Search for supersymmetry in events with one lepton and multiple jets exploiting the angular correlation between the lepton and the missing transverse momentum in proton-proton collisions at $\sqrt{s} = $ 13 TeV

Results are presented from a search for supersymmetry in events with a single electron or muon and hadronic jets. The data correspond to a sample of proton-proton collisions at $\sqrt{s} = $ 13 TeV with an integrated luminosity of 35.9 fb$^{-1}$, recorded in 2016 by the CMS experiment. A number of exclusive search regions are defined according to the number of jets, the number of b-tagged jets, the scalar sum of the transverse momenta of the jets, and the scalar sum of the missing transverse momentum and the transverse momentum of the lepton. Standard model background events are reduced significantly by requiring a large azimuthal angle between the direction of the lepton and of the reconstructed W boson, computed under the hypothesis that all of the missing transverse momentum in the event arises from a neutrino produced in the leptonic decay of the W boson. The numbers of observed events are consistent with the expectations from standard model processes, and the results are used to set lower limits on supersymmetric particle masses in the context of two simplified models of gluino pair production. In the first model, where each gluino decays to a top quark-antiquark pair and a neutralino, gluino masses up to 1.8 TeV are excluded at the 95% CL. The second model considers a three-body decay to a light quark-antiquark pair and a chargino, which subsequently decays to a W boson and a neutralino. In this model, gluinos are excluded up to 1.9 TeV.


Introduction
Supersymmetry (SUSY) [1][2][3][4][5][6][7][8] is a promising extension of the standard model (SM) of particle physics. The addition of supersymmetric partners to the SM particles can lead to the suppression of quadratically divergent loop corrections to the mass squared of the Higgs boson [9]. Furthermore, in SUSY models with R-parity conservation [10], the lightest supersymmetric particle (LSP) can provide a dark matter candidate [11,12]. This paper presents a search for SUSY in the single-lepton channel using data recorded in 2016 by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 35.9 fb −1 of proton-proton collisions at √ s = 13 TeV. The analysis is an update of the search in Ref. [13], which was performed using the significantly smaller data sample collected by CMS in 2015. Similar searches were performed by the CMS and ATLAS experiments at √ s = 7 TeV [14][15][16], 8 TeV [17][18][19], and 13 TeV [20][21][22].
The results are interpreted within the framework of simplified models [23][24][25][26] of gluino pair production in which the LSP is the lightest neutralino, χ 0 1 , and the lepton is produced in the decay of a W boson that originates either from top-quark (t) or chargino ( χ ± 1 ) decay. In the T1tttt model shown in Fig. 1 (upper), gluinos ( g) undergo three-body decays to tt + χ 0 1 . In the T5qqqqWW model shown in Fig. 1 (lower), the gluinos undergo three-body decays to a first-or second-generation quark-antiquark pair (qq ) and a χ ± 1 . The chargino is assumed to have mass m χ ± 1 = 0.5(m g + m χ 0 1 ) and to decay to a χ 0 1 and a W boson.

The CMS detector
The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.  and endcap detectors. Muons are detected in gas-ionization chambers embedded in the steel flux-return yoke outside the solenoid. A more detailed description of the CMS detector, together with a definition of the coordinate system used and the relevant kinematic variables, can be found in Ref. [27]. In what follows, the azimuthal angle around the counterclockwise beam axis is denoted by φ.

