Observation of a new baryon state in the Λ0bπ+π− mass spectrum

University of Groningen

Observation of a new baryon state in the Λ0bπ+π− mass spectrum

Onderwater, C. J. G.; LHCb Collaboration

Published in:

Journal of High Energy Physics DOI:

10.1007/JHEP06(2020)136

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Publication date: 2020

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Onderwater, C. J. G., & LHCb Collaboration (2020). Observation of a new baryon state in the Λ0bπ+π− mass spectrum. Journal of High Energy Physics, 2020(6), [136]. https://doi.org/10.1007/JHEP06(2020)136

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JHEP06(2020)136

Published for SISSA by Springer

Received: February 13, 2020 Accepted: June 1, 2020 Published: June 23, 2020

Observation of a new baryon state in the Λ

0_b

π

+

π

−

mass spectrum

The LHCb collaboration

E-mail: Ivan.Belyaev@itep.ru

Abstract: A new baryon state is observed in the Λ0bπ+π− mass spectrum with high

significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies √s= 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. The mass and natural width of the new state are measured to be

m= 6072.3_{± 2.9 ± 0.6 ± 0.2 MeV ,} Γ = 72± 11 ± 2 MeV ,

where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the Λ0_b baryon mass. The new state is consistent with the first radial excitation of the Λ0

bbaryon, the Λb(2S)

0 _{resonance. Updated}

measurements of the masses and the upper limits on the natural widths of the previously observed Λb(5912)0 and Λb(5920)0 states are also reported.

Keywords: B physics, Hadron-Hadron scattering (experiments), Heavy quark production, Spectroscopy

JHEP06(2020)136

Contents

1 Introduction 1

2 The LHCb detector 2

3 Event selection 3

4 Analysis of the high-mass region 5

5 Analysis of the low-mass region 9

6 Systematic uncertainties 10

7 Results and summary 14

The LHCb collaboration 20

1 Introduction

The constituent quark model [1,2] is very successful in describing and classifying the known hadrons based on their quantum numbers [4]. However, quantum chromodynamcs that lies in the origin of the quark model, being a nonperturbative theory, does not predict hadron properties, namely masses and decay widths, from first principles. Alternative theoretical approaches are developed, such as heavy quark effective theory or lattice cal-culations. These approaches require verification with experiment in various regimes, e.g. testing the agreement with data for hadrons with different quark content and quantum numbers. Baryons, containing a beauty quark form a particular family of hadrons, where the experimental data are still scarce.

Excited beauty baryons with two light quarks and quark content bqq0, where q, q0 = u, d, have been studied experimentally at the Tevatron and the LHC. The family of these baryons consists of the Λ0

b isosinglet and the Σb and Σ∗b isotriplet states. The lightest

charged Σ(_b∗)± baryons have been observed by the CDF collaboration [5, 6] in the Λ0 bπ±

spectrum. The measurement of the masses and widths of those states was updated by the LHCb collaboration and the heavier Σb(6097)± states were discovered [7].

The spectrum of excited beauty baryons decaying to the Λ0_bπ+π− final state near threshold has been studied by the LHCb collaboration using a data sample collected in 2011, which resulted in the discovery of two narrow states [8], denoted Λb(5912)0 and

Λb(5920)0. The most likely interpretation of these states is that they are a doublet of first

orbital excitations in the Λ0_b system, with quantum numbers JP= 1₂−and 3₂−, respectively. The heavier of these states was later confirmed by the CDF collaboration [9]. A doublet

JHEP06(2020)136

Baryon State JP _{Ref. [16] Ref. [17] Ref. [18] Ref. [19]}

Λ0_b 1S 1₂+ 5585 5612 5620 5619 1P 1 2 − 5912 5939 5930 5911 3 2 − _{5920 5941 5942 5920} 2S 1₂+ 6045 6107 6089 1D 3 2 + 6145 6181 6190 6147 5 2 + 6165 6183 6196 6153 Σ(_b∗)0 1S 1 2 + 5795 5833 5800 3 2 + 5805 5858 5834 1P 1 2 − _{6070 6099 6101} 3 2 − _{6070 6101 6096} 5 2 − 6090 6172 6084 2S 1 2 + 6200 6294 6213 3 2 + 6250 6308 6226

Table 1. Quark-model predictions for the masses of the lightest Λb and Σ(∗)b states (in MeV).

of narrow states, Λb(6146)0 and Λb(6152)0, was also observed by LHCb collaboration [10].

The measured masses and widths of these states are compatible with the expectations for the Λb(1D)0 doublet [11–14]. Recently, the CMS collaboration reported an evidence for

a broad excess of events in the Λ0_bπ+π− mass spectrum in the region of 6040_{− 6100 MeV} corresponding to a statistical significance of four standard deviations [15].1 _{The existence} of additional states in the Λ0_bπ+π− spectrum is predicted by the quark model [16–18], notably, in the region between the established narrow doublet states, with masses around 6.1 GeV. Quark-model predictions for the masses of the lightest Λb and Σ(_b∗) states are

shown in table 1.

This paper reports the observation of a new structure in the Λ0_bπ+π−mass spectrum, as well as updated measurements of the masses and widths of the Λb(5912)0 and Λb(5920)0

states with improved precision. The analysis uses pp collision data recorded by LHCb in 2011–2018 at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 1, 2 and 6 fb−1, respectively.

2 The LHCb detector

The LHCb detector [20, 21] is a single-arm forward spectrometer covering the pseudo-rapidity range 2 < η < 5, designed for the study of particles containing b or c quarks.

1

JHEP06(2020)136

The detector includes a high-precision tracking system consisting of a silicon-strip ver-tex detector surrounding the pp interaction region [22], 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 [23, 24] placed downstream of the magnet. 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. The momentum scale of the tracking system is calibrated using samples of J/ψ_{→ µ}+µ−and B+_{→ J/ψK}+decays collected concurrently with the data sample used for this analysis[25,26]. The relative accuracy of this procedure is estimated to be 3_×10−4 us-ing samples of other fully reconstructed b-hadron, K0S, and narrow Υ(1S) resonance decays. Different types of charged hadrons are distinguished by the particle identification (PID) system using information from two ring-imaging Cherenkov detectors [27]. Muons are identified by a system composed of alternating layers of iron and multiwire proportional chambers [28].

The online event selection is performed by a trigger [29] which consists of a hardware stage, based on information from the calorimeter and muon systems, followed by a software stage, which applies a full event reconstruction. At the hardware trigger stage, events are required to have a muon with high transverse momentum, pT, or a pair of opposite-sign

muons with a requirement on the product of muon transverse momenta, or a hadron, photon or electron with high transverse energy in the calorimeters. The software trigger requires a two-, three- or four-track secondary vertex with at least one charged particle with a large pT and inconsistent with originating from any reconstructed primary pp collision

vertex (PV) [30, 31] or two muons of opposite charge forming a good-quality secondary vertex with a mass in excess of 2.7 GeV.

