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Crimea 2006, 9/21 N. Giokaris 3 Run II with Record peak Luminosity: 2.3x10 32 cm -2 s -1 Integrated delivered luminosity: 1.5 fb -1 CDF recorded luminosity: 1.3 fb -1 TEVATRON Performance Expected: 2fb -1 by fb -1 by fb -1 by 2009
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RECENT CDF RESULTS ON THE TOP QURK
Nikos GiokarisUniversity of Athens
On behalf of the CDF Collaboration
September 21, 2006
Crimea 2006, 9/21 N. Giokaris 2
OUTLINEI. TEVATRON PERFORMANCEII. CDF DETECTORIII. TOP QUARK
I. DiscoveryII. Production & DecayIII. Top quark Properties
I. Cross sectionII. Top massIII. W helicity in Top decaysIV. Search for Single TopV. Search for Resonant Production
IV. Conclusions
Crimea 2006, 9/21 N. Giokaris 3
• Run II with
• Record peak Luminosity: 2.3x1032cm-2s-1
• Integrated delivered luminosity: 1.5 fb-1
• CDF recorded luminosity: 1.3 fb-1
TEVATRON PerformanceTeV96.1=s
Expected:
• 2fb-1 by 2006
• 4fb-1 by 2007
• 8fb-1 by 2009
Crimea 2006, 9/21 N. Giokaris 4
CDF Detector
Crimea 2006, 9/21 N. Giokaris 5
Top Quark History
• Searched for since the late ‘70s, after the discovery of the b quark
• Discovered by CDF and D0 in 1995 (Run I)– ∫Ldt~100pb-1
– Mass ~175 GeV – Decays to Wb, as Mtop>MW– ttbar Cross Section 7.6pb
Crimea 2006, 9/21 N. Giokaris 6
Top-Antitop Production and Decay
Half-life of top: ~10-25s•Top decays before hadronizing!
ttqq ttgg
e-e(1/81)
mu-mu (1/81)
tau-tau (1/81)
e -mu (2/81)
e -tau(2/81)
mu-tau (2/81)
e+jets (12/81)
mu+jets(12/81)
tau+jets(12/81)
jets (36/81)
W bosons decay either hadronically or leptonically.W decays define channel:
Dilepton: 12% Lepton+jets: 44% All-hadronic: 44%
Strong Production (6.7pb @ NLO) dominates at Tevatron Energy 85%: 15%:
TeV96.1=s
Crimea 2006, 9/21 N. Giokaris 7
Top Cross Section
Mtop sNLO(pb) ± ds
170 7.8±1175 6.7±0.8180 5.7±0.7
Theoretical predictions
TeV96.1=s
•Measured in all topologies.•Use complementary techniques:topological (counting) vs shape fit.
Deviation from SM expectations could indicate non-SM production mechanism or new physics in top sample.
Crimea 2006, 9/21 N. Giokaris 8
How we measure Top
Top decays before hadronizing:Observed through W decay products leptons (Lepton +Jet and Dilepton channels)
Jets (problem with jet combinations)
Two methods to measure top:
1. Use b-tagging Good S/B Lose ~50% in efficiency
2. Use kinematics (NN, etc) Also good S/B
Crimea 2006, 9/21 N. Giokaris 9
L+jets channel:
• Large BR ~44%
and
• Good S/B
bbvlqqbbWW tt
Lepton+Jets Cross Section
Results in 750 pb-1
Lepton + MET + ≥1b-tag
pb1.1±6.0±0.6=)notag(σpb0.1±6.0±2.8=)btag(σ
syststattt
syststattt
Crimea 2006, 9/21 N. Giokaris 10
Dilepton Cross Section
pb5.0±0.1±5.1±3.8=σ )lumi()syst()stat()notag(tt
Result in 750 pb-1
Dilepton channel:
• Small BR ~5% for e and μ leptons
BUT
• Easy to identify e and μ
• Very good S/B
bbvvllbbWW tt -+
Crimea 2006, 9/21 N. Giokaris 11
All Hadronic Cross Section
Result in 1 fb-1
pb5.0±1.5-0.2+.1±3.8=σ )lum()syst()stat()notag(tt
L+jets channel:
• Large BR ~44%
but
• Poor S/B
bbqqqqbbWW tt
Crimea 2006, 9/21 N. Giokaris 12
Cross Section Summary
NOW REACHED 12% uncertainty @760 pb-1
Expected
10% uncertainty/experiment with 2fb-1
We are doing much better than predicted in TDR!!
