Search for Chargino and Neutralino Production with a Higgs Boson in the Decay Chain in One Or Three Leptons ﬁnal State Events with ATLAS

Available online at www.sciencedirect.com

Nuclear and Particle Physics Proceedings 273–275 (2016) 2400–2402 www.elsevier.com/locate/nppp

Search for chargino and neutralino production with a Higgs boson in the decay chain in one or three leptons ﬁnal state events with ATLAS

Claire David, on behalf of the ATLAS collaboration University of Victoria - TRIUMF, Vancouver, Canada

Abstract χ± χ0 Searches for direct production of chargino (˜ 1 ) and neutralino (˜ 2) leading to final states characterized by the presence of a Higgs boson are reported. Events containing missing transverse momentum and one or three leptons −1 are selected, and various channels sensitive√ to different Higgs decays are considered. The analyses use 20.3 fb of proton-proton collision data at s = 8 TeV recorded in 2012 with the ATLAS detector at the Large Hadron Collider. Observations are consistent with the Standard Model expectations and limits are set in R-parity conserving phenomenological Minimal Supersymmetric Standard Models and in simplified supersymmetric models.

Supersymmetry (SUSY)1 is an extension to the Stan- dard Model (SM). It postulates the existence of supersymmetric particles, with spin differing by one-half unit with respect to that of their SM partners. Electroweaki- χ± χ0 nos (charginos ˜ 1,2 and neutralinos ˜ 1,2,3,4) are the or- dered mass eigenstates formed from the linear super- position of the SUSY partners of the Higgs and elec- troweak gauge bosons (higgsinos, winos and binos). In (a) One lepton, 2 b-tagged (b) One lepton, 2 b-tagged R-parity-conserving models, SUSY particles are pair- miss miss jets and ET final state. jets and ET final state. produced and the Lightest SUSY Particle (LSP), here χ˜ 0 Figure 1: The Feynman diagrams for the simplified model of the di- assumed to be the 1, is stable. Naturalness arguments χ± χ0 rect production of ˜1 and ˜2 studied in this paper. The dots in (b) suggest that the lightest electroweakinos are expected to depict possible additional decay products of the lightest Higgs boson have mass of order 100 GeV and can be detected at the decaying via intermediate ττ, WW or ZZ states. Large Hadron Collider (LHC). This review presents two searches for pair-produced charginos and neutralinos in −1 the Wh-mediated channel. The analyses√ use 20.3 fb of persymmetric model considered in both searches targets proton-proton collision data at s = 8 TeV recorded in ± the direct production of χ˜ and χ˜ 0, assumed to be mass 2012 with the ATLAS [1] detector at the LHC. Selected 1 2 degenerate and consisting purely of the wino compo- events must contain one or three leptons and missing χ˜ 0 transverse momentum (Emiss) originating from the two nent. The LSP 1 is considered bino-like. Sleptons and T χ˜ ± χ˜ 0 undetected LSPs and the neutrinos. The simplified su- sneutrinos are assumed to be heavy. The 1 and 2 decay via W and lightest Higgs bosons, respectively, with a branching fraction of 100%. The Higgs boson con- [email protected] Email address: (Claire David, on sidered is SM-like, with a mass of 125 GeV, and is as- behalf of the ATLAS collaboration) 1Theoretical references can be found in the respective experimen- sumed to decay with SM branching ratios. Diagrams of tal work cited. the presented searches are shown in Figure 1. http://dx.doi.org/10.1016/j.nuclphysbps.2015.09.405 2405-6014/© 2016 Published by Elsevier B.V. C. David / Nuclear and Particle Physics Proceedings 273–275 (2016) 2400–2402 2401