Simulation is required to model the effects of the detector acceptance, resolution, and selection requirements. In the simulation, pp collisions are generated using Pythia [32] with a specific LHCb configuration [33]. Decays of unstable particles are described by EvtGen [34], in which final-state radiation is generated using Photos [35]. The interac-tion of the generated particles with the detector, and its response, are implemented using the Geant4 toolkit [36] as described in ref. [38].

3 Event selection

The Λ0_b candidates are reconstructed in the Λ0_{b→ Λ}+_cπ− and the Λ0_{b→ J/ψpK}− decays.2 The selection of the Λ0

b candidates is similar to that used in ref. [10]. All charged

fi-nal-state particles are required to be positively identified by the PID systems. To reduce the background from random combinations of tracks, only the tracks with large impact parameter with respect to all PVs in the event are used. The Λ+

c candidates are

recon-structed in the pK−π+ final state. The Λ0_b→ J/ψpK− _{candidates are created by}

combin-ing the J/ψ candidates formed of µ+_µ− _{pairs with kaon and proton tracks. The masses of}

the Λ+_c and J/ψ candidates are required to be consistent with the known values of the masses 2_{Inclusion of charge-conjugate states is implied throughout this paper.}

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Figure 1. Mass distributions for selected (left) Λ0

b→ Λ+cπ− and (right) Λ0b→ J/ψpK− candidates

after BDT selection. A fit, composed of a sum of a double-sided Crystal Ball function [46] and a smooth background component, is overlaid.

of the respective states [4] and the Λ0_b candidate is required to have a good-quality vertex significantly displaced from all PVs.

Further suppression of the background is achieved by using a boosted decision tree (BDT) classifier [39,40] implemented in the TMVA toolkit [41]. Two separate BDTs are used for the Λ0_{b→ Λ}+_cπ− and Λ0_{b→ J/ψpK}− selections. The multivariate estimators are based on the kinematic properties, the reconstructed lifetime and vertex quality of the Λ0_b candidate and on variables describing the overall consistency of the selected candi-dates with the decay chain obtained from the kinematic fit described below [43]. In addi-tion, the reconstructed lifetime and vertex quality of the Λ+

c → pK−π+ candidate is used

for the Λ0_b→ Λ+

cπ− decay. The PID quality, transverse momentum and pseudorapidity of

the proton and kaon candidates (for Λ0

b→ J/ψpK−) or π− candidate (for Λ0b→ Λ+cπ−) are

also used. The BDT is trained using data, where the signal sample is obtained by sub-tracting the background using the sPlot technique [44], and the background sample is taken from the range 5.70_{− 5.85 GeV in the Λ}0

b→ Λ+cπ− and Λ0b→ J/ψpK− mass distributions.

A k-fold cross-validation technique is used to avoid introducing a bias in the evaluation [45]. A kinematic fit [43] is performed in order to improve the Λ0_b mass resolution. The momenta of the particles in the full decay chain are recomputed by constraining the Λ+

c or J/ψ mass

to their known values [4] and the Λ0_bbaryon to originate from the associated PV. The mass distributions for the selected Λ0_{b→ Λ}+_cπ− and Λ0_{b→ J/ψpK}− candidates are shown in fig-ure 1. The Λ0

b signal yield is (937.9± 1.6) × 103 and (223.0± 0.6) × 103 for Λ0b→ Λ+cπ−

and Λ0_b→ J/ψpK− _{decays, respectively.}

Selected Λ0_b→ Λ+

cπ−(Λ0b→ J/ψpK−) candidates with mass within ±50 (20) MeV from

the known Λ0_b mass are combined with pairs of opposite and same-sign pion tracks. To reduce the large combinatorial background, four separate BDT classifiers are trained for the Λ0_b→ Λ+

cπ− and Λ0b→ J/ψpK− samples in the high-mass (mΛ0

bππ<6.35 GeV) and the low-mass (m_Λ0

bππ<5.95 GeV) regions. The BDTs exploit the vertex quality, χ

2 vtx, of

JHEP06(2020)136

the Λ0

bππ combination, its transverse momentum, the pT of the ππ pair, the pT of each

pion, as well as their PID and track-reconstruction-quality variables. For the high-mass region, the pTof the dipion system is required to exceed 250 MeV. Simulated samples of

ex-cited Λ0_b baryons decaying into the Λ0_bπ+π− final state are used as signal training samples, while the background training sample is taken from the same-sign Λ0_bπ±π± combinations in data. For the low-mass region, simulated samples of Λb(5912)0 and Λb(5920)0 signal

decays are used, while for the high-mass region the simulated sample consists of decays of a narrow state with mass of 6.15 GeV and natural width of 7 MeV, and a broad state with mass of 6.08 GeV and natural width of 60 MeV. A k-fold cross-validation technique is used for training. A figure of merit ε/(5₂ +√B) [47] is used to optimise the requirement on the BDT estimator. The Λ0_bππ mass resolution is improved by a kinematic fit [43] constraining the mass of the pK−π+ and µ+_µ− _{combinations to the known masses of}

the Λ+_c baryon and J/ψ meson, respectively [4]. The mass of the Λ0_b baryon in the fit is constrained to the central value of m_Λ0

b = 5619.62± 0.16 ± 0.13 MeV [48]. It is also re-quired that the momentum vector of the Λ0

b candidate and the momenta of both pions

points back to the associated pp interaction vertex.

4 Analysis of the high-mass region

The distributions of the Λ0

bπ+π− and Λ0bπ±π± masses in the range 5.93 < mΛ0 bππ < 6.23 GeV for the Λ0_b→ Λ+

cπ− sample with the high-mass BDT selection applied are shown

in figure 2. The distributions of the same-sign Λ0_bπ±π± combinations are dominated by random combinations of a Λ0

b baryon and two pions. The Λ0bπ+π− spectrum features

the contributions of two narrow Λb(6146)0 and Λb(6152)0 states as well as a broad

struc-ture just below 6.1 GeV in addition to the smooth background. This new strucstruc-ture is referred to as Λ∗∗0_b hereafter. Figure 3shows the same distributions for the Λ0

b→ J/ψpK−

sample, where the same features are visible.

A simultaneous binned maximum-likelihood fit with a bin width of 200 keV is performed to the six distributions shown in figures 2 and 3 in order to determine the properties of the resonant shapes. Both signal and background Λ0_bππ combinations could include contributions from intermediate Σ±_b and Σ∗±_b states. The fitting function for the Λ0_bπ+π− spectra is the sum of five components: a combinatorial background, the two components corresponding to the combinations of Σ±_b→ Λ0

bπ± and Σ∗±b → Λ0bπ± with the addition of

a pion from the rest of the event, and three resonant contributions for the Λb(6146)0,

Λb(6152)0 and Λ∗∗0b states. The same-sign Λ0bπ±π± spectra are fitted with a function that

contains only the combinatorial, Σ±_bπ±, and Σ∗±_b π± components.

