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Search for Exotics with Top at ATLAS Search for exotics with top at ATLAS Diedi Hu Columbia University On behalf of the ATLAS collaboration EPSHEP2013, Stockholm July 18, 2013 Motivation Motivation Due to its large mass, top quark offers a unique window to search for new physics: mt ∼ ΛEWSB (246GeV): top may play a special role in the EWSB Many extensions of the SM explain the large top mass by allowing the top to participate in new dynamics. Approaches of new physics search Measure top quark properties: check with SM prediction. Directly search for new particles coupling to top tt resonances searches Search for anomalous single top production Vector-like quarks searches (Covered in another talk "Searches for fourth generation vector-like quarks with the ATLAS detector") Search for exotics with tt and single top D.Hu, Columbia Univ. 2 / 16 tt resonance search with 14.3 fb−1 @ 8TeV tt resonance: benchmark models 2 specific models used as examples of sensitivity Leptophobic topcolor Z 0 [2] Explains the top quark mass and EWSB through top quark condensate Z 0 couples strongly only to the first and third generation of quarks Narrow resonance: Γ=m 1:2% ∼ Kaluza-Klein gluons [3] Predicted by the Bulk Randall-Sundrum models with warped extra dimension Strongly coupled to the top quark Broad resonance: Γ=m 15% ∼ Search for exotics with tt and single top D.Hu, Columbia Univ. 3 / 16 tt resonance search with 14.3 fb−1 @ 8TeV tt resonance: lepton+jets(I) [4] Backgrounds SM tt, Z+jets, single top, diboson and W+jets shape: directly from MC W+jets normalization, multijet: estimated from data Event selection One top decays hadronically and The boosted selection the other semileptonically. helps improve efficiency Boosted selection in high signal mass 1 high pT R=1.0p jet with region mjet > 100GeV, d12 > 40GeV; 1 R=0.4 jet close to lepton; 20 18 ATLAS Preliminary Simulation ≥ 1 R=0.4 b-jet(could overlap s=8 TeV 16 µ + jets, combined with the former 2 jets.) 14 µ + jets, boosted e + jets, combined miss 12 1 isolated lepton; E . [%] Efficiency e + jets, boosted T 10 Resolved selection 8 6 3 or 4 R=0.4 jets with ≥ 1 b-jet 4 miss 2 1 isolated lepton; ET . 0 (Same as boosted channel) 0 0.5 1 1.5 2 2.5 3 3.5 m [TeV] tt Search for exotics with tt and single top D.Hu, Columbia Univ. 4 / 16 tt resonance search with 14.3 fb−1 @ 8TeV tt resonance: lepton+jets(II) tt invariant mass reconstruction miss pz (ν): from lepton+ET system with mW constraint 2 Resolved: χ algorithm using mt and Boosted: take R=1 jet as mW , top pair pT balance as constraint hadronically decaying top; build the other top from ν, lepton and R=0.4 jet 0.3 ATLAS ATLAS 0.25 Preliminary Preliminary Simulation, s=8TeV 0.25 Simulation, s=8TeV Resolved Boosted 0.2 Z’ (0.5 TeV) Z’ (1.0 TeV) 0.2 Z’ (1.0 TeV) Z’ (1.5 TeV) 0.15 Z’ (1.5 TeV) Z’ (2.0 TeV) Z’ (2.0 TeV) 0.15 Z’ (3.0 TeV) 0.1 0.1 Fraction of events / 50 GeV Fraction of events / 100 GeV 0.05 0.05 0 0 0 0.5 1 1.5 2 2.5 3 3.5 0 0.5 1 1.5 2 2.5 3 3.5 mreco[TeV] mreco[TeV] tt tt The tt mass spectra are used for statistical analysis Search for exotics with tt and single top D.Hu, Columbia Univ. 5 / 16 tt resonance search with 14.3 fb−1 @ 8TeV tt resonance: lepton+jets(III) Dominant systematics on yields 8 10 ATLAS Preliminary Data 5 × Z’ (1.5 TeV) 7 10 •1 5 × g (2.0 TeV) ∫ L dt = 14.2 fb tt KK Systematics Resolved Boosted Note: R=1. jet systematics 106 Multi•jets W+jets tt 105 Other Backgrounds normalization 8:0% 9:0% also affect the resolved channel 4 s = 8 TeV Events / TeV Events / 10 JES of because only events failing the 103 R=0.4 jets 6:0% 0:70% 2 JES+JMS of 10 R=1. jets 0:30% 17% boosted selection will be 10 1 b-tag efficiency 4:0% 3:4% examined with the resolved 1.5 0 0.5 1 1.5 2 2.5 3 3.5 PDF 2:9% 6:0% 1 selection criteria. 