]pK − and (right) Λ 0 b → J / ψ pK − candidates](https://thumb-eu.123doks.com/thumbv2/123doknet/14100338.465531/6.892.138.783.168.442/figure-mass-distributions-selected-left-λ-right-candidates.webp)
![Figure 3: (left) Mass distribution of selected Λ 0 b → ψ(2S)[→ J / ψ π + π − ]pK − candidates with an additional constraint for the ψ(2S) mass [33]](https://thumb-eu.123doks.com/thumbv2/123doknet/14100338.465531/12.892.140.780.165.437/figure-left-mass-distribution-selected-candidates-additional-constraint.webp)