The combinatorial background is parameterised with a positive, increasing third-order polynomial function, whose coefficients are left free to vary in the fit. The Σ±_bπ and Σ∗±_b π components are described by the product of a two-body phase-space function and an exponential function, accounting for the finite width of the Σ(_b∗) states. The exponential factor is determined from the fit to the background-subtracted Σ(_b∗)±π mass distributions in the 6.16 < m_Λ0

bππ<6.40 GeV range. The shapes of the Σ

(∗)±

b πcomponents are taken to

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Figure 2. Mass spectra of selected (top) Λ0

bπ+π−, (middle) Λ0bπ+π+ and (bottom) Λ0bπ−π−

com-binations for the Λ0

b→ Λ+cπ− sample. A simultaneous fit, described in the text, is superimposed.

in the opposite-sign Λ0_bπ+π− and same-sign Λ0_bπ±π± spectra, but is allowed to differ for the Λ0

b→ Λ+cπ− and Λ0b→ J/ψpK− samples. The yields of all background components are

left free to vary in the fit. A good description of both the Λ0_bπ+π+ and Λ0_bπ−π− mass spectra supports the chosen background model.

The narrow Λb(6146)0 and Λb(6152)0 components are parameterised using relativistic

Breit-Wigner distributions convolved with the experimental resolution. The detector res-olution function is described by the sum of two Gaussian functions with zero mean and parameters fixed from simulation. The obtained effective resolution increases from 0.5 MeV to 1.7 MeV when the Λ0_bπ+π− mass grows from the mass of the Λb(5912)0 state to that

of the Λb(6152)0 state. The masses and widths of the Λb(6146)0 and Λb(6152)0 states are

fixed to the values obtained in ref. [10]. The Λ∗∗0_b shape as a function of the Λ0

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π

+

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−

Λ

0_b

π

+

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+

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0_b

π

−

π

−

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Figure 3. Mass spectra of selected (top) Λ0

bπ+π−, (middle) Λ0bπ+π+ and (bottom) Λ0bπ−π−

com-binations for the Λ0

b→ J/ψpK− sample. A simultaneous fit, described in the text, is superimposed.

is parameterised as S(m|m0,Γ)∝ Γρ3(m) m2₀− m2
2 + m2₀Γ2 ρ3(m) ρ3(m0) 2, (4.1)

where ρ3(m) is a three-body phase space of the Λ0_bπ+π− system

ρ3(m)≡ π2 4m2 (m−mΛ0_b)2 Z 4m2 π dm2_ππ m2_ππ λ 1/2_m2 ππ, m2, m2Λ0 b  λ1/2 m2_ππ, m2_π, m2_π
, (4.2)

λ(x, y, z) stands for a K¨all´en function [49], and mπ and mΛ0

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Λ0_b→ Λ+ cπ− Λ0b→ J/ψpK− Λ∗∗0_b 2570_{± 260} 550_{± 80} Λb(6146)0 520± 50 103± 22 Λb(6152)0 480± 50 90± 21

Table 2. Yields of excited baryons from the simultaneous fit to Λ0

bππ spectra with Λ0b→ Λ+cπ−

and Λ0

b→ J/ψpK−.

of the charged π meson and Λ0_b baryon, respectively. The mass, m0, and width, Γ, of

the Λ∗∗0_b state are free parameters of the fit.

The yields of the fit components in the combined fit are reported in table 2. The mass difference with respect to the Λ0_b baryon mass and the natural width of the Λ∗∗0_b state are determined to be

∆m_Λ∗∗0

b = 452.7± 2.9 MeV , ΓΛ∗∗_b = 72 ± 11 MeV ,

where uncertainties are statistical only. The statistical significance of the Λ∗∗0_b signal in Λ0_b→ Λ+

cπ− and Λ0b→ J/ψpK− samples is obtained using Wilks’ theorem [50] and exceeds

14 and 7 standard deviations, respectively. The ratios of the Λ∗∗0_b , Λb(6146)0and Λb(6152)0

signal yields between the Λ0_b→ Λ+

cπ−and Λ0b→ J/ψpK−final state are larger than the ratio

of their yields reported in section3. This arises due to the differece in the pTspectra selected

by the trigger for these final states which is propagated to the ππ reconstruction effects. The earlier analysis of Λb(6146)0 and Λb(6152)0 states [10] has shown that a

signif-icant fraction of their decays into the Λ0_bπ+π− final state proceeds via the intermediate Σ±_bπ∓ and Σ∗±_b π∓ processes. Since the measured mass of the Λ∗∗0_b state is above the Σbπ

threshold, one might expect that this state decays via intermediate Σ(_b∗)±π∓states as well. However, performing the fits to the Σ(_b∗)πmass spectra as was done in ref. [10] is compli-cated by the fact that the Σ(_b∗)±π∓ and Σ(_b∗)∓π± kinematic regions overlap in the range of Λ0_bπ+π− masses used for the Λ∗∗0_b fit. Separating the contributions of the resonant and nonresonant Λ∗∗0_b decays would require a full multidimensional fit in the Λ0_bπ+π−, Λ0_bπ+ and Λ0

bπ− masses, which is beyond the scope of this paper.

The Λ0

bπ± mass spectra from Λ0bπ+π− and Λb0π±π± combinations with Λ0b→ Λ+cπ−

from the Λ∗∗0_b signal-enhanced region 6.00 < m_Λ0

bππ < 6.14 GeV are shown in fig-ure 4. The Λ0_bπ± mass spectrum from the signal Λ∗∗0_b decays is obtained assuming that the Λ0

bπ± spectra from the same-sign Λ0bπ±π± combinations represent the background.

The background-subtracted spectrum is consistent with the presence of relatively small contributions from Λ∗∗0_{b → Σ}±_bπ∓ and Λ∗∗0_{b → Σ}∗±_b π∓ decays and a dominant contribution from nonresonant Λ∗∗0_{b → Λ}0

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Figure 4. (Top) Spectra of Λ0

bπ± mass with Λ0b→ Λ+cπ− for Λ0bπ+π− combinations (red points

with error bars) and Λ0

bπ±π± combinations (open blue histogram). (Bottom) Difference between

Λ0

bπmass spectra from Λ0bπ+π−and Λ0bπ±π±combinations. The structures near 5.81 and 5.83 GeV

correspond to the Σ±_{b→ Λ}0

bπ± and Σ∗±b → Λ0bπ± signals, respectively.

