Probing compressed mass spectra in electroweak supersymmetry with Recursive Jigsaw Reconstruction

The lack of evidence for the production of colored supersymmetric particles at the LHC has increased interest in searches for superpartners of the electroweak SM gauge bosons, namely the neutralinos and charginos. These are challenging due to the weak nature of the production process, and the existing discovery reach has significant gaps in due to the difficulty of separating the supersymmetric signal from SM diboson events that produce similar final states and kinematics. We apply the Recursive Jigsaw Reconstruction technique to study final states enriched in charged leptons and missing transverse momentum, focusing on compressed topologies with direct production of charginos and neutralinos decaying to the lightest neutral supersymmetric particle through the emission of W and Z bosons. After presenting prototype analysis designs for future LHC runs, we demonstrate that its detectors have the potential to probe a significant amount of unexplored parameter space for chargino-neutralino associated production within the next few years, and show that the very challenging successful search for chargino pair production with compressed spectra might be possible by the end of the LHC lifetime.

degrees of freedom, when weakly interacting particles are present, and combinatoric challenges, due to the presence of indistinguishable visible particles from a detector prospective. The result is an estimate of the relevant reference frames and, hence, the definition of a complete basis of kinematic variables. These observables are sensitive to the masses and decay angles of the resonances appearing in the chosen tree, and can be used to distinguish signatures of new physics from the SM background.
In RJR involving compressed scenarios, the simplified decay tree shown in figure 1 is used for analyzing topologies with initial state radiation. A transverse view of the event is considered, namely all the z-momenta of the visible objects are set to zero.
We follow the procedure outlined in [21]. The estimate for the center-of-mass system of the whole reaction, SUSY + ISR, is labeled by CM; ISR is the system assigned to the radiation from the initial state, S is the signal or sparticle system decaying to visible and invisible products: the V and I systems. In each event, the missing transverse momentum is assigned to the I-system, while a jigsaw rule specifies the reconstructed objects hypothesized to come from the decay of sparticles, and assigned to the V-system, with respect to those associated with ISR. Jigsaw rules are implemented using the RestFrames software package [22].
Topology independent observables include: : variable sensitive to the mass ratio between LSP and parent superparticle.
• p CM ISR,T : magnitude of the vector-sum of the jets transverse momenta of the ISR-system evaluated in the CM frame.
• ∆φ ISR,I : transverse opening angle between the ISR-system and the I-system, evaluated in the CM frame.

JHEP05(2018)058
In final states with two LSPs and no other weakly interacting particles, the observable R ISR can be written in the laboratory frame as This approximation is valid for the extremely compressed scenarios, hence in the limit of a low-momentum of the LSP in the parent superparticle rest frame (pP χ 0 1 ) with respect to the parent superparticle mass (MP ). In eq. (2.1), mPP is the true mass of the S-system and sin Ω is a quantity which is zero on average. The observable scales with the mass ratio mPP . When visible decay objects are not reconstructed in the V-system, or additional neutrinos in the final state contribute to the missing transverse momentum, R ISR is expected to assume values between the mass ratio and unity, while the last term in eq. (2.1) decreases.

Compressed electroweakino production in leptonic channels
Simulated Monte Carlo (MC) samples of Standard Model backgrounds and SUSY signals are used to study distributions of the performance of the RJR observables. The SM background processes expected to be the largest contributions have been generated elsewhere [23]. These samples are proton-proton collisions at √ s = 14 TeV generated with MadGraph 5 [24]. The parton shower and hadronization is performed with Pythia 6 [25] followed by a detailed detector simulation with Delphes 3 [26]. The parameterization incorporates the performance of the existing ATLAS [27] and CMS [28] experiments. Jets are reconstructed by the anti-k T clustering algorithm [29] with R = 0.5 and p min T = 20 GeV, implemented with the FastJet [30] package. The simulation procedure involves generation of events at leading order in bins of the scalar sum of the generator level particles transverse momenta, with jet-parton matching and corrections for next-to-leading order (NLO) contributions [31].
