Search for pair production of heavy vector-like quarks decaying to high-pT W bosons and b quarks in the lepton-plus-jets final state in pp collisions at √s = 13TeV with the ATLAS detector

JHEP10(2017)141 Published for SISSA by Springer Received:July 12, 2017 Accepted:October 8, 2017 Published:October 20, 2017 Search for pair production of heavy vector-like quarks decaying to high-pTWbosons and bquarks in the lepton-plus-jets final state in pp collisions at √s= 13 TeV with the ATLAS detector The ATLAS collaboration E-mail: [email protected] Abstract: A search is presented for the pair production of heavy vector-like Tquarks, primarily targeting the Tquark decays to a Wboson and a b-quark. The search is based on 36.1 fb−1of pp collisions at √s= 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton-plus-jets final state, including at least one b-tagged jet and a large-radius jet identified as originating from the hadronic decay of a high-momentum Wboson. No significant deviation from the Standard Model expectation is observed in the reconstructed Tmass distribution. The observed 95% confidence level lower limit on the Tmass are 1350 GeV assuming 100% branching ratio to Wb. In the SU(2) singlet scenario, the lower mass limit is 1170 GeV. This search is also sensitive to a heavy vector-like Bquark decaying to Wt and other final states. The results are thus reinterpreted to provide a 95% confidence level lower limit on the Bquark mass at 1250 GeV assuming 100% branching ratio to Wt; in the SU(2) singlet scenario, the limit is 1080 GeV. Mass limits on both Tand Bproduction are also set as a function of the decay branching ratios. The 100% branching ratio limits are found to be applicable to heavy vector-like Yand Xproduction that decay to W b and W t, respectively. Keywords: Exotics, Hadron-Hadron scattering (experiments) ArXiv ePrint: 1707.03347 Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP3. https://doi.org/10.1007/JHEP10(2017)141 JHEP10(2017)141 Contents 1 Introduction 1 2 ATLAS detector 3 3 Data and simulation 3 4 Analysis object selection 5 5 Analysis strategy 6 5.1 Event preselection 7 5.2 T¯ Treconstruction 7 5.3 Classification of event topologies 8 5.3.1 Signal region definition 8 5.3.2 Control region definition 9 5.4 Multi-jet background estimation 9 6 Systematic uncertainties 10 6.1 Luminosity and normalisation uncertainties 11 6.2 Detector-related uncertainties 11 6.3 Generator modelling uncertainties 12 7 Results 12 7.1 Statistical interpretation 12 7.2 Likelihood fit results 13 7.3 Limits on VLQ pair production 15 8 Conclusions 15 The ATLAS collaboration 24 1 Introduction The discovery of the Higgs boson by the ATLAS and CMS collaborations is a major milestone in high-energy physics [1,2]. However, the underlying nature of electroweak symmetry breaking remains unknown. Naturalness arguments [3] require that quadratic divergences arising from radiative corrections to the Higgs boson mass are cancelled by a new mechanism to avoid fine-tuning. This paper presents a search for pair production of vector-like quarks (VLQs) decaying into third-generation quarks using the pp collision data collected at the Large Hadron Collider (LHC) in 2015 and 2016 at a centre-of-mass energy of 13 TeV. – 1 – JHEP10(2017)141 Several new mechanisms have been proposed in theories beyond the Standard Model (BSM). In supersymmetry, the cancellation comes from assigning superpartners to the Standard Model (SM) bosons and fermions. Alternatively, Little Higgs [4,5] and Composite Higgs [6,7] models introduce a spontaneously broken global symmetry, with the Higgs boson emerging as a pseudo Nambu–Goldstone boson [8]. These latter models predict the existence of VLQs, defined as colour-triplet spin-1/2 fermions whose leftand right-handed chiral components have the same transformation properties under the weak-isospin SU(2) gauge group [9,10]. Depending on the model, vector-like quarks are produced in SU(2) singlets, doublets or triplets of flavours T,B,Xor Y, in which the first two have the same charge as the SM top and bquarks while the vector-like Yand Xquarks have charge1 −4/3 and 5/3. In addition, in these models, VLQs are expected to couple preferentially to third-generation quarks [9,11] and can have flavour-changing neutral-current decays in addition to the charged-current decays characteristic of chiral quarks. As a result, an up-type Tquark can decay not only to a Wboson and a bquark, but also to a Zor Higgs boson and a top quark (T→Wb,Zt, and Ht). Similarly, a down-type Bquark can decay to a Zor Higgs boson and a bquark, in addition to decaying to a Wboson and a top quark (B→Wt,Zb, and Hb). Instead, due to their charge, vector-like Yquarks decay exclusively to Wb while vector-like Xquarks decay exclusively to W t. To be consistent with the results from precision electroweak measurements a small mass-splitting between VLQs belonging to the same SU(2) multiplet is required, but no requirement is placed on which member of the doublet is heavier [12]. Cascade decays such as T→WB →WWt are thus assumed to be kinematically forbidden. Decays of VLQs into final states with first and second generation quarks, although not favoured, are not excluded [13,14]. This search targets the T→Wb decay mode, although it is sensitive to a wide range of branching ratios to the other two decay modes as well as to vector-like B,Xand Y production. Previous searches in this decay mode by the ATLAS and CMS collaborations did not observe a significant deviation from the SM predictions. Those searches excluded VLQ masses below 740 GeV for any combination of branching ratios and below 920 GeV for the assumption of B(T→Wb) = 1 [15,16]. A recent search by the ATLAS collaboration at √s= 13 TeV sets a lower limit of 1160 GeV on the vector-like Tquark mass for the pure Zt mode [17]. The event selection is optimised for T¯ Tproduction with subsequent decay to two highpTWbosons and two b-quarks, where one of the Wbosons decays leptonically and the other decays hadronically. To suppress the SM background, boosted jet reconstruction techniques [18,19] are used to improve the identification of high-pTWbosons decaying hadronically while rejecting events with hadronically decaying, high-pTtop-quarks. The T¯ Tsystem is reconstructed and the mass of the semi-leptonically decaying VLQ candidate is used to discriminate between SM and VLQ events. Finally, a profile likelihood fit is used to test for the presence of a VLQ signal as a function of Tand Bquark masses and decay branching ratios. The results are found to be equally applicable to either singlet or doublet weak-isospin configurations as well as applicable to the decays of Xand Y. 1All charges are quoted in units of e. – 2 – JHEP10(2017)141 2 ATLAS detector The ATLAS detector [20] at the LHC is a multipurpose particle detector with a forwardbackward symmetric cylindrical geometry that covers nearly the entire solid angle around the collision point. It consists of an inner detector surrounded by a thin superconducting solenoid providing a 2 T axial magnetic field, electromagnetic and hadronic calorimeters, and a muon spectrometer. The inner detector covers the pseudorapidity range2|η|<2.5. It consists of a silicon pixel detector, including the insertable B-layer installed after Run 1 of the LHC [21,22], and a silicon microstrip detector surrounding the pixel detector, followed by a transition radiation straw-tube tracker. Lead/liquid-argon sampling calorimeters provide electromagnetic energy measurements with high granularity and a hadronic (steel/scintillator-tile) calorimeter covers the central pseudorapidity range (|η|<1.7). The end-cap and forward regions are instrumented with liquid-argon calorimeters for both the electromagnetic and hadronic energy measurements up to |η|= 4.9. The outer part of the detector consists of a muon spectrometer with high-precision tracking chambers for coverage up to |η|= 2.7, fast detectors for triggering over |η|¡ 2.4, and three large superconducting toroid magnets with eight coils each. The ATLAS detector has a two-level trigger system to select events for offline analysis [23]. 