5 Analysis of the low-mass region

The Λ0_bππ mass spectra in the low-mass region m_Λ0

bππ < 5.94 GeV for Λ

0

b→ Λ+cπ− and

Λ0

b→ J/ψpK− samples are shown in figures 5 and 6, respectively. These distributions are

used to measure the properties of the Λb(5912)0 and Λb(5920)0 states. A simultaneous

binned fit, with narrow bins of 50 keV width, is performed to the six distributions with the sum of the two resonance components (in Λ0

bπ+π− combinations only) and the

combi-natorial background component (in all six distributions). The combicombi-natorial component is parameterised with a product of the three-body phase-space function and a positive poly-nomial function. The resonant components are given by relativistic S-wave Breit-Wigner

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Figure 5. Mass spectra of selected (top) Λ0

bπ+π−, (middle) Λ0bπ+π+ and (bottom) Λ0bπ−π−

com-binations for the Λ0

b→ Λ+cπ− sample. A simultaneous fit, described in the text, is superimposed.

lineshapes convolved with the resolution function obtained from simulation. The shape of the combinatorial background is assumed to be the same in the opposite-sign Λ0_bπ+π− and same-sign Λ0_bπ±π± spectra, but is allowed to differ for the Λ0_{b→ Λ}+_cπ− and Λ0_{b→ J/ψpK}− samples. The results of the combined fit are presented in table 3. The natural widths of the Λb(5912)0 and Λb(5920)0 states are consistent with zero.

6 Systematic uncertainties

The systematic uncertainties of the mass and the width of the Λ∗∗0_b state and of the masses of the Λb(5912)0 and Λb(5920)0 states are summarised in table 4.

A large uncertainty in the measurement of the Λ∗∗0_b parameters comes from the pa-rameterisation of the Λ∗∗0_b signal distribution. The fit function from eq. (4.1) describes

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−

LHCb

Figure 6. Mass spectra of selected (top) Λ0

bπ+π−, (middle) Λ0bπ+π+ and (bottom) Λ0bπ−π−

com-binations for the Λ0

b→ J/ψpK− sample. A simultaneous fit, described in the text, is superimposed.

Λ0_b→ Λ+ cπ− Λ0b→ J/ψpK− N_Λ b(5912)0 234± 17 57± 9 N_Λ b(5920)0 843± 33 204± 17 ∆m_Λ b(5912)0 [MeV] 292.582± 0.029 ∆m_Λ b(5920)0 [MeV] 300.479± 0.019 m_Λ b(5920)0 − mΛb(5912)0 [MeV] 7.896± 0.034

Table 3. Results of the combined fit to the low-mass Λ0

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Source ∆mΛ∗∗0b ΓΛ∗∗0b ∆mΛb(1P)0. [MeV] [MeV] [MeV] Fit model

Signal parameterisation 0.50 1.50 Background parameterisation 0.03 0.25

Fit range 0.10 0.30

Λb(1D)0 parameters

Momentum scale uncertainty 0.08 — 0.010

Sum in quadrature 0.52 1.55 0.010

Table 4. Summary of systematic uncertainties for the mass difference with respect to the ground state Λ0

b and natural width of the Λ∗∗0b state and the mass-differences for the Λb(5912)0 and

Λb(5920)0 states, ∆mΛb(1P)0.

three-body phase-space decays, while figure 4 suggests some contribution from decays via the intermediate Σ(∗)±_b π∓ states. To assess the associated systematic uncertainty, the fit is repeated using a more complicated function that in addition to nonresonant decays, accounts for the P-wave decays via an intermediate Σ(_b∗)±π∓ state, but ignores inter-ference effects, constructed using the three-particle unitarity constraint approximated in the quasi-two-body interaction model [51]

S0m_|m0,ΓNR,ΓΣbπ,ΓΣ∗bπ  ∝ Γ (m) m2_{0− m}2
2 + m2 0Γ2(m) , (6.1)

where the mass-dependent width Γ (m) is defined as

Γ (m) = ΓNR ρ3 (m) ρ3(m0) + ΓΣbπ ρΣbπ(m) ρΣbπ(m0) + ΓΣ∗ bπ ρΣ∗ bπ(m) ρΣ∗ bπ(m0) .

The quasi-two-body phase-space functions ρ

Σ(∗)_b π(m) for the decays via the intermediate

Σbπand Σ∗bπ states are

ρ Σ(_b∗)π(m) = (m−mπ)2 Z (mπ+m_Λ0 b) 2  2p m 2q √ s R2p2 1 + R2_p2 R2q2 1 + R2_q2  (m2 Σ(∗)_b − s) 2_{+ m}2 Σ(∗)_b Γ 02 Σ(∗)_b (s) ds , Γ0 Σ(_b∗)(s) = ΓΣ(_b∗) m_Σ(∗) b √ s  q q0 3  1 + R2_q2 1 + R2_q2 0 2 ,

where s stands for a squared mass of the Λ0_bπ pair forming the Σ(∗)_b resonance, p denotes the momenta of the pion in the P-wave decay Λ∗∗0

b → Σ (∗)

b π, q denotes the momenta of

the pion in the decay Σ(∗)_b → Λ0

bπ, q0 is the value of q at s = m_Σ(∗) b

, R = 3.5 GeV−1 corresponds to the breakup momentum of the P-wave Blatt-Weisskopf centrifugal barrier

JHEP06(2020)136

factor [52], m_Σ(∗) b

and Γ_Σ(∗) b

are known mass and width of the Σ(_b∗) states [7]. The function is reparameterised as

ΓNR = (1− α − β) Γ ,

ΓΣbπ = α Γ , ΓΣ∗

bπ = β Γ ,

where the non-negative parameters α and β account for the relative contributions from the Λ∗∗0_{b → Σ}±_bπ∓ and Λ∗∗0_{b → Σ}∗±_b π∓ decays, respectively. A series of fits is performed with parameters α and β varied within the ranges 0 ≤ α < 0.2, 0 ≤ β < 0.2, and α+ β_{≤ 0.3, consistent with figure}4. The mass of the Λ∗∗0_b state is found to be very stable with respect to such variations. The fitted mass does not change more than 0.5 MeV while the fitted width increases up to 1.5 MeV. These values are taken as systematic uncertainties due to the signal parameterisation. The nominal fit does not take the variations of the de-tector efficiency with the Λ0

bπ+π−mass into account. An alternative fit is performed where

the signal shape is multiplied by the efficiency function obtained from simulation. The dif-ference with the nominal fit is added to the uncertainty on the signal parameterisation. Alternative parameterisations of the detector resolution functions, namely a symmetric variant of an Apollonios function [53], a double-sided Crystal Ball function [46], a modified Novosibirsk function [54,55], a Student’s t-distribution and a hyperbolic secant function, cause negligible variation for the measured mass and width of the Λ∗∗0_b state. The sig-nal parameterisation uncertainty in the measurement of the masses of the low-mass states is negligible.

