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”) <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">2 / 16 </li></ul>−1 <ul style="display: flex;"><li style="flex:1">tt resonance search with 14.3 fb </li><li style="flex:1">@ 8TeV </li></ul>tt resonance: benchmark models 2 specific models used as examples of sensitivity Leptophobic topcolor Z0 [2] Explains the top quark mass and EWSB through top quark condensate Z0 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% <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">3 / 16 </li></ul>−1 <ul style="display: flex;"><li style="flex:1">tt resonance search with 14.3 fb </li><li style="flex:1">@ 8TeV </li></ul>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 The boosted selection One top decays hadronically and the other semileptonically. Boosted selection helps improve efficiency in high signal mass region 1 high pT R=1.0 jet with √mjet > 100GeV, d12 > 40GeV; 1 R=0.4 jet close to lepton; 20 ATLAS Preliminary Simulation s=8 TeV 18 ≥ 1 R=0.4 b-jet(could overlap 16 µ + jets, combined with the former 2 jets.) µ + jets, boosted e + jets, combined e + jets, boosted 14 12 10 8<ul style="display: flex;"><li style="flex:1">1 isolated lepton; ETmiss </li><li style="flex:1">.</li></ul>Resolved selection 63 or 4 R=0.4 jets with ≥ 1 b-jet 4<ul style="display: flex;"><li style="flex:1">1 isolated lepton; ETmiss </li><li style="flex:1">.</li></ul>20<ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">0.5 </li><li style="flex:1">1</li><li style="flex:1">1.5 </li><li style="flex:1">2</li><li style="flex:1">2.5 </li><li style="flex:1">3</li><li style="flex:1">3.5 </li></ul>(Same as boosted channel) mtt [TeV] <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">4 / 16 </li></ul>−1 <ul style="display: flex;"><li style="flex:1">tt resonance search with 14.3 fb </li><li style="flex:1">@ 8TeV </li></ul>tt resonance: lepton+jets(II) tt invariant mass reconstruction pz (ν): from lepton+ETmiss system with mW constraint Resolved: χ2 algorithm using mt and Boosted: take R=1 jet as <ul style="display: flex;"><li style="flex:1">hadronically decaying top; build the </li><li style="flex:1">mW , top pair pT balance as constraint </li></ul>other top from ν, lepton and R=0.4 jet 0.3 ATLAS Preliminary Simulation, s=8TeV ATLAS Preliminary Simulation, s=8TeV 0.25 0.25 Boosted Resolved 0.2 Z’ (1.0 TeV) Z’ (0.5 TeV) 0.2 Z’ (1.5 TeV) Z’ (1.0 TeV) Z’ (2.0 TeV) Z’ (1.5 TeV) Z’ (2.0 TeV) 0.15 0.15 Z’ (3.0 TeV) 0.1 0.1 0.05 00.05 0<ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">0.5 </li><li style="flex:1">1</li><li style="flex:1">1.5 </li><li style="flex:1">2</li><li style="flex:1">2.5 </li><li style="flex:1">3</li><li style="flex:1">3.5 </li></ul>[TeV] <ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">0.5 </li><li style="flex:1">1</li><li style="flex:1">1.5 </li><li style="flex:1">2</li><li style="flex:1">2.5 </li><li style="flex:1">3</li><li style="flex:1">3.5 </li></ul>[TeV] reco tt reco tt mmThe tt mass spectra are used for statistical analysis <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">5 / 16 </li></ul>−1 <ul style="display: flex;"><li style="flex:1">tt resonance search with 14.3 fb </li><li style="flex:1">@ 8TeV </li></ul>tt resonance: lepton+jets(III) 108 107 106 105 104 103 102 10 Dominant systematics on yields 5 × Z’ (1.5 TeV) 5 × (2.0 TeV) ATLAS Preliminary Data g-1 L dt = 14.2 fb ∫tt KK W+jets Systematics Resolved Boosted Multi-jets Note: R=1. jet systematics Other Backgrounds tt s = 8 TeV normalization <ul style="display: flex;"><li style="flex:1">8.0% </li><li style="flex:1">9.0% </li></ul>also affect the resolved channel because only events failing the boosted selection will be examined with the resolved selection criteria. JES of R=0.4 jets JES+JMS of R=1. jets <ul style="display: flex;"><li style="flex:1">6.0% </li><li style="flex:1">0.70% </li></ul>0.30% 4.0% 2.9% 17% 3.4% 6.0% 11.5 0 <ul