The same procedure and parametrization are used to generate the signal samples. The topologies considered are associated chargino-neutralino production and chargino pair production assuming degenerate masses, Mχ± The cross sections for pure wino chargino pair production and chargino-neutralino associated production at √ s = 13 TeV at NLL can be found elsewhere [32,33], with relative uncertainties in the range 4.5% ∆σ 9% for the masses investigated. We estimate the NLL cross sections at √ s = 14 TeV, evaluating the NLO cross sections for the wino-like electroweakino pair production at 13 and 14 TeV with MadGraph, and assuming the same NLL/NLO k-factors for the corrections. The resulting NLL cross sections are shown in figure 2a and used as inputs for the analysis of the simplified supersymmetric topologies. This procedure provides small corrections ( 5%) from the k-factors, and it is a check for  Figure 2. Estimated NLL cross sections for pure wino chargino pair production (blue curve) and chargino-neutralino associated production (red curve) at √ s = 14 TeV (a). Feynman diagrams for electroweakino productions in final states with missing transverse momentum and three charged leptons (b) and two charged leptons (c). the matched MadGraph cross sections and their potential dependences on the cutoff scales chosen.
The focus of this work is on the leptonic decay channels of off-shell W and Z bosons, as depicted in the Feynman diagrams in figure 2b and figure 2c. Leptonic final states from charmonium and bottomonium are expected to be negligible in the phase space probed.
Focusing on electrons and muons as visible decay products provides several advantages. Firstly, the signal-to-background ratio increases progressively with lepton multiplicity in the final state. Secondly, the channels result in clean final states with high efficiencies for the lepton reconstruction. Although the minimum value for reconstructed lepton p T of 10 GeV is assumed in this study, recent work by the CMS collaboration has demonstrated improvements in the efficiency of identification of soft isolated electrons and muons (down to ∼ 3-4 GeV) [34], where dedicated triggers are described.
Moreover, for our purposes, all the leptons are identifiable as reconstructed objects produced via sparticle decays and assigned to the V-system, while all the jets can be assigned to the ISR-system with no ambiguity. A minimal value of the transverse momentum of the ISR-system, in concert with E T , can elicit an increase in the transverse momenta of the decay products of the SUSY system. For compressed scenarios, the lack of combinatoric ambiguity allows us to leverage the RJR technique without requiring a restrictive event selection based on a huge value of the ISR transverse momentum.
The two phenomenological studies, treated separately, are presented in the next two sections emphasizing the role of the RJR observables for discriminating compressed electroweakino signals with respect to the individual SM processes. In appendices B and C two examples of cut-flows are shown in table 3 and figure 16, and table 4 and figure 17 respectively, for the overall SM background and two benchmark signal samples.  Mχ0 1 = 15, 25, 35, 50 and 75 GeV. Event-by-event a basis of RJR variables is extracted and analyzed to probe compressed spectra for a projection of L dt = 300 fb −1 . To the previous variables, additional transverse observables for this study include: • M V T is the transverse mass of the V-system.
• M + − is the transverse mass of the two same flavor opposite sign leptons in final states where the third lepton has different flavor (corresponding to M T, e + e − , when the third lepton is a muon, and M T, µ + µ − , when the third lepton is an electron).
• ∆φ CM,I is the transverse opening angle between the CM-system and the I-system.
Three leptons (electrons and muons) are required in the final state with p T > 10 GeV, while at least one jet, with p T > 20 GeV, is associated with the ISR-system. A minimal value for the missing transverse momentum, E T > 50 GeV, is the last preselection requirement. Figure 3 shows the distributions of R ISR and p CM ISR,T after preselection criteria are imposed. All of the relevant Standard Model backgrounds are stacked together and categorized into five groups. The dominant contributions are associated W Z production and tt processes with an additional vector boson. The overlaid dashed curves refer to four chargino-neutralino production samples with different masses and mass splittings.
