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TOP QUARK STUDIES FROM CMS AT LHC. Marc M. Baarmand Florida Institute of Technology PHYSICS AT LHC Prague, Czech Republic, July 6-12, 2003. b. q’. p. Top Quark Physics. W Helicity. Top Mass. l +. Top Width. Anomalous Couplings. Production cross-section. Top Spin. W +. - PowerPoint PPT Presentation
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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
Marc M. Baarmand – Florida Tech
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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
Marc M. Baarmand – Florida Tech
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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
Marc M. Baarmand – Florida Tech
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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
Marc M. Baarmand – Florida Tech
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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
Marc M. Baarmand – Florida Tech
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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
Marc M. Baarmand – Florida Tech
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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
Marc M. Baarmand – Florida Tech
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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 !
Marc M. Baarmand – Florida Tech
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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
21
___
C
where
C
dd
d
L. Sonnenchein CMS PhD thesis
Marc M. Baarmand – Florida Tech
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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
Marc M. Baarmand – Florida Tech
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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!
Marc M. Baarmand – Florida Tech
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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…
SummarySummary