Higgs Boson Searches at the Tevatron Harald Fox Department of - PowerPoint PPT Presentation

Higgs Boson Searches at the Tevatron Harald Fox Department of Physics h.fox@lancaster.ac.uk

Contents evatron, DØ and CDF T Higgs production Search for heavy Higgs H → WW → ll νν b jet Search for light Higgs WH → l ν bb ̅ ZH → νν bb ̅ ZH → llbb ̅ Outlook b jet Conclusion

The Standard Model H Kane, Scientific American, June 2003 • W + W − H • • • H • W + W −

The Higgs Mechanism ‣ The Higgs field acquires a vacuum expectation value � − µ 2 v = 2 λ = 246GeV ‣ Particles interact with the Higgs field and acquire an effective mass V( Ф )= μ 2 | Ф |+ λ (| Ф | 2 ) 2 = 0 m γ 1 = ‣ The mass relation between m W 2 vg γ , W and Z bosons is 1 1 = m Z 2 vg cos θ W determined √ 2 λ v 2 = ‣ Couplings and branching m H 1 ratios are determined. = m f 2 g f v √

Constraints on the Higgs Mass Kolda, Murayama: JHEP 0007 (2000) 035 ‣ Excluded by LEP 600 Triviality m H < 144 GeV 95%C.L. 500 m Limit = 144 GeV 6 Higgs mass (GeV) Theory uncertainty 400 ∆α (5) ∆α had = 5 0.02758 ± 0.00035 0.02749 ± 0.00012 Electroweak 300 incl. low Q 2 data 4 Fine Tuning Δ FT < 10%/1% ∆χ 2 10% 200 3 1% 2 100 Vacuum Stability 2 1 10 10 1 � (TeV) Excluded Preliminary 0 30 100 300 m H [ GeV ] LEP EWWG

Tevatron

Delivered Recorded Run IIa 1.6 fb -1 1.3 fb -1 Run IIb (so far) 1.9 fb -1 1.7 fb -1 Total 3.5 fb -1 3.0 fb -1 2006 shutdown: • new Layer 0 silicon installed • trigger upgrades installed Passed 3fb -1 milestone in recorded luminosity on 16 January 2008 Run IIa Run IIb April 02 Jan 08

Two General Purpose Detectors: CDF DØ Electron acceptance | η |<2.0 | η |<3.0 Muon acceptance | η |<1.5 | η |<2.0 Silicon Precision tracking | η |<2.0 | η |<3.0 Hermetic Calorimeter | η |<3.6 | η |<4.2 Powerful trigger systems (2.5MHz → 50Hz) Dilepton triggers with p T >4GeV Tracker Solenoid Magnet protons antiprotons 3 Layer Muon System

Tevatron Cross Sections Total inelastic cross section. Light quarks are ubiquitous. Plenty of W and Z bosons → calibration. Evidence of single top production is an important milestone towards the Higgs boson. The Higgs cross section is 10-11 orders of magnitudes lower than the total inelastic cross section.

Higgs Production and Decay cross section (pb)

ℓ ℓ ℓ ℓ ℓ ℓ High Mass Higgs Channels Angular correlation of leptons due to V − A as H is a spin 0 particle: e + W + ν n W - e - • final states with charged leptons: ‣ e ± e ∓ L=1.2 fb − 1 entries entries 5 5 10 10 e + e − data DØ Run II ‣ e ± µ ∓ ← counts twice Preliminary 4 4 10 10 H → WW × 10 160 ‣ µ ± µ ∓ 3 3 10 10 Z → e e 2 2 10 10 ‣ l ± τ ∓ h ← difficult Diboson 10 10 W+jets/ γ • hadronic final state: 1 1 QCD ‣ very difficult -1 -1 10 10 ttbar 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 4 4 ∆ ∆ φ φ (e,e) (e,e)