The observable R ISR provides a remarkable signal-to-background discrimination in the absence of more stringent selection criteria as shown in figure 3a. The assignment of the different objects in the compressed tree is performed with no ambiguity, and it is not necessary to focus on the high ISR regime in order to improve the observable resolution for the signal samples. Notice that R ISR can assume larger values than unity when some objects are forced in the V-system. The observable is expected to be peaked for values beyond Mχ/MP due to the additional contribution to E T , deriving from one or more neutrinos. Values larger than the mass ratio will be considered for the definition of the R ISR requirements together with R ISR < 1.   Figure 3b shows the distribution of p CM ISR,T . The mass scales for the signal and background samples are similar, and the variable has limited impact. In the absence of other requirements, the slope of the signal distributions is paradoxically more severe than the background one, since events with non-radiative jets forced into the ISR-system. A minimal requirement on p CM ISR,T is essential to exploit the RJR technique with multi-lepton final states. The requirement applied to this variable, the only large-scale observable in this study together with E T , will be moderately tighter for the largest mass splittings probed since the criterion on R ISR is relaxed.
It is interesting to note that the number of events passing the preselection criteria is smaller for the signal sample with Mχ± GeV. There has been a conservative minimal choice of transverse momentum for electrons and muons of 10 GeV and, consequently, when the mass splitting approaches a much more compressed regime, the kinematics are such that one of the three leptons is less likely to satisfy this transverse momentum constraint. In order to probe the extreme compressed regime (∆M < 15 GeV), a parametrization of the efficiency in the reconstruction of soft electrons and muons (p T 10 GeV) must be implemented. This is considered beyond the scope of this paper, due to the difficulty of getting these details correct outside of an experimental collaboration. Figure 4 shows the two-dimensional distributions of M V T as a function of R ISR for the dominant Standard Model background and two representative signal samples for events passing the preselection criteria, and after applying a veto for jets tagged as being initiated by a b-quark (N ISR b-jet = 0). The final state signal events populate low values of M V T with a complementarity with high values of R ISR . Vice versa, for the diboson background, simultaneous low values of M V T and R ISR close to one are disfavored, as shown in figure 4a. Using the two RJR observables in concert provides an increasingly powerful discrimination the smaller the absolute and relative mass splitting of the signal sample. In the low M V T regime (M V T < 100 GeV), and for values of the ratio close to unity (R ISR > 0.6), additional handles to decrease the SM background yield are provided by the compressedtransverse RJR angles and M + − . Figure   Selection criteria applied on the compressed RJR observables, as shown in table 1, can be used to define signal regions for probing chargino-neutralino associated pair production in final states with three leptons and missing transverse momentum. One or more additional jets are assumed to be radiated from the initial state, and a minimal requirement on p CM ISR,T (and E T ) allows us to focus on the final states of interest and probe the compressed spectra. The signal regions target five particular mass splittings. A special treatment is assumed for the selection criteria applied to R ISR , since this observable is related to the mass ratio, Mχ/MP , rather than the absolute value of the mass splitting.
For the largest mass differences (∆M = 50, 75 GeV), tighter selection criteria are used for the only large-scale variables (p CM ISR,T and E T ), the jet multiplicity and ∆φ CM,I , since the R ISR requirement is relaxed. An upper bound is imposed for M V T , progressively more stringent to the decrease of ∆M ; while for M + − , the maximum required coincides with the mass splitting itself. In final states with three electrons or three muons, only the M V T requirement is applied; while for events with two same and one different flavor leptons, the selection on M + − is imposed together with M V T <100 GeV. The selection criteria applied to the observable R ISR are progressively more stringent the closer the mass ratio to unity, and the values are separated by 0.05, which provides a moderate optimization. Figure 6 shows the distributions of ∆φ CM,I and M V T applying respectively the N-1 requirements in column 2 and 3 of table 1; namely all the selection criteria except for the one imposed on the observable plotted.