Event reconstruction and simulation
The analysis makes use of the particle-flow event algorithm [28], which reconstructs and identifies each individual particle with an optimized combination of information from the various elements of the CMS detector. The energy of photons is directly obtained from the ECAL measurement, corrected for zero-suppression effects. The energy of electrons is determined from a combination of the electron momentum at the primary interaction vertex as determined by the tracker, the energy of the corresponding ECAL cluster, and the energy sum of all bremsstrahlung photons spatially compatible with originating from the electron track. The energy of muons is obtained from the curvature of the corresponding track. The energy of charged hadrons is determined from a combination of their momentum measured in the tracker and the matching ECAL and HCAL energy deposits, corrected for zero-suppression effects and for the response function of the calorimeters to hadronic showers. Finally, the energy of neutral hadrons is obtained from the corresponding corrected ECAL and HCAL energy.
The degree of isolation of a lepton from other particles provides a strong indication of whether it was produced within a jet, as would be expected from the fragmentation of a b quark, or in the leptonic decay of a W boson, which can be produced either directly or in decays of heavy particles such as the top quark. The isolation is characterized by the scalar sum of the transverse momenta (p T ) of all particles within a cone of radius R = √ ( η) 2 + ( φ) 2 around the lepton momentum vector, excluding the contribution of the lepton and the contribution of charged particles not associated with the primary interaction vertex. In the calculation of the isolation variable, an area-based correction is employed to remove the contribution of particles from "pileup" [29], i.e. additional protonproton collisions within the same or neighboring bunch crossings. The isolation variable I rel is defined as the ratio of the scalar sum of the p T in the cone to the transverse momentum of the lepton, p T . To maintain high efficiency for signal events, which can contain a large number of jets from the SUSY decay chains, a cone radius that depends on p T , is used: R = 0.2 for p T < 50 GeV, 10/p T [GeV] for 50 < p T < 200 GeV, and 0.05 for p T > 200 GeV.
This p T dependent isolation definition additionally reduces the accidental overlap between jets and the lepton in regions where the SUSY decay products are boosted. Accepted muons and electrons are required to satisfy I rel < 0.2 and I rel < 0.1, respectively.
Jets are clustered using the anti-k T algorithm [30] with a distance parameter of 0.4 [31], as implemented in the FastJet package [32]. The momentum of a jet, which is determined as the vectorial sum of all particle momenta in the jet, is found from simulation to be within 5 to 10% of the true momentum over the full p T spectrum and detector acceptance. An offset correction is applied to jet energies to take into account the contribution from pileup [29]. Jet energy corrections are derived from simulation and confirmed with in-situ measurements of the energy balance in dijet, Z+jets, and photon+jet events [33]. Additional selection criteria are applied to each event to remove spurious jet-like features originating from isolated noise patterns in certain HCAL regions. They have negligible impact on the efficiency for signal events. Jets originating from b quarks are identified with an inclusive combined secondary vertex tagging algorithm (CSVv2) [34,35] that uses both secondary-vertex and track-based information. The working point is chosen to provide a b tagging efficiency of ≈63%, a c tagging efficiency of ≈12%, and a light-flavor and gluon misidentification rate of ≈0.9% for jets with p T > 20 GeV in simulated tt events [35].
Double counting of objects is avoided by not considering jets that lie within a cone of radius 0.4 around a selected lepton. To avoid double counting of objects as both a lepton and a jet, jets that lie within a cone of radius R = 0.4 of a lepton are not considered.
The missing transverse momentum vector, p miss T , is defined as the projection onto the plane perpendicular to the beam axis of the negative vector sum of the momenta of all reconstructed particle-flow objects in an event. Jet energy corrections are propagated to p miss T . Its magnitude is referred to as p miss T .
Several benchmarks SUSY models, corresponding to different scenarios for the gluino and neutralino masses, are used to study the kinematic properties of the signal and to illustrate the numbers of events expected from SUSY. The benchmarks are denoted by the model name and the two key parameters, namely m g and m χ 0 The evolution and hadronization of partons is performed using pythia 8.212 [52] with the CUETP8M1 tune [58]. Pileup is generated for a nominal distribution in the number of pp interactions per bunch crossing, which is subsequently reweighted to match the corresponding distribution observed in data. The detector response for all backgrounds is modeled using a detailed simulation based Geant4 [59], while a fast simulation program [60] is used to reduce computation time for signal events. The fast simulation has been validated against detailed Geant4-based simulations in reconstructed objects relevant to this search, and corresponding efficiency corrections based on data are applied to simulated background and signal events, respectively.