3 Data and simulation This search utilises a data set corresponding to 36.1±1.2 fb−1of integrated luminosity from pp collisions at √s= 13 TeV collected by the ATLAS experiment, with 3.2 fb−1collected in 2015 and 32.9 fb−1collected in 2016 [24]. Data are only used if all ATLAS detector subsystems were operational. In all simulated events used in this search, the top quark and Higgs boson masses were set to 172.5 GeV and 125 GeV, respectively. Simulated T¯ Tevents were generated with the leading-order (LO) generator Protos v2.2 [25] using the NNPDF2.3 LO parton distribution function (PDF) set and a set of tuned parameters called the A14 tune [26] for the underlying-event description and passed to Pythia 8.186 [27] for parton showering and fragmentation. The samples were generated for an SU(2) singlet TVLQ, but with equal branching ratios of the Tquark to each final state. To check the dependence of the results on the weak-isospin of the VLQ, one sample was also generated using the SU(2) doublet model including only the Tcontributions. The signal samples are normalised to pair-production cross-sections computed using Top++ v2.0 [28], including next-to-next-to-leading-order (NNLO) quantum chromodynamics (QCD) corrections and soft-gluon resummation to NNLL accuracy [29–34], and using the MSTW 2008 NNLO PDF set. Their cross-sections vary from 3.38 ±0.25 pb (mT= 500 GeV) to 3.50 ±0.43 fb (mT= 1400 GeV). Theoretical uncertainties are evaluated from variations of the factorisation and renormalisation scales, as well as from un2The ATLAS Collaboration uses a right-handed coordinate system with its origin at the nominal interaction point (IP) in the centre of the detector and the z-axis along the beam pipe. The x-axis points from the IP to the centre of the LHC ring, and the y-axis points upwards. Cylindrical coordinates (r, φ) are used in the transverse plane, φbeing the azimuthal angle around the beam pipe. The pseudorapidity is defined in terms of the polar angle θas η=−ln tan(θ/2). Angular distance is measured in units of ∆R≡p(∆η)2+ (∆φ)2. – 3 – JHEP10(2017)141 certainties in the PDFs and αS. The latter two represent the largest contribution to the overall theoretical uncertainty in the signal cross-sections and are calculated using the PDF4LHC [35] prescription with the MSTW 2008 68% CL NNLO, CT10 NNLO [36,37] and NNPDF2.3 [38] 5f FFN PDF sets. Two benchmark signal scenarios are considered, along with a full scan of the branching-ratio plane. The first benchmark corresponds to aTquark that decays 100% to Wb and the second corresponds to the SU(2) singlet T quark scenario, which predicts branching ratios of ∼50%, ∼25%, ∼25% to W b,Zt and Ht, respectively [12]. Samples were also generated for B¯ Bproduction for the reinterpretation of this search. They were produced using the same generator and normalised in the same way as T¯ T. As with T¯ T, two benchmark signal scenarios are considered, along with a full scan of the branching-ratio plane. The first benchmark assumes B(B→Wt) = 1 — which also corresponds to the SU(2) (B,T) doublet hypothesis — and the second corresponds to the SU(2) singlet Bquark scenario, which predicts branching ratios of ∼50%, ∼25%, ∼25% to Wt,Zb and Hb, respectively [12]. The main SM backgrounds that are studied using simulated samples are due to t¯ t, W+ jets, Z+ jets, diboson, single top quark, and t¯ t+V(V=W,Z) production. The multi-jet background is estimated using a data-driven technique discussed in section 5.4. The nominal t¯ tMC sample was generated with Powheg-Box v2 interfaced with Pythia 6.428 [39,40] for the parton shower and hadronisation, using the Perugia2012 tune [41] and the CT10 PDF set, and setting the hdamp parameter to the mass of the top quark. To estimate t¯ tmodelling uncertainties, described in section 6.3, additional samples were generated using Powheg-Box v2 interfaced with Herwig++ 2.7.1 [42], Powheg-Box v2 interfaced with Pythia 8.186, and MG5 aMC@NLO 2.1.1 interfaced with Pythia 8.186 [43]. Further, samples with Powheg-Box v2 interfaced with Pythia 6.428 were generated varying the factorisation and normalisation scales by 2 and 0.5, as well as the next-to-leading-order (NLO) radiation factor, hdamp, between mtop and twice mtop. The t¯ t samples are normalised to the NNLO cross-section, including NNLO QCD corrections and soft-gluon resummation to NNLL accuracy, as done for the signal samples. Single top quark production (called ‘single top’ in the following) in the Wtand schannels was also generated with Powheg-Box v2 interfaced with Pythia 6.428, while single top production in the t-channel was generated with Powheg-Box v1 interfaced with Pythia 6.428 for the parton shower and hadronisation. Single-top samples were generated using the Perugia2012 tune and the CT10 PDF set. The single top crosssections for the tand s-channels are normalised to their next-to-leading-order (NLO) predictions, while for the Wt-channel the cross-section is normalised to its NLO+NNLL prediction [44]. For W+jets, Z+jets, and diboson (W W ,W Z,ZZ) samples, the Sherpa 2.2.1 generator [45] was used with the CT10 PDF set. The W+jets and Z+jets production samples are normalised to the NNLO cross-sections [46–48]. For diboson production, the generator cross-sections (already at NLO) are used for sample normalisation. The t¯ t+V background is modelled using samples produced with MG5 aMC@NLO 2.1.1 interfaced with Pythia 8.186, using the A14 tune and the NNPDF2.3 LO PDF set. The t¯ t+V samples are normalised to their respective NLO cross-sections [43]. All simulated samples were produced using the ATLAS simulation infrastructure [49], using the full GEANT4 [50] simulation of the ATLAS detector and reconstructed with the – 4 – JHEP10(2017)141 same software as used for the data. Multiple overlaid proton-proton collisions in the same or nearby bunch crossings (pile-up) were simulated at rates matching that of the data; they were modelled as low pTmulti-jet production using the Pythia 8.186 generator and tune A2 [51]. 4 Analysis object selection Reconstructed objects are defined by combining information from different detector subsystems. This section outlines the criteria used to identify and select the reconstructed objects used in the analysis. Events are required to have at least one vertex candidate with at least two tracks with pT>500 MeV. The primary vertex is taken to be the vertex candidate with the largest sum of squared transverse momenta of all associated tracks. To reconstruct jets, three-dimensional energy clusters in the calorimeter, assumed to represent massless particles coming from the primary vertex, are grouped together using the anti-ktclustering algorithm [52–54] with a radius parameter of 0.4 (1.0) for small-R (large-R) jets. Small-Rjets and large-Rjets are clustered independently. Small-Rjets are calibrated using an energyand η-dependent calibration scheme, with in situ corrections based on data [55], and are selected if they have pT>25 GeV and |η|<2.5. A multivariate jet vertex tagger (JVT) selectively removes small-Rjets that are identified as having originated from pile-up collisions rather than the hard scatter [56]. Jets containing b-hadrons are identified via an algorithm that uses multivariate techniques to combine information from the impact parameters of displaced tracks as well as topological properties of secondary and tertiary decay vertices reconstructed within the jet. A jet is considered b-tagged if the value for the multivariate discriminant is above the threshold corresponding to an efficiency of 77% for tagging a b-quark-initiated jet. The corresponding light-jet rejection factor is ∼130 and the charm-jet rejection factor is ∼6, as determined for jets with pT>20 GeV and |η|<2.5 in simulated t¯ tevents. Large-Rjets are built using the energy clusters in the calorimeter [57,58] and then trimmed [59] to mitigate the effects of contamination from multiple interactions and improve background