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Search for Exotics with Top at ATLAS

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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
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−1

  • tt resonance search with 14.3 fb
  • @ 8TeV

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%

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−1

  • tt resonance search with 14.3 fb
  • @ 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

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

  • 1 isolated lepton; ETmiss
  • .

Resolved selection

6

3 or 4 R=0.4 jets with ≥ 1 b-jet

4

  • 1 isolated lepton; ETmiss
  • .

20

  • 0
  • 0.5
  • 1
  • 1.5
  • 2
  • 2.5
  • 3
  • 3.5

(Same as boosted channel)

mtt [TeV]

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−1

  • tt resonance search with 14.3 fb
  • @ 8TeV

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

  • hadronically decaying top; build the
  • mW , top pair pT balance as constraint

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
0

0.05
0

  • 0
  • 0.5
  • 1
  • 1.5
  • 2
  • 2.5
  • 3
  • 3.5

[TeV]

  • 0
  • 0.5
  • 1
  • 1.5
  • 2
  • 2.5
  • 3
  • 3.5

[TeV]

reco tt

reco tt

m

m

The tt mass spectra are used for statistical analysis

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−1

  • tt resonance search with 14.3 fb
  • @ 8TeV

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

  • 8.0%
  • 9.0%

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

  • 6.0%
  • 0.70%

0.30%
4.0% 2.9%
17% 3.4% 6.0%

1

1.5 0

  • 0.5
  • 1
  • 1.5
  • 2
  • 2.5
  • 3
  • 3.5

b-tag efficiency
PDF

1
0.5

  • 0
  • 0.5
  • 1
  • 1.5
  • 2
  • 2.5
  • 3
  • 3.5

reco

Exclusion ranges @ 95% C.L.

  • m
  • [TeV]

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

∫

∫

  • Exclusion ranges
  • Observed

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

1

4.7 fb−1 @ 7TeV [5]

Exclusion ranges

1

10-1 10-2

10-1 10-2

Observed

Z0 0.50-1.74TeV

  • 0.5
  • 1
  • 1.5
  • 2
  • 2.5

mass [TeV]

  • 0.5
  • 1
  • 1.5
  • 2
  • 2.5
  • 3

KK gluon 0.70-2.07TeV

g

Z’ mass [TeV]

KK

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−1

  • tt resonance search with 14.3 fb
  • @ 8TeV

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
1

Leptophobic Z' (LOx1.3)

substructure are used to identify top:

ATLAS

HEPTopTagger

ATLAS

HEPTopTagger
1

HEPTopTagger

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.

  • 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

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)

  • Exclusion ranges
  • Observed

Z0 0.70-1.00TeV

1

1.28-1.32TeV

1

KK 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

∫

∫

  • Exclusion ranges
  • Observed

10-2

Top Template Tagger

Top Template Tagger

ATLAS

ATLAS

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

gKK Mass [TeV]

Z' Boson Mass [TeV]

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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

0

fi γµg (1 + γ5) + gL0 (1 − γ5)W 0µfj + h.c. ¯

√

L =

Rij

ij

  • 2
  • 2

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

0

R

Leptophobic W 0 W 0 may couple more strongly to the third generation quarks

Can exploit the distinct signature of top quark.

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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

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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

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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

  • ranges
  • Expected
  • Observed

WL0 0.50 − 1.56TeV 0.50 − 1.74TeV WR0 0.50 − 1.72TeV 0.50 − 1.84TeV

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∗

−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

t

Left-handed: kRb = gR = 0

b∗

g

Right-handed: kLb = gL = 0

  • b
  • W

Vector-like: kLb = gL, kRb = gR

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∗

−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
1

10-1 10-2 10-3

m(ll) < 81GeV or m(ll) > 101GeV

Dilepton channel

  • Veto to suppress Zττ
  • :

∆φ(l

) + ∆φ(l

> 2.5

miss Tmiss T

  • ,E
  • ,E

)

  • 1
  • 2

Discriminating variable:

  • 0
  • 500
  • 1000
  • 1500

HT [GeV]

HT the scalar sum of ET of leptons, jet and

ETmiss

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  • Strong Top Dynamics in Light of LHC Data

    Strong Top Dynamics in Light of LHC Data

    Strong Top Dynamics in Light of LHC Data Elizabeth H. Simmons Michigan State University - EWSB and Strong Top Quark Dynamics - Models - States Connected to the New Dynamics - LHC Prospects - Conclusions JLAB 4 April 2012 Looking Beyond the Standard Model technicolor topcolor susy extra dim. Fundamental scalars observed? Hierarchy/Naturalness? Triviality? Dynamics causing EWSB? EWSB and Strong Top Quark Dynamics Dynamical EWSB: Technicolor: (inspired by QCD) Introduce SU(N)TC with technigluons, inspired by QCD gluons techniquarks carrying SU(N)TC charge: • e.g. weak doublet TL = (UL, DL); weak singlet UR, DR • Lagrangian has SU(2)L x SU(2)R chiral symmetry SU(N)TC gauge coupling becomes large at Λ 1TeV TC ≈ • ! T L T R "≈ 250 GeV causes EWSB • `technipions’ Π TC become the WL, Z L Susskind, Weinberg Dynamical Fermion Masses: ETC* METC > ΛTC ETC boson technigluon E.g. the top quark mass arises from: gETC 2 and its size is ( ) !TT¯ " x (flavor-dependent factor) METC Challenge: ETC must violate custodial symmetry to make mt >> mb. But how to avoid large changes to ∆ ρ ? *Dimpoulos & Susskind; Eichten & Lane Isospin Violation (I) mt = 172 GeV References Isospin Violation (2) Conclusion: t,b feel a Text new strong force not shared by other quarks References or technifermions Top Condensation and EWSB If the top quark feels a new strong interaction, a top-quark condensate can provide some or even all of electroweak symmetry breaking v2 = f 2 + f 2 sin ! f /v TC t ⌘ t some (topcolor*, topcolor-assisted technicolor*) in these models the top quark
  • Top–Bottom Condensation Model: Symmetries and Spectrum of the Induced 2HDM