Crimea 2006, 9/21 N. Giokaris 13
Top Mass
)L.C%95(GeV175<M)L.C%68(GeV89=M
H
42+30H
• Fundamental parameter of SM.• Recent Tevatron combination: Mtop=171.4 ± 2.1 GeV• EWK fit gives:
• In Run II, expect δMW= ±25MeV and δMtop= ± 2 GeV35% constraint on the Higgs Mass.• Sensitive to new physics through radiative corrections
Crimea 2006, 9/21 N. Giokaris 14
Top Mass MeasurementMass measurement is hard• Jet combinatorics• ISR/FSR jets• Jet Energy Scale (JES) uncertainty
Two methods•Template Methods•Matrix Element Method (ME)The idea in both methods is try to reconstruct the parton level quantities
Crimea 2006, 9/21 N. Giokaris 15
Top Mass with Template Method1. Evaluate event-by-event best “reconstructed mass”, Mrec, by using observed kinematics
of ttbar event (e.g.: χ2 fitter)
2. Create “templates”, i.e. MC predictions for Mrec using different true masses of Mtop.
3. Measure top mass with likelihood fit of data Mrec to signal + background template.
Background
Crimea 2006, 9/21 N. Giokaris 16
Top Mass in lepton+jets• JES uncertainties are the largest source of systematics:
±1σJES σMtop = ±3GeV
• Fit simultaneously for MWjj and Mbjj using 2D templates of true Mtop and σJES
• (940 pb-1) achieves world single best measurement with Matrix Element Analysis Technique (MEAT)
Mtop = 170.9 ± 2.2 (stat+JES) ± 1.4 (syst) GeV/c2=170.9 ± 2.6 GeV/c2
Crimea 2006, 9/21 N. Giokaris 17
Top Mass with ME• Calculate event-by-event signal probability curve (rather than single Mrec) using
decay matrix element and transfer functions.• Calculate event-by-event background probability (no dependence on Mtop!).• Combine signal and background probability in one likelihood vs Mtop for entire
sample
ME method uses maximal information per event at a price of simplifiedassumptions.Final mass result and uncertainty is calibrated against simulatedevents.
Crimea 2006, 9/21 N. Giokaris 18
Top Mass in DileptonUnderconstrained system: two neutrinos but only one MET measurement.Remind that the major difficulty in reconstructing top is the parton-level cambinatoric problem
(1 fb-1) assumes highest two ET jets are the b-jets and integrate ME probability over 8 unknowns
Using 78 events (27.8 bkgr)
– Confirmed in b-tag dilepton sample(S:B~30:1) .– Consistent results in template measurements.
)tt(p),v(p),v(p T21
GeV9.3±9.3±5.164=M syststattop
Crimea 2006, 9/21 N. Giokaris 19
Top Mass in All HadronicLow S/B (~1/8) and large combinatorial background (90 permutations for 6 jets)
Top Mass Measurement with Template method using NN Selection has measured @1fb-1:
Mt = 174.0 ± 2.2 (stat) ± 4.8 (syst) Gev/c2
Crimea 2006, 9/21 N. Giokaris 20
Top Mass Summary
CDF Mtop@1fb-1:
Mtop= 170.9±1.4stat ±1.9syst
Crimea 2006, 9/21 N. Giokaris 21
Top LifetimeTop in SM has very short lifetime (SM ct ~ 3x10-10 μm)
look for anomalous lifetime by fitting impactparameter of lepton in l+jets events
ct< 52.5μm(@95%C.L.)