ℓ ℓ ℓ ℓ ℓ ℓ High Mass Higgs Channels Before Cut Z � � � After HT Cut, M =160 After Preselection, M =160 Before Cut Z � � � H WZ H Z � � � QCD 2 2 10 10 QCD t t QCD }(250-500) 4 4 t t 10 10 10 10 � QCD t t � t t ZZ 10 10 3 3 10 10 ZZ 10 10 WW ZZ WZ W WZ � µ � WZ 2 2 WW 10 10 1 1 1 1 Z � µ µ ZZ Z � µ µ W � µ � 10 10 W W � µ � � � µ � Z � � � 1 1 Z � µ µ WW WW -1 -1 Z � µ µ 10 10 1 1 Data Data Data -1 -1 Data 10 10 H120 -1 -1 H160 10 10 H160 H160 -2 -2 10 10 • 2 leptons with high p T -1 -1 10 10 -2 -2 10 10 0 0 20 20 40 40 60 60 80 80 100 120 100 120 140 160 180 140 160 180 200 220 240 200 220 240 • Isolation of e/µ against QCD and b-jets -2 -2 10 10 0 0 50 50 100 100 150 150 200 200 250 250 300 300 350 350 400 400 450 450 500 500 M M / GeV / GeV 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 0 0 10 10 20 20 30 30 40 40 50 50 60 60 70 70 80 80 90 90 100 100 µ µ µ µ HT / GeV HT / GeV � � � � ( ( µ µ , , µ µ ) ) MET / GeV MET / GeV 1 1 2 2 • E ̷ T due to 2 neutrinos • E ̷ T significance: S/B ≈ 15/300k ‣ not from mis-measured lepton p T ‣ not from mis-measured jet p T • m ll < m Z S/B ≈ 5/50 • Σ jets p T < 100 against tt ̅ background

Cuts Optimised for m H =120 - 200 Selection criterion m H = 120 m H = 140 m H = 160 m H = 180 m H = 200 Cut 1 Preselection Trigger, ID, leptons with opposite charge, z V T X < 60 cm, M µµ > 17 GeV p T > 20/10GeV 20/15 25/15 25/15 25/15 Cut 2 Missing trans- 25 < E / T < 70 25 < E / T < 80 30 < E / T < 90 35 < E / T < 100 35 < E / T < 110 verse energy E / T Cut 3 Sig (E / T ) Sig (E / T ) > 5 (for N Jet > 0) Cut 4 M T M T M T M T M T M T min ( l, E / T ) min > 30 min > 30 min > 40 min > 45 min > 45 Cut 5 Invariant mass 17 < M µµ < 60 17 < M µµ < 70 17 < M µµ < 75 17 < M µµ < 85 17 < M µµ < 95 M µµ T + p l � Cut 6 Σ p T = p l T + 60 < Σ p T < 135 70 < Σ p T < 160 80 < Σ p T < 170 90 < Σ p T < 180 90 < Σ p T < 200 E / T Cut 7 H T (scalar sum of H T < 60 H T < 60 H T < 60 H T < 60 H T < 50 p Jet T ) Info Neural Net NN > 0 . 5

