CMS-PAS-FTR-18-001

CMS-PAS-FTR-18-001
Searches for light higgsino-like charginos and neutralinos at the HL-LHC with the Phase-2 CMS detector
CMS Collaboration
November 2018

Abstract: A search for the pair production of light higgsino-like charginos $\tilde{\chi}_{1}^{\pm}$ and neutralinos $\tilde{\chi}^{0}_{2}$ is presented, based on a simulation of 3000 fb $^{-1}$ 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 $\tilde{\chi}_{1}^{\pm}$ and $\tilde{\chi}^{0}_{2}$ are assumed to be mass-degenerate, to be pair-produced ( $\tilde{\chi}_{1}^{\pm}\tilde{\chi}^{0}_{2}$ , $\tilde{\chi}^{0}_{2}\tilde{\chi}^{0}_{1}$ ), and to decay into the lightest stable superymmetric particle $\tilde{\chi}^{0}_{1}$ via off-shell W and Z bosons. The $\tilde{\chi}^{0}_{1}$ 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.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1: Example Feynman diagrams for ${\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}}$ (left) and ${\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}$ (right) $s$ -channel pair production, followed by the leptonic decay of the ${\tilde{\chi}^{0}_{2}}$ .
png pdf	Figure 1-a: Example Feynman diagram for ${\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}}$ $s$ -channel pair production, followed by the leptonic decay of the ${\tilde{\chi}^{0}_{2}}$ .
png pdf	Figure 1-b: Example Feynman diagram for ${\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}$ $s$ -channel pair production, followed by the leptonic decay of the ${\tilde{\chi}^{0}_{2}}$ .
png pdf	Figure 2: Distributions of the candidate lepton with the highest ${p_{\mathrm {T}}}$ (left) and the second-highest ${p_{\mathrm {T}}}$ (right) for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of the ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of the ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties.
png pdf	Figure 2-a: Distributions of the candidate lepton with the highest ${p_{\mathrm {T}}}$ for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of the ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of the ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties.
png pdf	Figure 2-b: Distributions of the candidate lepton with the second-highest ${p_{\mathrm {T}}}$ for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of the ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of the ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties.
png pdf	Figure 3: Distributions of the ${{p_{\mathrm {T}}} ^\text {miss}}$ (left) and ${m_{\ell _1, \ell _2}}$ (right) for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties.
png pdf	Figure 3-a: Distributions of the ${{p_{\mathrm {T}}} ^\text {miss}}$ for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties.
png pdf	Figure 3-b: Distributions of the ${m_{\ell _1, \ell _2}}$ for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties.
png pdf	Figure 4: The $5\sigma$ discovery contours and expected 95% CL exclusion contours for the combined ${\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}}$ and ${\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}$ production. Results are presented for $\Delta M({\tilde{\chi}^{0}_{2}}, {\tilde{\chi}^{0}_{1}}) >$ 7.5 GeV.

Tables
png pdf	Table 1: Definition of the baseline signal region. In the table below, ${N_{\ell}}$ is the number of lepton candidates; ${\Delta R(\ell _1,\ell _2)}$ is the angular separation between the two candidate leptons in the $\phi, \eta$ space; ${N_{\text {b-jet}}}$ is the number of b jets; ${N_{\text {jet}}}$ is the number of candidate jets (including any ISR jet reconstructed in the event); ${N_{\text {ISR}}}$ is the number of ISR jets; ${\Delta \phi ({{p_{\mathrm {T}}} ^\text {miss}} , {p_{\text {T}}({j_{\text {ISR}}})})}$ is the azimuthal distance between the ${{p_{\mathrm {T}}} ^\text {miss}}$ vector and the ${j_{\text {ISR}}} {p_{\mathrm {T}}}$ vector; and ${m_{\ell _1, \ell _2}}$ is the invariant mass of the two candidate leptons.
png pdf	Table 2: Summary of the experimental systematic uncertainties assumed in the prediction of the yields for processes with prompt leptons.
png pdf	Table 3: Signal and background yields in two representative event categories. SR1 is defined by ${{p_{\mathrm {T}}} ^\text {miss}} >$ 500 GeV, ${m_{\ell _1, \ell _2}}$ in [10, 20] GeV, and ${p_{\text {T}}({\ell _2})}$ in [13, 21] GeV. SR2 is defined by ${{p_{\mathrm {T}}} ^\text {miss}} >$ 500 GeV, ${m_{\ell _1, \ell _2}}$ in [10, 20] GeV, and ${p_{\text {T}}({\ell _2})}$ in [5, 13] GeV. The signal model considered here has $m_{{\tilde{\chi}_{1}^{\pm}}}=m_{{\tilde{\chi}^{0}_{2}}} =$ 300 GeV and $m_{{\tilde{\chi}^{0}_{1}}} =$ 280 GeV. Only systematic uncertainties are given.