The uncertainty in the combinatorial background shape parameterisation is accounted for by varying the degree of the polynomial functions from 3 to 4. The uncertainty in the Σbπ and Σ∗_bπ background functions is evaluated by modifying the parameters

of the exponential parameterisation within the limits allowed by the fits to the back-ground-subtracted Σ(∗)_b πspectra. In order to assess a possible sensitivity of the fit parame-ters to the features of the background shape not accounted for by the variations mentioned above, fits are performed in narrower and broader Λ0_bππregions and variations are included as an additional source of systematic uncertainty.

To assess the effect of the fixed parameters of the narrow Λb(6146)0 and Λb(6152)0

states from the previous analysis [10] in the higher-mass fit, the fits are performed with the masses and the widths of each of the two states left free to vary one by one. The resulting variations of the Λ∗∗0_b parameters are found to be negligible.

The effect of the calibration of the momentum scale is evaluated by varying the scale within its known uncertainty [8,10,26]. All systematic uncertainties for the mass difference m_Λ

b(5920)0 − mΛb(5912)0 are found to be negligible.

The upper limits on the natural widths of the Λb(5912)0 and Λb(5920)0 states are

ob-tained by performing profile likelihood scans. In the calculation of the likelihood, the un-certainties in the knowledge of mass resolution are included by using various resolution models, as listed above, and by varying the mass-resolution scaling factor obtained from

JHEP06(2020)136

simulations within 5% [10, 56, 57] and the maximum upper limits across all variations are reported.

7 Results and summary

Using the LHCb data set taken in 2011–2018, corresponding to an integrated luminos-ity of 9 fb−1 collected in pp collisions at centre-of-mass energies of 7, 8 and 13 TeV, the Λ0

bπ+π− mass spectrum is studied with Λ0b baryons reconstructed in the Λ0b→ Λ+cπ−

and Λ0_b→ J/ψpK−_{decay modes. A new broad resonance-like state is observed with a}

statis-tical significance exceeding 14 and 7 standard deviations for Λ0_bπ+π−samples reconstructed using the Λ0

b→ Λ+cπ− and Λ0b→ J/ψpK− decay modes, respectively. The mass difference

with respect to the Λ0_bmass and natural width of the state are determined from a combined fit to both samples and are found to be

∆m_Λ∗∗0

b = 452.7± 2.9 ± 0.5 MeV , Γ_Λ∗∗0

b = 72 ± 11 ± 2 MeV ,

where the first uncertainty is statistical and the second systematic. Taking the mass of the Λ0_b baryon m_Λ0

b = 5619.62± 0.16 ± 0.13 MeV [48], obtained by a combination of measurements at the LHCb experiment in Λ0_{b→ χ}c1,2pK− [48], Λ0b→ ψ(2S)pK−,

Λ0

b→ J/ψπ+π−pK− [58] and Λ0b→ J/ψΛ decay modes [25,59], and accounting for the

cor-related systematic uncertainty, the mass of the Λ∗∗0_b state is found to be m_Λ∗∗0

b = 6072.3± 2.9 ± 0.6 ± 0.2 MeV ,

where the last uncertainty is due to that on the mass of the Λ0_bbaryon. The new resonance is consistent with the broad excess of events reported by the CMS collaboration [15] and the measured mass and width agree with expectations for the Λb(2S)0state [16–18,60,61].

Several excited Σb(1P) states are expected with a mass close to the measured value, but

the partial decay widths for Σb(1P) states into Λ0bππ are predicted to be very small [62].

If the observed broad peak corresponds to the Σb(1P)(∗)0 state, two peaks with similar

masses and widths and significantly larger yields should be visible in the Λ0_bπ± mass spec-tra due to decays of the charged isospin partners Σb(1P)(∗)±→ Λ0bπ±. However, no signs of

states with such a mass and width, and large production yields are observed in the analysis of the Λ0_bπ±mass spectra; the observed Σb(6097)±states have significantly smaller natural

width and relatively small yields [7]. It cannot be excluded that the observed broad struc-ture corresponds to a superposition of more than one narrow states, but the interpretation of these states as excited Σb resonances is disfavoured.

The mass differences for the Λb(5912)0 and Λb(5920)0 states with respect to the mass

of the Λ0

b baryon are measured to be

∆m_Λ

b(5912)0 = 292.589± 0.029 ± 0.010 MeV , ∆m_Λ

JHEP06(2020)136

and the corresponding masses are m_Λ

b(5912)0 = 5912.21± 0.03 ± 0.01 ± 0.21 MeV , m_Λ

b(5920)0 = 5920.11± 0.02 ± 0.01 ± 0.21 MeV ,

where the last uncertainty is due to imprecise knowledge of the Λ0_bmass. The mass splitting between the narrow states is

m_Λ

b(5920)0− mΛb(5912)0 = 7.896± 0.034 MeV . The following upper limits on the natural widths are obtained:

Γ_Λ

b(5912)0 < 0.25 (0.28) MeV , Γ_Λ

b(5920)0 < 0.19 (0.20) MeV ,

at 90% (95%) confidence level, respectively. The measurements of the parameters of the Λb(5912)0 and Λb(5920)0 states are about four times more precise and supersede those

reported in ref. [8].

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 ad-ministrative 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 comput-ing 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 AvH Foundation (Germany); EPLANET, Marie Sk lodowska-Curie Actions and ERC (European Union); ANR, Labex P2IO and OCEVU, and R´egion Auvergne-Rhˆone-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 Lever-hulme Trust (United Kingdom).

Open Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.

JHEP06(2020)136

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P. Carniti24,i_{, K. Carvalho Akiba}31_{, A. Casais Vidal}45_{, G. Casse}59_{, M. Cattaneo}47_{, G. Cavallero}47_,

S. Celani48, R. Cenci28,p, J. Cerasoli10, M.G. Chapman53, M. Charles12,47, Ph. Charpentier47, G. Chatzikonstantinidis52_{, M. Chefdeville}8_{, V. Chekalina}41_{, C. Chen}3_{, S. Chen}26_{, A. Chernov}33_,

S.-G. Chitic47_{, V. Chobanova}45_{, S. Cholak}48_{, M. Chrzaszcz}33_{, A. Chubykin}37_{, P. Ciambrone}22_,

M.F. Cicala55_{, X. Cid Vidal}45_{, G. Ciezarek}47_{, F. Cindolo}19_{, P.E.L. Clarke}57_{, M. Clemencic}47_,

H.V. Cliff54_{, J. Closier}47_{, J.L. Cobbledick}61_{, V. Coco}47_{, J.A.B. Coelho}11_{, J. Cogan}10_,

