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CMS-PAS-FTR-18-001
Searches for light higgsino-like charginos and neutralinos at the HL-LHC with the Phase-2 CMS detector
Abstract: A search for the pair production of light higgsino-like charginos ˜χ±1 and neutralinos ˜χ02 is presented, based on a simulation of 3000 fb1 of proton-proton collision data produced by the HL-LHC at a center-of-mass energy of 14 TeV. The Phase-2 CMS detector is simulated using Delphes. The ˜χ±1 and ˜χ02 are assumed to be mass-degenerate, to be pair-produced (˜χ±1˜χ02, ˜χ02˜χ01), and to decay into the lightest stable superymmetric particle ˜χ01 via off-shell W and Z bosons. The ˜χ01 is also assumed to be higgsino-like. Candidate signal events are required to have two same-flavor, opposite-charge, low transverse momentum leptons (electrons or muons), one jet, and significant missing transverse momentum.
Figures & Tables Summary Additional Figures References CMS Publications
Figures

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Figure 1:
Example Feynman diagrams for ˜χ±1˜χ02 (left) and ˜χ02˜χ01 (right) s-channel pair production, followed by the leptonic decay of the ˜χ02.

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Figure 1-a:
Example Feynman diagram for ˜χ±1˜χ02 s-channel pair production, followed by the leptonic decay of the ˜χ02.

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Figure 1-b:
Example Feynman diagram for ˜χ02˜χ01 s-channel pair production, followed by the leptonic decay of the ˜χ02.

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Figure 2:
Distributions of the candidate lepton with the highest pT (left) and the second-highest pT (right) for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of the ˜χ02 (and ˜χ±1) and the second one to the mass of the ˜χ01. The uncertainty band represents systematical uncertainties.

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Figure 2-a:
Distributions of the candidate lepton with the highest pT for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of the ˜χ02 (and ˜χ±1) and the second one to the mass of the ˜χ01. The uncertainty band represents systematical uncertainties.

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Figure 2-b:
Distributions of the candidate lepton with the second-highest pT for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of the ˜χ02 (and ˜χ±1) and the second one to the mass of the ˜χ01. The uncertainty band represents systematical uncertainties.

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Figure 3:
Distributions of the pTmiss (left) and m1,2 (right) for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of ˜χ02 (and ˜χ±1) and the second one to the mass of ˜χ01. The uncertainty band represents systematical uncertainties.

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Figure 3-a:
Distributions of the pTmiss for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of ˜χ02 (and ˜χ±1) and the second one to the mass of ˜χ01. The uncertainty band represents systematical uncertainties.

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Figure 3-b:
Distributions of the m1,2 for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of ˜χ02 (and ˜χ±1) and the second one to the mass of ˜χ01. The uncertainty band represents systematical uncertainties.

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Figure 4:
The 5σ discovery contours and expected 95% CL exclusion contours for the combined ˜χ±1˜χ02 and ˜χ02˜χ01 production. Results are presented for ΔM(˜χ02,˜χ01)> 7.5 GeV.
Tables

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Table 1:
Definition of the baseline signal region. In the table below, N is the number of lepton candidates; ΔR(1,2) is the angular separation between the two candidate leptons in the ϕ,η space; Nb-jet is the number of b jets; Njet is the number of candidate jets (including any ISR jet reconstructed in the event); NISR is the number of ISR jets; Δϕ(pTmiss,pT(jISR)) is the azimuthal distance between the pTmiss vector and the jISRpT vector; and m1,2 is the invariant mass of the two candidate leptons.

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Table 2:
Summary of the experimental systematic uncertainties assumed in the prediction of the yields for processes with prompt leptons.

