Future ATLAS Higgs Studies, On behalf of the ATLAS collaboration
The Plan For The Future: LHC To improve our measurements and searches, the LHC and ATLAS will be upgraded: The LHC will become the High-Luminosity-LHC, to produce 3000 fb-1 of integrated luminosity by 2035. Instantaneous luminosity x5-7 Particle densities x5-7 Integrated luminosity x10 Radiation damage x10 Higher Energy benefits searches for new particles. Higher integrated luminosity benefits precision measurements and studies of rare processes. 2
ATLAS Detector Run-4 Upgrades ATLAS upgrades will include: Longer-latency trigger system, higher event rates. Upgraded TileCal electronics. New inner Muon barrel trigger chambers. New all-silicon Inner Tracker (ITk), with acceptance up to η <4. Possible new forward muon tagger, and timing detector. Reduction of material from current Inner Detector to Run-4 ITk. 3
ATLAS Run-2 HH Results SM di-higgs gives us access to the Higgs self-coupling, λhhh. (Deviation of λhhh/λsm from 1 suggests new physics.) Diagrams above interfere destructively. SM di-higgs production (40 fb) is three orders of magnitude smaller than single Higgs production (48 pb). Final states: H bb has the highest branching ratio. H γγ has good mass resolution and the cleanest final state. H WW and H ττ are reasonable compromises. 4
ATLAS Run-2 Di-Higgs Results bbbb Run-2 s = 13 TeV, 13.3 fb-1. non resonant limit: σ BR < 330 fb, (29 SM) largest systematics come from b-tagging and tt background. ATLAS-CONF-2016-049 γγww ττbb γγbb Run-2 s = 13 TeV, 3.2 fb-1. non resonant limit: σ BR < 3.9 pb, (117 SM) ATLAS-CONF-2016-004 Run-2 s = 13 TeV, 13.3 fb-1. non resonant limit: σ BR < 25 pb, (749 SM) ATLAS-CONF-2016-071 Run-1 only s = 8 TeV, 20.3 fb-1. non resonant limit: σ BR < 1.6 pb, (160 SM) CERN-PH-EP-2015-225 5
ATLAS Higgs Prospects Analysis Strategy Higgs prospects analyses have been performed for HL-LHC-era ATLAS, assuming s = 14 TeV and <μpu> = 140 or 200. Fully-simulating all required MC with <μpu> = 200 is too costly, so instead only truth-level MC is generated. 'Upgrade Performance Functions' have then been developed, (by comparing limited <μpu> = 200 full-sim MC to MC-truth), to 'smear' MC truth samples, and add pile-up. Full Simulation (<μpu>=200) MC Truth Smearing Functions Analysis Analyses are then performed on 'smeared' truth MC samples. 6
ATLAS Higgs Prospects Di-Higgs (ATL-PHYS-PUB-2017-001) HH γγbb Photon performance based on upgrade Scoping Document. Most recent ITk layout used for b-tagging. Significance: 1.05 σ -0.8 < λhhh/λsm < 7.7 (95% CL. no syst.) HH bbbb Extrapolation from Run-2 analysis. Main background: Mj QCD, estimated from Run-2 data. -0.2 < λhhh/λsm < 7 (95% CL. no syst.) -3.5 < λhhh/λsm < 11 (95% CL. 2016 syst.) (ATL-PHYS-PUB-2016-024) 7
ATLAS Higgs Prospects Di-Higgs (ATL-PHYS-PUB-2016-023) tthh, HH bbbb σ(tthh) 1 fb (σ(hh) 40 fb) Cut-based analysis aiming at final state: HH bbbb, tt bblνqq Significance: 0.35 σ (no syst.) HH ττbb All τ decays used except τlepτlep. Different triggers used, optimised for different τ decay channels. Significance: 0.60 σ -4 < λhhh/λsm < 12 (95% CL. with syst.) (ATL-PHYS-PUB-2015-046) 8
ATLAS Higgs Prospects Higgs Couplings Run-1 Higgs coupling analyses have been extrapolated to future runs: Run-1 Run-1 μ/μ Run-2 μ/μ Run-3 and HL-LHC μ/μ = 0.23 μ/μ = 0.14 μ/μ = 0.28 μ/μ = 0.16 μ/μ = 0.21 μ/μ = 1.63* μ/μ = 0.8 μ/μ = 0.31 μ/μ = 0.29 Dashed areas indicate μ/μ with current theory uncertainties. (ATLASHiggsSummaryPlots) (ATLAS-CONF-2017-045) (ATLAS-CONF-2017-043) (ATLAS-CONF-2016-112 *not all prod modes) (ATLAS-CONF-2017-041) Vertical blue lines are Run-1 values. Vertical red lines are Run-2 values. (ATL-PHYS-PUB-2014-016) 9
ATLAS Higgs Prospects Rare Higgs Boson Decays Two channels studied. Run-1 detector performance has been assumed. H J/ψγ, J/ψ μ+μ- H J/ψγ uses multivariate analysis with pt(γ), pt(μ+μ-), γ and μ+μ- isolation. -6 BR(H J/ψγ) < 44+19-12 10 (95% CL) SM: 2.9 ± 0.2 10-6 (Run-1: 1.5 10-3) (ATL-PHYS-PUB-2015-043) H μ+μ H μ+μ- uses data-driven methods based on Run-1 with cut optimisation. With 3000 fb-1: Significance = 7.0 σ Δμ/μ = 21% (ATL-PHYS-PUB-2013-014) 10
ATLAS Higgs Prospects VBF VBF, with its forward jets, is an important channel used to motivate the upgraded ATLAS layouts, (with ITk acceptance up to η <4). Two channels studied: H WW eνμν (ATL-PHYS-PUB-2016-018) H ZZ 4l (ATL-PHYS-PUB-2016-008) μ=σ/σsm Cut based analyses, using Run-1 (e/μ) and SD (jet/met) detector performances. WW (no syst.) WW (syst.) ZZ (no syst.) ZZ (syst.) Δμ 0.14 0.20 0.15 0.18 Sig: σ 8.0 5.7 10.2 7.2 11
Summary Summary of ATLAS HL-LHC Higgs results. HH Final State HH γγbb HH bbbb tthh, HH bbbb Significance Higgs Channel Results Self-Coupling Limit (95% CL) 1.05 σ H J/ψγ, J/ψ μ+μ- -6 BR < 44+19-12 10 (95% CL) H μ+μ- Δμ/μ 15% tth, H γγ Δμ/μ 17 to 20% VH, H γγ Δμ/μ 25 to 35% H Zγ Δμ/μ 30% VBF H WW Δμ/μ 14 to 20% VBF H ZZ Δμ/μ 15 to 18% -0.8 < λhhh/λsm < 7.7-3.5 < λhhh/λsm < 11.0 0.35 σ 0.6 σ HH ττbb -4.0 < λhhh/λsm < 12.0 12
Conclusion The HL-LHC will present a challenging environment for ATLAS analyses. Nonetheless, the HL-LHC will also present great opportunities for new studies, and greater understanding of the Higgs boson. Current ATLAS HL-LHC analyses are conservative: Current detector models are still in the development stage (TDR). In Run-4, data-driven methods will give us greater control over backgrounds. Theoretical uncertainties are expected to be reduced! Overall, the HL-LHC era will be an exciting time for Higgs research! 13