Trigger and event selection
This analysis requires events containing a loosely isolated electron or muon with p T > 15 GeV and a scalar sum of the jet transverse momenta in the event, H T , with values greater than 400 GeV at the trigger level. To maximize the overall efficiency, additional trigger paths were added requiring missing transverse momentum (p miss T > 100, 110, or 120 GeV), isolated leptons (p T > 27 GeV for electrons and p T > 24 GeV for muons) or leptons with no isolation requirement but with a higher p T threshold (p T > 105 GeV or p T > 115 GeV for electrons and p T > 50 GeV for muons). The trigger efficiency is measured in control samples recorded either with single-lepton triggers or with triggers with a requirement on H T . After applying the offline event selection requirements, an overall trigger efficiency of (98 ± 1)% is observed for the electron channel and negligible inefficiency for the muon channel.
The event selection is similar to that presented in Ref. [13], with improvements as noted to enhance the sensitivity of the analysis. Leptons (electrons or muons) must satisfy p T > 25 GeV. Additional leptons with p T > 10 GeV that satisfy looser selection criteria of I rel < 0.4 are referred to as "veto" leptons. To reduce the contribution from standard model processes that produce higher lepton multiplicities, events with one or more veto leptons are rejected.
Jets are required to have p T > 30 GeV and |η| < 2.4 to be considered for the calculation of higher level quantities such as H T , the number of jets (n jet ), and the number of b-tagged jets (n b ). A number of exclusive kinematic regions, denoted as "search bins", are defined according to n jet , n b , H T , and the quantity p T + p miss T (L T ). All search bins are required to contain at least five jets with the two highest-p T jets satisfying p T > 80 GeV. Search bins with zero b-tagged jets, called "0-b", are mainly sensitive to the T5qqqqWW model, while search bins with at least one b-tagged jet, called "multi-b", are mainly sensitive to the T1tttt model. For the latter, the requirement on the number of jets is increased to six, since the presence of four top quarks results in an increased jet multiplicity in signal events.
To ensure that the analysis is sensitive both to signals with high p miss T as well as with small p miss T but with large lepton p T , no explicit threshold on p miss T is imposed. Instead, L T is required to be >250 GeV. Because of the trigger requirements and the extensive jet activity expected in the chosen SUSY models, H T is required to be >500 GeV.
An important background arises from tt+jets events in which both W bosons decay leptonically and one lepton does not fulfill the selection criteria for veto leptons. In an extension of the previous analysis [13], and to suppress this background, events containing at least one isolated high-p T charged track are rejected in certain cases. The high-p T track can arise from τ → ν τ + hadron decays or muon or electron tracks of poor quality. The relative isolation of such tracks within a cone of R = 0.3 around the track candidate is required to be smaller than 0.1 or 0.2 for hadron or lepton particle-flow candidates, respectively. For events containing such isolated track candidates, the M T2 variable [61] is used: where p t T and p T are the transverse momenta of the isolated track and the selected lepton respectively, and M T is the transverse mass. The minimization runs over all possible splittings of p miss T assuming two lost massless particles, as in dileptonic tt decays that contain two neutrinos. The isolated track with highest p T and opposite charge relative to the selected lepton is chosen where p t T is required to be >5 GeV. Events with a hadronic or leptonic isolated track with M T2 below 60 or 80 GeV, respectively, are rejected. This requirement removes approximately 40% of dilepton tt+jets events, while rejecting only 8-15% of the events in the SUSY benchmark models. After these selections, the dominant remaining backgrounds are W+jets events in which the W boson decays leptonically, and tt+jets events in which one of the W bosons from the top quarks decays leptonically and the other W boson decays hadronically. Both backgrounds are suppressed by requiring a large azimuthal angle φ between the lepton and the presumed W boson. The transverse momentum of the leptonically decaying W boson is estimated as the sum of p T and p miss T vectors. In background events from W+jets and tt+jets with a single W-boson's leptonic decay, the φ distribution falls sharply and has a maximum value determined by the mass and p T of the W boson. In the SUSY models investigated here, p miss T receives a large contribution from the two neutralino LSPs. As a consequence, large values of φ are possible and the resulting φ distribution in signal events is roughly uniform. The φ variable can therefore be used to define the search region (SR) as events with large φ, while events with small φ constitute the control region (CR), which is used to estimate the SM background in the SR. For illustration, Fig. 2 shows the φ distributions in two tightened multi-b and 0-b search bins as defined in Table 6. The magnitude of the angle between the W boson and the lepton is inversely proportional to the W boson momentum, which at high p T is approximated by L T . Therefore, the φ threshold used in defining the SR varies between 0.5 and 1, depending on L T .
The definitions of the search bins, along with the φ values selected for the SRs, are given in Tables 4 and 5 for the multi-b and 0-b analyses, respectively. The name convention assigns a letter to each n jet and n b category and a number from 0 up to 10 for each H T and L T selection. The multi-b and the 0-b analysis employ 39 and 28 search bins, respectively.

