Search for di-higgs to 4b with the ATLAS detector. Tony(Baojia)Tong, Harvard University CLHCP, PKU, Dec. 18, 2016

Transcription

1 Search for di-higgs to 4b with the ATLAS detector Tony(Baojia)Tong, Harvard University CLHCP, PKU, Dec. 8, 6

2 Motivation Di-Higgs production Cross section small in SM: 8 TeV ~ fb (NNLO) 3 TeV ~ 38 fb (NNLO + NNLL) Larger if BSM ( ) physics exists Non-resonant Examples tthh, tth vertex modifications λ hhh triple-higgs coupling Resonant Examples KK Graviton Heavy Higgs: HDM Dec 8, 6

3 Motivation Di-Higgs production Cross section small in SM: 8 TeV ~ fb (NNLO) 3 TeV ~ 38 fb (NNLO + NNLL) Larger if BSM ( ) physics exists Non-resonant Examples tthh, tth vertex modifications λ hhh triple-higgs coupling Resonant Examples KK Graviton Heavy Higgs: HDM 3 Dec 8, 6

4 Motivation Di-Higgs production Cross section small in SM: 8 TeV ~ fb (NNLO) 3 TeV ~ 38 fb (NNLO + NNLL) Larger if BSM ( ) physics exists Non-resonant Examples tthh, tth vertex modifications λ hhh triple-higgs coupling h Resonant Examples (?) KK Graviton Heavy Higgs: HDM h 4 Dec 8, 6

5 Motivation Di-Higgs decay larger branching ratio higher yield e-3 5 Dec 8, 6

6 Motivation Di-Higgs decay larger branching ratio higher yield e-3 4b better limit for mass > 5 GeV 6 Dec 8, 6

7 RunII 4b: object definition Jets Merging and the Two Channels ATLAS-CONF-6-49 Standard resolved 4b jets for the low mass range.5 TeV resonance ~ 6 GeV pt Higgs ΔRbb ~mh/pt ~.4 Objects/ Final State Resolved (5 GeV) Boosted (-3 GeV) Trigger Mixed b Trigger Large R-jet Trigger Two. trimmed Jets Four.4 Anti-kt Jets Anti-kt Jets Leading > 45 GeV pt cuts Jet pt > 3 GeV Subleading > 5 GeV 77% WP on Anti-kt B-tagging 7% WP on EM Jets R=. track jets 7 Dec 8, 6

8 RunII 4b: object definition Jets Merging and the Two Channels ATLAS-CONF-6-49 Standard resolved 4b jets for the low mass range.5 TeV resonance ~ 6 GeV pt Higgs ΔRbb ~mh/pt ~.4 Objects/ Final State Resolved (5 GeV) Boosted (-3 GeV) Trigger Mixed b Trigger Large R-jet Trigger Two. trimmed Jets Four.4 Anti-kt Jets Anti-kt Jets Leading > 45 GeV pt cuts Jet pt > 3 GeV Subleading > 5 GeV 77% WP on Anti-kt B-tagging 7% WP on EM Jets R=. track jets 8 Dec 8, 6

9 RunII 4b: object definition Jets Merging and the Two Channels ATLAS-CONF-6-49 Standard resolved 4b jets for the low mass range.5 TeV resonance ~ 6 GeV pt Higgs ΔRbb ~mh/pt ~.4 Objects/ Final State Resolved (5 GeV) Boosted (-3 GeV) Trigger Mixed b Trigger Large R-jet Trigger Two. trimmed Jets Four.4 Anti-kt Jets Anti-kt Jets Leading > 45 GeV pt cuts Jet pt > 3 GeV Subleading > 5 GeV 77% WP on Anti-kt B-tagging 7% WP on EM Jets R=. track jets 9 Dec 8, 6

10 RunII 4b: object definition Two Higgs Mass Plane ATLAS-CONF-6-49 Signal Region (SR): Circle centered at h mass subl m j 3 5 ATLAS Preliminary s = 3 TeV, 6,. fb Resolved 6 5 Events/9 GeV Control Region (CR) : 4 Ring outside SR (for validation) 5 3 SR Sideband (SB) CR Ring outside CR (for modeling) SB mlead j Dec 8, 6