style="display: flex;"><li style="flex:1">0.5 </li><li style="flex:1">1</li><li style="flex:1">1.5 </li><li style="flex:1">2</li><li style="flex:1">2.5 </li><li style="flex:1">3</li><li style="flex:1">3.5 </li></ul>b-tag efficiency PDF 1 0.5 <ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">0.5 </li><li style="flex:1">1</li><li style="flex:1">1.5 </li><li style="flex:1">2</li><li style="flex:1">2.5 </li><li style="flex:1">3</li><li style="flex:1">3.5 </li></ul>reco Exclusion ranges @ 95% C.L. <ul style="display: flex;"><li style="flex:1">m</li><li style="flex:1">[TeV] </li></ul>tt 14.3 fb−1 @ 8TeV [4] s = 8 TeV Obs. 95% CL upper limit Exp. 95% CL upper limit Exp. 1σ uncertainty s = 8 TeV dt = 14.3 fb-1 Obs. 95% CL upper limit Exp. 95% CL upper limit Exp. 1 σ uncertainty 103 102 10 103 102 10 L dt = 14.3 fb-1 L∫∫<ul style="display: flex;"><li style="flex:1">Exclusion ranges </li><li style="flex:1">Observed </li></ul>Exp. 2 σ uncertainty Exp. 2 σ uncertainty Z0 0.5-1.8TeV Kaluza-Klein gluon (LO) Leptophobic Z’ (LO x 1.3) ATLAS Preliminary ATLAS Preliminary KK gluon 0.5-2.0TeV 14.7 fb−1 @ 7TeV [5] Exclusion ranges 110-1 10-2 10-1 10-2 Observed Z0 0.50-1.74TeV <ul style="display: flex;"><li style="flex:1">0.5 </li><li style="flex:1">1</li><li style="flex:1">1.5 </li><li style="flex:1">2</li><li style="flex:1">2.5 </li></ul>mass [TeV] <ul style="display: flex;"><li style="flex:1">0.5 </li><li style="flex:1">1</li><li style="flex:1">1.5 </li><li style="flex:1">2</li><li style="flex:1">2.5 </li><li style="flex:1">3</li></ul>KK gluon 0.70-2.07TeV gZ’ mass [TeV] KK <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">6 / 16 </li></ul>−1 <ul style="display: flex;"><li style="flex:1">tt resonance search with 14.3 fb </li><li style="flex:1">@ 8TeV </li></ul>tt resonance: full hadronic decays [6] 102 10 Two complementary Obs. 95% CL upper limit Obs. 95% CL upper limit Exp. 95% CL upper limit Exp. 1σ uncertainty Exp. 2 σ uncertainty KK gluon (LO) 102 Exp. 95% CL upper limit Exp. 1σ uncertainty techniques relying on jet Exp. 2 σ uncertainty 10 1Leptophobic Z' (LOx1.3) substructure are used to identify top: ATLAS HEPTopTagger ATLAS HEPTopTagger 1HEPTopTagger 10-1 s = 7 TeV s = 7 TeV Top Template Tagger L dt = 4.7 fb-1 L dt = 4.7 fb-1 10-1 ∫∫Exclusion ranges @ 95% C.L. <ul style="display: flex;"><li style="flex:1">0.6 </li><li style="flex:1">0.8 </li><li style="flex:1">1</li><li style="flex:1">1.2 </li><li style="flex:1">1.4 </li><li style="flex:1">1.6 </li><li style="flex:1">1.8 </li><li style="flex:1">2</li></ul><ul style="display: flex;"><li style="flex:1">0.8 </li><li style="flex:1">1</li><li style="flex:1">1.2 </li><li style="flex:1">1.4 </li><li style="flex:1">1.6 </li><li style="flex:1">1.8 </li><li style="flex:1">2</li></ul>with 4.7 fb−1 @ 7TeV gKK Mass [TeV] Z' Boson Mass [TeV] 102 10 10 Use HepTopTagger Obs. 95% CL upper limit Exp. 95% CL upper limit Exp. 1σ uncertainty Exp. 2σ uncertainty KK gluon (LO) Obs. 95% CL upper limit Exp. 95% CL upper limit Exp. 1σ uncertainty Exp. 2σ uncertainty Leptophobic Z' (LOx1.3) <ul style="display: flex;"><li style="flex:1">Exclusion ranges </li><li style="flex:1">Observed </li></ul>Z0 0.70-1.00TeV 11.28-1.32TeV 1KK gluon 0.70-1.48TeV 10-1 s = 7 TeV L dt = 4.7 fb-1 Use Top Template Tagger s = 7 TeV L dt = 4.7 fb-1 10-1 ∫∫<ul style="display: flex;"><li style="flex:1">Exclusion ranges </li><li style="flex:1">Observed </li></ul>10-2 Top Template Tagger Top Template Tagger ATLAS ATLAS KK gluon 1.02-1.62TeV <ul style="display: flex;"><li style="flex:1">1</li><li style="flex:1">1.2 </li><li style="flex:1">1.4 </li><li style="flex:1">1.6 </li><li style="flex:1">1.8 </li><li style="flex:1">2</li></ul><ul style="display: flex;"><li style="flex:1">1</li><li style="flex:1">1.2 </li><li style="flex:1">1.4 </li><li style="flex:1">1.6 </li><li style="flex:1">1.8 </li><li style="flex:1">2</li></ul>gKK Mass [TeV] Z' Boson Mass [TeV] <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">7 / 16 </li></ul>0−1 @ 8TeV W→ tb search with 14.3 fb 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. Vi0j 0fi γµg (1 + γ5) + gL0 (1 − γ5)W 0µfj + h.c. ¯√L = Rij ij <ul style="display: flex;"><li style="flex:1">2</li><li style="flex:1">2</li></ul>Search for W 0 in t+b decay channel Explore models potentially inaccessible to leptonic search (W 0 → lν). WR0 can not decay to a lepton and νR if mν > mW 0RLeptophobic W 0 W 0 may couple more strongly to the third generation quarks Can exploit the distinct signature of top quark. <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">8 / 16 </li></ul>0−1 @ 8TeV W→ tb search with 14.3 fb 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 Preselection: 1 lepton, ETmiss , 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 pz (ν): from lepton+ETmiss system with mW constraint b from top: the b-jet/jet giving the mWb closest to mt b from W 0: the other b-jet or highest pT jet <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">9 / 16 </li></ul>0−1 @ 8TeV W→ tb search with 14.3 fb 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 <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">10 / 16 </li></ul>0−1 @ 8TeV W→ tb search with 14.3 fb W 0 → tb: result Dominant systematics tt MC generator 10% b-tag efficiency 15% − 25% for events with ≥ 2b The BDT output distributions are used for statistical analysis Exclusion ranges @ 95% C.L. with 14.3 fb−1 @ 8TeV Exclusion <ul style="display: flex;"><li style="flex:1">ranges </li><li style="flex:1">Expected </li><li style="flex:1">Observed </li></ul>WL0 0.50 − 1.56TeV 0.50 − 1.74TeV WR0 0.50 − 1.72TeV 0.50 − 1.84TeV <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">11 / 16 </li></ul>∗−1 @ 7TeV b→ Wt search with 4.7 fb b∗ → Wt: theory [8] Phenomenological models Randall-Sundrum models; Composite Higgs models. Consider b∗ produced singly through its coupling to a b and gluon gs 2Λ L = Gµνbσµν(kLbPL + kRb PR)b∗ + h.c. ¯Exploit the weak coupling of excited-quarks to the third generation quarks gs +µ√¯L = 2 Wµ tγ (gLPL + gRPR)b∗ + h.c. b∗ can also decay to bZ and bH cross-section and branching ratio of b∗ → Wt depend on the couplings and b∗ mass general search for Wt resonances under 3 b∗ coupling scenarios tLeft-handed: kRb = gR = 0 b∗ gRight-handed: kLb = gL = 0 <ul style="display: flex;"><li style="flex:1">b</li><li style="flex:1">W</li></ul>Vector-like: kLb = gL, kRb = gR <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">12 / 16 </li></ul>∗−1 @ 7TeV b→ Wt search with 4.7 fb b∗ → Wt: dilepton channel Background tt, Wt, diboson, Drell-Yan shape: from MC Drell-Yan normalization, and fake dileptons: estimated from data Event selection 2 leptons with opposite charges, ETmiss 1 jet ee, µµ channels: ATLAS Data b* (800 GeV) Wt 10 -1 ,L dt = 4.7 fb ∫tt Diboson Z(e+e-/µ+µ-)+jets Z(τ+τ-)+jets Fake dileptons s = 7 TeV 110-1 10-2 10-3 m(ll) < 81GeV or m(ll) > 101GeV Dilepton channel <ul style="display: flex;"><li style="flex:1">Veto to suppress Zττ </li><li style="flex:1">:</li></ul>∆φ(l ) + ∆φ(l > 2.5 miss Tmiss T<ul style="display: flex;"><li style="flex:1">,E </li><li style="flex:1">,E </li></ul>)<ul style="display: flex;"><li style="flex:1">1</li><li style="flex:1">2</li></ul>Discriminating variable: <ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">500 </li><li style="flex:1">1000 </li><li style="flex:1">1500 </li></ul>HT [GeV] HT the scalar sum of ET of leptons, jet and ETmiss <ul style="display: flex;"><li style="flex:1">Search for exotics with tt and single top </li><li style="flex:1">D.Hu, Columbia Univ. </li><li style="flex:1">13 / 16 </li></ul>

Search for Exotics with Top at ATLAS

Details

Download

Copyright

We respect the copyrights and intellectual property rights of all users. All uploaded documents are either original works of the uploader or authorized works of the rightful owners.

Support