The signal regions expressed by the selection criteria of the RJR observables defined in table 1 are applied to calculate projected sensitivities for compressed spectra signal samples. Figures 7 shows the value of Z Bi , calculated assuming the metric [35], at √ s = 14 TeV for an integrated luminosity of 300 fb −1 . A systematic uncertainty of 20% is assumed constant in the SUSY phase space, with the dominant contribution to the background arising from associated WZ production.
The signal yields in the extreme compressed scenarios can benefit from an improvement in the efficiencies of the detector in the reconstruction of low-momentum leptons, which Object multiplicity 3 Leptons (e and µ) with p lep T > 10 GeV, selection criteria At least one jet, p jet T > 20 GeV,  Table 1. A loosely optimized set of selection criteria for signal regions in the analysis of chargino neutralino production in trilepton final states.   is outside the scope of this work. On the other hand, the significances decrease for mass differences close to the W pole mass, due to the difficulty to discriminate background events derived from topologies with absolute and relative mass scales very close to the signal ones.
The value ∆M =15 GeV must not be considered as a threshold: the minimum mass difference achievable with any technique is strongly related to the efficiencies for the detector to reconstruct low-momentum leptons. For extremely compressed scenarios, a similar analysis could be used to probe the same final state topologies with only two low-momentum leptons reconstructed. Although the background would differ in that case, one could require two same-sign leptons to suppress the SM yield.
The highest impact of the compressed RJR observables is for the samples of mass splittings in the range 20-40 GeV, a challenging phase space for SUSY searches [36]. For an integrated luminosity of 300 fb −1 , degenerate charginos and neutralinos would be discovered with masses Mχ± 1 = Mχ0 2 > 150 GeV, for a large portion of the samples investigated, and excluded up to 300 GeV for the best scenarios.
Overall, one can improve the performance of the RJR technique by adopting a strategy based not only on transverse observables, exploiting a three-dimensional reconstruction, as in the following study.  Figure 8. The decay tree for the analysis of compressed chargino pair production in events with ISR. The substructure of the S system is specified: each chargino decays to a visible (lepton) and an invisible (neutrino + LSP) object. The lepton multiplicity of the final state determines the main contributions of the Standard Model processes. In the absence of hadronic jets, the dileptonic channel of a pair of W bosons, constitutes the dominant process, producing a final state with two opposite sign leptons and missing transverse momentum. Searches for chargino pair production in a final state with two leptons are challenging for open mass spectra due to the W + W − irreducible background, while other contributions are often negligible. In the compressed regime, the difficulty is exacerbated by the low momenta of invisible and visible objects and by the subsequent kinematics. Moreover, requiring a transverse momentum for the ISRsystem introduces an additional complication for the analysis in the compressed regime: Standard Model backgrounds other than W W will contribute quite significantly.
In order to improve the signal-to-background discrimination, the simplified version of the compressed RJR tree in figure 1 is enriched specifying the substructure of the S-system. This is feasible for the dilepton final state, since the provenance of the reconstructed visible sparticle decay products is unambiguous. These decay products can then be assigned to the appropriate position in the tree.
The RJR decay tree is shown in figure 8. Electrons and muons are associated with the + and − systems, depending on the electric charge, while the jets are assigned to the ISR-system. The S-system frame is the approximation for the center-of-mass of the two charginos, and each one decays to a lepton and an invisible system. Each invisible system collects theχ 0 1 + ν contribution of the hemisphere a or b. In this approach, a three-dimensional view of the event is considered, and jigsaw rules are applied for reconstructing the topology and the relevant frames of reference. In the overall center-of-mass frame, the ISR and S systems are back-to-back. A Lorentz invariant jigsaw rule is assumed for the estimate of the mass of the invisible objects, while the rapidity

JHEP05(2018)058
is assigned as to the chargino center-of-mass (equal to the rapidity of the visible objects in the S-system). Finally, a contra-boost invariant jigsaw rule partitions the remaining unknown degrees of freedom associated with I a and I b . More information can be found elsewhere [37,38].