Crimea 2006, 9/21 N. Giokaris 22
W helicity in Top Decays
F0+F-+F+=1• Helicity states of the W:
• Because top is heavy:
• SM test: if V-A interaction F-˜ 0.3 F+ ˜ 0if V+A interaction F- ˜ 0 F+ ˜ 0.3
012.0±703.0=m+m+M2m
~F 2b
2top
2W
2top
0
Top in SM has V-A decay. Longitudinal Left-handed Right-handed
F0 F- F+
suppressed by factorsof order m2
b/m2t
Variables sensitive to W helicity are angular distributions of W products in W rest frame.
• cos(θ*) distribution• M2
l b
• Lepton pT spectrum
Crimea 2006, 9/21 N. Giokaris 23
CDF has 3 measurements1. cos(θ*) with full tt reconstruction in l+jets
2. M2lb in dil and l+jets
3. cos(θ*) in l+jet samples using the mass χ2 fitter
W helicity measurements
.)L.C%95(@26.0<F06.0±19.0±85.0=F
+
syststat0
.L.C%[email protected]<F+
Assume V-A and measure F0/F- with other components fixed at SM value.Measure F+ and put limits on V+A/new physics.
318pb-1
)L.C%95(@11.0<F06.0±06.0±06.0=F
04.0±12.0±61.0=F
+
syststat+
syststat0
750pb-1
955pb-1
Crimea 2006, 9/21 N. Giokaris 24
Single top
NLO σ
t-channel 1.98±0.25 pb
s-channel 0.88±0.11 pb
TeV96.1=s
• Single top is produced via weak interaction at a rate ~1/3 that of top. Allows direct measurement of Vtb.
B.W. Harris et al. Phys. Rev. D 66 054024 (2002) • Kinematically wedged between non-top and top signal, plus high backgrounds (S/B~1/20) requires very sophisticated analysis techniques.• Use l +MET+2jet (>=1 btag) events: same signature as )bb WH(Htt• s and t-channel searched jointly and separately (have different sensitivityto new physics).
s-channel production
(W*)
Vtb
t-channel production (Wg fusion)
Vtb
Vtb
Crimea 2006, 9/21 N. Giokaris 25
Single Top LimitsCDF has 2 methods
1. Multivariate Likelihood Function2. Neural Network
Channel s+t t(pb) s(pb)SM σNLO 2.9±0.4 2.0±0.3 0.9±).1
Lhood σ95% 4.3(3.4) 2.9(2.6) 5.1(5.7)
NN σ95% 3.4(5.7) 3.1(4.2) 3.2(3.7)695 pb-1
95% observed (expected) exclusion limit getting close to SM expectations!
Statistical errors onlyBased on SM single-top cross section
Projections• 2.4 s excess with 1 fb-1 expected by end of ‘06• 3 s excess around 1.5 fb-1
(syst ignored)
Crimea 2006, 9/21 N. Giokaris 26
Search for Resonant ProductionttXpp 0Look for bumps in the ttbar invariant mass spectrum
CDF looks for generic spin 1 resonance (X0)• Assume ΓX0 = 1.2%xMX0 (narrow resonance)• Test masses between 450 GeV and 900 GeV in 50 GeV increments.
Set 95% confidence level limit for σX0 ateach mass.
Exclude leptophobic Z’ with Mz’ < 725 GeV.
Crimea 2006, 9/21 N. Giokaris 27
ConclusionsCDF II has used as much as x10 the RUN I statistics to perform several studies on the top quark
– ttbar production cross section has been measured to about 12% level
– Top mass precision is already known to ~1.5% level – expect to go down to ~1% by the end of RunII, thus further constraining the SM Higgs mass
– Single top should be detected soon– All the, up to now, measurements show that top
quark behaves as predicted by the Standard Model
Crimea 2006, 9/21 N. Giokaris 28
Acknowledgments
R. ErbacherV. GiakoumopoulouT. MaruyamaM. Tecchio