Di-Higgs production and Higgs self-coupling in ATLAS at HL-LHC Petar Bokan on behalf of the ATLAS collaboration HL/HE LHC Meeting, Fermilab 4-6 April 2018
Overview o Higgs self-coupling o Di-Higgs production at the LHC o Run-2 results o Di-Higgs prospects at the HL-LHC − hh → b ¯ bb ¯ b − hh → b ¯ bγγ − hh → b ¯ bτ + τ − 2/22
Higgs potential o Important to measure the shape of the Higgs potential V ( φ ) = − 1 2 µ 2 φ 2 + 1 4 λφ 4 Expanding about minimum: V ( φ ) → V ( v + h ) V = V 0 + λv 2 h 2 + λvh 3 + 1 4 λh 4 + ... Standard Model (SM): m 2 m 2 h h 2 + 2 v 2 vh 3 + 2 v 2 h 4 + ... 2 m 2 1 1 = V 0 + h h µ 4 v = = 246 GeV √ λ mass term hh -production hhh -production λ = m 2 h 2 v 2 ≈ 0 . 13 3/22
SM Higgs boson pair production at the LHC o SM Higgs boson pair production (gluon-gluon fusion - ggF): h h h h h Higgs-fermion Yukawa coupling Higgs boson self-coupling 4/22
SM Higgs boson pair production at the LHC o SM Higgs boson pair production (gluon-gluon fusion - ggF): h h h h h Higgs-fermion Yukawa coupling Higgs boson self-coupling Production cross-section small σ ( pp → HH + X ) [fb] gg → HH − two massive final state particles M H = 125 GeV 1000 NLO QCD − destructive interference qq ′ → HHqq ′ 100 production mode Cross-section qq / gg → t¯ tHH NLO QCD (14 TeV) LO QCD 10 q ′ → WHH q¯ gluon-gluon fusion ∼ 40 fb NNLO QCD q¯ q → ZHH vector boson fusion ∼ 2 fb 1 arXiv:1212.5581 Higgs-strahlung ∼ 1 fb t ¯ thh ∼ 1 fb 0.1 8 25 50 75 100 √ s [TeV] arXiv:1610.07922 4/22
SM Higgs boson pair production at the LHC arXiv:1712.08677 Single Higgs boson production o SM hh -production ∼ 1000 × smaller compared to h -production o Current LHC dataset won’t be large enough to reach the sensitivity 5/22
BSM Higgs boson pair production Sensitivities to BSM hh -production interesting already at LHC. Non-resonant enhancements: o Modified Yukawa/self-coupling Absent in SM o New couplings 6/22
BSM Higgs boson pair production Sensitivities to BSM hh -production interesting already at LHC. Non-resonant enhancements: o Modified Yukawa/self-coupling Absent in SM o New couplings Resonant Higgs boson pair h production Benchmark BSM hypotheses: X o Randall-Sundrum graviton G → hh (spin = 2) h o Heavy Higgs H → hh (spin = 0) Resonant production 6/22
Di-Higgs final states Di-Higgs decay modes and relative branching fractions: γγ bb WW ZZ ττ The most sensitive channels bb 34% to the SM hh : 10.23731/CYRM-2017-002 WW hh → b ¯ bb ¯ 25% 4.6% b : the highest branching fraction, large multijet background ττ 7.3% 2.7% 0.39% hh → b ¯ bτ + τ − : relatively large ZZ 3.1% 1.1% 0.33% 0.070% branching fraction, cleaner final state γγ 0.26% 0.10% 0.028% 0.012% 0.00052% hh → b ¯ bγγ : small branching fraction, clean signal extraction due to the narrow h → γγ mass peak 7/22
Di-Higgs final states Di-Higgs decay modes and relative branching fractions: γγ bb WW ZZ ττ bb 34% 10.23731/CYRM-2017-002 WW 25% 4.6% ττ 7.3% 2.7% 0.39% ZZ 3.1% 1.1% 0.33% 0.070% γγ 0.26% 0.10% 0.028% 0.012% 0.00052% other channels being considered: bbWW , 4 W and WWγγ 7/22
Di-Higgs final states Di-Higgs decay modes and relative branching fractions: γγ bb WW ZZ ττ bb 34% 10.23731/CYRM-2017-002 WW 25% 4.6% ττ 7.3% 2.7% 0.39% ZZ 3.1% 1.1% 0.33% 0.070% γγ 0.26% 0.10% 0.028% 0.012% 0.00052% feasibility studies: bbZZ , WWττ and 4 τ 7/22
Di-Higgs final states Di-Higgs decay modes and relative branching fractions: γγ bb WW ZZ ττ The most sensitive channels bb 34% to the SM hh : 10.23731/CYRM-2017-002 WW hh → b ¯ bb ¯ 25% 4.6% b : the highest branching fraction, large multijet background ττ 7.3% 2.7% 0.39% hh → b ¯ bτ + τ − : relatively large ZZ 3.1% 1.1% 0.33% 0.070% branching fraction, cleaner final state γγ 0.26% 0.10% 0.028% 0.012% 0.00052% hh → b ¯ bγγ : small branching fraction, clean signal extraction due to the narrow other channels being considered: h → γγ mass peak bbWW , 4 W and WWγγ feasibility studies: bbZZ , WWττ and 4 τ dedicated boosted analyses, VBF- hh investigated 7/22