20 1. One lepton and 2 b-jets scenario ATLAS Preliminary Data = 8 TeVs 18 SM Total -1 tt Events 16 ∫L dt ~ 20.3 fb single top This search [2] is performed on events containing ex- W+jets 14 SRA Z+jets t +W/Zt WW/WZ/ZZ actly one isolated lepton, two jets originating from the 12 miss WH hadronisation of the b-quarks (b-tagged) and E . The ZH 10 m ± 0, m = 130, 0 GeV T χ ,χ χ0 1 2 1 mχ±,χ0, m 0 = 225, 0 GeV 1 2 χ used b-tagging algorithm, which exploits the long life- 8 1 time of b- and c-hadron inside a candidate jet, is MV1 6 at a 70% efficiency. Events should contain exactly two 4 2 leading b-jets and no fourth jet of pT > 25 GeV. Two 0 2.5 discriminating variables, the contransverse mass mCT, m [GeV] 2 bb 1.5 defined as 1 0.5 Data/SM 00 50 100 150 200 250 300 350 400 = + 2 − − 2 m [GeV] mCT [ET(v1) ET(v2)] pT(v1) pT(v2) (1) bb 20 ATLAS Preliminary Data = 8 TeVs 18 SM Total and the transverse mass mT, given by -1 tt Events 16 L dt ~ 20.3 fb single top ∫ W+jets Z+jets 14 SRB t +W/Zt miss miss WW/WZ/ZZ = − · 12 mT 2pTET 2pT pT (2) WH ZH 10 m ± 0, m = 130, 0 GeV χ ,χ χ0 1 2 1 mχ±,χ0, m 0 = 225, 0 GeV 1 2 χ are significantly reducing the tt¯and W+jets background 8 1 contributions respectively. Two orthogonal signal re- 6 gions SRA and SRB are designed to provide the best 4 2 sensitivity for low and high Δm = mχ± χ0 − mχ0 respec- ˜1 , ˜2 ˜1 0 2.5 m [GeV] tively. In both regions, events must satisfy the condi- 2 bb miss 1.5 tions E > 100 GeV, mCT > 160 GeV, mT > 100 GeV 1 T 0.5 and mbb> 50 GeV, where mbb is the invariant mass of the Data/SM 00 50 100 150 200 250 300 350 400 mbb [GeV] two b-jets. Events satisfying (failing) mT < 130 GeV are classified in SRA (SRB). Figure 2: Distributions of mbb in SRA (up) and SRB (bottom). The main SM irreducible background contributions in the signal regions, estimated with Monte Carlo (MC), arise from tt¯, single-top and W+jets production. The re- shows the results based both on pseudo-experiments ducible background, mostly from QCD multi-jet events, and asymptotic formulae for a profile-log-likelihood test where a lepton originating from the b-decay fakes a sig- statistic. Figure 3 displays 95% CL exclusion region obtained in the mχ± χ0 − mχ0 plane. For a massless nal lepton, is estimated through the “matrix method” ˜1 ,˜2 ˜1 LSP, the mass ranges of 125 < mχ± χ0 < 141 GeV and and found to be negligible. The main systematics un- ˜1 /˜2 166 < mχ± χ0 < 287 GeV are excluded at 95% CL, de- certainties on the background are the Jet Energy Scale, ˜1 /˜2 b-tagging and the single-top theoretical production. termined at 1σ signal theoretical uncertainty, with an expected exclusion range of 225 < mχ± χ0 < 235 GeV. A simultaneous fit of the control and signal regions is ˜1 /˜2 performed. Overall normalizations of the main back- + grounds (tt¯ and W jets) are allowed to float, along 2. Three leptons scenario with the signal strength to account for potential signal contamination in the control regions. Figure 2 This search [3] targets events containing exactly three shows the mbb distributions in SRA and SRB. The num- signal tagged leptons separated from each other by a ber of observed events in the signal bin (mbb [GeV] ∈ distance parameter ΔR > 0.3. At least one electron or [105, 135]) is found in agreement with the SM expecta- muon is required and must have fired one of the single- tions. or double-lepton triggers. Events with b-jets are vetoed. Given the absence of signal, exclusion limits are set at To identify the hadronically decaying τ, a jet anti-kt 95% confidence level (CL). Model-independent limits algorithm has been optimised with a boosted decision σ95 on the visible cross-section vis (product of production tree (BDT). Signal regions are defined according to the cross-section, acceptance and efficiency) are derived in flavour and charge of the leptons and are labelled by the each signal bin from the number of observed and pre- number of τ leptons selected. dicted events, the latter being extrapolated to the signal Processes leading to three real (isolated) leptons are regions from the background-only fit results. Table 1 classified into the irreducible background and are gen- 2402 C. David / Nuclear and Particle Physics Proceedings 273–275 (2016) 2400–2402