rejection. The jet energy and pseudorapidity are further calibrated to account for residual detector effects using energy and pseudorapidity dependent calibration factors derived from simulation. The kt-based trimming algorithm reclusters the jet constituents into subjets with a finer-grained resolution (the R-parameter for subjets is set to Rsub = 0.2). Subjets that contribute less than 5% to the pTof the large-Rjets are discarded. The properties (e.g. transverse momentum and invariant mass) of the jet are recalculated using only the constituents of the remaining subjets. Trimmed large-Rjets are only considered if they have pT>200 GeV and |η|<2.0. To identify large-Rjets that are likely to have originated from the hadronic decay of Wbosons (Whad) and not from the hadronic decay of top quarks or multi-jet background, jet substructure information is exploited using the ratio of the energy correlation functions Dβ=1 2[60,61] and jet mass [58]. Selected large-Rjets must pass both the substructure and mass requirements of the 50%- efficient W-tagging working point [18]. To reduce the contribution from the t¯ tbackground, the Whad candidate must not overlap any b-tagged small-Rjets within ∆R < 1.0. If mul- – 5 – JHEP10(2017)141 tiple large-Rjets satisfy the above requirements, the one with a mass closest to the mass of the Wboson is selected as the Whad candidate. Electrons are reconstructed from energy deposits in the electromagnetic calorimeter matched to inner detector tracks. Electron candidates are required to satisfy likelihoodbased identification criteria [62] and must have plep T>30 GeV and |η|<2.47. Electron candidates in the transition region between the barrel and endcap electromagnetic calorimeters, 1.37 <|η|<1.52, are excluded from this analysis. A lepton isolation requirement is implemented by calculating the quantity IR=P∆R(track,lep)<Rcut ptrack T, where Rcut is the smaller of 10 GeV/plep Tand 0.2; the track associated with the lepton is excluded from the calculation. The electron must satisfy IR<0.06 ·plep T. Additionally, electrons are required to have a track satisfying |d0| σd0<5 and |z0sin θ|<0.5 mm, where d0is the transverse impact parameter and z0is the r–φprojection of the impact point onto the z-axis. An overlapremoval procedure prevents double-counting of energy between an electron and nearby jets by removing jets if the separation between the electron and jet is within ∆R < 0.2 and removing electrons if the separation is within 0.2 <∆R < 0.4. In addition, a large-Rjet is removed if the separation between the electron and the large-Rjet is within ∆R < 1.0. Muons are reconstructed from an inner detector track matched to muon spectrometer tracks or track segments [63]. Candidate muons are required to pass quality specifications based on information from the muon spectrometer and inner detector. Furthermore, muons are required to be isolated from detector activity using the same criterion that is applied to electrons and their associated tracks must satisfy |z0sin θ|<0.5 mm and |d0| σd0<3. Muons are selected if they have pT>30 GeV and |η|<2.5. An overlap-removal procedure is also applied to muons and jets. If a muon and a jet with at least three tracks are separated by ∆R < min(0.4,0.04 + 10 GeV/pTµ) the muon is removed; if the jet has fewer than three tracks, the jet is removed. For a given reconstructed event, the magnitude of the negative vector sum of the pTof all reconstructed leptons and small-Rjets is defined as the missing transverse momentum (Emiss T) [64]. An extra term is included to account for ‘soft’ energy from inner detector tracks that are not matched to any of the selected objects but are consistent with originating from the primary vertex. The four-momentum of the neutrino can be analytically determined in each event using the missing transverse momentum vector ~ Emiss Tand assuming the lepton-neutrino system has an invariant mass equal to that of the Wboson. Nearly half of the events are found to produce two complex solutions. When complex solutions are obtained, a real solution is determined by minimising a χ2parameter based on the difference between the mass of the lepton-neutrino system and the measured value of the Wboson mass. In the case of two real solutions, the solution with the smaller absolute value of the longitudinal momentum is used. 5 Analysis strategy This search targets the decay of pair-produced VLQs, T¯ T, where one Tquark decays to Wb and the other decays to Wb,Zt or Ht. Since previous searches from ATLAS and CMS have – 6 – JHEP10(2017)141 excluded VLQs decaying to Wb at 95% confidence level (CL) for masses below 920 GeV, this search focuses on the decays of higher-mass VLQs. The final state consists of a high-pT charged lepton and missing transverse momentum from the decay of one of the Wbosons, a high-momentum large-Rjet from the hadronically decaying Wboson, and multiple btagged jets. The event preselection is described in section 5.1 and the reconstruction of the T¯ Tsystem is discussed in section 5.2. The classification of events into signal and control regions follows in section 5.3. The search for the B¯ Bsignal uses the same selection criteria, with no further optimization. 5.1 Event preselection Events are required to pass a single-electron or single-muon trigger. The 2015 data were collected using electron triggers with ETthresholds of 24, 60, and 120 GeV. The 2016 data were collected using electron triggers with ETthresholds of 26, 60, and 140 GeV. For the 2015 electron triggers, the highest-ETtrigger had a looser quality requirement on the trigger object than the triggers with lower ETthresholds. For the 2016 electron triggers, the trigger with the lowest ETthreshold had stringent requirements on the quality of the trigger object, as well as requirements on its isolation from other activity in the detector. The highest and second highest ETtriggers had no requirement on isolation and had progressively looser quality requirements. Muon triggers with pTthresholds of 20 (26) GeV and requirements on isolation were used in 2015 (2016). Additionally, a high-pT muon trigger with a threshold of 50 GeV and no isolation requirement was used in both 2015 and 2016 data. In addition to the trigger requirement, events must have at least one primary vertex with at least two associated tracks. Exactly one lepton candidate (electron or muon), as described in section 4, is required. Signal events are expected to have a high jet multiplicity, since they include two b-jets as well as one jet from the hadronic decay of the Wboson. Therefore, at least three small-Rjets are required, of which at least one must be b-tagged. At least one boosted hadronic Wcandidate is required and the Emiss Tis required to be greater than 60 GeV. After this selection, backgrounds with large contributions include t¯ t,W+ jets, and single-top events. Other SM processes, including diboson, Z+ jets, t¯ tV and multi-jet production, make a smaller but non-negligible contribution; these small backgrounds are collectively referred to as ‘Others’. 