11 RunII 4b: object definition Two Higgs Mass Plane ATLAS-CONF-6-49 Signal Region (SR): Circle centered at h mass subl m j 3 5 ATLAS Preliminary s = 3 TeV, 6,. fb Resolved 6 5 Events/9 GeV Control Region (CR) : 4 Ring outside SR (for validation) 5 3 SR Sideband (SB) CR Ring outside CR (for modeling) SB mlead j Dec 8, 6

12 RunII 4b: object definition Two Higgs Mass Plane ATLAS-CONF-6-49 Signal Region (SR): Circle centered at h mass subl m j 3 5 ATLAS Preliminary s = 3 TeV, 6,. fb Resolved 6 5 Events/9 GeV Control Region (CR) : 4 Ring outside SR (for validation) 5 3 SR Sideband (SB) CR Ring outside CR (for modeling) SB mlead j Dec 8, 6

13 RunII 4b: resolved selection Jets Pair Combinatorics and Cuts ATLAS-CONF-6-49 Select hh pair that has the minimal distance to the diagonal line on the D mass plane m4j dependent requirements on h pt, eta, and drjj Good signal efficiency across large mass ranges 3 Dec 8, 6

14 RunII 4b: resolved selection Jets Pair Combinatorics and Cuts ATLAS-CONF-6-49 Select hh pair that has the minimal distance to the diagonal line on the D mass plane m4j dependent requirements on h pt, eta, and drjj Good signal efficiency across large mass ranges Efficiency Acceptance b-tagged jets R jj m 4j X hh Trigger Dependent Cuts, R hh ATLAS Preliminary s = 3 TeV, 6,. fb Resolved m G* KK Dec 8, 6 SMNR

15 RunII 4b: resolved background estimation Resolved 4b Background ATLAS-CONF-6-49 Background: 93% qcd data driven 7% ttbar MC subl m j 3 5 ATLAS Preliminary s = 3 TeV, 6,. fb Resolved 6 5 Events/9 GeV Background shape estimation comes 4 5 from Tag SB(sideband)/CR(control)/ SR 3 SR(signal) regions CR SB b inclusive sample is used to derive 5 the normalization estimation in 4b mlead j 5 Dec 8, 6

16 RunII 4b: resolved background estimation Resolved 4b Background 4b SR SB ATLAS-CONF-6-49 Background: 93% qcd data driven b SR SB 7% ttbar MC subl m j 3 5 ATLAS Preliminary s = 3 TeV, 6,. fb Resolved 6 5 Events/9 GeV Background shape estimation comes 4 5 from Tag SB(sideband)/CR(control)/ SR 3 SR(signal) regions CR SB b inclusive sample is used to derive 5 the normalization estimation in 4b mlead j 6 Dec 8, 6

17 RunII 4b: boosted selection Track Jets Tagging and Signal Regions ATLAS-CONF Tag: 3Tag: (recover efficiency) b b Tag Split: one b Tag in each large R jet Three Signal Regions: 4Tag, 3Tag and Tag Split b b 7 Dec 8, 6

18 RunII 4b: boosted selection Track Jets Tagging and Signal Regions ATLAS-CONF Tag: 3Tag: (recover efficiency) b b Tag Split: one b Tag in each large R jet Three Signal Regions: 4Tag, 3Tag and Tag Split Acceptance x Efficiency.8 b-tagged track-jets ATLAS Preliminary G c=., s = 3 TeV 3 b-tagged track-jets Boosted 4 b-tagged track-jets b b Mass 8 Dec 8, 6

19 RunII 4b: boosted selection Track Jets Tagging and Signal Regions ATLAS-CONF Tag: 3Tag: (recover efficiency) b b Tag Split: one b Tag in each large R jet Three Signal Regions: 4Tag, 3Tag and Tag Split Acceptance x Efficiency.8 b-tagged track-jets ATLAS Preliminary G c=., s = 3 TeV 3 b-tagged track-jets Boosted 4 b-tagged track-jets Acceptance x Efficiency..8.6 ATLAS Preliminary G c=., s = 3 TeV Boosted large-r jets η <.7 hh b-tagged track-jets X hh <.6 b b Mass Mass 9 Dec 8, 6

20 RunII 4b: boosted background estimation Boosted 4b Background ATLAS-CONF-6-49 Background: 85% qcd data driven 5% ttbar data driven Background shape estimation comes from b SB(sideband)/ subl m J 5 ATLAS Preliminary s=3 TeV, 3.3 fb Boosted 5 Events/ GeV CR(control)/SR(signal) regions 5 Fit the leading jet mass in SB to SR extract ttbar and qcd fraction, then SB CR 5 take the b to N(, 3, 4)b ratio to get signal region normalization lead m J Dec 8, 6