0.5 Data/Bkg 0 0.5 1 1.5 2 2.5 3 3.5 mreco [TeV] Exclusion ranges @ 95% C.L. tt −1 14.3 fb @ 8TeV [4] s = 8 TeV Obs. 95% CL upper limit s = 8 TeV Obs. 95% CL upper limit 3 ) [pb] ) [pb] 3 t t 10 Exp. 95% CL upper limit Exp. 95% CL upper limit •1 10 L dt ­1 L dt t t ∫ = 14.3 fb ∫ = 14.3 fb Exp. 1 σ uncertainty Exp. 1 σ uncertainty → Exclusion ranges Observed → σ Exp. 2 σ uncertainty 2 Exp. 2 uncertainty KK 0 10 2 Z 0.5-1.8TeV Leptophobic Z’ (LO x 1.3) 10 Kaluza­Klein gluon (LO) BR(Z’ ATLAS ATLAS × Preliminary BR(g Preliminary KK gluon 0.5-2.0TeV 10 × Z’ 10 KK σ g σ −1 1 4.7 fb @ 7TeV [5] 1 10•1 10­1 Exclusion ranges Observed 0 10•2 Z 0.50-1.74TeV 10­2 0.5 1 1.5 2 2.5 3 0.5 1 1.5 2 2.5 KK gluon 0.70-2.07TeV g mass [TeV] Z’ mass [TeV] KK Search for exotics with tt and single top D.Hu, Columbia Univ. 6 / 16 tt resonance search with 14.3 fb−1 @ 8TeV tt resonance: full hadronic decays [6] 102 Two complementary 2 Obs. 95% CL upper limit Obs. 95% CL upper limit ) [pb] 10 ) [pb] t Exp. 95% CL upper limit t Exp. 95% CL upper limit t t Exp. 1 σ uncertainty Exp. 1 σ uncertainty techniques relying on jet → → Exp. 2 σ uncertainty KK Exp. 2 σ uncertainty 10 substructure are used to 10 Leptophobic Z' (LOx1.3) KK gluon (LO) BR(Z' × BR(g ATLAS ATLAS × σ identify top: HEPTopTagger σ HEPTopTagger 1 HEPTopTagger 1 Top Template Tagger 10-1 s = 7 TeV s = 7 TeV -1 -1 ∫ L dt = 4.7 fb 10-1 ∫ L dt = 4.7 fb Exclusion ranges @ 95% C.L. 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0.8 1 1.2 1.4 1.6 1.8 2 −1 with 4.7 fb @ 7TeV g Mass [TeV] Z' Boson Mass [TeV] KK Use HepTopTagger 102 10 Obs. 95% CL upper limit Obs. 95% CL upper limit ) [pb] ) [pb] t Exp. 95% CL upper limit t Exp. 95% CL upper limit t t σ Exp. 1σ uncertainty Exp. 1 uncertainty Exclusion ranges Observed → → 10 σ Exp. 2σ uncertainty Exp. 2 uncertainty Z 0 0.70-1.00TeV KK Leptophobic Z' (LOx1.3) KK gluon (LO) BR(Z' 1 1.28-1.32TeV × BR(g 1 × σ KK gluon 0.70-1.48TeV σ -1 Use Top Template Tagger 10 s = 7 TeV s = 7 TeV -1 -1 ∫ L dt = 4.7 fb 10-1 ∫ L dt = 4.7 fb Exclusion ranges Observed 10-2 ATLAS Top Template Tagger ATLAS Top Template Tagger KK gluon 1.02-1.62TeV 1 1.2 1.4 1.6 1.8 2 1 1.2 1.4 1.6 1.8 2 g Mass [TeV] Z' Boson Mass [TeV] KK Search for exotics with tt and single top D.Hu, Columbia Univ. 7 / 16 W 0 ! tb search with 14.3 fb−1 @ 8TeV W 0 tb: theory [7] ! W 0 carries new charged interaction as a result of enlarged symmetry group. Example of phenomenological models Extra dimensions: Kaluza-Klein excitations of SM W Little Higgs: predicts new particles including W 0 Model-independent search Use an effective model describing the coupling of the W 0 to the fermions. 0 Vij 0 5 0 5 0µ L = p f¯i γµg (1 + γ ) + g (1 γ )W fj + h:c: 2 2 Rij Lij − Search for W 0 in t+b decay channel Explore models potentially inaccessible to leptonic search (W 0 ! lν). 0 WR can not decay to a lepton and νR if mνR > mW 0 Leptophobic W 0 W 0 may couple more strongly to the third generation quarks Can exploit the distinct signature of top quark. Search for exotics with tt and single top D.Hu, Columbia Univ. 8 / 16 W 0 ! tb search with 14.3 fb−1 @ 8TeV W 0 tb: analysis strategy ! Background tt, Z+jets, single top, diboson, W+jets shape: from MC W+jets normalization, multijet: estimated from data Event selection miss Preselection: 1 lepton, ET , 2 or 3 jets with ≥ 1 b-jet Signal region: ≥ 2 b-jets, MW 0 ≥ 270GeV Control region: ≥ 2 b-jets, mW 0 < 270GeV: Derive W+jets normalization; verify the variable modeling =1 b-jet: check the modeling of kinematic variables tb invariant mass reconstruction miss pz (ν): from lepton+ET system with mW constraint b from top: the b-jet/jet giving the mWb closest to mt 0 b from W : the other b-jet or highest pT jet Search for exotics with tt and single top D.Hu, Columbia Univ. 9 / 16 W 0 ! tb search with 14.3 fb−1 @ 8TeV W 0 tb: TMVA ! Use Boosted Decision Tree discriminators (BDT) 1 BDT for 2-jet events: 14 variables used for training Most discriminating variables: mtb, pT (t), ∆φ(l;top−jet) 1 BDT for 3-jet events: 13 variables used for training Most discriminating variables: mtb, pT (t), sphericity Search for exotics with tt and single top D.Hu, Columbia Univ.
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