E. Cogneras9_{, L. Cojocariu}36_{, P. Collins}47_{, T. Colombo}47_{, A. Comerma-Montells}16_{, A. Contu}26_,

N. Cooke52_{, G. Coombs}58_{, S. Coquereau}44_{, G. Corti}47_{, C.M. Costa Sobral}55_{, B. Couturier}47_,

D.C. Craik63_{, J. Crkovsk´a}66_{, A. Crocombe}55_{, M. Cruz Torres}1,ab_{, R. Currie}57_{, C.L. Da Silva}66_,

E. Dall’Occo14_{, J. Dalseno}45,53_{, C. D’Ambrosio}47_{, A. Danilina}38_{, P. d’Argent}47_{, A. Davis}61_,

O. De Aguiar Francisco47_{, K. De Bruyn}47_{, S. De Capua}61_{, M. De Cian}48_{, J.M. De Miranda}1_,

L. De Paula2_{, M. De Serio}18,d_{, P. De Simone}22_{, J.A. de Vries}31_{, C.T. Dean}66_{, W. Dean}80_,

D. Decamp8_{, L. Del Buono}12_{, B. Delaney}54_{, H.-P. Dembinski}15_{, A. Dendek}34_{, V. Denysenko}49_,

D. Derkach78_{, O. Deschamps}9_{, F. Desse}11_{, F. Dettori}26,f_{, B. Dey}7_{, A. Di Canto}47_{, P. Di Nezza}22_,

S. Didenko77_{, H. Dijkstra}47_{, V. Dobishuk}51_{, F. Dordei}26_{, M. Dorigo}28,y_{, A.C. dos Reis}1_,

L. Douglas58_{, A. Dovbnya}50_{, K. Dreimanis}59_{, M.W. Dudek}33_{, L. Dufour}47_{, G. Dujany}12_,

P. Durante47_{, J.M. Durham}66_{, D. Dutta}61_{, M. Dziewiecki}16_{, A. Dziurda}33_{, A. Dzyuba}37_,

S. Easo56_{, U. Egede}69_{, V. Egorychev}38_{, S. Eidelman}42,x_{, S. Eisenhardt}57_{, R. Ekelhof}14_{, S. Ek-In}48_,

L. Eklund58_{, S. Ely}67_{, A. Ene}36_{, E. Epple}66_{, S. Escher}13_{, S. Esen}31_{, T. Evans}47_{, A. Falabella}19_,

J. Fan3_{, N. Farley}52_{, S. Farry}59_{, D. Fazzini}11_{, P. Fedin}38_{, M. F´eo}47_{, P. Fernandez Declara}47_,

A. Fernandez Prieto45_{, F. Ferrari}19,e_{, L. Ferreira Lopes}48_{, F. Ferreira Rodrigues}2_,

S. Ferreres Sole31_{, M. Ferrillo}49_{, M. Ferro-Luzzi}47_{, S. Filippov}40_{, R.A. Fini}18_{, M. Fiorini}20,g_,

M. Firlej34_{, K.M. Fischer}62_{, C. Fitzpatrick}47_{, T. Fiutowski}34_{, F. Fleuret}11,b_{, M. Fontana}47_,

JHEP06(2020)136

D.A. Friday58, J. Fu25,q, Q. Fuehring14, W. Funk47, E. Gabriel57, A. Gallas Torreira45,

D. Galli19,e_{, S. Gallorini}27_{, S. Gambetta}57_{, Y. Gan}3_{, M. Gandelman}2_{, P. Gandini}25_{, Y. Gao}4_,

L.M. Garcia Martin46_{, J. Garc´ıa Pardi˜nas}49_{, B. Garcia Plana}45_{, F.A. Garcia Rosales}11_,

L. Garrido44_{, D. Gascon}44_{, C. Gaspar}47_{, D. Gerick}16_{, E. Gersabeck}61_{, M. Gersabeck}61_,

T. Gershon55_{, D. Gerstel}10_{, Ph. Ghez}8_{, V. Gibson}54_{, A. Giovent`u}45_{, O.G. Girard}48_,

P. Gironella Gironell44_{, L. Giubega}36_{, C. Giugliano}20_{, K. Gizdov}57_{, V.V. Gligorov}12_{, C. G¨obel}70_,

E. Golobardes44,m_{, D. Golubkov}38_{, A. Golutvin}60,77_{, A. Gomes}1,a_{, P. Gorbounov}38,6_,

I.V. Gorelov39_{, C. Gotti}24,i_{, E. Govorkova}31_{, J.P. Grabowski}16_{, R. Graciani Diaz}44_,

T. Grammatico12_{, L.A. Granado Cardoso}47_{, E. Graug´es}44_{, E. Graverini}48_{, G. Graziani}21_,

A. Grecu36_{, R. Greim}31_{, P. Griffith}20_{, L. Grillo}61_{, L. Gruber}47_{, B.R. Gruberg Cazon}62_{, C. Gu}3_,

E. Gushchin40_{, A. Guth}13_{, Yu. Guz}43,47_{, T. Gys}47_{, P. A. G¨unther}16_{, T. Hadavizadeh}62_,

G. Haefeli48, C. Haen47, S.C. Haines54, P.M. Hamilton65, Q. Han7, X. Han16, T.H. Hancock62, S. Hansmann-Menzemer16_{, N. Harnew}62_{, T. Harrison}59_{, R. Hart}31_{, C. Hasse}14_{, M. Hatch}47_,

J. He5_{, M. Hecker}60_{, K. Heijhoff}31_{, K. Heinicke}14_{, A.M. Hennequin}47_{, K. Hennessy}59_{, L. Henry}46_,

J. Heuel13_{, A. Hicheur}68_{, D. Hill}62_{, M. Hilton}61_{, P.H. Hopchev}48_{, J. Hu}16_{, W. Hu}7_{, W. Huang}5_,

W. Hulsbergen31_{, T. Humair}60_{, R.J. Hunter}55_{, M. Hushchyn}78_{, D. Hutchcroft}59_{, D. Hynds}31_,

P. Ibis14_{, M. Idzik}34_{, P. Ilten}52_{, A. Inglessi}37_{, K. Ivshin}37_{, R. Jacobsson}47_{, S. Jakobsen}47_,

E. Jans31_{, B.K. Jashal}46_{, A. Jawahery}65_{, V. Jevtic}14_{, F. Jiang}3_{, M. John}62_{, D. Johnson}47_,

C.R. Jones54_{, B. Jost}47_{, N. Jurik}62_{, S. Kandybei}50_{, M. Karacson}47_{, J.M. Kariuki}53_{, N. Kazeev}78_,