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Table 3:
Signal and background yields in two representative event categories. SR1 is defined by pTmiss> 500 GeV, m1,2 in [10, 20] GeV, and pT(2) in [13, 21] GeV. SR2 is defined by pTmiss> 500 GeV, m1,2 in [10, 20] GeV, and pT(2) in [5, 13] GeV. The signal model considered here has m˜χ±1=m˜χ02= 300 GeV and m˜χ01= 280 GeV. Only systematic uncertainties are given.
Summary
A search for the pair production of light higgsino-like charginos ˜χ±1 and neutralinos ˜χ02 (˜χ±1˜χ02, ˜χ02˜χ01) is presented using 3000 fb1 of simulated proton-proton collision data produced by the HL-LHC at 14 TeV. The ˜χ±1 and ˜χ02 particles are assumed to be mass-degenerate, to be pair-produced, and to decay into the lightest stable superymmetric particle ˜χ01 via off-shell W and Z bosons. The ˜χ01 is also assumed to be higgsino-like. Higgsino-like mass-degenerate ˜χ±1 and ˜χ02 particles with masses up to 250 GeV can be discovered for a mass difference of 15 GeV relative to the lightest neutralino ˜χ01. For this mass splitting, ˜χ±1 and ˜χ02 with masses up to 360 GeV can be excluded at 95% confidence level.
Additional Figures

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Additional Figure 1:
Distributions of the candidate lepton with the highest pT (left) and the second-highest pT (right) for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of the ˜χ02 (and ˜χ±1) and the second one to the mass of the ˜χ01. The uncertainty band represents systematical uncertainties. The pTmiss is formed here as negative vector sum of the transverse momenta of all objects in the event.

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Additional Figure 1-a:
Distributions of the candidate lepton with highest pT for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of the ˜χ02 (and ˜χ±1) and the second one to the mass of the ˜χ01. The uncertainty band represents systematical uncertainties. The pTmiss is formed here as negative vector sum of the transverse momenta of all objects in the event.

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Additional Figure 1-b:
Distributions of the candidate lepton with second-highest pT for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of the ˜χ02 (and ˜χ±1) and the second one to the mass of the ˜χ01. The uncertainty band represents systematical uncertainties. The pTmiss is formed here as negative vector sum of the transverse momenta of all objects in the event.

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Additional Figure 2:
Distributions of the pTmiss (left) and m1,2 (right) for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of ˜χ02 (and ˜χ±1) and the second one to the mass of ˜χ01. The uncertainty band represents systematical uncertainties. The pTmiss is formed here as negative vector sum of the transverse momenta of all objects in the event.

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Additional Figure 2-a:
Distributions of pTmiss or background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of ˜χ02 (and ˜χ±1) and the second one to the mass of ˜χ01. The uncertainty band represents systematical uncertainties. The pTmiss is formed here as negative vector sum of the transverse momenta of all objects in the event.

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Additional Figure 2-b:
Distributions of m1,2 for background and signal events in the baseline signal region. Three selected ˜χ±1˜χ02+˜χ02˜χ01 signal models are shown, where the first number corresponds to the mass of ˜χ02 (and ˜χ±1) and the second one to the mass of ˜χ01. The uncertainty band represents systematical uncertainties. The pTmiss is formed here as negative vector sum of the transverse momenta of all objects in the event.

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Additional Figure 3:
The 5σ discovery contours and expected 95% CL exclusion contours for the combined ˜χ±1˜χ02 and ˜χ02˜χ01 production. The missing transverse momentum pTmiss here is defined as the negative vector sum of the transverse momentum of all candidate objects in the event (candidate electrons, candidate muons and candidate jets as defined in the main body of the document).

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Additional Figure 4:
Projection of the HL-LHC 5σ discovery contours and expected 95% CL exclusion contours for the combined ˜χ±1˜χ02 and ˜χ02˜χ01 production for a center-of-mass energy of 27 TeV and an integrated luminosity of 15 ab1 (HE-LHC). Except for the cross sections and the integrated luminosity, the HL-LHC analysis was not modified. Results are presented for ΔM(˜χ02,˜χ01)> 7.5 GeV.
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