Search for chargino-neutralino production in events with Higgs and W bosons using 137 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for electroweak production of supersymmetric (SUSY) particles in final states with one lepton, a Higgs boson decaying to a pair of bottom quarks, and large missing transverse momentum is presented. The search uses data from proton-proton collisions at a center-of-mass energy of 13 TeV collected using the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb$^{-1}$. The observed yields are consistent with backgrounds expected from the standard model. The results are interpreted in the context of a simplified SUSY model of chargino-neutralino production, with the chargino decaying to a W boson and the lightest SUSY particle (LSP) and the neutralino decaying to a Higgs boson and the LSP. Charginos and neutralinos with masses up to 820 GeV are excluded at 95% confidence level when the LSP mass is small, and LSPs with mass up to 350 GeV are excluded when the masses of the chargino and neutralino are approximately 700 GeV.


Introduction
Supersymmetry (SUSY) [1][2][3] is an appealing extension of the standard model (SM) that predicts the existence of a superpartner for every SM particle, with the same gauge quantum numbers but differing by one half unit of spin. SUSY allows addressing several shortcomings of the SM. For example, the superpartners can play an important role in stabilizing the mass of the Higgs boson (H) [4,5]. In R-parity conserving SUSY models, the lightest supersymmetric particle (LSP) is stable and therefore is a viable dark matter candidate [6].
The SUSY partners of the SM gauge bosons and the Higgs boson are known as winos (partners of the SU(2) L gauge fields), the bino (partner of the U(1) gauge field), and higgsinos. Neutralinos ( χ 0 ) and charginos ( χ ± ) are the corresponding mass eigenstates of the winos, bino and higgsinos. They do not carry color charge and are therefore produced only via electroweak interactions or in the decay of colored superpartners. Because of the smaller cross sections for electroweak processes, the masses of these particles are experimentally less constrained than the masses of colored SUSY particles. Depending on the mass spectrum, the neutralinos and charginos can have significant decay branching fractions to vector or scalar bosons. In particular, the decays via the W and the Higgs boson are expected to be significant if the χ ± 1 and χ 0 2 particles are wino-like, the χ 0 1 is bino-like, and the difference between their masses is larger than the Higgs boson mass, where the subscript 1(2) denotes the lightest (second lightest) neutralino or chargino, respectively. These considerations strongly motivate a search for the electroweak production of SUSY partners presented in this paper. This paper reports the results of a search for chargino-neutralino production with subsequent χ ± 1 → W ± χ 0 1 and χ 0 2 → H χ 0 1 decays, as shown in Fig. 1. The data analysis focuses on the final state with a charged lepton produced in the W boson decay, two jets reconstructed from the H → bb decay, and significant missing transverse momentum (p miss T ) resulting from the LSPs and the neutrino. This final state benefits from the large branching fraction for H → bb, 58%. The chargino and neutralino are assumed to be wino-like, and the χ 0 1 produced in their decays is assumed to be the stable LSP. As wino-like charginos χ ± 1 and neutralinos χ 0 2 would be nearly degenerate, this analysis considers a simplified model [7][8][9] with a single mass parameter for both the chargino and neutralino (m ). Results of searches in this final state were previously presented by ATLAS [10,11] and CMS [12][13][14] using data sets at center of mass energy 8 and 13 TeV.  Figure 1: Diagram for a simplified SUSY model with electroweak production of the lightest chargino χ ± 1 and next-to-lightest neutralino χ 0 2 . The χ ± 1 decays to a W boson and the lightest neutralino χ 0 1 . The χ 0 2 decays to a Higgs boson and a χ 0 1 . This analysis uses 13 TeV proton-proton (pp) collision data collected with the CMS detector during the 2016-2018 data-taking periods, corresponding to an integrated luminosity of 137 fb −1 .
Relative to the most recent result from the CMS Collaboration targeting this signature [12], the results significantly extend the sensitivity to the mass of the chargino and neutralino. The improved sensitivity is achieved through a nearly four-fold increase in the integrated luminosity, as well as from numerous improvements in the analysis, including the addition of a discriminant that identifies Higgs boson decays collimated into large-radius jets, regions that include additional jets from the initial-state radiation, and an expanded categorization in p miss T .
to normalize the MC samples of W+jets [34], and at NLO in QCD to normalize single top quark samples [35,36]. The tt samples are normalized to a cross section determined at NNLO in QCD that includes the resummation of the next-to-next-to-leading-logarithmic soft-gluon terms [37][38][39][40][41][42][43]. MC samples of other SM background processes are normalized to cross sections obtained from the MC event generators at either LO or NLO in QCD. Cross sections for winolike chargino-neutralino production are computed at approximate NLO plus next-to-leading logarithmic (NLL) precision. Other SUSY particles except for the LSP are assumed to be heavy and decoupled [44][45][46][47]. A SM-like H → bb branching fraction of 58.24% [48] is assumed.