The useful transverse variables of the simplified tree can be computed along with additional experimental observables. Having in mind the simplified tree in figure 1, one can reconstruct the I-system, corresponding to the sum of the two invisible systems, I = I a + I b , and V, as the sum of the two lepton systems, V = + + − , and hence compute the transverse observables: R ISR , p CM ISR,T and ∆φ ISR,I . Three-dimensional scale-sensitive variables and additional angular observables include: • M V is the mass associated with the V-system: invariant mass of ( + + − ).
• Mχ ± is the mass associated with the chargino system.
• ∆φ + ,I (∆φ − ,I ) is the polar angle between the positive (negative) charge lepton and E T , computed in the Lab frame.
• ∆φ CM,I is the opening angle between the CM-system and the I-system.
• cos θ ≡β CM S · p S I,T is the dot product between the direction of the boost from CM to the reconstructed S-frame and the transverse momentum of the I-system in the S-frame.
Finally, jet multiplicities are considered. For the signal samples, the mass-observable associated with the chargino system, Mχ + = Mχ − , do not reproduce the actual chargino mass since the true LSPs are massive. The I a,b systems, assumed massless by RJR, are simplifications of the lightest neutralino plus neutrino contribution in each hemisphere.
The dominant SM backgrounds are categorized into four groups: 1) Vector boson + jets, mainly populated by Z → + − + jets; 2) Production of at least one top quark (t+X), with single-top and dileptonic tt both contributing; 3) Irreducible diboson processes mostly arising from W + W − with two leptons and missing transverse momentum; and 4) Contributions such as vector boson fusion, tri-boson, and gluon fusion plus jets with H → W + W − , are categorized as "others".
Two leptons (electrons and muons), with p T > 10 GeV, are required in the final state and at least one jet, with p T > 20 GeV, which is assigned to the ISR-system. Figure 9 shows the distribution of the invariant mass of the two leptons for same and different flavor, assuming a minimal value for the missing transverse momentum E T > 20 GeV. Standard Model background samples are stacked together, while the overlaid dashed curves refer to chargino pair production samples with different masses and mass splittings. Notice the peak around 90 GeV for same flavor leptons, due to the Standard Model backgrounds containing Z bosons produced in association with jets (in blue), with a moderate contribution from W Z (in green), and vector boson fusion and tri-boson (in red). In the compressed regime, the final state events for all the signal distributions tend to populate lower values of M V , and the requirement M V < 70 GeV, or tighter, will be used to specify the signal regions. Notice the additional peak for low values of M V , arising from Z+ jets and vector boson fusion contributions, resulting in a comparable number of events for the cases with two leptons with same or different flavor. The dominant process that contributes in this region is Z → τ + τ − → + − νννν, and sub-dominant contributions arise from Drell-Yan processes with missing transverse momentum (Z * (γ * ) → τ + τ − ), or W boson production decaying leptonically, with an additional lepton faked by a jet or a photon. For the dileptonic decay of the Z boson via taus, the value for M V is reconstructed to be below the Z mass, representing a challenge to the analysis in search of compressed charginos.
Herein, we consider the preselection criteria as follows: final states with two leptons and at least one light jet. A veto is applied for the jets tagged as b, τ and fat: N ISR b-jet = 0, N ISR τ -jet = 0 and N ISR fat = 0. 1 A minimal value for the missing transverse momentum ( E T > 50 GeV) in concert with p CM ISR,T > 50 GeV is imposed. In addition, preselection includes the criterion M V < 70 GeV. This last requirement excludes a large portion of the Standard Model background events, in particular tt and multi-bosons processes, independently of the flavor of the two leptons reconstructed. Standard Model processes involving a meson decaying in two same flavor leptons are expected with a small value of the invariant mass ( 10 GeV); notably, signal sample events tend to assume larger values.
