Search for di-Higgs to 4b with the ATLAS detector 2016 Public (13 fb -1 ) and 2017 Expected (24/36 fb -1 ) Results Tony(Baojia)Tong, Harvard University DPF, Aug.2, 2016
Motivation Di-Higgs production • A “Beyond Standard Model” Standard Model process • Cross section small in SM: • 8 TeV ~ 10 fb (NNLO) • 13 TeV ~ 34 fb (NNLO + NNLL) D.Florian,J.Mazzitelli, Arxiv1505.07122 Tony Tong (Harvard) 2 Aug 2, 2017
Motivation Di-Higgs production • Cross section small in SM: • 8 TeV ~ 10 fb • 13 TeV ~ 34 fb • Larger if BSM physics exists • Non-resonant Examples • tth vertex modifications • λ hhh triple-Higgs coupling • Resonant Examples • KK Graviton • Heavy Higgs: 2HDM Tony Tong (Harvard) 3 Aug 2, 2017
Motivation Di-Higgs production • Cross section small in SM: • 8 TeV ~ 10 fb • 13 TeV ~ 34 fb • Larger if BSM physics exists • Non-resonant Examples • tthh, tth vertex modifications • λ hhh triple-Higgs coupling h • Resonant Examples (G/H) • KK Graviton, spin 2 • Heavy Higgs: 2HDM, spin 0 h Tony Tong (Harvard) 4 Aug 2, 2017
Motivation Di-Higgs decay b larger branching ratio—higher yield h - b b single Higgs h decay 2e-3 - b single Higgs decay Tony Tong (Harvard) 5 Aug 2, 2017
Motivation Di-Higgs decay larger branching ratio—higher yield single Higgs decay 2e-3 Phys. Rev. D 92, 092004 (2015) 4b better limit for higher mass single Higgs decay Tony Tong (Harvard) 6 Aug 2, 2017
RunII 4b: object definition Channels: Resolved ATLAS-CONF-2016-049 • Standard resolved 4b jets for the low mass range Tony Tong (Harvard) 7 Aug 2, 2017
RunII 4b: object definition Channels: Resolved + Boosted ATLAS-CONF-2016-049 • Standard resolved 4b jets for the low mass range • 1.5 TeV resonance → ~ 600 GeV p T Higgs → Δ R bb ~2m h /p T ~ 0.4 trackjet Tony Tong (Harvard) 8 Aug 2, 2017
RunII 4b: object definition Channels: Resolved + Boosted ATLAS-CONF-2016-049 • Standard resolved 4b jets for the low mass range • 1.5 TeV resonance → ~ 600 GeV p T Higgs → Δ R bb ~2m h /p T ~ 0.4 Objects/ Resolved Boosted Final State (250–1100 GeV) (1100-3000 GeV) Trigger Mixed b Trigger Large R-jet Trigger Two 1.0 trimmed Four 0.4 Anti-kt Jets Jets Anti-kt Jets Leading > 450 GeV pT cuts Jet pT > 40 GeV Subleading > 250 GeV B-tagging 70% on Jets 77% on R= 0.2 trk jets Tony Tong (Harvard) 9 Aug 2, 2017
RunII 4b: resolved selection Resolved: Jets Pairing and Cuts ATLAS-CONF-2016-049 • Select hh pair that has the minimal distance to a diagonal line on the 2D mass plane • Minimize the Higgs candidates mass difference which pair? Tony Tong (Harvard) 10 Aug 2, 2017
RunII 4b: resolved selection Resolved: Jets Pairing and Cuts ATLAS-CONF-2016-049 • Select hh pair that has the minimal distance 0.08 Efficiency 0.2 ATLAS Preliminary 4 b-tagged jets to a diagonal line on -1 s = 13 TeV, 2016, 10.1 fb 0.07 0.18 R ∆ jj Resolved m Dependent Cuts, R ∆ the 2D mass plane 4j hh 0.16 0.06 × X Acceptance hh 0.14 • m 4j dependent Trigger 0.05 0.12 requirements on h pT, 0.04 0.1 eta, and dR jj 0.08 0.03 0.06 • Fine signal efficiency 0.02 0.04 across large mass 0.01 0.02 ranges 0 0 300 400 500 600 700 800 900 1000 1100 1200 SMNR m [GeV] G* non-res KK Tony Tong (Harvard) 11 Aug 2, 2017
RunII 4b: boosted selection Boosted: Number of b-tagging • Three Signal Regions: b b • 4b • 3b: (recover b b efficiency) • 2b split (merging of trackjets) Tony Tong (Harvard) 12 Aug 2, 2017
RunII 4b: boosted selection Boosted: Number of b-tagging • Three Signal Regions: Acceptance x Efficiency b b ATLAS Internal 2 b-tagged track-jets ATLAS work in s 0.35 3 b-tagged track-jets progress G c=1.0, s = 13 TeV • 4b 4 b-tagged track-jets Boosted 0.3 All of above 0.25 • 3b: (recover b b 0.2 efficiency) 0.15 0.1 • 2b split 0.05 (merging of 0 1000 1500 2000 2500 3000 trackjets) Mass [GeV] Tony Tong (Harvard) 13 Aug 2, 2017