Nominal distributions of additional pp collisions in the same or adjacent bunch crossings (pileup) are used in the generation of simulated samples. These samples are reweighted such that the number of interactions per bunch crossing matches the observation.

Event selection and search strategy
In order to search for the chargino-neutralino production mechanism shown in Fig. 1, the analysis targets decay modes of the W boson to leptons and the H to a bottom quark-antiquark pair. The analysis considers events with a single isolated electron or muon, two jets identified as originating from two bottom quarks, and large p miss T from the LSPs and the neutrino. The major backgrounds in this final state arise from SM processes containing top quarks and W bosons. These backgrounds are suppressed with the analysis strategy described below that uses physics objects summarized in Table 1, which are similar to those presented in Ref. [49].
Events are reconstructed using the particle-flow (PF) algorithm [50], which combines information from the CMS subdetectors to identify charged and neutral hadrons, photons, electrons, and muons, collectively referred to as PF candidates. These candidates are associated with reconstructed vertices, and the vertex with the largest sum of squared physics-object transverse momenta is taken to be the primary pp interaction vertex. The physics objects used for the primary vertex determination include a special collection of jets reconstructed by clustering only tracks associated to the vertex, and the magnitude of the associated missing transverse momentum. The missing transverse momentum in this case is defined as the negative vector sum of the transverse momentum (p T ) of the jets in this collection. In all other cases, the missing transverse momentum ( p miss T ) is taken as the negative vector sum of the p T of all PF candidates, excluding charged hadron candidates that do not originate from the primary vertex [51].
Electron candidates are reconstructed by combining clusters of energy deposits in the electromagnetic calorimeter with charged tracks [52]. The electron identification is performed using shower shape variables, track-cluster matching variables, and track quality variables. The selection on these variables is optimized to identify electrons from the decay of W and Z bosons while rejecting electron candidates originating from jets. To reject electrons originating from photon conversions inside the detector, electrons are required to have at most one missing measurement in the innermost tracker layers and to be incompatible with any conversionlike secondary vertices. Muon candidates are reconstructed by geometrically matching tracks from measurements in the muon system and tracker, and fitting them to form a global muon track. Muons are selected using the quality of the geometrical matching and the quality of the tracks [53].
Selected muons (electrons) are required to have p T > 25 (30) GeV, |η| < 2.1 (1.44), and be isolated. Events containing electrons with |η| > 1.44 have been found to exhibit an anomalous tail in the transverse mass distribution and are not included in the search. Lepton isolation is determined from the scalar p T sum (p sum T ) of PF candidates not associated with the lepton within a cone of p T -dependent radius starting at ∆R = (∆φ) 2 + (∆η) 2 = 0.2, where φ is the azimuthal angle in radians. This radius is reduced to ∆R = max(0.05, 10 GeV/p T ) for a lepton with p T > 50 GeV. Leptons are considered isolated if the scalar p T sum within this radius is less than 10% of the lepton p T . Additionally, leptons are required to have a scalar p T sum within a fixed radius of ∆R = 0.3 less than 5 GeV. Typical lepton selection efficiencies are approximately 85% for electrons and 95% for muons, depending on the p T and η of the lepton.
Events containing a second lepton passing a looser "veto lepton" selection, a τ passing a "veto tau" selection, or an isolated charged PF candidate are rejected. Hadronic τ decays are identified by a multi-variate analysis (MVA) isolation algorithm that selects both one-and threepronged topologies and allows for the presence of additional neutral pions [54,55]. These vetoes are designed to provide additional rejection against events containing two leptons, or a lepton and a hadronic τ decay.
Hadronic jets are reconstructed from neutral and charged PF candidates associated with the primary vertex, using the anti-k T clustering algorithm [56,57]. Two collections of jets are produced, with different values of the distance parameter R. Both collections of jets are corrected for contributions from event pileup and the effects of nonuniform detector response [58].