21 RunII 4b: boosted background estimation Boosted 4b Background ATLAS-CONF b SR SB Background: 85% qcd data driven b SR SB 5% ttbar data driven Background shape estimation comes from b SB(sideband)/ subl m J 5 ATLAS Preliminary s=3 TeV, 3.3 fb Boosted 5 Events/ GeV CR(control)/SR(signal) regions 5 Fit the leading jet mass in SB to SR extract ttbar and qcd fraction, then SB CR 5 take the b to N(, 3, 4)b ratio to get signal region normalization lead m J Dec 8, 6

22 Systematics Uncertainties Countdown ATLAS-CONF-6-49 Resolved Signal uncertainty mainly comes from b-tagging Bkg uncertainty is dominated by data driven Boosted control region estimates Background/QCD shape uncertainty is also applied Dec 8, 6

23 RunII 4b: resolved results Signal Region: Resolved ATLAS-CONF-6-49 Final discriminant: four jets s invariant mass; no significant excess observed Data 5 6 Obs Exp 89 ± ± 3 Events/ GeV ATLAS Preliminary s = 3 TeV, 5, 3. fb Signal Region: Resolved Data Multijet tt G(3) G(8) SM hh 5 Stat+Syst Uncertainty Events/ GeV 3 ATLAS Preliminary Data s = 3 TeV, 6,. fb Signal Region: Resolved Multijet tt G(3) G(8) SM hh 5 Stat+Syst Uncertainty 5 6 Data/Bkgd m 4j Data/Bkgd m 4j *5 and 6 have different trigger selection due to different run conditions 3 Dec 8, 6

24 RunII 4b: boosted results Signal Region: Boosted ATLAS-CONF-6-49 Final discriminant: dijet invariant mass; no significant excess observed Channel bs 3b 4b Obs Exp 77 ± ± ± 9 Events / GeV 3 ATLAS Preliminary s=3 TeV, 3.3 fb Signal Region, Boosted -tag Data Multijet tt Stat+Syst G() bs Events / GeV 3 ATLAS Preliminary s=3 TeV, 3.3 fb Signal Region, Boosted 3-tag 3b Data Multijet tt Stat+Syst G() Events / GeV ATLAS Preliminary s=3 TeV, 3.3 fb Signal Region, Boosted 4-tag 4b Data Multijet tt Stat+Syst G() Data / Bkgd m JJ m J Data / Bkgd m J Data / Bkgd m J 4 Dec 8, 6

25 RunII 4b: limits Combined Limits ATLAS-CONF-6-49 Resolved + Boosted Combined Asymptotic Limits [fb] hh bbbb 4 3 ATLAS Preliminary s = 3 TeV Ldt = 3.3 fb Bulk RS, k/m Pl =. Observed Limit (95% CL) Expected Limit (95% CL) Expected ± σ Expected ± σ Non-Resonance limit: pp G* KK Resolved Boosted pb (.3 pb expected) σ μ ~ m G*KK 5 Dec 8, 6

26 Summary Conclusion ATLAS-CONF-6-4 ATLAS hh bbbb search 6 summer results have been presented So far no significant excess observed, 3 TeV non-resonance limit at pb HL-LHC prospectives have been studied as well, limits depends on detector conditions, set on non-resonant μ ~ Search teams are actively working on [fb] pp hh bbbb σ Non-resonant prediction Expected Limit (95% CL) s = 4 TeV, L = 3 fb Expected ± σ Expected ± σ ATLAS Internal Preliminary SM λ HHH /λ HHH 6 data! Stay tuned! 6 Dec 8, 6

27 Back Up Back up Slides 7 Dec 8, 6

28 HH ATLAS Results Summary of HH ATLAS Results ATLAS Search Results 8TeV, fb 3TeV, fb HL-LHC (links) bbbb 3 / 3 prospect bbττ prospect bbγγ 3 prospect WW*γγ 3 Combination 8 Dec 8, 6