Summary

A search for the pair production of light higgsino-like charginos

${\tilde{\chi}_{1}^{\pm}}$ and neutralinos

${\tilde{\chi}^{0}_{2}}$ (

${\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}}$ ,

${\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}$ ) is presented using 3000 fb

$^{-1}$ of simulated proton-proton collision data produced by the HL-LHC at 14 TeV. The

${\tilde{\chi}_{1}^{\pm}}$ and

${\tilde{\chi}^{0}_{2}}$ particles are assumed to be mass-degenerate, to be pair-produced, and to decay into the lightest stable superymmetric particle

${\tilde{\chi}^{0}_{1}}$ via off-shell W and Z bosons. The

${\tilde{\chi}^{0}_{1}}$ is also assumed to be higgsino-like. Higgsino-like mass-degenerate

${\tilde{\chi}_{1}^{\pm}}$ and

${\tilde{\chi}^{0}_{2}}$ particles with masses up to 250 GeV can be discovered for a mass difference of 15 GeV relative to the lightest neutralino

${\tilde{\chi}^{0}_{1}}$ . For this mass splitting,

${\tilde{\chi}_{1}^{\pm}}$ and

${\tilde{\chi}^{0}_{2}}$ with masses up to 360 GeV can be excluded at 95% confidence level.

Additional Figures
png pdf	Additional Figure 1: Distributions of the candidate lepton with the highest ${p_{\mathrm {T}}}$ (left) and the second-highest ${p_{\mathrm {T}}}$ (right) for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of the ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of the ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties. The ${{p_{\mathrm {T}}} ^\text {miss}}$ is formed here as negative vector sum of the transverse momenta of all objects in the event.
png pdf	Additional Figure 1-a: Distributions of the candidate lepton with highest ${p_{\mathrm {T}}}$ for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of the ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of the ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties. The ${{p_{\mathrm {T}}} ^\text {miss}}$ is formed here as negative vector sum of the transverse momenta of all objects in the event.
png pdf	Additional Figure 1-b: Distributions of the candidate lepton with second-highest ${p_{\mathrm {T}}}$ for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of the ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of the ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties. The ${{p_{\mathrm {T}}} ^\text {miss}}$ is formed here as negative vector sum of the transverse momenta of all objects in the event.
png pdf	Additional Figure 2: Distributions of the ${{p_{\mathrm {T}}} ^\text {miss}}$ (left) and ${m_{\ell _1, \ell _2}}$ (right) for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties. The ${{p_{\mathrm {T}}} ^\text {miss}}$ is formed here as negative vector sum of the transverse momenta of all objects in the event.
png pdf	Additional Figure 2-a: Distributions of ${{p_{\mathrm {T}}} ^\text {miss}}$ or background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties. The ${{p_{\mathrm {T}}} ^\text {miss}}$ is formed here as negative vector sum of the transverse momenta of all objects in the event.
png pdf	Additional Figure 2-b: Distributions of ${m_{\ell _1, \ell _2}}$ for background and signal events in the baseline signal region. Three selected ${{\tilde{\chi}_{1}^{\pm}} {} {\tilde{\chi}^{0}_{2}} + {\tilde{\chi}^{0}_{2}} {} {\tilde{\chi}^{0}_{1}}}$ signal models are shown, where the first number corresponds to the mass of ${\tilde{\chi}^{0}_{2}}$ (and ${\tilde{\chi}_{1}^{\pm}}$ ) and the second one to the mass of ${\tilde{\chi}^{0}_{1}}$ . The uncertainty band represents systematical uncertainties. The ${{p_{\mathrm {T}}} ^\text {miss}}$ is formed here as negative vector sum of the transverse momenta of all objects in the event.
png pdf	Additional Figure 3: The 5 $\sigma$ discovery contours and expected 95% CL exclusion contours for the combined ${\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}}$ and ${\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}$ production. The missing transverse momentum ${{p_{\mathrm {T}}} ^\text {miss}}$ 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).
png pdf	Additional Figure 4: Projection of the HL-LHC 5 $\sigma$ discovery contours and expected 95% CL exclusion contours for the combined ${\tilde{\chi}_{1}^{\pm}} {\tilde{\chi}^{0}_{2}}$ and ${\tilde{\chi}^{0}_{2}} {\tilde{\chi}^{0}_{1}}$ production for a center-of-mass energy of 27 TeV and an integrated luminosity of 15 ab $^{-1}$ (HE-LHC). Except for the cross sections and the integrated luminosity, the HL-LHC analysis was not modified. Results are presented for $\Delta M({\tilde{\chi}^{0}_{2}}, {\tilde{\chi}^{0}_{1}}) >$ 7.5 GeV.

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