Background estimation
The method for estimating the background from SM processes is the same as the one presented in Ref. [13]. For completeness, a summary of the procedure is presented below.
The dominant backgrounds in all search bins arise from semileptonically decaying tt and leptonic W+jets events. In each search bin, the number of background events in the SR, i.e. the yield of events at high φ, is determined using the number of events in the CR, i.e. the events at low φ, along with a transfer factor R CS that relates the events observed in the CR,

Table 1
Overview of the definitions of the various regions and samples employed in the analysis. For the QCD fit the electron (e) sample is used, while for the determination (det.) of R CS (W ± ) the muon (μ) sample is used. Regions corresponding to blank cells are not used in the analysis.

Analysis
Multi-b analysis 0-b analysis This transfer factor is measured in kinematic regions in data with a lower number of jets, n jet , where the contribution from the signal is negligible. Potential residual differences in transfer factors in the low-and high-n jet regions are determined through simulation, where a correction factor, denoted by κ, is determined for each search bin as κ = R MC CS (high-n jet )/R MC CS (low-n jet ).
In the multi-b analysis, the regions with one b tag and four or five jets consist of approximately 80% tt+jets and 15-20% W+jets and single top quark events. In all other multi-b regions the tt background is dominant. For this reason, only one transfer factor is calculated in the CRs with four or five jets to account for all backgrounds except QCD for each L T , H T and n b range. This factor is then used to estimate the background in each SR of the search bins with n jet ∈ [6][7][8] or n jet ≥ 9. A single transfer factor is used for the n b ≥ 2 search bins with the same H T and L T , since these factors are found to be essentially independent of n b .
In the 0-b search bins, the contributions from W+jets and tt+jets are roughly equal, and a transfer factor for each background is determined in each of the search bins in n jet , H T , and L T . The transfer factor for tt+jets events is measured in data using events with n jet ∈ [4,5] and n b ≥ 1. For W+jets events, the transfer factor is measured also in data in events with n jet ∈ [3,4] and n b = 0; the jet multiplicity used for W+jets is lower than in tt+jets to limit the contamination from tt+jets events. The relative contribution of the tt+jets and W+jets components in the CR of each search bin is determined by a fit of the n b multiplicity distribution in the CR of the high-n jet regions, using templates of the n b multiplicity distributions for W+jets and tt+jets that are obtained from simulation. Additional backgrounds, including those from single top quark production, are found to be small and are taken from simulation.
About 10-15% of the SM background events in the electron channel CRs are expected to be QCD, and arise mainly from jets misidentified as electrons or from photon conversions in the tracker. In the SRs, however, the QCD background has been found to be negligible. It is estimated from data, using "antiselected" events in which the electrons fail the criteria for selected electrons but satisfy looser identification and isolation requirements. These events are scaled by the ratio of jets and photons that pass the tight electron-identification requirements to the number of antiselected electron candidates in a QCD-enriched sample that consists of no b-tagged jets and three or four jets. To account for the QCD background in the data, the QCD background is subtracted from the number of events in the CR in the calculation of the transfer factor R CS as well as from the number of events in the CR in each search bin. The prediction of the number of events in the SR of each search bin is then defined as: The various (n jet , n b ) regions employed in the analysis are described in Table 1.