"Small-R" jets are reconstructed with a distance parameter R = 0.4, and aim to reconstruct jets arising from a single parton. Selected small-R jets have p T > 30 GeV, |η| < 2.4, and are separated from isolated leptons by ∆R > 0.4. Small-R jets that contain the decay of a b-flavored hadron are identified as bottom quark jets (b-tagged jets) using a deep neural network algorithm, DEEPCSV. The discriminator working point is chosen so that the misidentification rate to tag light-flavor or gluon jets is approximately 1-2%. This choice results in an efficiency to identify a bottom quark jet in the range 65-80% for jets with p T between 30 and 400 GeV, and an efficiency of 10-15% for jets originating from a charm quark. The b tagging efficiency in simulation is corrected using scale factors derived from comparisons of data with simulation in control samples [59].
When the p T of the Higgs boson is not too large compared to its mass, the b jets resulting from its decay to bottom quarks are spatially separated. As the Higgs boson p T increases, the separation between the b jets decreases. For the SUSY signal, this becomes important when the mass splitting between the neutralino χ 0 2 and the LSP is large. To improve the sensitivity to large χ 0 2 masses, a second collection of "large-R" jets is formed with distance parameter R = 0.8.
Selected large-R jets have p T > 250 GeV, |η| < 2.4, and are separated from isolated leptons by ∆R > 0.8. Large-R jets containing a candidate H → bb decay are identified as H-tagged jets using a dedicated deep neural network algorithm [60]. We use the mass-decorrelated version of the DEEPAK8 algorithm, which considers the properties of jet constituent particles and secondary vertices. The imposed requirement on the neural network score corresponds to a misidentification rate of approximately 2.5% for large-R jets with a p T of 500-700 GeV without an H → bb decay in multijet events. The efficiency to identify an H decay to bottom quarks is 60-80% depending on the p T of the large-R jet.
The p miss T is modified to account for corrections to the energy scale of the reconstructed jets in the event. Events with possible p miss T contributions from beam halo interactions or anomalous noise in the calorimeter are rejected using dedicated filters [61]. Additionally, during part of the 2018 data-taking period, two sectors of the endcap hadronic calorimeter experienced a power loss, affecting approximately 39 fb −1 of data. As the identification of both electrons and jets depends on correct energy fraction measurements, events from the affected data-taking periods containing an electron or a jet in the region −2.4 < η < −1.4 and −1.6 < φ < −0.8 are rejected. The total loss in signal efficiency considering all event filters is less than 1%.
Data events are selected using a logical "or" of triggers that require either the presence of an isolated electron or muon; or large p miss T and H miss T , where H miss T is the magnitude of the negative vector p T sum of all jets and leptons. The combined trigger efficiency, measured with an independent data sample of events with a large scalar p T sum of small-R jets, is greater than 99% for events with p miss T > 225 GeV and lepton p T > 20 GeV. The trigger requirements are summarized in Table 2. Table 3 defines the event preselection common to all signal regions, which requires exactly one isolated lepton, p miss T > 125 GeV, two or three small-R jets, and no isolated tracks or veto tau candidates.
Exactly two of the small-R jets must be b-tagged. The primary SM processes that contribute to the preselection region are tt, single top quark (mostly in the tW channel), and W+jets production.
The SM processes with one W boson that decays to leptons, originating primarily from semileptonic tt and W+jets, are suppressed by requiring the transverse mass, m T , to be greater than 150 GeV. m T is defined as where p T denotes the lepton p T and ∆φ is the azimuthal separation between p T and p miss T . After requiring a large m T , the dominant remaining background comes from processes with two W bosons that decay to leptons (including τ leptons), primarily tt and tW. To suppress Table 1: Summary of the requirements for the physics objects used in this analysis. veto track, and absolute isolation: ∆R = 0.3 Table 2: Summary of the triggers used to select the analysis data set. Events are selected using a logical "or" of the following triggers. these backgrounds, events with an additional veto lepton or a hadronic τ decay are rejected, as described above.