In the following, the impact of the main RJR observables in reducing the specific Standard Model contributions is presented. Selection criteria will be imposed progressively on the observables sensitive to probe compressed chargino pair mass spectra, with distributions shown in appendix A.
Numerous Standard Model processes result in a low value of M V , in particular, the boson plus jets contribution. The focus is on the process Z → τ + τ − → + − νννν plus jets. For such events, the role of the chargino system in figure 8 is assumed by the tau's leptonic decay, while the I systems reconstruct the information of the two neutrinos in each hemisphere. The kinematics of these background events is such that Mχ ± is a reconstruction of the mass of the lepton and two neutrinos resulting from the τ decays. 1 In this work a fat jet is defined with M > 60 GeV and is a candidate for boosted SM Higgs, vector bosons and top-quark decaying hadronically.

JHEP05(2018)058
The first two plots in figure 12 show the two-dimensional distributions between Mχ ± and the ratio R ISR for the boson plus jets backgrounds and the signal sample Mχ± 1 = 200 GeV and Mχ0 1 = 150 GeV, figure 12c shows the distribution of Mχ ± for the five signal samples and for the on-shell/off-shell boson plus jets backgrounds. The lower bound Mχ ± > 24 GeV is required to suppress the V+jets background. With this requirement the SM background is dominated by top processes, specifically a pair of (on-or off-shell) top quarks in the dileptonic channel. Figure 13 shows the distribution of the light jet multiplicity as a function of the ratio.
In order to attenuate the tt contribution, we demand only one jet in the final state. Despite the requirement of N ISR jet = 1, and vetoing on jets coming from the fragmentation of bottoms, the tt background is still not suppressed. Although the requirement N ISR fat = 0 attenuates the contribution with the two jets reconstructed in similar directions, one of the two jets could be outside the geometrical acceptance, mismeasured, or of too low momentum to be reconstructed. Also if these events are relatively rare, their contribution is not negligible due to their high cross section, σ pp→tt ∼ O(10 3 pb), at 14 TeV LHC collisions. Figure 14a shows the distribution of ∆φ + ,I for the signal samples and the t + X backgrounds, categorized in four sub-processes and stacked together. The events from the top pair contributions tend to populate value close to π, while signal-like events populate low values. Figures 14b and 14c show the two-dimensional distribution ∆φ + ,I vs. ∆φ − ,I for the tt background and the signal sample Mχ± 1 = 200 GeV and Mχ0 1 = 150 GeV, assuming the same selection criteria, and requiring R ISR > 0.6. The requirements select background events with kinematics similar to the signal events, and in particular, a simultaneously large value of ∆φ ± ,I is disfavored.
Such events contain predominantly two top quarks produced with low transverse momenta resulting in final states with two reconstructed leptons and one jet not properly tagged. In the transverse plane, one of the two leptons is expected to fly close to the reconstructed jet (associated with the ISR-system), while the other is expected to be closer to the invisible system. Consequently, background events tend to assume larger values of ∆φ + ,I + ∆φ − ,I than signal events. A similar two-dimensional distribution as in figure 14c is demonstrated by all signal samples studied. A unique light jet associated with the ISR-system together with ∆φ + ,I + ∆φ − ,I < 2 dramatically reduce the t+X background.
Applying these selection criteria, the dominant Standard Model contribution is the irreducible diboson background: W + W − . The goal is to distinguish between signal and background events with similar event topologies and kinematics, in particular when selection criteria close to the final configuration are imposed. The key difference to exploit is that of the I-system (I a + I b ) for the W + W − background composed of two neutrinos. For signal events, on the contrary, a minimum of four weakly interacting particles comprises the invisible system. Figure 15 shows the angular observables sensitive to the composition of the I-system and used to separate events resulting from compressed chargino samples with respect to W W events. Figure 15a shows the distribution of ∆φ ISR,I . Signal events tend to populate values closer to π, as the mass difference ∆M = MP −Mχ is reduced. Figure 15b Table 2. Selection criteria for signal regions in the analysis of chargino pair production in final states with two leptons and missing transverse energy.