Systematic uncertainties
The systematic uncertainties are divided into two categories: those that affect the estimate of the background from SM processes, and those that affect the expected signal yields.
The main systematic uncertainty on the background estimate arises from the uncertainty on the value of the transfer factor R CS . The latter is measured in low-n jet data but is then applied in the search bins that have higher jet multiplicities. The modeling of jets from initial-state radiation (ISR) is obtained from a data sample populated mainly by dilepton tt+jets events. This sample is defined by two opposite-sign leptons (electrons or muons), excluding events with same-flavor leptons within a window of ±10 GeV around the Z-boson mass, and two b-tagged jets, such that any other remaining jets are interpreted as ISR. In simulation, all jets that cannot be matched to daughter particles from the hard interaction are treated as ISR jets. The difference between the number of ISR jets observed and simulated is then used to reweigh simulated tt+jets events in all analysis selections. The reweighting factors vary between 0.92 and 0.51 for N ISR J between 1 and 6. We take one half of the deviation from unity as the systematic uncertainty on these reweighting factors.
The presence of two neutrinos in dilepton tt+jets events tends to produce larger angles between the lepton and the presumed W boson than in single-lepton tt+jets events. As a result, the fraction of dilepton tt+jets in which the second lepton does not pass the veto lepton requirements, is larger at high φ values, i.e. in the SR, than in the CR. This fraction as a function of n jet must be described well in the simulation, as the differences in the transfer factors between the low-n jet and high-n jet events, i.e. the κ factors, are determined in simulation. This assumption is tested using dilepton events, selected as described in the previous paragraph and split into a 0-b and a multi-b category. To study the behavior of the background from dilepton events that remain in the singlelepton selection because of the loss of one lepton, one of the two leptons is removed from the event. Since in this type of background, the lost leptons arise principally from τ → hadrons + ν decays, and to account for the p miss T due to the neutrino from the τ decay, the lepton removed is replaced by a jet with 2/3 of the p T of the original lepton and the L T , φ, and H T values are recalculated for the resulting "single-lepton" event. To maximize the number of events in the dilepton tt+jets control sample, no φ requirement is applied, and all events are used twice, with each reconstructed lepton considered as the lost lepton. The jet multiplicity in the single-lepton baseline selection (excluding the SR) is compared with that in the corresponding simulated event sample. In addition, the jet multiplicity in the dilepton tt+jets control sample in data is compared with the corresponding simulated event sample. From these two comparisons a double-ratio is formed. The remaining differences in the double-ratio, which are of the order of 3-6% per n jet bin, are corrected through the calculated κ factors, and propagated as a systematic uncertainty.
Uncertainties in the background estimate that also affect the signal arise from uncertainties in the jet energy scale (JES) [31], from uncertainties in the scale factors correcting the efficiencies and misidentification rate for b tagging [35], and from uncertainties in the reconstruction and identification efficiencies of leptons [62,63].
In each case, the systematic uncertainty in the background is estimated by changing the corresponding correction factors within their uncertainties. After each such change in the JES, the H T and p miss T in each event are recalculated. Similarly, the uncertainty arising from pileup is estimated by varying the inelastic cross section by its 5% uncertainty [64].
The W+jets and tt+jets cross sections are varied independently by 30% [65] to account for possible biases in the estimation of the background composition in terms of W+jets vs. tt+jets events, which changes slightly the value of κ. These changes have only a small impact on the 0-b analysis, where the relative fraction of the two processes is determined from a fit. In the multi-b analysis, the differences in the κ values of less than 3% are propagated to the background estimates. The ttV cross section is varied by 100%. The Table 2 Summary of systematic uncertainties in the total background estimates for the multi-b and for the 0-b analyses.

