TOP QUARK STUDIES FROM CMS AT LHC

Marc M. Baarmand – Florida Tech

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TOP QUARK STUDIES TOP QUARK STUDIES FROM CMS AT LHCFROM CMS AT LHC

TOP QUARK STUDIES TOP QUARK STUDIES FROM CMS AT LHCFROM CMS AT LHC

Marc M. BaarmandFlorida Institute of Technology

PHYSICS AT LHCPrague, Czech Republic, July 6-12, 2003


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p

p t

b

W

q

q’

t b

W+

l

X

Production cross-section

Resonance production

Production kinematics

Top MassW Helicity

|Vtb| ; Single top production

Branching Ratios

Rare/non SM Decays

Anomalous Couplings

CP Violation

Top Spin

Top Charge

Top Width

_ _

_

_

Top Quark PhysicsTop Quark Physics


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Topics in This TalkTopics in This Talk

Top production properties• Top cross section • Top mass

Top spin effects• Top-antitop spin correlations

Anomalous couplings• FCNC in top physics

Non-Standard-Model decays of top• Search for charged Higgs

Single top production; top partial width, Vtb and spin effects… see talk by Sherstnev

More in proceedings of “SM physics (and more) at the LHC” CERN 2000-004


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Top Quark Production and DecayTop Quark Production and Decay Strong tt pair production EW single top quark

production

Standard Model: t Wb dominates, BR for tt final states

ttqq

ttgg

btqq (Drell-Yan)

btqqg ' (W-g fusion)

21%

15%

15%1%3%1%

44%

+ X

+ jetse + jets

e + e

e + + all - hadronic


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Motivation• tt cross section is a test of QCD predictions

• Inclusive and differential cross sections• A discrepancy may indicate possible new physics

• Production via a high mass intermediate state• Non Wb decay model

Measurements performed using various final states• Dilepton channels

• ee, e and • Lepton + jets channels

• e+jets, +jets: topological analysis and b-tagging

• All hadronic channel• Topological variables and b-tagging• Neural networks techniques

• Trilepton channels

ttt Production Cross Sectiont Production Cross Section


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D: PRL 79 1203 (1997); CDF: PRL 80 2773 (1998)(+updates)

pb 4.8 5.45.3

pb 3.34.6

0 2 4 6 8 10 12 14 16

cross section (pb)

pb 1.21.4

pb 5.33.8

pb 2.31.7

pb 7.19.5

pb 6.7 5.37.2

pb 3.42.9

pb 5.11.5

pb 5.6 7.14.1

theory

CDF dileptonDØ dilepton

DØ topological

CDF lepton-tagDØ lepton-tag

CDF SVX-tag

CDF hadronicDØ hadronic

DØ combinedCDF combined

Berger et al. Bonciani et al.Laenen et al.Nason et al.

4.7 - 6.2 pb

Tevatron tTevatron tt Cross Sectiont Cross Section

RUN 1


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ttt Production at LHCt Production at LHC

tt cross section at LHC (√s = 14 TeV) 830 pb• LHC is a Top factory: 108 tt in 100 fb-1

Measurement of with high statistical precision Measurement of d/pT up to TeV in pT

Full understanding of top needed for evaluation of backgrounds to Higgs, SUSY, etc.

Challenge is to control systematics• Experiment: a few percent?!• Theory: currently 12% but expect improvements

(next slide) Relation to top mass:

• Within SM expect mt/mt 0.2 (tt)/(tt)

• If 5% precision in cross section is achieved Indirect determination of mt with mt 1.8 GeV!

PDF: ±10% scale: ±6%

Theoretical UncertaintiesTheoretical Uncertainties


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Fundamental parameter of Standard Model • Tevatron Run 1: 174.3 5.1 GeV

Affects predictions of SM via radiative correctionsMeasurements of MW = 80.398±0.041 GeV

and mt constrain MH

Large mass of top quark • Yukawa coupling 1• Clues about electroweak

symmetry breaking!

)ln(,2HtW MmM )ln(,2HtW MmM

W Wt

bW W

H

Top Quark MassTop Quark Mass

Light Higgs !


