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M.Weber, Aspen 2005 1
Top quark physics review(results from the Tevatron)
CDF
M.Weber, FNAL
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M.Weber, Aspen 2005 2
Outline
• The top quark• The detectors and collected data• Top quark production cross sections• Is there more than the top quark?• Top quark properties
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M.Weber, Aspen 2005 3
The top quark
p
p tb
W-
q
q’
t b
W+
l+
n
X
Resonance production
Production kinematics
Top Spin Polarization
Top Mass
|Vtb|
Branching Ratios
Rare/non SM Decays
Anomalous Couplings
CP violation
Top Spin
Top Charge
Top Width
_ __
_
W helicity
The top quark decays before it canhadronize
Yt = ≅ 1
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M.Weber, Aspen 2005 4
Top Quark Production
6.7 pb (1.96TeV, mt=175GeV/c2)
85%
15%
Single top quark production via weak interaction
RunII 30% higher than RunI
Cacciari etal, JHEP 0404:068,2004
Top quark pair production via strong interaction
s-channel: 0.88pb
Sullivan, Phys.Rev.D70:114012,2004
t-channel: 1.98pb
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M.Weber, Aspen 2005 5
Top quark identificationAll jet46%
Lepton + jet29%dilepton (e+µ)
4.5%
t→Wb ≅100%
decay product have:• good angular separation in the
lab frame• high transverse momentum
Need to reconstruct and identifyElectrons, muons, jets, b-jetsand missing transverse energy
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M.Weber, Aspen 2005 6
CDF and D0 in Run IITracker Solenoid Magnet
3 LayerMuon System
Calorimeter
New Silicon DetectorNew Central Drift ChamberNew End Plug CalorimetryExtended muon coverageNew trigger and electronics
Silicon Detector and central fiber trackerin a 2 T solenoidSubstantially upgraded muon systemNew trigger and electronics
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M.Weber, Aspen 2005 7
Luminosity
1.1032 cm-2sec-1
instantaneous luminosity
0
1
2
3
4
5
6
7
8
9
10
9/29/03 9/29/04 9/30/05 10/1/06 10/2/07 10/2/08 10/3/09
Start of Fiscal Year
Inte
grat
ed L
umin
osity
(fb
-1)
Design Projection
Base Projection
2009
8.5fb-1
D0: recorded 0.53 fb-1
CDF recorded 0.61 fb-1
4.4fb-1we are here
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M.Weber, Aspen 2005 8
Production Cross section
• many results:different decay channels,different methods,with/without b-tagging
• Is there more than the top quark ?• single top (weak top production)
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M.Weber, Aspen 2005 9
Di-lepton
combined di-lepton and lepton + opposite charge track:
with b-tagging
Ultra-pure sample of top quark events: S/N>50
eµ only
pb)()(1.11)( 4.14.1
8.53.4 syststattt +
−+−=σ
lepton + oppositecharged track
pb )(1.1)(6.8)( 5.24.2 syststattt ±= +
−σ
pb )()(0.7)( 5.14.1
7.23.2 syststattt +
−+−=σ
Both W decay intolepton and neutrino:2 jets (b), 2leptons,high missing Etlow BG but low yield
PRL 93, 142001 (2004)
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M.Weber, Aspen 2005 10
All jets cross section
CDF
Both W decay in q-qbar4jets + 2 bjets, high transverse energyHigh yield, high BG
220 dataexpect 186 BG
requires b-tagging
pb )(5.0)()(7.7)( 7.48.3
4.33.3 lumisyststattt ±= +
−+−σ
pb )()(5.28.7)( 7.43.2 syststattt +
−±=σ
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M.Weber, Aspen 2005 11
Lepton+jets
pb )()(2.7)( 9.14.1
3.12.1 syststattt +
−+−=σ
both bjetstagged One W decay in q-qbar,
one in lepton + neutrino2jets + 2 bjets + lepton +missing Etmedium yield, medium BG
l+jets with soft lepton tagging
new
CDF
pb )()(2.5)( 3.10.1
9.29.1 syststattt +
−+−=σ
pb)()(2.7)( 6.17.1
6.24.2 syststattt +
−+−=σ
e and mu
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M.Weber, Aspen 2005 12
Cross section summary
many measurements with 30-40% precisioncompatible with SM, compatible with NPAiming for 10% with 2fb-1
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M.Weber, Aspen 2005 13
Anomalous Top kinematicsRunII dilepton 193pb-1CDF probability to measure a
sample less consistentwith SM is 1%-4.5%
use the cross section analysis preselectionand look for events with topologyinconsistent with a t-tbar dilepton event
Submitted to PRL
result is dominated by these 9 eventsin the whole sample.No subset with significant deviations
more top like
no excess of events with high missing Et and lepton pt seen in RunII
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M.Weber, Aspen 2005 14
Examplelikelihood fitfor m=225GeV/c2
CDF
lepton+jets event selectiondiscriminate between t and t’ with Ht
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M.Weber, Aspen 2005 15
Single top quark limitshigh pt leptonhigh missEttwo bjets(+1 light q)
s-channel < 19pbt-channel < 25pb (95%CL)combined < 23pbCDFcombined s+t limit: <17.8pb (95%CL)
PRD 71 (2005) 012005 and update from D0is about to be released
Q: charge of the leptonη: pseudorapidity of the non b jet
s-channel: <13.6pb (95%CL)t-channel: <10.1 pb
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M.Weber, Aspen 2005 16
Top quark Properties
• Mass
• R=B(t->Wb)/B(t->Wq)
• W helicity
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M.Weber, Aspen 2005 17
Top Mass• 10 years of top quark mass measurement:
from kinematical fit and template comparison, to likelihood calculations using maximum information
• RunI has a 2.5% uncertaintyRunII 5%, aim for 1% (~2GeV/c2).