5.2 T¯ Treconstruction After preselection, the four-momenta of the hadronic and semi-leptonic VLQ candidates are reconstructed using the selected lepton candidates, large-Rjets, small-Rjets, and missing transverse momentum of the event. VLQ candidates (T→Wb) are formed by pairing each Wboson candidate with a b-quark candidate. If there are two or more b-tagged jets in the event, the two highest-pTb-tagged jets are selected as the b-quark candidates. Both possible pairings of the b-quark candidates with the Whad and semi-leptonically decaying Wboson (Wlep) candidates are tested and the pairing that minimises the absolute value – 7 – JHEP10(2017)141 [GeV] lep T m 0 200 400 600 800 1000 1200 1400 1600 Event fraction 0 0.1 0.2 0.3 0.4 t t = 500 GeV T m = 700 GeV T m = 900 GeV T m = 1100 GeV T m = 1300 GeV T m ATLAS Simulation = 13 TeVs ℬ(T →Wb) = 1 Signal Region [GeV] lep T m 0 200 400 600 800 1000 1200 1400 1600 Event fraction 0 0.05 0.1 0.15 0.2 0.25 t t = 700 GeV B m = 900 GeV B m = 1100 GeV B m = 1300 GeV B m ATLAS Simulation = 13 TeVs ℬ(B →Wt) = 1 Signal Region Figure 1. The reconstructed leptonic Tquark mass in the signal region is shown for the t¯ t background and a few signal mass points, for the signal models B(T→Wb) = 1 (left) and for the signal models B(B→W t) = 1 (right). In both figures, the distributions are normalised to unity for comparison of the relative shapes at each mass point. Due to the limited Monte Carlo sample size, the t¯ tdistribution has been smoothed. of the mass difference between the semi-leptonically and hadronically reconstructed VLQ candidates, |∆m|, is chosen. If the event has only one b-tagged jet, that jet is used as one of the b-quark candidates and then all permutations with the remaining small-Rjets are tested to find the configuration that minimises |∆m|. The final discriminating variable used in the statistical analysis is mlep T, the reconstructed mass of the semi-leptonically decaying vector-like Tquark candidate. This is found to provide the best expected signal sensitivity. Figure 1shows mlep Tfor benchmark T and Bquark signal models and t¯ tproduction in the signal region (defined in section 5.3.1) after the reconstruction algorithm is applied. The reconstructed masses for the signal and t¯ tbackground are shown to peak at the generated Tand top-quark masses, respectively. The tails arise from misreconstructed Tcandidates. As expected, the reconstruction algorithm does not reconstruct the Bmass, yet the variable nonetheless provides separation power between the signal and the t¯ tbackground. 5.3 Classification of event topologies At¯ tcontrol region is used to constrain the production rate of t¯ tevents as well as systematic uncertainties related to t¯ tmodelling. The signal and control regions are described in detail in section 5.3.1 and section 5.3.2. The scalar sum of Emiss Tand the transverse momenta of the lepton and all small-Rjets, ST, and the separation between the lepton and neutrino, ∆R(lep, ν), are used to define the two regions. These regions are shown in figure 2after applying the event pre-selection, and described below. 5.3.1 Signal region definition After the event pre-selection described in section 5.1, further requirements are applied to reduce the contribution of SM backgrounds relative to signal. Events in the signal region are selected based on their characteristic boosted topology with a high-pTWboson and larger separation between the Wboson and the bquarks. Events are required to have – 8 – JHEP10(2017)141 7.3 Limits on VLQ pair production Upper limits at the 95% CL on the T¯ Tproduction cross-section are set for two benchmark scenarios as a function of Tquark mass mTand compared to the theoretical prediction from Top++ v2.0 (figure 4). The resulting lower limit on mTis determined using the central value of the theoretical cross-section prediction. These results are only valid for new particles of narrow width. Assuming B(T→W b) =1, the observed (expected) lower limit is mT= 1350 GeV (1310 GeV). For branching ratios corresponding to the SU(2) singlet T scenario, the observed (expected) 95% CL lower limit is mT= 1170 GeV (1080 GeV). This represents a significant improvement compared to Run-1 searches [15,16], for which the observed 95% CL limit was 920 GeV when assuming B(T→W b) =1. To check that the results do not depend on the weak-isospin of the Tquark in the simulated signal events, a sample of T¯ Tevents with a mass of 1.2 TeV was generated for an SU(2) doublet Tquark and compared to the nominal sample of the same mass generated with an SU(2) singlet Tquark. Both the expected number of events and expected excluded cross-section are found to be consistent between those two samples. Thus the limits obtained are also applicable to VLQ models with non-zero weak-isospin. As there is no explicit use of charge identification, the B(T→Wb) = 1 limits are found to be applicable to the pair-production of vector-like Yquarks of charge −4/3, which decay exclusively to Wb. Exclusion limits on Tquark pair-production are also obtained for different values of mTand as a function of branching ratios to each of the three decays. In order to probe the complete branching-ratio plane spanned by both processes, the signal samples are weighted by the ratios of the respective branching ratios to the original branching ratios in Protos. Then, the complete analysis is repeated for each point in the Bplane. Figure 5shows the corresponding expected and observed Tquark mass limits in the plane B(T→Ht) versus B(T→Wb), obtained by linear interpolation of the calculated CLsversus mT. In this search, the acceptance for VLQ B¯ Bpair production is ∼3% for the B(B→ Wt) = 1 scenario and ∼1.3% for the SU(2) singlet Bscenario, which is similar to the T¯ Tfinal state. Nonetheless, the sensitivity to B¯ Bproduction is expected to be weaker, as the reconstructed Tmass distribution is used as the final discriminant. Without any modifications to the analysis to specifically target B¯ Bproduction, observed (expected) lower limits at 95% CL are set at 1250 (1150) GeV when assuming B(B→Wt) = 1 and at 1080 (980) GeV for the SU(2) singlet Bscenario. This represents a significant improvement compared to Run-1 [76] and recent Run-2 searches [77] when assuming B(B→W t) =1, for which the observed 95% CL limit was 880 GeV and 1020 GeV, respectively. Being agnostic to the charge of the VLQ, the limits for B(B→W t) = 1 are found to be applicable to vector-like Xquarks of charge +5/3, which exclusively decay to Wt. Figure 6shows the corresponding expected and observed Bquark mass limits in the plane B(B→Hb) versus B(B→Wt), assuming B(B→Hb) + B(B→Wt) + B(B→Zb) = 1 . 8 Conclusions A search for the pair production of a heavy vector-like Tquark, based on pp collisions at √s= 13 TeV recorded in 2015 (3.2 fb−1) and 2016 (32.9 fb−1) with the ATLAS detector at – 15 – JHEP10(2017)141 [GeV] T m 500 600 700 800 900 1000 1100 1200 1300 1400 ) [pb]T T→(pp σ 3− 10 2− 10 1− 10 1 10 Theory Observed Limit Expected Limit σ1±Expected σ2±Expected All limits at 95% CL Wb+X 1-lepton→TT ℬ(T →Wb) = 1 ATLAS -1 = 13 TeV, 36.1 fbs [GeV] T m 500 600 700 800 900 1000 1100 1200 1300 1400 ) [pb]T T→(pp σ 3− 10 2− 10 1− 10 1 10 Theory Observed Limit Expected Limit σ1±Expected σ2±Expected All limits at 95% CL Wb+X 1-lepton→TT SU(2) singlet ATLAS -1 = 13 TeV, 36.1 fbs Figure 4. Expected (dashed black line) and observed (solid black line) upper limits at the 95% CL on the T¯ Tcross-section as a function of Tquark mass assuming B(T→Wb) = 1 (top) and in the SU(2) singlet Tscenario (bottom). The green and yellow bands correspond to ±1 and ±2 standard deviations around the expected limit. The thin red line and band show the theoretical prediction and its ±1 standard deviation uncertainty. the CERN Large Hadron Collider, is presented. Data are analysed in the lepton-plus-jets final state and no significant deviation from the Standard Model expectation is observed. Assuming a branching ratio B(T→Wb) = 1, the observed (expected) 95% CL lower limit on the vector-like quark mass is 1350 GeV (1310 GeV). For the scenario of an SU(2) singlet Tquark, the observed (expected) mass limit is 1170 GeV (1080 GeV). Assuming the Tquark can only decay to Wb,Zt and Ht, 95% CL lower limits are derived for various masses in the two-dimensional plane of B(T→W b) versus B(T→Ht). This search is also reinterpreted to provide limits on Bquark masses. These are found to be – 16 – JHEP10(2017)141 ℬ(T →Wb) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 ℬ(T →Ht) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Expected 95% CL mass limit [GeV] 500 600 700 800 900 1000 1100 1200 1300 1400 ATLAS -1 = 13 TeV, 36.1 fbs Wb+X 1-lepton→ TT 600 700 800 900 1000 1100 1200 1300 SU(2) singlet SU(2) doublet SU(2) singlet SU(2) doublet ℬ(T →Wb) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 ℬ(T →Ht) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Observed 95% CL mass limit [GeV] 500 600 700 800 900 1000 1100 1200 1300 1400 ATLAS -1 = 13 TeV, 36.1 fbs Wb+X 1-lepton→ TT 600 700 800 900 1000 1100 1200 1300 SU(2) singlet SU(2) doublet SU(2) singlet SU(2) doublet Figure 5. Expected (top) and observed (bottom) 95% CL lower limits on the mass of the Tquark as a function of the decay branching ratios into B(T→Wb) and B(T→Ht). Contour lines are provided to guide the eye. The markers indicate the branching ratios for the SU(2) singlet and doublet scenarios with masses above ∼0.8 TeV, where they are approximately independent of the VLQ Tmass. The white region is due to the limit falling below 500 GeV, the lowest simulated signal mass. 1250 GeV (1150 GeV) assuming 100% branching ratio to W t and 1080 GeV (980 GeV) under the SU(2) singlet Bquark scenario. These limits are found to be equally applicable to VLQ Yquark and Xquark production, that decay to Wb and W t, respectively. Mass limits are also set as a function of the decay branching ratios B(T→Hb) versus B(T→Wt) assuming only the B→Wt,B→Zb and B→Hb decay modes contribute. – 17 – JHEP10(2017)141 ℬ(B →Wt) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 ℬ(B →Hb) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Expected 95% CL mass limit [GeV] 500 600 700 800 900 1000 1100 1200 1300 1400 ATLAS -1 = 13 TeV, 36.1 fbs 1-leptonBB 600 700 800 900 1000 1100 SU(2) singlet SU(2) doublet SU(2) singlet SU(2) doublet ℬ(B →Wt) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 ℬ(B →Hb) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Observed 95% CL mass limit [GeV] 500 600 700 800 900 1000 1100 1200 1300 1400 ATLAS -1 = 13 TeV, 36.1 fbs 1-leptonBB 600 700 800 900 1000 1100 1200 SU(2) singlet SU(2) doublet SU(2) singlet SU(2) doublet Figure 6. Expected (top) and observed (bottom) 95% CL lower limits on the mass of the Bquark as a function of the decay branching ratios into B(B→Wt) and B(B→Hb). Contour lines are provided to guide the eye. The markers indicate the branching ratios for the SU(2) singlet and doublet scenarios with masses above ∼0.8 TeV, where they are approximately independent of the VLQ Bmass. The white regions are due to the limit falling below 500 GeV, the lowest simulated signal mass. Acknowledgments We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and – 18 – JHEP10(2017)141 FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS, CEA-DSM/IRFU, France; SRNSF, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF, I-CORE and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZˇ S, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, the Canada Council, CANARIE, CRC, Compute Canada, FQRNT, and the Ontario Innovation Trust, Canada; EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Sk lodowska-Curie Actions, European Union; Investissements d’Avenir Labex and Idex, ANR, R´egion Auvergne and Fondation Partager le Savoir, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF; BSF, GIF and Minerva, Israel; BRF, Norway; CERCA Programme Generalitat de Catalunya, Generalitat Valenciana, Spain; the Royal Society and Leverhulme Trust, United Kingdom. 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Beresford122, M. Beretta50, D. Berge109, E. Bergeaas Kuutmann168, N. Berger5, J. Beringer16, S. Berlendis58, N.R. Bernard89, G. Bernardi83, C. Bernius145, F.U. Bernlochner23, T. Berry80, P. Berta86, C. Bertella35a, G. Bertoli148a,148b, F. Bertolucci126a,126b, I.A. Bertram75, C. Bertsche45, D. Bertsche115, G.J. Besjes39, O. Bessidskaia Bylund148a,148b, M. Bessner45, N. Besson138, A. Bethani87, S. Bethke103, A.J. Bevan79, J. Beyer103, R.M. Bianchi127, O. Biebel102, D. Biedermann17, R. Bielski87, K. Bierwagen86, N.V. Biesuz126a,126b, M. Biglietti136a, T.R.V. Billoud97, H. Bilokon50, M. Bindi57, A. Bingul20b, C. Bini134a,134b, S. Biondi22a,22b, T. Bisanz57, C. Bittrich47, D.M. Bjergaard48, J.E. Black145, K.M. Black24, R.E. Blair6, T. Blazek146a, I. Bloch45, C. Blocker25, A. Blue56, W. Blum86,∗, U. Blumenschein79, S. Blunier34a, G.J. Bobbink109, V.S. Bobrovnikov111,c, S.S. Bocchetta84, A. Bocci48, C. Bock102, M. Boehler51, D. Boerner178, D. Bogavac102, A.G. Bogdanchikov111, C. Bohm148a, V. Boisvert80, P. Bokan168,i, T. Bold41a, A.S. Boldyrev101, A.E. Bolz60b, M. Bomben83, M. Bona79, M. Boonekamp138, A. Borisov132, G. Borissov75, J. Bortfeldt32, D. Bortoletto122, V. Bortolotto62a,62b,62c, – 24 – JHEP10(2017)141 E.D. Resseguie124, S. Rettie171, E. Reynolds19, O.L. Rezanova111,c, P. Reznicek131, R. Rezvani97, R. Richter103, S. Richter81, E. Richter-Was41b, O. Ricken23, M. Ridel83, P. Rieck103, C.J. Riegel178, J. Rieger57, O. Rifki115, M. Rijssenbeek150, A. Rimoldi123a,123b, M. Rimoldi18, L. Rinaldi22a, G. Ripellino149, B. Risti´c32, E. Ritsch32, I. Riu13, F. Rizatdinova116, E. Rizvi79, C. Rizzi13, R.T. Roberts87, S.H. Robertson90,o, A. Robichaud-Veronneau90, D. Robinson30, J.E.M. Robinson45, A. Robson56, E. Rocco86, C. Roda126a,126b, Y. Rodina88,am, S. Rodriguez Bosca170, A. Rodriguez Perez13, D. Rodriguez Rodriguez170, S. Roe32, C.S. Rogan59, O. Røhne121, J. Roloff59, A. Romaniouk100, M. Romano22a,22b, S.M. Romano Saez37, E. Romero Adam170, N. Rompotis77, M. Ronzani51, L. Roos83, S. Rosati134a, K. Rosbach51, P. Rose139, N.-A. Rosien57, E. Rossi106a,106b, L.P. Rossi53a, J.H.N. Rosten30, R. Rosten140, M. Rotaru28b, J. Rothberg140, D. Rousseau119, A. Rozanov88, Y. Rozen154, X. Ruan147c, F. Rubbo145, F. R¨uhr51, A. Ruiz-Martinez31, Z. Rurikova51, N.A. Rusakovich68, H.L. Russell90, J.P. Rutherfoord7, N. Ruthmann32, Y.F. Ryabov125, M. Rybar169, G. Rybkin119, S. Ryu6, A. Ryzhov132, G.F. Rzehorz57, A.F. Saavedra152, G. Sabato109, S. Sacerdoti29, H.F-W. Sadrozinski139, R. Sadykov68, F. Safai Tehrani134a, P. Saha110, M. Sahinsoy60a, M. Saimpert45, M. Saito157, T. Saito157, H. Sakamoto157, Y. Sakurai174, G. Salamanna136a,136b, J.E. Salazar Loyola34b, D. Salek109, P.H. Sales De Bruin168, D. Salihagic103, A. Salnikov145, J. Salt170, D. Salvatore40a,40b, F. Salvatore151, A. Salvucci62a,62b,62c, A. Salzburger32, D. Sammel51, D. Sampsonidis156, D. Sampsonidou156, J. S´anchez170, V. Sanchez Martinez170, A. Sanchez Pineda167a,167c, H. Sandaker121, R.L. Sandbach79, C.O. Sander45, M. Sandhoff178, C. Sandoval21, D.P.C. Sankey133, M. Sannino53a,53b, Y. Sano105, A. Sansoni50, C. Santoni37, H. Santos128a, I. Santoyo Castillo151, A. Sapronov68, J.G. Saraiva128a,128d, B. Sarrazin23, O. Sasaki69, K. Sato164, E. Sauvan5, G. Savage80, P. Savard161,d, N. Savic103, C. Sawyer133, L. Sawyer82,u, J. Saxon33, C. Sbarra22a, A. Sbrizzi22a,22b, T. Scanlon81, D.A. Scannicchio166, J. Schaarschmidt140, P. Schacht103, B.M. Schachtner102, D. Schaefer32, L. Schaefer124, R. Schaefer45, J. Schaeffer86, S. Schaepe23, S. Schaetzel60b, U. Sch¨afer86, A.C. Schaffer119, D. Schaile102, R.D. Schamberger150, V.A. Schegelsky125, D. Scheirich131, M. Schernau166, C. Schiavi53a,53b, S. Schier139, L.K. Schildgen23, C. Schillo51, M. Schioppa40a,40b, S. Schlenker32, K.R. Schmidt-Sommerfeld103, K. Schmieden32, C. Schmitt86, S. Schmitt45, S. Schmitz86, U. Schnoor51, L. Schoeffel138, A. Schoening60b, B.D. Schoenrock93, E. Schopf23, M. Schott86, J.F.P. Schouwenberg108, J. Schovancova32, S. Schramm52, N. Schuh86, A. Schulte86, M.J. Schultens23, H.-C. Schultz-Coulon60a, H. Schulz17, M. Schumacher51, B.A. Schumm139, Ph. Schune138, A. Schwartzman145, T.A. Schwarz92, H. Schweiger87, Ph. Schwemling138, R. Schwienhorst93, J. Schwindling138, A. Sciandra23, G. Sciolla25, M. Scornajenghi40a,40b, F. Scuri126a,126b, F. Scutti91, J. Searcy92, P. Seema23, S.C. Seidel107, A. Seiden139, J.M. Seixas26a, G. Sekhniaidze106a, K. Sekhon92, S.J. Sekula43, N. Semprini-Cesari22a,22b, S. Senkin37, C. Serfon121, L. Serin119, L. Serkin167a,167b, M. Sessa136a,136b, R. Seuster172, H. Severini115, T. Sfiligoj78, F. Sforza165, A. Sfyrla52, E. Shabalina57, N.W. Shaikh148a,148b, L.Y. Shan35a, R. Shang169, J.T. Shank24, M. Shapiro16, P.B. Shatalov99, K. Shaw167a,167b, S.M. Shaw87, A. Shcherbakova148a,148b, C.Y. Shehu151, Y. Shen115, N. Sherafati31, P. Sherwood81, L. Shi153,an, S. Shimizu70, C.O. Shimmin179, M. Shimojima104, I.P.J. Shipsey122, S. Shirabe73, M. Shiyakova68,ao, J. Shlomi175, A. 