Source
Uncertainty   For the 0-b analysis, an additional systematic uncertainty is based on linear fits of R CS as a function of n jet that are found to describe the dependence within statistical uncertainties. A 50% cross section uncertainty is used for all backgrounds other than W+jets, tt+jets, ttV, and QCD.
For the signal, an uncertainty in ISR is applied using the approach described previously for the reweighting of the distribution of ISR jets in tt+jets as both, signal and tt+jets, rely on Mad-Graph5_amc@nlo for event generation. Half of the correction is used as an estimate of the uncertainty as is propagated to the signal acceptance. To gauge their impact, the factorization and renormalization scales are changed up and down by a factor of 2.
Finally, the luminosity is measured using the pixel cluster counting method [74], with the absolute luminosity obtained using Van der Meer scans. The resulting uncertainty is estimated to be 2.5% [75].
The impact of the systematic uncertainties on the estimate of the total background in the multi-b and 0-b analyses is summarized in Table 2. While systematic uncertainties are determined for each signal point, typical values for most signals are summarized for illustration in Table 3.  Table 4. Upper panel: the data are represented by black points with error bars, while the total SM background expected is shown as a hatched region that represents the uncertainty. For illustration, the relative fraction of the different SM background contributions determined in simulation is shown by the stacked, colored histograms, normalized so that their sum is equal to the background estimated using data control regions, as described in the text. The expected event yields for two T1tttt SUSY benchmark models are represented by the open histograms. Lower panel: the ratio of the number of events observed in data to the number of events expected from the SM background in each search bin. The error bars on the data points indicate the statistical uncertainty in the ratio, while the gray hatched region indicates the uncertainty on this ratio from the uncertainty in the background estimate.  Table 5. Upper panel: the data are represented by black points with error bars, while the total SM background expected is shown as a hatched region that represents the uncertainty. The filled, stacked histograms represent the predictions for tt+jets, W+jets events, and the remaining backgrounds. The expected yields from two T5qqqqWW SUSY benchmark models are represented as solid lines. Lower panel: the ratio of the number of events observed in data to the number of events expected from the SM background in each search bin. The error bars on the data points indicate the statistical uncertainty in the ratio, while the gray hatched region indicates the uncertainty on this ratio from the uncertainty in the background estimate.

Results and interpretation
The data in the search regions are compared to the background estimates in Fig. 3 for the multi-b events, where the outline of the filled histogram represents the total estimated number of background events. For illustration, the expected composition of the background is shown, assuming the relative fractions of the different SM processes (tt+jets, W+jets, and other backgrounds), as determinated from simulation. Fig. 4 displays the estimates and data observed in the 0-b events. The filled histogram represents the estimates from data for tt+jets and W+jets events and the remaining backgrounds, which include the QCD estimate determined from data and rare backgrounds determined from simulation.
To facilitate the reinterpretation of the results in terms of models not considered here, a comparison of the background estimates and the observed number of events in the SR of a few aggregated search bins is presented in Table 6. The results for all bins, compared to two benchmark points, are given in Tables 4 and 5 for the multi-b and 0-b analyses, respectively. The data agree with the expectations from the SM and no significant excess is observed.
The absence of any significant excess consistent with the SUSY signals considered in the analysis is used to set limits in the parameter space of the gluino and lightest neutralino masses. Separate likelihood functions, one for the multi-b analysis and one for the 0-b analysis, are constructed from the Poisson probability functions for the CR and SR at both high and low jet multiplicities.
This includes the κ values that correct any residual differences in Table 4 Definition of search bins and naming convention in the multi-b search. Also given are the φ values that are used to define the CRs and the SRs, the numbers of expected background events with combined statistical and systematic uncertainties, the observed numbers of events, and the expected numbers of signal events in the multi-b search bins. As discussed previously, the values of κ are obtained from simulation, and their uncertainties are incorporated in the likelihood through log-normal constraints. The estimated contribution from QCD events in the CR is also included. A possible signal contamination, which can be up to 10% for the shown benchmark points, is taken into account by including signal terms in the likelihood for both the low-n jet regions as well as for the lowφ CR of the search bins. For the 0-b analysis, the relative contributions from W+jets and tt+jets events determined in the fits to the n b distribution in the CR are treated as external measurements. The correlation between the W+jets and tt+jets production that is introduced by such fits is also taken into account. A "profile" likelihood ratio is used as test statistic. The limits at the 95% confidence level (CL) are calculated using the asymptotic formulae [76] of the CL s criterion [77,78]. The 95% CL upper limits on the cross sections, set in the T1tttt model using the multi-b analysis, and in the T5qqqqWW model using the 0-b analysis, are shown in Fig. 5. Using the g g pair production cross section calculated at NLO within NLL accuracy, exclusion limits are provided as a function of the (m g , m χ 0 1 ) mass hy-pothesis for the data and for the simulation. For neutralino masses below 800 GeV, gluino masses up to 1.8 TeV are excluded at the 95% CL in the T1tttt model. Neutralinos are excluded up to 1.1 TeV for gluino masses below 1.7 TeV. In the T5qqqqWW model, gluino masses up to 1.9 TeV are excluded at the 95% CL for neutralino masses below 300 GeV. Neutralinos are excluded up to 950 GeV for gluino masses below 1.2 TeV.