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CMS Top Mass StudiesCMS Top Mass Studies Lepton + jets

• mt = 1.0 – 1.5 GeV depending on pT modeling and calibration precision

• W-jj, b-jet resolution, combinatorics…

Dilepton

• mt ≤ 2 GeV obtained from correlation between M(e ) and mt


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Promising ChannelPromising Channel l + J/ channel

• mt ≤ 1 GeV strong correlation between M(l J/) and mt

• Sensitivity to b fragmentation function

• Small BR (5x10-5) Suitable for high

luminosity data !


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ttt Spin Correlationst Spin Correlations

tt → l+ l’- X (l=e,) with pure V-A top decays

• Expect C = 0.332 for LHC using CTEQ4L

basishelicity in n correlatiospin of degree

frame.rest )t(in t direction )(l l and CMS tin t )t(between t angle )(

1

4

coscos1

coscos

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___

C

where

C

dd

d

L. Sonnenchein CMS PhD thesis


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CMS StudyCMS Study

Fit C = -0.021 ± 0.022 C = 0.331 ± 0.023

ISR, FSR, multiple int., detector response included, corrected for selection cuts

PYTHIA 6.1 + M.E.

by S. Slabospitsky


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FCNC in Top Quark PhysicsFCNC in Top Quark Physics Flavor Changing Neutral Current couplings tVc and tVu; V =

g, , Z• Absent at tree-level and highly suppressed in SM• Present through loop contributions

Observation of top quark FCNC processes New Physics!

CDF & LEP2 Present Limits

BR < 17%

BR < 3.2%

BR < 18%


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FCNC in Top DecaysFCNC in Top Decays tt pair production

Background processes


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Branching Ratios Branching Ratios Expected constraints on “BR” = Г(tVq) / Г(SM)

• Tevatron Run 2• LHC – CMS• Linear e+ e- collider

BR’s significantly constrained –

allowing test of SUSY scenarios


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Supersymmetry • Presently observed bosons and fermions would

have more massive superpartners (SUSY is a broken symmetry)

SUSY Higgs sector – two Higgs doublets (MSSM)• 5 states (h0,H0,A0,H+,H-) survive after giving W & Z

masses• H LEP limit 77.4 GeV (LEP Working Group 2000)• Decay t H+ b can compete with t W+ b

• H couples to heaviest fermions detection through breakdown of e / / universality in tt production

Non-SM Decays of TopNon-SM Decays of Top


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Tevatron Search - Run 1Tevatron Search - Run 1DØDØIndirect search for t H+ b; disappearance of SM t W+ bDirect search for t H+ b; with H+ for large tan

PRL 88, 151803 (2002)

H+ W bb

H+

H+ c s

B(t H+ b) < 0.36 @ 95% CL if B(H+ ) 1 and MH < 160 GeV

CDFDirect search for t H+ b; withH+ for large tan

PRD 62, 012004 (2000)


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Expectation from Tevatron Run 2Expectation from Tevatron Run 2

Excluded regions expected from Run 2

Large regions of parameter space for MH < mt remain to be searched!


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CMS SearchCMS Search

One CMS study searches for excess of jets in tt events

• jets identified as narrow hadronic jets• dilepton deficit used to enhance the search

min L to exclude tWb (2)

min L to discover tHb (5)

Possible to explore MH < 160 GeV and 2<tan<40 with 30 fb-1


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Charged Higgs BosonCharged Higgs Boson

5 discovery reach for light and heavy Higgs

• See talks by A. NikitenkoR. Kinnunen

Search in top quark decays


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Top quark physics is rich, exciting and doable at low luminosity LHC• SM: EW and QCD tests• BSM: probe SUSY

Today’s signal, tomorrow’s background • Top quark (pair and single) production is the

main background to processes with multi lepton + jets in final state, e.g. SUSY

Although top will be explored at Tevatron, it will have to be re-visited at LHC for high statistics studies

• mt ≤ 1 GeV

• BR for FCNC tVq 10-3 - 10-6

Lots of work and fun ahead…

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TOP QUARK STUDIES FROM CMS AT LHC

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