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Soldatov100, U. Soldevila170, A.A. Solodkov132, A. Soloshenko68, O.V. Solovyanov132, V. Solovyev125, P. Sommer51, H. Son165, A. Sopczak130, D. Sosa60b, C.L. Sotiropoulou126a,126b, R. Soualah167a,167c, A.M. Soukharev111,c, D. South45, B.C. Sowden80, S. Spagnolo76a,76b, M. Spalla126a,126b, M. Spangenberg173, F. Span`o80, D. Sperlich17, F. Spettel103, T.M. Spieker60a, R. Spighi22a, G. Spigo32, L.A. Spiller91, M. Spousta131, R.D. St. Denis56,∗, A. Stabile94a, R. Stamen60a, S. Stamm17, E. Stanecka42, R.W. Stanek6, C. Stanescu136a, M.M. Stanitzki45, B.S. Stapf109, S. Stapnes121, E.A. Starchenko132, G.H. Stark33, J. Stark58, S.H Stark39, P. Staroba129, P. Starovoitov60a, S. St¨arz32, R. Staszewski42, P. Steinberg27, B. Stelzer144, H.J. Stelzer32, O. Stelzer-Chilton163a, H. Stenzel55, G.A. Stewart56, M.C. Stockton118, M. Stoebe90, G. Stoicea28b, P. Stolte57, S. Stonjek103, A.R. Stradling8, A. Straessner47, M.E. Stramaglia18, J. Strandberg149, S. Strandberg148a,148b, M. Strauss115, P. 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Yusuff30,aw, B. Zabinski42, G. Zacharis10, R. Zaidan13, A.M. Zaitsev132,ak, N. Zakharchuk45, J. Zalieckas15, A. Zaman150, S. Zambito59, D. Zanzi91, C. Zeitnitz178, G. Zemaityte122, A. Zemla41a, J.C. Zeng169, Q. Zeng145, O. Zenin132, T. ˇ Zeniˇs146a, D. Zerwas119, D. Zhang92, F. Zhang176, G. Zhang36a,ax, H. Zhang35b, J. Zhang6, L. Zhang51, L. Zhang36a, M. Zhang169, P. Zhang35b, R. Zhang23, R. Zhang36a,au, X. Zhang36b, Y. Zhang35a, Z. Zhang119, X. Zhao43, Y. Zhao36b,ay, Z. Zhao36a, A. Zhemchugov68, B. Zhou92, C. Zhou176, L. Zhou43, M. Zhou35a, M. Zhou150, N. Zhou35c, C.G. Zhu36b, H. Zhu35a, J. Zhu92, Y. Zhu36a, X. Zhuang35a, K. Zhukov98, A. Zibell177, D. Zieminska64, N.I. Zimine68, C. Zimmermann86, S. Zimmermann51, Z. Zinonos103, M. Zinser86, M. Ziolkowski143, L. ˇ Zivkovi´c14, G. Zobernig176, A. Zoccoli22a,22b, R. Zou33, M. zur Nedden17, L. Zwalinski32 1Department of Physics, University of Adelaide, Adelaide, Australia 2Physics Department, SUNY Albany, Albany NY, United States of America 3Department of Physics, University of Alberta, Edmonton AB, Canada 4 (a)Department of Physics, Ankara University, Ankara; (b)Istanbul Aydin University, Istanbul; (c) Division of Physics, TOBB University of Economics and Technology, Ankara, Turkey 5LAPP, CNRS/IN2P3 and Universit´e Savoie Mont Blanc, Annecy-le-Vieux, France 6High Energy Physics Division, Argonne National Laboratory, Argonne IL, United States of America 7Department of Physics, University of Arizona, Tucson AZ, United States of America 8Department of Physics, The University of Texas at Arlington, Arlington TX, United States of America 9Physics Department, National and Kapodistrian University of Athens, Athens, Greece 10 Physics Department, National Technical University of Athens, Zografou, Greece 11 Department of Physics, The University of Texas at Austin, Austin TX, United States of America 12 Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan 13 Institut de F´ısica d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Barcelona, Spain 14 Institute of Physics, University of Belgrade, Belgrade, Serbia – 33 – JHEP10(2017)141 15 Department for Physics and Technology, University of Bergen, Bergen, Norway 16 Physics Division, Lawrence Berkeley National Laboratory and University of California, Berkeley CA, United States of America 17 Department of Physics, Humboldt University, Berlin, Germany 18 Albert Einstein Center for Fundamental Physics and Laboratory for High Energy Physics, University of Bern, Bern, Switzerland 19 School of Physics and Astronomy, University of Birmingham, Birmingham, United Kingdom 20 (a)Department of Physics, Bogazici University, Istanbul; (b)Department of Physics Engineering, Gaziantep University, Gaziantep; (d)Istanbul Bilgi University, Faculty of Engineering and Natural Sciences, Istanbul; (e)Bahcesehir University, Faculty of Engineering and Natural Sciences, Istanbul, Turkey 21 Centro de Investigaciones, Universidad Antonio Narino, Bogota, Colombia 22 (a)INFN Sezione di Bologna; (b)Dipartimento di Fisica e Astronomia, Universit`a di Bologna, Bologna, Italy 23 Physikalisches Institut, University of Bonn, Bonn, Germany 24 Department of Physics, Boston University, Boston MA, United States of America 25 Department of Physics, Brandeis University, Waltham MA, United States of America 26 (a)Universidade Federal do Rio De Janeiro COPPE/EE/IF, Rio de Janeiro; (b)Electrical Circuits Department, Federal University of Juiz de Fora (UFJF), Juiz de Fora; (c)Federal University of Sao Joao del Rei (UFSJ), Sao Joao del Rei; (d)Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo, Brazil 27 Physics Department, Brookhaven National Laboratory, Upton NY, United States of America 28 (a)Transilvania University of Brasov, Brasov; (b)Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest; (c)Department of Physics, Alexandru Ioan Cuza University of Iasi, Iasi; (d)National Institute for Research and Development of Isotopic and Molecular Technologies, Physics Department, Cluj Napoca; (e)University Politehnica Bucharest, Bucharest; (f)West University in Timisoara, Timisoara, Romania 29 Departamento de F´ısica, Universidad de Buenos Aires, Buenos Aires, Argentina 30 Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom 31 Department of Physics, Carleton University, Ottawa ON, Canada 32 CERN, Geneva, Switzerland 33 Enrico Fermi Institute, University of Chicago, Chicago IL, United States of America 34 (a)Departamento de F´ısica, Pontificia Universidad Cat´olica de Chile, Santiago; (b)Departamento de F´ısica, Universidad T´ecnica Federico Santa Mar´ıa, Valpara´ıso, Chile 35 (a)Institute of High Energy Physics, Chinese Academy of Sciences, Beijing; (b)Department of Physics, Nanjing University, Jiangsu; (c)Physics Department, Tsinghua University, Beijing 100084, China 36 (a)Department of Modern Physics and State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Anhui; (b)School of Physics, Shandong University, Shandong; (c)Department of Physics and Astronomy, Key Laboratory for Particle Physics, Astrophysics and Cosmology, Ministry of Education; Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University, Shanghai(also at PKU-CHEP), China 37 Universit´e Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France 38 Nevis Laboratory, Columbia University, Irvington NY, United States of America 39 Niels Bohr Institute, University of Copenhagen, Kobenhavn, Denmark 40 (a)INFN Gruppo Collegato di Cosenza, Laboratori Nazionali di Frascati; (b)Dipartimento di Fisica, Universit`a della Calabria, Rende, Italy 41 (a)AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakow; (b)Marian Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland 42 Institute of Nuclear Physics Polish Academy of Sciences, Krakow, Poland 43 Physics Department, Southern Methodist University, Dallas TX, United States of America 44 Physics Department, University of Texas at Dallas, Richardson TX, United States of America – 34 – JHEP10(2017)141 45 DESY, Hamburg and Zeuthen, Germany 46 Lehrstuhl f¨ur Experimentelle Physik IV, Technische Universit¨at Dortmund, Dortmund, Germany 47 Institut f¨ur Kernund Teilchenphysik, Technische Universit¨at Dresden, Dresden, Germany 48 Department of Physics, Duke University, Durham NC, United States of America 49 SUPA - School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 50 INFN e Laboratori Nazionali di Frascati, Frascati, Italy 51 Fakult¨at f¨ur Mathematik und Physik, Albert-Ludwigs-Universit¨at, Freiburg, Germany 52 Departement de Physique Nucleaire et Corpusculaire, Universit´e de Gen`eve, Geneva, Switzerland 53 (a)INFN Sezione di Genova; (b)Dipartimento di Fisica, Universit`a di Genova, Genova, Italy 54 (a)E. Andronikashvili Institute of Physics, Iv. Javakhishvili Tbilisi State University, Tbilisi; (b) High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia 55 II Physikalisches Institut, Justus-Liebig-Universit¨at Giessen, Giessen, Germany 56 SUPA - School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 