RunII 4b: object definition Regions: Two Higgs Mass Plane ATLAS-CONF-2016-049 Boosted 2Tag Background Prediction 250 [GeV] • Signal Region (SR): ATLAS Preliminary 200 -1 s =13 TeV, 13.3 fb subl • “Circle” centered at h mass Boosted J 200 m 150 • Validation Region (VR) : • Ring outside SR (for validation) 150 100 • Sideband (SB) SR 100 50 VR • Ring outside VR (for modeling) SB 50 0 50 100 150 200 250 lead m [GeV] J Tony Tong (Harvard) 14 Aug 2, 2017
RunII 4b: object definition Regions: Two Higgs Mass Plane ATLAS-CONF-2016-049 Boosted 2Tag Background Prediction 250 [GeV] • Signal Region (SR): ATLAS Preliminary 200 -1 s =13 TeV, 13.3 fb subl • “Circle” centered at h mass Boosted J 200 m 150 • Validation Region (VR): • Ring outside SR (for validation) 150 100 • Sideband (SB) SR 100 50 VR • Ring outside VR (for modeling) SB 50 0 50 100 150 200 250 lead m [GeV] J Tony Tong (Harvard) 15 Aug 2, 2017
RunII 4b: object definition Regions: Two Higgs Mass Plane ATLAS-CONF-2016-049 Boosted 2Tag Background Prediction 250 [GeV] • Signal Region (SR): ATLAS Preliminary 200 -1 s =13 TeV, 13.3 fb subl • “Circle” centered at h mass Boosted J 200 m 150 • Validation Region (VR): • Ring outside SR (for validation) 150 100 • Sideband Region (SB): SR 100 50 VR • Ring outside VR (for modeling) SB 50 0 50 100 150 200 250 lead m [GeV] J Tony Tong (Harvard) 16 Aug 2, 2017
RunII 4b: background estimation Background ATLAS-CONF-2016-049 Boosted 2Tag Background Prediction • Background: 250 [GeV] ATLAS Preliminary 200 -1 • 90-85% qcd—data driven s =13 TeV, 13.3 fb subl Boosted J 200 m 150 • 10-15% ttbar—MC 150 100 • use lower-b-tag low-signal yield SR 100 50 VR region to model higher-b-tag regions SB • derive the normalization factor from 50 0 50 100 150 200 250 the Sideband, check in Validation lead m [GeV] J Tony Tong (Harvard) 17 Aug 2, 2017
RunII 4b: background estimation ATLAS-CONF-2016-049 Background • Background: 4b SR • 90-85% qcd—data driven VR SB • 10-15% ttbar—MC N 4b SR/VR ??? • Need shape and normalization estimates for qcd events • derive the normalization factor from the Sideband, check in Validation Tony Tong (Harvard) 18 Aug 2, 2017
RunII 4b: background estimation ATLAS-CONF-2016-049 Background • Background: 4b SR • 90-85% qcd—data driven VR SB • 10-15% ttbar—MC N 4b SR/VR ~ N 0b SR/VR • use lower-b-tag low-signal yield region to model higher-b-tag regions 0b SR • derive the normalization factor from VR the Sideband, check in Validation SB Tony Tong (Harvard) 19 Aug 2, 2017
RunII 4b: background estimation ATLAS-CONF-2016-049 Background • Background: 4b SR • 90-85% qcd—data driven VR SB • 10-15% ttbar—MC N 4b SR/VR = N 4b SB / N 0b SB * N 0b SR/VR • use lower-b-tag low-signal yield region to model higher-b-tag regions 0b SR • derive the normalization factor from VR the Sideband, check in Validation SB Tony Tong (Harvard) 20 Aug 2, 2017
RunII 4b: resolved results Signal Region: Resolved ATLAS-CONF-2016-049 • Final discriminant: m4j , four jets’s invariant mass ; no significant excess observed Data 2015 2016 Obs 1231 3990 Exp 1189 ± 76 3860 ± 230 Events/10 GeV Events/10 GeV 3 10 ATLAS Preliminary Data ATLAS Preliminary Data Multijet -1 s = 13 TeV, 2016, 10.1 fb Multijet -1 t t s = 13 TeV, 2015, 3.2 fb 2 Signal Region: Resolved 10 t t G(300) 10 × Signal Region: Resolved G(300) 10 × 2 10 G(800) 10 × G(800) 10 × SM hh 500 × SM hh 500 × Stat+Syst Uncertainty 10 Stat+Syst Uncertainty 2015 2016 10 1 1 1 − 10 − 1 10 2 Data/Bkgd 2 Data/Bkgd 1 1 0 200 400 600 800 1000 1200 0 200 400 600 800 1000 1200 m [GeV] 4j m [GeV] *2015 and 2016 have different trigger selection due to different run conditions 4j Tony Tong (Harvard) 21 Aug 2, 2017
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