M. Kecke16_{, F. Keizer}54,47_{, M. Kelsey}67_{, M. Kenzie}55_{, T. Ketel}32_{, B. Khanji}47_{, A. Kharisova}79_,

K.E. Kim67_{, T. Kirn}13_{, V.S. Kirsebom}48_{, S. Klaver}22_{, K. Klimaszewski}35_{, S. Koliiev}51_,

A. Kondybayeva77_{, A. Konoplyannikov}38_{, P. Kopciewicz}34_{, R. Kopecna}16_{, P. Koppenburg}31_,

M. Korolev39_{, I. Kostiuk}31,51_{, O. Kot}51_{, S. Kotriakhova}37_{, L. Kravchuk}40_{, R.D. Krawczyk}47_,

M. Kreps55_{, F. Kress}60_{, S. Kretzschmar}13_{, P. Krokovny}42,x_{, W. Krupa}34_{, W. Krzemien}35_,

W. Kucewicz33,l_{, M. Kucharczyk}33_{, V. Kudryavtsev}42,x_{, H.S. Kuindersma}31_{, G.J. Kunde}66_,

T. Kvaratskheliya38_{, D. Lacarrere}47_{, G. Lafferty}61_{, A. Lai}26_{, D. Lancierini}49_{, J.J. Lane}61_,

G. Lanfranchi22_{, C. Langenbruch}13_{, O. Lantwin}49_{, T. Latham}55_{, F. Lazzari}28,v_{, C. Lazzeroni}52_,

R. Le Gac10_{, R. Lef`evre}9_{, A. Leflat}39_{, O. Leroy}10_{, T. Lesiak}33_{, B. Leverington}16_{, H. Li}71_{, L. Li}62_,

X. Li66_{, Y. Li}6_{, Z. Li}67_{, X. Liang}67_{, R. Lindner}47_{, V. Lisovskyi}14_{, G. Liu}71_{, X. Liu}3_{, D. Loh}55_,

A. Loi26_{, J. Lomba Castro}45_{, I. Longstaff}58_{, J.H. Lopes}2_{, G. Loustau}49_{, G.H. Lovell}54_{, Y. Lu}6_,

D. Lucchesi27,o_{, M. Lucio Martinez}31_{, Y. Luo}3_{, A. Lupato}27_{, E. Luppi}20,g_{, O. Lupton}55_,

A. Lusiani28,t_{, X. Lyu}5_{, S. Maccolini}19,e_{, F. Machefert}11_{, F. Maciuc}36_{, V. Macko}48_,

P. Mackowiak14_{, S. Maddrell-Mander}53_{, L.R. Madhan Mohan}53_{, O. Maev}37,47_{, A. Maevskiy}78_,

D. Maisuzenko37_{, M.W. Majewski}34_{, S. Malde}62_{, B. Malecki}47_{, A. Malinin}76_{, T. Maltsev}42,x_,

H. Malygina16_{, G. Manca}26,f_{, G. Mancinelli}10_{, R. Manera Escalero}44_{, D. Manuzzi}19,e_,

D. Marangotto25,q_{, J. Maratas}9,w_{, J.F. Marchand}8_{, U. Marconi}19_{, S. Mariani}21_,

C. Marin Benito11_{, M. Marinangeli}48_{, P. Marino}48_{, J. Marks}16_{, P.J. Marshall}59_{, G. Martellotti}30_,

L. Martinazzoli47_{, M. Martinelli}24,i_{, D. Martinez Santos}45_{, F. Martinez Vidal}46_{, A. Massafferri}1_,

M. Materok13_{, R. Matev}47_{, A. Mathad}49_{, Z. Mathe}47_{, V. Matiunin}38_{, C. Matteuzzi}24_,

K.R. Mattioli80_{, A. Mauri}49_{, E. Maurice}11,b_{, M. McCann}60_{, L. Mcconnell}17_{, A. McNab}61_,

R. McNulty17_{, J.V. Mead}59_{, B. Meadows}64_{, C. Meaux}10_{, G. Meier}14_{, N. Meinert}74_,

D. Melnychuk35_{, S. Meloni}24,i_{, M. Merk}31_{, A. Merli}25_{, M. Mikhasenko}47_{, D.A. Milanes}73_,

E. Millard55_{, M.-N. Minard}8_{, O. Mineev}38_{, L. Minzoni}20,g_{, S.E. Mitchell}57_{, B. Mitreska}61_,

D.S. Mitzel47_{, A. M¨odden}14_{, A. Mogini}12_{, R.D. Moise}60_{, T. Momb¨acher}14_{, I.A. Monroy}73_,

S. Monteil9_{, M. Morandin}27_{, G. Morello}22_{, M.J. Morello}28,t_{, J. Moron}34_{, A.B. Morris}10_,

A.G. Morris55_{, R. Mountain}67_{, H. Mu}3_{, F. Muheim}57_{, M. Mukherjee}7_{, M. Mulder}47_{, D. M¨uller}47_,

K. M¨uller49_{, C.H. Murphy}62_{, D. Murray}61_{, P. Muzzetto}26_{, P. Naik}53_{, T. Nakada}48_,

JHEP06(2020)136

N. Neufeld47, R. Newcombe60, T.D. Nguyen48, C. Nguyen-Mau48,n, E.M. Niel11, S. Nieswand13,

N. Nikitin39_{, N.S. Nolte}47_{, C. Nunez}80_{, A. Oblakowska-Mucha}34_{, V. Obraztsov}43_{, S. Ogilvy}58_,

D.P. O’Hanlon53_{, R. Oldeman}26,f_{, C.J.G. Onderwater}75_{, J. D. Osborn}80_{, A. Ossowska}33_,

J.M. Otalora Goicochea2_{, T. Ovsiannikova}38_{, P. Owen}49_{, A. Oyanguren}46_{, P.R. Pais}48_,

T. Pajero28,t_{, A. Palano}18_{, M. Palutan}22_{, G. Panshin}79_{, A. Papanestis}56_{, M. Pappagallo}57_,

L.L. Pappalardo20,g_{, C. Pappenheimer}64_{, W. Parker}65_{, C. Parkes}61_{, G. Passaleva}21,47_,