Table 1: Model-independent limits in the mbb signal bin on the ex- Table 2: Expected numbers of SM background events and observed 95 pected number of signal events S exp and observed 95% upper limit numbers of data events in the signal regions sensitive to the Wh- σ95 mediated scenario. For p0-values below 0.5, the observed number on the visible cross-section vis for non-SM events (obtained by di- viding the limits on the number of non-SM events by the integrated of standard deviations, σ, is shown in parentheses. luminosity). SR0τb SR1τ SR2τb ± ± +0.7 SRA SRB Total SM 3.8 1.2 10.3 1.2 7.2−0.8 95 σ95 Data 3 13 5 Observed S obs ( vis ) 6.5 (0.32 fb) 4.4 (0.21 fb) Asymptotic + . + . 95 . 3 1 . 2 5 p0 0.50 0.19 (0.86 σ) 0.50 Expected S exp 7 0−1.9 4 4−1.5 95 σ95 Pseudo- Observed S obs ( vis) 6.9 (0.34 fb) 4.4 (0.21 fb) 95 . +2.8 . +1.8 experiments Expected S exp 7 0−1.6 4 4−0.8 200 GeV and M2 > 200 GeV, the sensitivity is reduced χ0 χ0 as the decay mode ˜ 2 → h ˜ 1 is kinematically allowed. 140 ATLAS Preliminary Expected limit 68% CL [GeV] 0 1 SUSY 50 ∼ χ Observed limit (±1 σ ) 120 -1 theory m L dt = 20.3 fb , =8 TeVs ± σ SUSY ∫ Expected limit ( 1 exp) Observed limit ( 1 ) 45 ATLAS ± σtheory

SRA+SRB [GeV] 0 1 -1 ∼ 100 χ L dt = 20.3 fb , =8 TeVs Expected limit ( 1 )

0 0 0 m χ∼± χ∼ → W±χ∼ h0χ∼ 40 ∫ ± σexp 1 2 1 1 ∼± ∼0 W± ∼0 h ∼0 χ1 χ2 → χ1 χ1 All limits at 95% CL 80 35

h m = m 0 χ∼± ∼ 1 χ2 0 forbidden 30 < m ∼ 0 χ 1 1 60 ∼ χ 0 + h 0 → - m 25 0 ∼χ 2 2 ∼ χ 40 m 20

20 15

10 0 120 140 160 180 200 220 240 260 280 300 5 m∼± ∼0 [GeV] χ ,χ 1 2 0 100 110 120 130 140 150 160 170 180 190 200 ± − m 0 [GeV] Figure 3: Exclusion limits in the mχ ,χ0 mχ0 plane in the one lepton ∼χ , ∼χ± ˜1 ˜2 ˜1 2 1 and two b-jets search. M1 = 50 GeV, tan β = 10 3000550 ATLAS 500 [GeV] -1 2 L dt = 20.3 fb , =8 TeVs M ∫ Observed limit ( 1 SUSY) erated using MC samples. The main contribution arises 450 ± σtheory Expected limit ( 1 ) from WZ∗ processes. Events containing at least one fake ± σexp 400 LEP2 ∼± χ1 or non-prompt lepton form the reducible background, All limits at 95% CL 350 estimated using the “matrix method”. The dominant re- ∼χ± (300 GeV) ducible background component is tt¯, followed by Z+jets 300 1 ∼ χ ± and W+jets for 2-τ signal regions. The main theoretical 250 1 (200 GeV) uncertainties are related to the MC generation and the 200 ∼ ∼ ∼ χ χ χ

0 0 0

1 1 1

(45 GeV) (47 GeV) (48 GeV) cross-section calculation. In the 2-τ signal regions, the 150 total uncertainty is dominated by the statistical and tau 100 fake rate uncertainties on the reducible background. 100 150 200 250 300 350 400 450 5003000 550 μ [GeV] Data and SM expectation yields are found to be in good agreement. The compatibility of the data with Figure 4: Exclusion limits in the μ − M2 plane in the three leptons the background only hypothesis is assessed using a pro- search for simplified models (up) and pMSSM (bottom). file likelihood ratio as a test statistic. The resulting p- values are reported in Table 2. In the absence of signal, 95% CL limits are set on simplified models and References phenomenological Minimal Supersymmetric Standard Model (pMSSM), displayed in Figure 4. [1] ATLAS Collaboration, JINST 3 (2008) S08003. [2] ATLAS Collaboration, ATLAS-CONF-2013-093, For the simplified model with intermediate Higgs bo- https://cdsweb.cern.ch/record/1595756. χ± χ0 son decays, ˜ 1 and ˜ 1 masses up to 148 GeV are ex- [3] ATLAS Collaboration, JHEP 1404 (2014) 169. arXiv:1402.7029. cluded. The pMSSM here assumes heavy Higgses, squarks and gluinos to be all decoupled and sleptons to be heavy (no slepton scenario). In the region with μ>