SM Higgs pair production, Run-2 Results o Observed (expected) 95% C.L. limit on σ/σ SM (Run-2 published results): channel bbbb bbWW bb ττ bb γγ WW γγ ATLAS 13 (21) - - 117 (161) 747 (386) CMS 342 (308) 79 (89) 28 (25) 19 (17) - 2.3-3.2 fb − 1 13.3 fb − 1 27.5-35.9 fb − 1 o ATLAS publications using the 2015 + 2016 dataset expected. o In the context of the HL-LHC prospects studies this is important for those analyses which perform an extrapolation of the Run-2 result. o Possible statistical combination. ATLAS b ¯ bb ¯ b : Preliminary ATLAS b ¯ bγγ : ATLAS-CONF-2016-004 ATLAS W W γγ : ATLAS-CONF-2016-071 CMS b ¯ bb ¯ CMS b ¯ b : PAS HIG-16-002 bW W : PAS-HIG-17-006 CMS b ¯ CMS b ¯ bττ : Phys. Lett. B 778 (2018) 101 bγγ : PAS-HIG-17-008 8/22
SM hh HL-LHC prospects Two alternative approaches: (1) extrapolation of the Run-2 results → √ s = 14 TeV , � Ldt = 3000 fb − 1 (2) 14 TeV samples with the upgraded detector geometry, upgrade performance functions 9/22
Run-2 resolved hh → b ¯ bb ¯ b o Background: [GeV] 2 Events / 25 GeV ∼ 90% multijet and ∼ 10% t ¯ ATLAS Preliminary 220 t 200 -1 s = 13 TeV, 24.3 fb subl 200 2j Resolved, 2016 m 180 o Data-driven estimation of the 180 multijet background 160 160 → 2 b + 2 j events model 4 b 140 140 120 7 10 Events / 100 GeV 120 Signal Region 100 Data ATLAS Preliminary 6 10 Multijet -1 s = 13 TeV, 24.3 fb 80 100 Hadronic t t Control Region Resolved Signal Region, 2016 5 10 60 Semi-leptonic t t Sideband Region 80 Scalar (280 GeV) 4 10 40 × SM HH 100 3 G (800 GeV, k/ M =1) 60 20 10 KK Pl G (1200 GeV, k/ M =2) Pl KK 0 2 10 Stat+Syst Uncertainty 60 80 100 120 140 160 180 200 m lead [GeV] 2j 10 1 o The reweighting is performed − 1 10 using one-dimensional 1.5 Data / Bkgd distributions iteratively 1 o t ¯ t normalization from data 0.5 200 400 600 800 1000 1200 1400 m [GeV] 4j 10/22
b b h p p h b b SM hh → b ¯ bb ¯ b HL-LHC prospects ATL-PHYS-PUB-2016-024 Ldt = 3000 fb − 1 extrapolation of the previous Run-2 result: � Ldt = 10 . 1 → � Signal and background distributions scaled by f = � Ldt | target / � Ldt | current All distributions are scaled by 1.18 to account for an increase in cross-section. Normalizations fixed to the best Run-2 fit values. 11/22
Extrapolated sensitivity ATL-PHYS-PUB-2016-024 SM 20 ATLAS Preliminary ATLAS Internal σ No systematic uncertainties / σ -1 s = 13 TeV, 2016, 10.1 fb 18 95% C.L. exclusion limit on s = 14 TeV 16 Current systematic uncertainties systematic uncertainties 14 in units of signal strength 12 10 8 Source ∆ µ 6 Luminosity 0.05 4 2 Jet Energy 0.09 Limits w. no Syst. 0 500 1000 1500 2000 2500 3000 b -tagging 0.34 Limits w. Syst. 3 Theoretical 0.10 2 Multijet 1.85 1 t ¯ t 2.83 0 0 500 1000 1500 2000 2500 3000 -1 Integrated Luminosity [fb ] o Extrapolation of the 95% C.L. exclusion limit: without systematics: σ/σ SM = 1 . 5 with current level of systematics: σ/σ SM = 5 . 2 12/22
Background uncertainty reduction ATL-PHYS-PUB-2016-024 SM σ 5 / ATLAS Internal ATLAS Preliminary σ -1 s = 13 TeV, 2016, 10.1 fb -1 s = 14 TeV, L = 3000 fb 4.5 4 3.5 3 2.5 Expected 95% C.L. limit Expected 95% C.L. limit, background uncertainties ∝ 1/ L 2 Expected 95% C.L. limit, statistical uncertainties only 1.5 0 0.2 0.4 0.6 0.8 1 Background uncertainty scale relative to current level o Significant improvements in (data-driven) background modeling possible with larger dataset 13/22
Limits on Higgs self-coupling (Pixel TDR) Updated in respect to ATL-PHYS-PUB-2016-024 o extrapolated using a full 2015 + 2016 dataset and o includes improved ITk b -tagging expected efficiency 200 450 [fb] [fb] Non-resonant prediction Non-resonant prediction ATLAS Simulation Internal ATLAS Simulation Internal 180 400 Expected Limit (95% CL) Expected Limit (95% CL) σ pp → HH → bbbb σ pp → HH → bbbb Baseline, no systematic uncertainties Baseline, current systematic uncertainties Expected ± 1 σ Expected ± 1 σ 160 Expected ± 2 σ Expected ± 2 σ -1 350 -1 s = 14 TeV, L = 3000 fb s = 14 TeV, L = 3000 fb 140 300 120 250 100 200 80 150 60 100 40 50 20 − 20 − 15 − 10 − 5 0 5 10 15 20 − 20 − 15 − 10 − 5 0 5 10 15 20 SM SM λ / λ λ / λ HHH HHH HHH HHH o Extrapolation of the 95% C.L. exclusion limit: without systematics: 0 . 2 < λ hhh /λ SM hhh < 7 . 0 with systematics: − 3 . 5 < λ hhh /λ SM hhh < 11 . 0 14/22
Recommend
More recommend