distribution of the angle between the CM-system and I-system, where in this case signal events are towards zero, almost independently of ∆M or MP /Mχ. The distribution of cos θ ≡β CM S · p S I,T is shown in figure 15c. Selection criteria defined with the compressed RJR observables result in signal regions used to investigate chargino pair production in final states with two leptons and missing transverse momentum. The requirements for the observable R ISR are tuned depending on the mass ratio, and are more stringent than the chargino-neutralino associated study, due to the larger multiplicity of weakly interacting particles in the final state. Figure 10 shows the distributions of R ISR and Mχ ± for SM background and signal sample events passing the selection criteria in table 2. For the lowest mass splitting the requirement R ISR > 0.85 is applied only for the sample Mχ± 1 = 100 GeV, while for ∆M = 25 GeV, one demands this criterion for three samples (Mχ± 1 ≤ 150 GeV). The signal regions expressed by the selection criteria of the RJR observables defined in table 2 are applied to calculate projected sensitivities for compressed spectra signal samples. Figure 11 shows the value of Z Bi , the binomial score representing the significance of a given signal, expressed in standard deviations, in the presence of a background hypothesis, at √ s = 14 TeV for an integrated luminosity of 3000 fb −1 . One considers a systematic uncertainty of 20% for the overall Standard Model background: a compromise between a large data sample projection and stringent selection criteria assumed to suppress the individual background yields. Exploiting the RJR technique, one can set limits for the compressed chargino pair production topology at the high luminosity LHC14, with masses ∼ 150 GeV being excluded in the best scenarios.

Conclusions
We have introduced an original approach to searches for compressed electroweakinos based on the imposition of the decay trees as in figures 1 and 8 for the interpretation of reconstructed events, using the Recursive Jigsaw Reconstruction technique.
Putative wino-likeχ ± 1 andχ 0 2 could be discovered at the LHC14 with masses Mχ± narios in the compressed regime. A strategy based on several experimental observables has been used to reduce the W + W − and the other main background yields due to the necessity of requiring jets in the final state to be associated with the ISR-system. A potential 95% confidence level exclusion limit can be obtained for an assumed dataset of 3 ab −1 , assuming a 20% of systematic uncertainty, for sample spectra with ∆M 50 GeV.
For both the topologies, the signal yields in the extreme compressed scenarios can benefit from an improvement in the efficiencies of the detector in the reconstruction of low transverse momentum leptons (< 10 GeV). On the other hand, for large mass splittings (∆M M Z ), the bulk analysis should be preferred to a compressed investigation, while for intermediate scenarios (50 GeV ∆M M Z ), one can exploit the complementarity of observables based on a reconstruction of the event with or without the ISR-system and include cases with vector bosons decaying hadronically.
The method is expected to have still more impact in the cases of final state topologies with larger lepton multiplicity: pair production of charginos and/or neutralinos with slepton mediated decays. The RJR technique can be extended to these studies and to the pair production of heavy neutralinos in final states with four leptons, exploiting the simplified tree in figure 1, with a modification in the assignment of the objects in the case of sleptons of the third generation.
The results from the simplified models investigated in this work can be partially reinterpreted assuming different compositions for the electroweakinos. The method can be applied for higgsino-dominated charginos and neutralinos, with the latter decaying via an off-shell SM Higgs boson, requiring two b-jets and one lepton in the V-system. When decay modes via off-shell gauge bosons are dominant, the comparison would be straightforward. In particular, for chargino pair production with a mixed higgsino-wino nature, one can simply re-weight the signal yields with the appropriate cross sections: typically, the contributions from off-shell charged Higgs or other sparticles can be neglected since M S , M H ± M W in most SUSY models.  Table 3. Cut-flow for the total SM background (B) and the two benchmark signal samples Mχ±           Table 4. Cut-flow for the total SM background (B) and the two signal samples Mχ+ Open Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.