Additional background rejection is obtained using the cotransverse mass variable, m CT , which is defined as where p b 1 T and p b 2 T are the magnitudes of the transverse momenta of the two b-tagged jets and ∆φ bb is the azimuthal angle between the two b-tagged jets [62]. This variable has a kinematic endpoint close to 150 GeV for tt events when both b jets are correctly identified, while signal events tend to have higher values of m CT . Requiring m CT > 200 GeV is effective at reducing the dilepton tt and tW backgrounds. Table 3: Summary of the preselection requirements common to all signal regions. The N b is the multiplicity of b-tagged jets and p non-b T is the p T of the non-b-tagged jet.

Lepton
Single e or µ and no additional veto lepton, track or tau Events entering the signal regions must pass the preselection and satisfy the m T and m CT requirements above. We also require that the invariant mass of the pair of b-tagged jets, m bb , be between 90 and 150 GeV, consistent with the mass of an SM Higgs boson. In events with 3 small-R jets, the non-b-tagged jet must have p T < 300 GeV. This requirement rejects some tt events that survive the m CT and p miss T selections. These requirements define the baseline signal selection. Figure 2 shows the distributions of p miss T , m CT , m bb , m T , the number of small-R jets (N jets ), and the discriminator output of the H tagging algorithm in simulated signal and background samples. All preselection requirements specified in Table 3 are applied except the one on the plotted variable, illustrating the discrimination power of each variable.
Events passing the baseline signal selection are further categorized into signal regions according to N jets , the number of H-tagged large-R jets N H , and the value of p miss T . The twelve nonoverlapping signal regions are defined in Table 4.   Table 3 except for the one on the plotted variable. The shaded areas correspond to the statistical uncertainty of the simulated backgrounds. The dashed vertical lines indicate the thresholds used to define the signal regions. These indicators are not shown on the H tagging discriminator score distribution because the required values vary between 0.83 and 0.90, depending on the data-taking year.

Background estimation
There are two dominant background categories relevant for this search: top quark production and W boson production. The contributions of these backgrounds to the yields in the signal regions are estimated using observed yields in control regions (CRs) and transfer factors obtained from simulated samples. The transfer factors are validated in non-overlapping regions adjacent to the signal regions. The top quark backgrounds include tt pair production, single top quark production (tW), and a small contribution from ttW and ttZ production. These backgrounds dominate in the lower-p miss T search regions and are estimated from CRs in data using the method described in Section 5.1. In the high-p miss T regions, W boson production becomes the dominant background. The method described in Section 5.2 estimates the background arising from W+jets, WW, and WZ production using CRs in data. The remaining background arises from standard model WH production. This process contributes less than 5% of the total background in any of the search regions, and its yield is estimated from simulation. A 25% uncertainty in the cross section of this process is assigned, based on the uncertainty in the WH cross section measurement [63].

Top quark background
Events containing top quarks constitute the dominant background, particularly in bins with N jets = 3 or low p miss T . These events contain b jets and isolated leptons from W bosons, so they lead to similar final states as the signal. Owing to the high m T requirement, the majority of the top quark background stems from events with two leptonically decaying W bosons. In this case, one of the leptons either is not reconstructed, fails the identification requirements, is not isolated, or is outside of kinematic acceptance.
The tt background is further suppressed by the m CT requirement, which has an endpoint at approximately 150 GeV for tt events in the case when both daughter b jets are reconstructed and identified. The m CT value for tt events can exceed the cutoff for three reasons: (i) if there are mistagged light-flavor jets or extra b jets, (ii) if a b jet is reconstructed with excess p T because it overlaps with other objects, or (iii) because of excess b jet p T arising due to the finite jet energy resolution.
A control sample enriched in top quark events is obtained by inverting the m CT requirement. For each signal region (SR), we form a corresponding control region spanning a range of m CT from 100 to 200 GeV. These CRs are used to normalize the top quark background to data in a single-lepton, high-m T region in each bin of p miss T , N H , and N jets . In each CR, a transfer factor from MC simulation (R top ) is used to extrapolate the yield for the corresponding high-m CT signal regions. The top quark background estimate is then given by where the N top SR is the number of expected events in the SR, N obs. CR is the number of observed events in the CR, and R top are defined as The The contamination from other processes (primarily W boson production) in the low-m CT CRs is as low as 2% in the lower-p miss T regions, growing to 25% in the highest p miss T control region. This contamination is included in the denominator of R top as shown in Eq. (4). Additionally, to increase the expected yields in the CRs, two modifications to the CR definitions are made. First, for the CRs with an H-tagged large-R jet, the m CT lower bound is removed (for a total range of 0-200 GeV). Second, for CRs with p miss T > 300 GeV, the m bb window is expanded to 90-300 GeV.