    Top–Bottom Condensation Model: Symmetries and Spectrum of the Induced 2HDM

    S S symmetry Article Top–Bottom Condensation Model: Symmetries and Spectrum of the Induced 2HDM Alexander A. Osipov 1 , Brigitte Hiller 2,*, Alex H. Blin 2 and Marcos Sampaio 3 1 Bogoliubov Laboratory of Theoretical Physics, JINR, 141980 Dubna, Russia; [email protected] 2 CFisUC, Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal; [email protected] 3 CCNH Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André 09210-580, SP, Brazil; [email protected] * Correspondence: brigitte@fis.uc.pt Abstract: Here, we use the Schwinger–DeWitt approach to address the four-fermion composite Higgs effective model proposed by Miransky, Tanabashi and Yamawaki (MTY). The surprising benefit of such an approach is that it is possible to ascribe to a SM-type Higgs a quark–antiquark structure of predominantly a bb¯ nature with a small tt¯ admixture, which in turn yields a Higgs mass compatible with the observed value of 125 GeV. We discuss this result in a detailed and pedagogical way, as it goes against the common belief that this model and akin composite descriptions should predict a Higgs mass-of-order of twice the top quark mass, contrary to empirical evidence. A further aspect of this approach is that it highlights the link of the SU(2)L × U(1)R symmetric four-fermion MTY model interactions of the heavy quark family to a specific two-Higgs-doublet model (2HDM), and the necessity to go beyond the one Higgs doublet to obtain the empirical Higgs mass within composite models. By appropriately fixing the symmetry-defining interaction parameters, we show Citation: Osipov, A.A.; Hiller, B.; that the resulting CP-preserving spectrum harbors the following collective states at the electroweak Blin, A.H.; Sampaio, M.
  • A Tumbling Top-Quark Condensate Model

    A Tumbling Top-Quark Condensate Model

    UFIFT-HEP-92-7 March, 1992 A Tumbling Top-Quark Condensate Model Stephen P. Martin Department of Physics University of Florida Gainesville, FL 32611 ABSTRACT: We propose a renormalizable model with no fundamental scalars which breaks itself in the manner of a “tumbling” gauge theory down to the stan- dard model with a top-quark condensate. Because of anomaly cancellation require- ments, this model contains two color sextet fermions (quixes), which are vector-like with respect to the standard model gauge group. The model also has a large num- ber of pseudo-Nambu-Goldstone bosons, some of which can be light. The top-quark arXiv:hep-ph/9204204v2 24 Jul 2008 condensate is responsible for breaking the electroweak gauge symmetry and gives the top quark a large mass. We discuss the qualitative features and instructive shortcomings of the model in its present form. We also show that this model can be naturally embedded into an aesthetically pleasing model in which the standard model fermion families appear symmetrically. Recently there has been a great deal of interest in the idea[1-4] that the electroweak symmetry of the standard model is broken by a top-quark condensate. This would give a natural explanation for the fact that the top quark has a much larger mass than any of the other quarks and leptons, while simultaneously providing an electroweak symmetry breaking mechanism without a fundamental Higgs scalar. In early versions of this idea, the top-quark condensate was supposed to be induced by a gauge-invariant but non-renormalizable four-fermion interaction 2 g i L ∼ (Q t)(tQ ) (1) eff M 2 i introduced at a scale M which must be larger than the electroweak breaking scale.
  • Dynamical Electroweak Symmetry Breaking

    Dynamical Electroweak Symmetry Breaking

    DYNAMICAL ELECTROWEAK SYMMETRY BREAKING AND THE TOP QUARK R. Sekhar Chivukula DepartmentofPhysics, Boston University 590 Commonwealth Ave., Boston MA 02215 E-mail: [email protected] Talk presented at the SLACTopical Workshop Stanford, July 19-21, 1995 BUHEP-95-23 & hep-ph/9509384 ABSTRACT In this talk, I discuss theories of dynamical electroweak symmetry breaking, with emphasis on the implications of a heavy top-quark on the weak-interaction pa- rameter. 1 AN ABBREVIATED VERSION OF THIS TALK WAS PRESENTED AT THE WORKSHOP ON TOP QUARK PHYSICS,IOWASTATE UNIVERSITY, AMES, IA, MAY 25-26, 1995 AND THE YUKAWA IN- TERNATIONAL SEMINAR `95, YUKAWA INSTITUTE, KYOTO, AUG. 21-25, 1995. 1 What's Wrong with the Standard Mo del? In the standard one-doublet Higgs mo del, one intro duces a fundamental scalar doublet of SU 2 : W ! + ; 1.1 = 0 which has a p otential of the form ! 2 2 v y V = : 1.2 2 2 In the p otential, v is assumed to b e p ositive in order to favor the generation of a nonzero vac- uum exp ectation value for . This vacuum exp ectation value breaks the electroweak symmetry, giving mass to the W and Z . This explanation of electroweak symmetry breaking is unsatisfactory for a numb er of reasons. For one thing, this mo del do es not give a dynamical explanation of electroweak symmetry breaking. For another, when emb edded in theories with additional dynamics at higher energy 2 scales, these theories are technically unnatural. Perhaps most unsatisfactory,however, is that theories of fundamental scalars are probably 3 \trivial," i.e., it is not p ossible to construct an interacting theory of scalars in four dimensions that is valid to arbitrarily short-distance scales.