57 II Physikalisches Institut, Georg-August-Universit¨at, G¨ottingen, Germany 58 Laboratoire de Physique Subatomique et de Cosmologie, Universit´e Grenoble-Alpes, CNRS/IN2P3, Grenoble, France 59 Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge MA, United States of America 60 (a)Kirchhoff-Institut f¨ur Physik, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg; (b) Physikalisches Institut, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg, Germany 61 Faculty of Applied Information Science, Hiroshima Institute of Technology, Hiroshima, Japan 62 (a)Department of Physics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong; (b) Department of Physics, The University of Hong Kong, Hong Kong; (c)Department of Physics and Institute for Advanced Study, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China 63 Department of Physics, National Tsing Hua University, Taiwan 64 Department of Physics, Indiana University, Bloomington IN, United States of America 65 Institut f¨ur Astround Teilchenphysik, Leopold-Franzens-Universit¨at, Innsbruck, Austria 66 University of Iowa, Iowa City IA, United States of America 67 Department of Physics and Astronomy, Iowa State University, Ames IA, United States of America 68 Joint Institute for Nuclear Research, JINR Dubna, Dubna, Russia 69 KEK, High Energy Accelerator Research Organization, Tsukuba, Japan 70 Graduate School of Science, Kobe University, Kobe, Japan 71 Faculty of Science, Kyoto University, Kyoto, Japan 72 Kyoto University of Education, Kyoto, Japan 73 Research Center for Advanced Particle Physics and Department of Physics, Kyushu University, Fukuoka, Japan 74 Instituto de F´ısica La Plata, Universidad Nacional de La Plata and CONICET, La Plata, Argentina 75 Physics Department, Lancaster University, Lancaster, United Kingdom 76 (a)INFN Sezione di Lecce; (b)Dipartimento di Matematica e Fisica, Universit`a del Salento, Lecce, Italy 77 Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom 78 Department of Experimental Particle Physics, Joˇzef Stefan Institute and Department of Physics, University of Ljubljana, Ljubljana, Slovenia 79 School of Physics and Astronomy, Queen Mary University of London, London, United Kingdom 80 Department of Physics, Royal Holloway University of London, Surrey, United Kingdom 81 Department of Physics and Astronomy, University College London, London, United Kingdom 82 Louisiana Tech University, Ruston LA, United States of America 83 Laboratoire de Physique Nucl´eaire et de Hautes Energies, UPMC and Universit´e Paris-Diderot and CNRS/IN2P3, Paris, France 84 Fysiska institutionen, Lunds universitet, Lund, Sweden 85 Departamento de Fisica Teorica C-15, Universidad Autonoma de Madrid, Madrid, Spain – 35 – JHEP10(2017)141 86 Institut f¨ur Physik, Universit¨at Mainz, Mainz, Germany 87 School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 88 CPPM, Aix-Marseille Universit´e and CNRS/IN2P3, Marseille, France 89 Department of Physics, University of Massachusetts, Amherst MA, United States of America 90 Department of Physics, McGill University, Montreal QC, Canada 91 School of Physics, University of Melbourne, Victoria, Australia 92 Department of Physics, The University of Michigan, Ann Arbor MI, United States of America 93 Department of Physics and Astronomy, Michigan State University, East Lansing MI, United States of America 94 (a)INFN Sezione di Milano; (b)Dipartimento di Fisica, Universit`a di Milano, Milano, Italy 95 B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk, Republic of Belarus 96 Research Institute for Nuclear Problems of Byelorussian State University, Minsk, Republic of Belarus 97 Group of Particle Physics, University of Montreal, Montreal QC, Canada 98 P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia 99 Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia 100 National Research Nuclear University MEPhI, Moscow, Russia 101 D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow, Russia 102 Fakult¨at f¨ur Physik, Ludwig-Maximilians-Universit¨at M¨unchen, M¨unchen, Germany 103 Max-Planck-Institut f¨ur Physik (Werner-Heisenberg-Institut), M¨unchen, Germany 104 Nagasaki Institute of Applied Science, Nagasaki, Japan 105 Graduate School of Science and Kobayashi-Maskawa Institute, Nagoya University, Nagoya, Japan 106 (a)INFN Sezione di Napoli; (b)Dipartimento di Fisica, Universit`a di Napoli, Napoli, Italy 107 Department of Physics and Astronomy, University of New Mexico, Albuquerque NM, United States of America 108 Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen, Netherlands 109 Nikhef National Institute for Subatomic Physics and University of Amsterdam, Amsterdam, Netherlands 110 Department of Physics, Northern Illinois University, DeKalb IL, United States of America 111 Budker Institute of Nuclear Physics, SB RAS, Novosibirsk, Russia 112 Department of Physics, New York University, New York NY, United States of America 113 Ohio State University, Columbus OH, United States of America 114 Faculty of Science, Okayama University, Okayama, Japan 115 Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman OK, United States of America 116 Department of Physics, Oklahoma State University, Stillwater OK, United States of America 117 Palack´y University, RCPTM, Olomouc, Czech Republic 118 Center for High Energy Physics, University of Oregon, Eugene OR, United States of America 119 LAL, Univ. Paris-Sud, CNRS/IN2P3, Universit´e Paris-Saclay, Orsay, France 120 Graduate School of Science, Osaka University, Osaka, Japan 121 Department of Physics, University of Oslo, Oslo, Norway 122 Department of Physics, Oxford University, Oxford, United Kingdom 123 (a)INFN Sezione di Pavia; (b)Dipartimento di Fisica, Universit`a di Pavia, Pavia, Italy 124 Department of Physics, University of Pennsylvania, Philadelphia PA, United States of America 125 National Research Centre “Kurchatov Institute” B.P.Konstantinov Petersburg Nuclear Physics Institute, St. Petersburg, Russia 126 (a)INFN Sezione di Pisa; (b)Dipartimento di Fisica E. Fermi, Universit`a di Pisa, Pisa, Italy 127 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh PA, United States of America – 36 – JHEP10(2017)141 128 (a)Laborat´orio de Instrumenta¸c˜ao e F´ısica Experimental de Part´ıculas - LIP, Lisboa; (b)Faculdade de Ciˆencias, Universidade de Lisboa, Lisboa; (c)Department of Physics, University of Coimbra, Coimbra; (d)Centro de F´ısica Nuclear da Universidade de Lisboa, Lisboa; (e)Departamento de Fisica, Universidade do Minho, Braga; (f)Departamento de Fisica Teorica y del Cosmos and CAFPE, Universidad de Granada, Granada; (g)Dep Fisica and CEFITEC of Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal 129 Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic 130 Czech Technical University in Prague, Praha, Czech Republic 131 Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic 132 State Research Center Institute for High Energy Physics (Protvino), NRC KI, Russia 133 Particle Physics Department, Rutherford Appleton Laboratory, Didcot, United Kingdom 134 (a)INFN Sezione di Roma; (b)Dipartimento di Fisica, Sapienza Universit`a di Roma, Roma, Italy 135 (a)INFN Sezione di Roma Tor Vergata; (b)Dipartimento di Fisica, Universit`a di Roma Tor Vergata, Roma, Italy 136 (a)INFN Sezione di Roma Tre; (b)Dipartimento di Matematica e Fisica, Universit`a Roma Tre, Roma, Italy 137 (a)Facult´e des Sciences Ain Chock, R´eseau Universitaire de Physique des Hautes Energies - Universit´e Hassan II, Casablanca; (b)Centre National de l’Energie des Sciences Techniques Nucleaires, Rabat; (c)Facult´e des Sciences Semlalia, Universit´e Cadi Ayyad, LPHEA-Marrakech; (d)Facult´e des Sciences, Universit´e Mohamed Premier and LPTPM, Oujda; (e)Facult´e des sciences, Universit´e Mohammed V, Rabat, Morocco 138 DSM/IRFU (Institut de Recherches sur les Lois Fondamentales de l’Univers), CEA Saclay (Commissariat `a l’Energie Atomique et aux Energies Alternatives), Gif-sur-Yvette, France 139 Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz CA, United States of America 140 Department of