The data yields, transfer factors, and the resulting top quark background predictions are summarized in Table 5. These predictions, combined with the other background estimates, are compared with the observed yields in Section 6. To assess the modeling of the top quark background, we conduct a validation test in a sideband requiring m bb > 150 GeV and the same m CT and m T requirements as the SR. The relative contributions from SM processes are similar in the sideband and the signal regions. The modeling of the top quark background in this region is also affected by the same sources of uncertainty, including the imperfect knowledge of the object efficiencies, jet energy scale and resolution, and the distribution of additional pileup interactions. An analogous background prediction is performed in this region, and the level of agreement observed is used to derive a systematic uncertainty in the R top factors.
The yields in the m bb > 150 GeV validation regions (VRs) are estimated using CRs defined with the same m T and m CT requirements as the CRs for the SR predictions: m T > 150 GeV, and m CT > 100 (0) GeV for N H = 0 (1). Two modifications are introduced to improve the statistical precision of the test: first, the N jets = 2 and N jets = 3 bins are combined; and second, all regions with p miss T > 300 GeV and p miss T > 400 GeV are combined. Additionally, to avoid overlap with the low-m CT control regions used to estimate the top quark background in the SR, the low-m CT regions used for the VR predictions in bins with p miss T > 300 GeV are restricted to m bb > 300 GeV.
A comparison of the R top factors obtained from data and simulation in the VRs is shown in Fig. 3. Good agreement is observed, and we assign the statistical uncertainties in the differences of the observed and simulated values as the systematic uncertainties in the corresponding R top factors. These uncertainties reflect the degree to which we can evaluate the modeling of R top factors in data. This validation approach has the advantage of probing both the known sources of uncertainty as well as any unknown sources that could affect the m CT extrapolation. The uncertainties derived from this test, together with those associated with the finite yields in the low-m CT CRs and the MC statistical precision form the complete set of uncertainties assigned to the top quark background prediction.
Additional cross-checks of the top quark background estimate are performed in a dilepton validation region and in a region with exactly one b jet. These studies are performed in all 12 bins of p miss T , N jets , and N H , and the results agree with those obtained from the studies performed in the m bb sideband. A second, independent estimate of the top quark background is performed following the "lost-lepton" method described in Ref. [49]. In this method, the contribution from top quark processes in each signal region is normalized using a corresponding control region requiring two leptons and all other signal region selections. The estimates obtained from the two methods are consistent. These additional cross-checks are not used quantitatively to determine uncertainties, but they build confidence in the modeling of the R top factors.

W boson background
Events arising from W boson production, mainly W+jets, WW, and WZ, are the second largest background in this search and are the dominant SM contribution in bins with high p miss T . Events from W+jets production satisfy the baseline selection when they contain true b jets originating from g → bb (associated W production with heavy-flavor jets, W+HF) or when light-flavor jets are misidentified as b jets (associated W production with light flavor jets, W+LF). Because of the low misidentification rate of light-flavor jets, more than 75% of the selected W+jets events contain at least one genuine b jet. The W+jets background is reduced by the m T > 150 GeV requirement. In absence of large mismeasurements of the p miss T , the W boson must be produced off-shell in order to satisfy this threshold.
The W boson background is normalized in a data control sample obtained by requiring the number of b-tagged jets (N b ) to be less or equal to 1 and the same m T , m CT , and m bb requirements as the signal regions. The N b = 0 region of this sample is used to normalize the W boson background while the N b = 1 region is used to constrain the contamination from top quark events. The two jets with the highest b tagging discriminator values are used to calculate m bb and m CT . The control sample is binned in N jets and p miss T following the definition of the signal regions and has a high purity of W boson events for N b = 0.
The contribution from processes involving top quarks, mostly single or pair production of top quarks, is up to 20% in some N b = 0 CRs. The contamination is estimated by fitting the N b distribution in each CR using templates of W+jets and top quark events obtained from simulation. The templates are extracted from simulated W boson and top quark samples, respectively. The number of W boson events in each CR, N W CR , is obtained by subtracting from the observed yield, N obs. CR , the contribution of top quark events N top CR . For the yield N top CR , a correction factor obtained from the fit, which is typically close to 1.1, is taken into account.