Summary
A search for supersymmetry has been performed using a 35.9 fb −1 sample of proton-proton collisions at √ s = 13 TeV, recorded by the CMS experiment in 2016. Several exclusive search bins are defined that differ in the number of jets, the number of b-tagged jets, the scalar sum of all jet transverse momenta as well as the scalar sum of the missing transverse momentum and the transverse momentum of the lepton. The main background processes, which arise from W+jets and tt+jets in a final state with exactly one lepton and multiple jets, is reduced significantly by requiring a large azimuthal angle between the direction of the lepton and of the reconstructed W boson, computed under the hypothesis Table 5 Definition of search bins and naming convention in the 0-b search. Also given are the φ values that are used to define the CRs and the SRs, the numbers of expected background events with combined statistical and systematic uncertainties, the observed numbers of events, and the expected numbers of signal events in the 0-b search bins.  Table 6 Numbers of expected background events with combined statistical and systematic uncertainty and the observed numbers of events in aggregated search bins. The expected number of signal events for the two corresponding benchmark signals for the multi-b and 0-b analyses, respectively, are given as well. that all of the missing transverse momentum in the event arises from a neutrino produced in the leptonic decay of the W boson. The event yields observed in data are in agreement with the standard model background, which is estimated using control regions in data and corrections based on simulation. The lack of any significant excess of events is interpreted in terms of limits on the parameters of two simplified models that describe gluino pair production.
For the T1tttt simplified model, in which each gluino decays to a tt pair and the lightest neutralino, gluino masses up to 1.8 TeV are excluded for neutralino masses below 800 GeV. Neutralino masses below 1.1 TeV are excluded for a gluino mass up to 1.7 TeV. This result extends the exclusion limit from the previous analysis [13] on gluino masses by about 250 GeV. The second simplified model, T5qqqqWW, also describes gluino pair production, but with decays to first-or second-generation quarks and a chargino, which decays to a W boson and the lightest neutralino. The chargino mass in this decay channel is assumed to be m χ ± 1 = 0.5(m g + m χ 0 1 ). Gluino masses below 1.9 TeV are excluded for neutralino masses below 300 GeV. This corresponds to an improvement of about 500 GeV over the previous result [13]. For a gluino mass of 1.2 TeV, neutralinos with masses up to 950 GeV are excluded.

Acknowledgements
We congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC and thank the technical and administrative staffs at CERN and at other CMS institutes for their contributions to the success of the CMS effort. In addition, we gratefully acknowledge the computing centers and personnel of the Worldwide LHC Computing Grid for delivering so effectively the computing infrastructure essential to our analyses.