29 RunII 4b Fit on Leading Jet Mass Distribution ATLAS-CONF-6-49 Given: Simultaneous fit of μqcd, att to extract the normalization factors All fits are independent Events / GeV ATLAS Preliminary s=3 TeV, 3.3 fb Sideband Region, Boosted -tag bs Data Multijet tt Stat Events / GeV ATLAS Preliminary s=3 TeV, 3.3 fb Sideband Region, Boosted 3-tag 3b Data Multijet tt Stat Events / GeV 8 6 ATLAS Preliminary s=3 TeV, 3.3 fb Sideband Region, Boosted 4-tag 4b Data Multijet tt Stat Data / Bkgd Mass Leading large-r jet mass Data / Bkgd Leading large-r jet mass Data / Bkgd Leading large-r jet mass 9 Dec 8, 6

30 RunII 4b Reweighting Details Kinematics dependence of μqcd is corrected by reweighting Resolved: Njet distribution, leading Higgs candidate pt, subleading Higgs candidate E Boosted; leading Higgs candidate pt, leading track jet pt of the leading Higgs candidate, leading track jet pt of the subleading Higgs candidate Iterated reweighting is used such that the correlations are taken into account. 3 Dec 8, 6

31 RunII 4b Control Region: Resolved ATLAS-CONF-6-49 Good agreement in shape and normalization Obs Exp 4 ± ± Events/ GeV 3 ATLAS Preliminary s = 3 TeV, 5, 3. fb Control Region: Resolved Data Multijet tt Fit to Tail Tail Up Tail Down Stat. Uncertainty Events/ GeV 4 3 ATLAS Preliminary s = 3 TeV, 6,. fb Control Region: Resolved Data Multijet tt Fit to Tail Tail Up Tail Down Stat. Uncertainty 5 6 Data/Bkgd m 4j Data/Bkgd m 4j 3 Dec 8, 6

32 RunII 4b Control Region: Boosted ATLAS-CONF-6-49 Good agreement in shape and normalization Obs Exp 6954 ± 5 57 ± ± 5.8 Events / GeV 4 3 ATLAS Preliminary s=3 TeV, 3.3 fb Control Region, Boosted -tag Data Multijet tt Stat+Syst bs Events / GeV 3 ATLAS Preliminary s=3 TeV, 3.3 fb Control Region, Boosted 3-tag Data Multijet tt Stat+Syst 3b Events / GeV ATLAS Preliminary s=3 TeV, 3.3 fb Control Region, Boosted 4-tag Data Multijet tt Stat+Syst 4b Data / Bkgd mhh m J Data / Bkgd m J Data / Bkgd m J 3 Dec 8, 6

33 RunII 4b Limit Comparison ATLAS-CONF-6-49 ICHEP-Moriond [fb] hh bbbb 4 3 ATLAS Preliminary s = 3 TeV Ldt = 3.3 fb Bulk RS, k/m Pl =. Observed Limit (95% CL) Expected Limit (95% CL) Expected ± σ Expected ± σ Previous Obs. Limit (L = 3. fb Previous Exp. Limit (L = 3. fb ) ) Limit Direct Comparison pp G* KK Resolved Boosted σ m G*KK 33 Dec 8, 6

34 Run I 4b Resolved and Boosted Results Eur. Phys. J. C (5) 75:4 Sample Signal Region Yield Multijet 8.4 ± 4.9 t t Resolved 5. ±.6 Z+jets.4 ±. Total 87. ± 5.6 Data 87 SM hh.34 ±.5 G KK (5 GeV ), k/ M Pl = 7 ± 5.9 Sample Signal Region Yield Multijet 3.5 ± 4. Boosted t t. ±.9 Z+jets.4 ±.6 Total 5.7 ± 4. Data 34 G KK ( GeV ), k/ M Pl =. ±.6 Events / GeV ATLAS s = 8 TeV Ldt = 9.5 fb Signal Region Data Multijet tt Syst+Stat Uncertainty G*(7), k/m Pl G*(), k/m Pl =. =., 3 Events / 5 GeV 8 6 ATLAS s = 8 TeV Ldt = 9.5 fb Signal Region Data Multijet tt Syst+Stat Uncertainty G*(), k/m Pl =., G*(5), k/m Pl =., Data / Bkgd m 4j Data / Bkgd m J m J 34 Dec 8, 6

35 RunI 4b Combined Limit Eur. Phys. J. C (5) 75:4 hh bbbb) [fb] ATLAS s = 8 TeV Ldt = 9.5 fb Bulk RS, k/m Pl =. Observed Limit (95% CL) Expected Limit (95% CL) Expected ±σ Expected ±σ σ(pp G* KK m G* KK 35 Dec 8, 6