We define a transfer factor R W to extrapolate from each N b = 0 CR to the corresponding N b = 2 signal region. Simulated samples of W boson processes are used to calculate R W . Since there are very few events with an H-tagged large-R jet in the control samples, it is not feasible to form dedicated CRs with N H = 1. Instead, the control samples are inclusive in N H , and the extrapolation into N H = 0 and N H = 1 is handled by the R W factors. The predicted yield of the W boson background in each of the signal regions, N W SR , is therefore given by and R W is defined as The resulting predictions are shown in Table 6. Section 6 shows a comparison with the observed yields after combining with the other background estimates. To assess the modeling of heavy-flavor jets in the simulated W+HF samples, we perform a similar extrapolation in N b in a Drell-Yan (DY) validation sample assuming Z → . The large contribution from tt in the N b = 2 region is suppressed by requiring two opposite-charge, same-flavor leptons with an invariant mass compatible with a Z boson, |m( ) − m Z | < 5 GeV.
In the validation sample, the predicted and observed DY+HF yields agree within 20%. Based on this test, we vary the fraction of W+jets events with at least one generated b jet by 20% and assign the resulting variation of R W as a systematic uncertainty. We also study the distribution of N b in a low-m T control sample, obtained by selecting events with p miss T > 125 GeV, 50 < m T < 150 GeV, N jets = 2, and without a requirement on m bb . The top quark contribution in this region is largely suppressed by the m CT > 200 GeV requirement, yielding a sample with a W+HF purity of approximately 40% for N b = 2. Good agreement between data and simulation is observed in this region, as shown in Fig. 4.
Additional contributions to the uncertainty in the factor R W are evaluated. The difference of the W+HF fraction with respect to the one derived from the DY+HF validation test results in a systematic uncertainty of up to 16% in R W . Based on the latest measurements [64-66] and considering the delicate phase space requiring significant p miss T and N b = 2, the diboson production cross section is varied by 25%, yielding a maximum systematic uncertainty of 12%. The uncertainties from the measurement of the b tagging efficiency scale factors are propagated to the simulated W+jets and diboson events resulting in an uncertainty of up to 10% in R W . The simulated samples are reweighted according to the distribution of the true number of interactions per bunch crossing. The uncertainty in the total inelastic pp cross section results in uncertainties of 2-6% in R W . The uncertainty arising from the jet energy calibration [67] is assessed by shifting jet momenta in simulated samples up and down, and propagating the resulting changes to R W . Typical values for the systematic uncertainty from the jet energy scale range from 2-10%, reaching up to 20% for events with a boosted Higgs boson candidate.
The mistag rate of the H tagging algorithm for large-R jets that do not contain a true H is measured in a control sample obtained by requiring low-m T , N b = 2, and at least one large-R jet. Scale factors are measured and applied to simulation to correct for differences in the observed mistag rates. The uncertainty in the scale factors is dominated by the limited statistical precision of the control sample and results in a systematic uncertainty up to 14% in R W .
The renormalization (µ R ) and factorization (µ F ) scales are varied up and down by a factor of 2, omitting the combination of variations in opposite directions. The envelope of the variations reaches values up to 15% and is assigned as systematic uncertainty. The uncertainties resulting from variations of the PDF and the strong coupling α S are less than 2%. The systematic uncertainties in R W are summarized in Table 7.

Results and interpretation
The observed data yields and the expected yields from SM processes in the signal regions are summarized in Table 8. No significant disagreement is observed. A binned maximum likelihood fit for the SUSY signal strength, the yields of background events, and various nuisance parameters is performed. The likelihood function is built using Poisson probability functions for all signal regions, and log-normal or gamma function PDFs for all nuisance parameters.  , as well as small contributions from standard model WH production. The values shown are taken before the signal extraction fit to the observed yields in the signal regions is performed. The uncertainties include the statistical and systematic components. For each benchmark model column, the ordered pairs indicate the masses (in GeV) of the χ 0 2 / χ ± 1 and χ 0 1 , respectively. We next evaluate the experimental and theoretical uncertainties in the expected signal yield. Varying the lepton, b tagging, and H tagging efficiency scale factors by their respective uncertainties varies the signal yield by less than 1, 4, and 20%. For the H tagger, this scale factor is measured as a function of the H candidate p T using a sample of jets in data and simulation that mimic the rare H → bb case [60].  The efficiencies obtained using the fast or full detector simulation are found to be compatible, with no significant dependence on the mass splitting ∆m = m . The systematic uncertainty in the signal yields, due to the uncertainty in the trigger efficiency measurement, is generally less than 5%.