New Mass measurement with RunIdata from D0.
Single most precise top mass measurement
mt = 180.1±3.6(stat)±3.9(syst) GeV/c2
Published in Nature, June 2004
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M.Weber, Aspen 2005 18
New Top Mass World Average (Run I)
mtop = 178.0 ± 4.3 GeV/c2
D0 weightmH = 114+69
-45 GeV/ccmH < 260 GeV @ 95% C.L.
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M.Weber, Aspen 2005 19
Mass in Run II, D0Measurements in lepton+jets channel (~150 pb-1)
template method uses templates for signal and background mass spectraideogram method uses analytical likelihood for event to be signal or background
TemplateIdeogram
22.107.5 GeV/c )()(5.60.170 syststatmt
+−±= 2GeV/c )(1.7)(8.55.177 syststatmt ±±=
Systematical error dominated by the (un)knowledge of the jet energy scaleWill improve very soon !
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M.Weber, Aspen 2005 20
Mass in RunII, CDFCDF di-leptonsl+jets, b taggedl+jets, multivariate
22.170.16 GeV/c )(9.6)(5.176 syststatmt ±= +
−24.6
3.6 GeV/c )(8.6)(6.179 syststatmt ±= +−
21.77.7 GeV/c )(5.6)(9.174 syststatmt ±= +
−
Dynamical Likelihood Methodsimilar to D0 “matrix element method”
25.40.5 GeV/c )(2.6)(8.177 syststatmt ±= +
−
Single most precise Run II measurement
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M.Weber, Aspen 2005 21
Branching ratioR=B(t->Wb)/B(t->Wq)
Ratios of number of events in b-tag bins2D fit to the cross section and R for tagged eventsMeasure R* εb (εb = tagging efficiency)
SM: R=0.998
158pb-1 mu and 169pb-1 e
SVT
CDF
R*εb
R = 1.11+ 0.21- 0.19 (stat+syst)
> 0.62 @ 95% C.L.SVT: R = 0.70 +0.27
-0.24 (stat) +0.11-0.10 (syst)
CSIP: R = 0.65 +0.34-0.30 (stat) +0.17
-0.12 (syst)
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M.Weber, Aspen 2005 22
W helicity
In SM F-=0.30, F0 =0.70, F+ =0
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M.Weber, Aspen 2005 23
W helicityCDF RunI result: F+<0.18(95%CL)
CDF
F0=0.89+0.30-0.34 (stat) ±0.17 (syst)
F0>0.25 (95%CL)lep+jets
CDF
F0=0.27+0.35-0.24
F0 < 0.88 (95% CL)lep+jets & dilepton
F+ <0.24 (90% CL) with tagF+ <0.24 (90% CL)dilepton
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M.Weber, Aspen 2005 24
Conclusion• The top quark is very heavy = very interesting.• With the Tevatron running really well, we are at the door-
step of learning much more, in more detail about the top quark and what it can tell us about undisclosed physics.
• Cross section measurements at the Tevatron RunII are consistent with SM, but also with new physics. More expected soon and aim for 10% with RunII.
• New Mass average from RunI. Measurements from RunII. More statistics and better jet energy scale should reduce the uncertainty very soon.
• Still only limits on single top quark production, should be seen in 1fb-1 to 2fb-1
• Analyses with double statistics almost ready, double again next year.
• More results to come (new physics ?).