Neural Net L=1.2 fb − 1 L=1.2 fb − 1 entries entries entries entries W+jets/ e + e − γ e + e − DØ Run II data data DØ Run II 4 4 4 4 10 10 10 10 Preliminary Preliminary H → WW × 10 → × 160 H WW 10 160 3 3 3 3 10 10 10 10 M ll Σ p T data Z e e Z → e e → QCD → Z e e 2 2 10 10 2 2 10 10 Diboson Diboson 10 10 10 10 γ H WW 10 W+jets/ W+jets/ γ → × Diboson ttbar 160 1 1 1 1 QCD QCD -1 -1 10 10 10 10 -1 -1 L=1.2 fb − 1 ttbar ttbar entries entries 0 0 20 20 40 40 60 60 80 80 100 100 120 120 140 140 160 160 180 180 200 200 50 50 100 100 150 150 200 200 250 250 300 300 ∑ ∑ 10 e + e − M M [GeV] [GeV] p p [GeV] [GeV] inv inv DØ Run II T T L=1.2 fb − 1 3 3 10 entries entries Preliminary e + e − DØ Run II data 4 4 Preliminary 10 10 H → WW × 10 160 2 2 10 10 m H =160 3 3 E ̷ T 10 10 Z → e e NN NN Output 2 2 10 10 x 10 Diboson 10 10 10 10 W+jets/ γ 1 1 QCD 1 1 -1 -1 10 10 ttbar 0 0 20 20 40 40 60 60 80 80 100 100 120 120 140 140 160 160 180 180 200 200 -1 -1 miss miss E E [GeV] [GeV] 10 10 L=1.2 fb − 1 T T entries entries L=1.2 fb − 1 5 5 10 10 e + e − DØ Run II data entries entries e + e − Preliminary DØ Run II data Δϕ ll 4 4 10 10 4 4 10 10 0 0 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.6 0.7 0.7 0.8 0.8 0.9 0.9 1 1 H → WW × 10 Preliminary 160 H → WW × 10 NN NN 160 3 3 3 3 10 10 10 10 M Tmin (l,E ̷ T ) Z → e e Z → e e 2 2 10 10 2 2 10 10 Diboson ≈ 30% improvement Diboson 10 10 10 10 W+jets/ γ from NN W+jets/ γ 1 1 1 1 QCD QCD -1 -1 10 10 ttbar 10 10 -1 -1 ttbar 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 4 4 (e,e) (e,e) ∆ ∆ φ φ 0 0 20 20 40 40 60 60 80 80 100 100 120 120 min min M M [GeV] [GeV] T T

Neural Net L=1.2 fb − 1 L=1.2 fb − 1 entries entries entries entries e + e − e + e − DØ Run II data data DØ Run II 4 4 4 4 10 10 10 10 Preliminary Preliminary H → WW × 10 → × 160 H WW 10 160 3 3 3 3 10 10 10 10 M ll Σ p T Z → e e → Z e e 2 2 10 10 2 2 10 10 Diboson Diboson 10 10 10 10 γ W+jets/ W+jets/ γ 1 1 1 1 dphiL1L2 QCD QCD -1 -1 10 10 10 10 -1 -1 L=1.2 fb − 1 ttbar ttbar minMt entries entries 0 0 20 20 40 40 60 60 80 80 100 100 120 120 140 140 160 160 180 180 200 200 50 50 100 100 150 150 200 200 250 250 300 300 ∑ ∑ 10 e + e − M M [GeV] [GeV] p p [GeV] [GeV] inv inv DØ Run II T T L=1.2 fb − 1 3 3 10 entries entries M Preliminary e + e − DØ Run II data 4 4 Preliminary 10 10 H → WW × 10 160 2 2 10 10 dphiMetL2 3 3 E ̷ T 10 10 NN Output Z → e e NN type 2 2 10 10 Diboson dphiMetL1 10 10 10 10 W+jets/ γ 1 1 met QCD 1 1 -1 -1 10 10 ttbar pt2 0 0 20 20 40 40 60 60 80 80 100 100 120 120 140 140 160 160 180 180 200 200 -1 -1 miss miss E E [GeV] [GeV] 10 10 L=1.2 fb − 1 T T entries entries L=1.2 fb − 1 5 5 10 10 e + e − DØ Run II data pt1 entries entries e + e − Preliminary DØ Run II data Δϕ ll 4 4 10 10 4 4 10 10 0 0 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.6 0.7 0.7 0.8 0.8 0.9 0.9 1 1 H → WW × 10 Preliminary 160 H → WW × 10 NN NN 160 3 3 3 3 10 10 10 10 M Tmin (l,E ̷ T ) Z → e e Z → e e 2 2 10 10 2 2 10 10 Diboson Diboson 10 10 10 10 W+jets/ γ W+jets/ γ 1 1 1 1 QCD QCD -1 -1 10 10 ttbar 10 10 -1 -1 ttbar 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 4 4 (e,e) (e,e) ∆ ∆ φ φ 0 0 20 20 40 40 60 60 80 80 100 100 120 120 min min M M [GeV] [GeV] T T