High energy Physics on Search for chargino and neutralino Fabrizio Trovato production with three leptons and missing July 10th-17th 2019 - Ghent, Belgium transverse momentum in the final states at √s = 13 TeV European Physics society Conference
bstract with the ATLAS detector ± 0 Searches are presented for the direct production of a chargino and a neutralino, pp → χ˜1 χ˜2 , where the chargino decays to A ± 0 ± ± the lightest neutralino and the W boson, χ˜1 → χ˜1 (W → ℓ ν), while the neutralino decays to the lightest neutralino and χ 0 χ 0 χ 0 χ 0 either the Z boson ˜2 → ˜1 (Z → ℓℓ) or the 125 GeV Higgs boson, ˜2 → ˜1 (h → ℓℓ). The final states considered for the search The ATLAS detector have large missing transverse momentum and three isolated light leptons (electrons and muons). The analyses are based on 36.1 fb-1 of √s = 13 TeV proton-proton collision data delivered by the Large Hadron Collider (LHC) and recorded with the ATLAS detector. Physics scenario • Supersymmetry (SUSY) is a principle that predicts a fermion-boson symmetry [1] (Figure 1); • SUSY doubles particle content compared to Standard Model (SM). Many free parameters (masses, couplings); • The electroweakinos are eigenstates of the SUSY partners of charged SM bosons (charginos) and neutral SM bosons (neutralinos).
Why is Electroweak SUSY interesting? Analysis strategy Signal Regions (SRs) Figure 1. Particle content of the Minimal Supersymmetric Standand Model (MSSM).
Cut-and-count optimisation of
cuts that permit a good Chargino/neutralino via WZ and Wh signal/background discrimination Control Regions (CRs) √s = 13 TeV. Irreducible Fake or non-prompt (FNP) backgrounds normalised to Estimation of reducible data in dedicated background with dedicated data-driven techniques
production becomes becomes production background-enriched regions If squarks and gluinos gluinos and squarks If then electroweak SUSY SUSY then electroweak dominant at at dominant
heavier than electroweakinos, electroweakinos, than heavier Validation Regions (VRs) Data/MC comparison in Mostly WW, ττ, ZZ Figure 2. Typical SUSY cross sections at the nominal Run2 centre of mass energy of the LHC, taken from regions close to SRs https://twiki.cern.ch/twiki/bin/view/LHCPhysics/SUSYCrossSections.
χ˜ 0 • R-parity-conserving model: 1 R-parity Signal region definitions stable (Dark Matter candidate); 3(B L)+2s PR =( 1) • A Same Flavour Same Sign (SFSS) lepton • Considered final state: three • At least one Same Flavour Opposite Sign ± W ℓ ± pair and an additional DifferentF lavour W ℓ electrons or muons and missing transverse momentum; (SFOS) lepton pair; ΔΦSS -1 Opposite Sign (DFOS) lepton;
• TheWh and WZ analyses have been explored with 36.1 fb • Binned in jet multiplicity, missing ΔR OS,near ±
Z/h ℓ ± • Binning approach in jet multiplicity, using h ℓ' dataset collected with the ATLAS detector [3][4]. transverse energy and transverse mass. ( ) ℓ ± ℓ ' topological variables. Irreducible background estimation In both analyses, W+Z background is normalised to data, using two different control regions. For example, in theWh analysis, events in a 20-GeV window around the Z boson miss mass and with ET > 80 GeV were selected. Table 1. Signal regions used in the SFOS flavour/sign selection, targeting WZ model. Table 3. Signal regions used in the SFSS+DFOS flavour/sign selection, targetingWh model.
Conclusion and outlook
Table 2. Signal regions used in the SFOS flavour/sign selection, targeting Wh model.
Results
Figure 7. Data/MC comparison in the W+Z CR and VRs used in the multileptonic searches for Wh.
FNP background estimation Data-driven techniques are used to estimate the FNP in the SRs. In the WZ analysis, the Fake Factor method [5] correlates the number of FNP leptons to the number of leptons that pass specific Figure 9. Data/MC comparisons for some of the WZ and Wh analyses SRs (left and right, respectively). Figure 9. Summary plot for chargino/neutralino searches with the ATLAS detector. Wh SFSS+DFOS region exploits the invariant mass of the leptons used in the definition of theΔR . “loose” (antiID) or “tight” OS,near -1 (ID) selections. • The analyses with the full Run2 139 fb will target the same The method is validated in class of simplified models, addressing WZ and Wh searches VRs (Figure 8). simultaneously: • Similar backgrounds and challenges. • Chargino/neutralino searches with boson-mediated decays NID F = Figure 8. Data/MC agreement in a jet multiplicity to multileptonic final states will remain one of the key NantiID inclusive W+Z VR for the WZ analysis. analyses to search for SUSY in the long term, also in view of FNP MC prompt future luminosity upgrades of the LHC. NT = F (NL NL ) Figure 10. 1D limit at 95% of C.L. for the Wh analysis when the mass splitting is equal to 130 GeV (kinematic limit for on-shell Higgs boson) (left). Limits at 95% of C.L. for theWZ analysis (right).
[1] S. P. Martin, A Supersymmetry primer, (1997), [Adv. Ser. Direct. High Energy Phys.18,1(1998)]. Author: [email protected] [2] ATLAS Collaboration, The ATLAS Experiment at the CERN Large Hadron Collider, JINST 3 (2008) S08003. [3] ATLAS Collaboration, Search for electroweak production of supersymmetric particles in the two and three lepton final state at √s = 13 TeV with the ATLAS detector, Eur. Phys. J. C 78 (2018) 995. https://doi.org/10.1140/epjc/s10052-018-6423-7. [4] ATLAS Collaboration, Search for chargino and neutralino production in final states with a Higgs boson and missing transverse momentum at √s = 13 TeV with the ATLAS detector. arXiv:1812.09432 [hep-ex] (accepted by PRD). [5] ATLAS Collaboration, Measurement of the W±Z boson pair-production cross section in pp collisions at √s = 13 TeV with the ATLAS Detector, Phys. Lett. B 762 (2016) 1. arXiv: 1606.04017 [hep-ex].