A. Pastore18_{, M. Patel}60_{, C. Patrignani}19,e_{, A. Pearce}47_{, A. Pellegrino}31_{, M. Pepe Altarelli}47_,

S. Perazzini19_{, D. Pereima}38_{, P. Perret}9_{, L. Pescatore}48_{, K. Petridis}53_{, A. Petrolini}23,h_,

A. Petrov76_{, S. Petrucci}57_{, M. Petruzzo}25,q_{, B. Pietrzyk}8_{, G. Pietrzyk}48_{, M. Pili}62_{, D. Pinci}30_,

J. Pinzino47_{, F. Pisani}19_{, A. Piucci}16_{, V. Placinta}36_{, S. Playfer}57_{, J. Plews}52_{, M. Plo Casasus}45_,

F. Polci12_{, M. Poli Lener}22_{, M. Poliakova}67_{, A. Poluektov}10_{, N. Polukhina}77,c_{, I. Polyakov}67_,

E. Polycarpo2, G.J. Pomery53, S. Ponce47, A. Popov43, D. Popov52, S. Poslavskii43,

K. Prasanth33_{, L. Promberger}47_{, C. Prouve}45_{, V. Pugatch}51_{, A. Puig Navarro}49_{, H. Pullen}62_,

G. Punzi28,p_{, W. Qian}5_{, J. Qin}5_{, R. Quagliani}12_{, B. Quintana}8_{, N.V. Raab}17_,

R.I. Rabadan Trejo10_{, B. Rachwal}34_{, J.H. Rademacker}53_{, M. Rama}28_{, M. Ramos Pernas}45_,

M.S. Rangel2_{, F. Ratnikov}41,78_{, G. Raven}32_{, M. Reboud}8_{, F. Redi}48_{, F. Reiss}12_,

C. Remon Alepuz46_{, Z. Ren}3_{, V. Renaudin}62_{, S. Ricciardi}56_{, D.S. Richards}56_{, S. Richards}53_,

K. Rinnert59_{, P. Robbe}11_{, A. Robert}12_{, A.B. Rodrigues}48_{, E. Rodrigues}64_,

J.A. Rodriguez Lopez73_{, M. Roehrken}47_{, S. Roiser}47_{, A. Rollings}62_{, V. Romanovskiy}43_,

M. Romero Lamas45_{, A. Romero Vidal}45_{, J.D. Roth}80_{, M. Rotondo}22_{, M.S. Rudolph}67_{, T. Ruf}47_,

J. Ruiz Vidal46_{, A. Ryzhikov}78_{, J. Ryzka}34_{, J.J. Saborido Silva}45_{, N. Sagidova}37_{, N. Sahoo}55_,

B. Saitta26,f_{, C. Sanchez Gras}31_{, C. Sanchez Mayordomo}46_{, R. Santacesaria}30_,

C. Santamarina Rios45_{, M. Santimaria}22_{, E. Santovetti}29,j_{, G. Sarpis}61_{, A. Sarti}30_{, C. Satriano}30,s_,

A. Satta29_{, M. Saur}5_{, D. Savrina}38,39_{, L.G. Scantlebury Smead}62_{, S. Schael}13_{, M. Schellenberg}14_,

M. Schiller58_{, H. Schindler}47_{, M. Schmelling}15_{, T. Schmelzer}14_{, B. Schmidt}47_{, O. Schneider}48_,

A. Schopper47_{, H.F. Schreiner}64_{, M. Schubiger}31_{, S. Schulte}48_{, M.H. Schune}11_{, R. Schwemmer}47_,

B. Sciascia22_{, A. Sciubba}30,k_{, S. Sellam}68_{, A. Semennikov}38_{, A. Sergi}52,47_{, N. Serra}49_{, J. Serrano}10_,

L. Sestini27_{, A. Seuthe}14_{, P. Seyfert}47_{, D.M. Shangase}80_{, M. Shapkin}43_{, L. Shchutska}48_,

T. Shears59_{, L. Shekhtman}42,x_{, V. Shevchenko}76,77_{, E. Shmanin}77_{, J.D. Shupperd}67_{, B.G. Siddi}20_,

R. Silva Coutinho49_{, L. Silva de Oliveira}2_{, G. Simi}27,o_{, S. Simone}18,d_{, I. Skiba}20_{, N. Skidmore}16_,

T. Skwarnicki67_{, M.W. Slater}52_{, J.G. Smeaton}54_{, A. Smetkina}38_{, E. Smith}13_{, I.T. Smith}57_,

M. Smith60_{, A. Snoch}31_{, M. Soares}19_{, L. Soares Lavra}9_{, M.D. Sokoloff}64_{, F.J.P. Soler}58_,

B. Souza De Paula2_{, B. Spaan}14_{, E. Spadaro Norella}25,q_{, P. Spradlin}58_{, F. Stagni}47_{, M. Stahl}64_,

S. Stahl47_{, P. Stefko}48_{, O. Steinkamp}49_{, S. Stemmle}16_{, O. Stenyakin}43_{, M. Stepanova}37_,

H. Stevens14_{, S. Stone}67_{, S. Stracka}28_{, M.E. Stramaglia}48_{, M. Straticiuc}36_{, S. Strokov}79_{, J. Sun}26_,

L. Sun72_{, Y. Sun}65_{, P. Svihra}61_{, K. Swientek}34_{, A. Szabelski}35_{, T. Szumlak}34_{, M. Szymanski}47_,

S. Taneja61_{, Z. Tang}3_{, T. Tekampe}14_{, F. Teubert}47_{, E. Thomas}47_{, K.A. Thomson}59_{, M.J. Tilley}60_,

V. Tisserand9_{, S. T’Jampens}8_{, M. Tobin}6_{, S. Tolk}47_{, L. Tomassetti}20,g_{, D. Tonelli}28_,

D. Torres Machado1_{, D.Y. Tou}12_{, E. Tournefier}8_{, M. Traill}58_{, M.T. Tran}48_{, E. Trifonova}77_,

C. Trippl48_{, A. Trisovic}54_{, A. Tsaregorodtsev}10_{, G. Tuci}28,47,p_{, A. Tully}48_{, N. Tuning}31_,

A. Ukleja35_{, A. Usachov}31_{, A. Ustyuzhanin}41,78_{, U. Uwer}16_{, A. Vagner}79_{, V. Vagnoni}19_,

A. Valassi47_{, G. Valenti}19_{, M. van Beuzekom}31_{, H. Van Hecke}66_{, E. van Herwijnen}47_,

C.B. Van Hulse17_{, M. van Veghel}75_{, R. Vazquez Gomez}44,22_{, P. Vazquez Regueiro}45_,

C. V´azquez Sierra31_{, S. Vecchi}20_{, J.J. Velthuis}53_{, M. Veltri}21,r_{, A. Venkateswaran}67_{, M. Vernet}9_,

M. Veronesi31_{, M. Vesterinen}55_{, J.V. Viana Barbosa}47_{, D. Vieira}64_{, M. Vieites Diaz}48_,

H. Viemann74_{, X. Vilasis-Cardona}44,m_{, A. Vitkovskiy}31_{, A. Vollhardt}49_{, D. Vom Bruch}12_,

A. Vorobyev37_{, V. Vorobyev}42,x_{, N. Voropaev}37_{, R. Waldi}74_{, J. Walsh}28_{, J. Wang}3_{, J. Wang}72_,