The uncertainties in the simulated yields obtained by varying the jet energy scale and the jet energy resolution are each between 1 and 7%. A 3% difference in the b jet energy scale between the fast and full detector simulations is observed, resulting in a 1-10% change in the expected signal yield.
The effect of missing higher-order corrections on the signal acceptance is estimated by varying µ R and µ F [68-70] up and down by a factor of 2, omitting the combination of variations in opposite directions. The envelope of the variations reaches values up to 15% and is assigned as a systematic uncertainty. The resulting variation of the expected signal yield is less than 1%. To account for uncertainty in the modeling of the multiplicity of additional jets from initial state radiation, a 1% uncertainty is applied to the N jets = 3 signal regions.
The integrated luminosities of the 2016, 2017, and 2018 data-taking periods are individually known with uncertainties in the 2.3-2.5% range [71][72][73], while the total Run 2 (2016-2018) integrated luminosity has an uncertainty of 1.8%, the improvement in precision reflecting the (uncorrelated) time evolution of some systematic effects. The signal samples are reweighted according to the distribution of the true number of interactions per bunch crossing. The uncertainty in the total inelastic pp cross section leads to changes in the expected signal yield of less than 2%. A summary of the systematic uncertainties in the signal yields is given in Table 9.
The results are interpreted in the context of the simplified SUSY model shown in Fig. 1. The chargino and second-lightest neutralino are assumed to have the same mass, and the branching fractions for the decays shown are taken to be 100%. Wino-like cross sections are assumed. Cross section limits as a function of the masses of the produced particles are set using a modified frequentist approach at 95% confidence level (CL), with the CL s criterion and an asymptotic formulation [74][75][76]. All signal regions are considered simultaneously and correlations among uncertainties are included. plane for chargino-neutralino production. The effect of the uncertainty in the total production cross section due to the PDF model and the renormalization and refactorization scales is considered separately from the experimental uncertainties on the acceptance [47], and is shown as the uncertainty band on the observed exclusion limits.
This analysis excludes charginos with mass below 820 GeV for a low-mass LSP, and values of the LSP mass up to approximately 350 GeV for a chargino mass near 700 GeV. The excluded cross section for models with large mass splitting reaches approximately 5 fb.

Summary
This paper presents the results of a search for chargino-neutralino production in a final state containing a W boson decaying to leptons, a Higgs boson decaying to a bottom quarkantiquark pair, and missing transverse momentum. Expected yields from standard model processes are estimated by extrapolating the yields observed in control regions using transfer factors obtained from simulation. The observed yields agree with those expected from the standard model. The results are interpreted as an exclusion of a simplified model of charginoneutralino production. In the simplified model, the chargino decays to a W boson and a lightest supersymmetric particle (LSP), and the next-to-lightest neutralino decays to a Higgs boson and an LSP. Charginos with mass below 820 GeV are excluded at 95% confidence level for an LSP with mass below 200 GeV, and values of LSP mass up to approximately 350 GeV are excluded for a chargino mass near 700 GeV.
Relative to the previous result from the CMS Collaboration targeting this signature [12], the sensitivity of the search has been significantly extended. The constraints on the masses of the chargino and LSP exceed those from the previous analysis by nearly 350 and 250 GeV, respectively. This represents a factor of 14 reduction in the excluded cross section for models with large mass splittings. Roughly half of this improvement is the result of the four-fold increase in integrated luminosity, with the remainder coming from analysis optimizations such as the inclusion of the H tagger and events with N jets = 3, as well as finer categorization of events based on p miss T made possible by the increased size of the data set.
acknowledge the computing centers and personnel of the Worldwide LHC Computing Grid and other centers for delivering so effectively the computing infrastructure essential to our analyses. Finally, we acknowledge the enduring support for the construction and operation of the LHC, the CMS detector, and the supporting computing infrastructure provided by the following funding agencies:  [10] ATLAS Collaboration, "Search for direct production of electroweakinos in final states with one lepton, missing transverse momentum and a Higgs boson decaying into two b-jets in pp collisions √ s = 13 TeV with the ATLAS detector", Eur. Phys. J. C 80 (2020) 691, doi:10.1140/epjc/s10052-020-8050-3, arXiv:1909.09226.