Physics, University of Washington, Seattle WA, United States of America 141 Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom 142 Department of Physics, Shinshu University, Nagano, Japan 143 Department Physik, Universit¨at Siegen, Siegen, Germany 144 Department of Physics, Simon Fraser University, Burnaby BC, Canada 145 SLAC National Accelerator Laboratory, Stanford CA, United States of America 146 (a)Faculty of Mathematics, Physics & Informatics, Comenius University, Bratislava; (b) Department of Subnuclear Physics, Institute of Experimental Physics of the Slovak Academy of Sciences, Kosice, Slovak Republic 147 (a)Department of Physics, University of Cape Town, Cape Town; (b)Department of Physics, University of Johannesburg, Johannesburg; (c)School of Physics, University of the Witwatersrand, Johannesburg, South Africa 148 (a)Department of Physics, Stockholm University; (b)The Oskar Klein Centre, Stockholm, Sweden 149 Physics Department, Royal Institute of Technology, Stockholm, Sweden 150 Departments of Physics & Astronomy and Chemistry, Stony Brook University, Stony Brook NY, United States of America 151 Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom 152 School of Physics, University of Sydney, Sydney, Australia 153 Institute of Physics, Academia Sinica, Taipei, Taiwan 154 Department of Physics, Technion: Israel Institute of Technology, Haifa, Israel 155 Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel 156 Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece 157 International Center for Elementary Particle Physics and Department of Physics, The University of Tokyo, Tokyo, Japan 158 Graduate School of Science and Technology, Tokyo Metropolitan University, Tokyo, Japan 159 Department of Physics, Tokyo Institute of Technology, Tokyo, Japan – 37 – JHEP10(2017)141 160 Tomsk State University, Tomsk, Russia 161 Department of Physics, University of Toronto, Toronto ON, Canada 162 (a)INFN-TIFPA; (b)University of Trento, Trento, Italy 163 (a)TRIUMF, Vancouver BC; (b)Department of Physics and Astronomy, York University, Toronto ON, Canada 164 Faculty of Pure and Applied Sciences, and Center for Integrated Research in Fundamental Science and Engineering, University of Tsukuba, Tsukuba, Japan 165 Department of Physics and Astronomy, Tufts University, Medford MA, United States of America 166 Department of Physics and Astronomy, University of California Irvine, Irvine CA, United States of America 167 (a)INFN Gruppo Collegato di Udine, Sezione di Trieste, Udine; (b)ICTP, Trieste; (c)Dipartimento di Chimica, Fisica e Ambiente, Universit`a di Udine, Udine, Italy 168 Department of Physics and Astronomy, University of Uppsala, Uppsala, Sweden 169 Department of Physics, University of Illinois, Urbana IL, United States of America 170 Instituto de Fisica Corpuscular (IFIC), Centro Mixto Universidad de Valencia - CSIC, Spain 171 Department of Physics, University of British Columbia, Vancouver BC, Canada 172 Department of Physics and Astronomy, University of Victoria, Victoria BC, Canada 173 Department of Physics, University of Warwick, Coventry, United Kingdom 174 Waseda University, Tokyo, Japan 175 Department of Particle Physics, The Weizmann Institute of Science, Rehovot, Israel 176 Department of Physics, University of Wisconsin, Madison WI, United States of America 177 Fakult¨at f¨ur Physik und Astronomie, Julius-Maximilians-Universit¨at, W¨urzburg, Germany 178 Fakult¨at f¨ur Mathematik und Naturwissenschaften, Fachgruppe Physik, Bergische Universit¨at Wuppertal, Wuppertal, Germany 179 Department of Physics, Yale University, New Haven CT, United States of America 180 Yerevan Physics Institute, Yerevan, Armenia 181 Centre de Calcul de l’Institut National de Physique Nucl´eaire et de Physique des Particules (IN2P3), Villeurbanne, France 182 Academia Sinica Grid Computing, Institute of Physics, Academia Sinica, Taipei, Taiwan aAlso at Department of Physics, King’s College London, London, United Kingdom bAlso at Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan cAlso at Novosibirsk State University, Novosibirsk, Russia dAlso at TRIUMF, Vancouver BC, Canada eAlso at Department of Physics & Astronomy, University of Louisville, Louisville, KY, United States of America fAlso at Physics Department, An-Najah National University, Nablus, Palestine gAlso at Department of Physics, California State University, Fresno CA, United States of America hAlso at Department of Physics, University of Fribourg, Fribourg, Switzerland iAlso at II Physikalisches Institut, Georg-August-Universit¨at, G¨ottingen, Germany jAlso at Departament de Fisica de la Universitat Autonoma de Barcelona, Barcelona, Spain kAlso at Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Portugal lAlso at Tomsk State University, Tomsk, Russia mAlso at The Collaborative Innovation Center of Quantum Matter (CICQM), Beijing, China nAlso at Universita di Napoli Parthenope, Napoli, Italy oAlso at Institute of Particle Physics (IPP), Canada pAlso at Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania qAlso at Department of Physics, St. Petersburg State Polytechnical University, St. Petersburg, Russia rAlso at Borough of Manhattan Community College, City University of New York, New York City, United States of America – 38 – JHEP10(2017)141 sAlso at Department of Financial and Management Engineering, University of the Aegean, Chios, Greece tAlso at Centre for High Performance Computing, CSIR Campus, Rosebank, Cape Town, South Africa uAlso at Louisiana Tech University, Ruston LA, United States of America vAlso at Institucio Catalana de Recerca i Estudis Avancats, ICREA, Barcelona, Spain wAlso at Graduate School of Science, Osaka University, Osaka, Japan xAlso at Fakult¨at f¨ur Mathematik und Physik, Albert-Ludwigs-Universit¨at, Freiburg, Germany yAlso at Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen, Netherlands zAlso at Department of Physics, The University of Texas at Austin, Austin TX, United States of America aa Also at Institute of Theoretical Physics, Ilia State University, Tbilisi, Georgia ab Also at CERN, Geneva, Switzerland ac Also at Georgian Technical University (GTU),Tbilisi, Georgia ad Also at Ochadai Academic Production, Ochanomizu University, Tokyo, Japan ae Also at Manhattan College, New York NY, United States of America af Also at Departamento de F´ısica, Pontificia Universidad Cat´olica de Chile, Santiago, Chile ag Also at Department of Physics, The University of Michigan, Ann Arbor MI, United States of America ah Also at The City College of New York, New York NY, United States of America ai Also at Departamento de Fisica Teorica y del Cosmos and CAFPE, Universidad de Granada, Granada, Portugal aj Also at Department of Physics, California State University, Sacramento CA, United States of America ak Also at Moscow Institute of Physics and Technology State University, Dolgoprudny, Russia al Also at Departement de Physique Nucleaire et Corpusculaire, Universit´e de Gen`eve, Geneva, Switzerland am Also at Institut de F´ısica d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Barcelona, Spain an Also at School of Physics, Sun Yat-sen University, Guangzhou, China ao Also at Institute for Nuclear Research and Nuclear Energy (INRNE) of the Bulgarian Academy of Sciences, Sofia, Bulgaria ap Also at Faculty of Physics, M.V.Lomonosov Moscow State University, Moscow, Russia aq Also at National Research Nuclear University MEPhI, Moscow, Russia ar Also at Department of Physics, Stanford University, Stanford CA, United States of America as Also at Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Budapest, Hungary at Also at Giresun University, Faculty of Engineering, Turkey au Also at CPPM, Aix-Marseille Universit´e and CNRS/IN2P3, Marseille, France av Also at Department of Physics, Nanjing University, Jiangsu, China aw Also at University of Malaya, Department of Physics, Kuala Lumpur, Malaysia ax Also at Institute of Physics, Academia Sinica, Taipei, Taiwan ay Also at LAL, Univ. Paris-Sud, CNRS/IN2P3, Universit´e Paris-Saclay, Orsay, France ∗Deceased – 39 –