Christophe Clment

1
Tevatron Top Results
Flavor Physics and CP Violation Vancouver 2006

• Christophe Clément
• University of Stockholm
• For CDF and DØ Collaborations

2
Top and the Tevatron

• Top the heaviest elementary particle,
• Speculated to be related to EWSB,
• its mass is important SM parameter.
• As close as we can get to a free quark
• Top decays in 0.510-24s, before hadronizes
• Only a handful of top candidates in Run I,
• but is it standard model top quark?
• Run II measure detailed properties
• with much larger data sets.
• Test production and decay mechanisms, does it
• have SM quantum numbers...
• Heavy enough to decay to exotic particles (H,
  W)

Tevatron vs1.96 TeV, L1032cm-2s-1
April 11, 2006
C.Clément FPCP 2006
2/18
3
Top Quark Production and Decay

• So far only observed in pairs produced via
  QCD
• Single top production via electroweak interaction
  
• expected but not yet observed (coming back to
  this topic)

stt6.81.2pb (theory)

• SM predicts FCNC decays are tiny, t?Wq is
  dominant
• 3 quark generations direct measurements of Vub
  and Vcb predict Vtb, B(t?Wb)1

April 11, 2006
C.Clément FPCP 2006
3/18
4
Top Pair Final States

• How top quark was discovered!
• Used for all measured top quark properties so far

April 11, 2006
C.Clément FPCP 2006
4/18
5
Top Pair Cross Section

• Test of pQCD at high energy, prediction for stt
  (6.81.2)pb, non-SM production?
• Exotic top decays (t?Hb,...) compare stt in
  various channels
• ljets/ll andt/non- t ratios so far weak
  constraints.

ltrack DØ dilepton 370pb-1
April 11, 2006
C.Clément FPCP 2006
5/18
6
B(t?Wb) and Vtb

• Test whether B(t?Wb)1
• Count events with 0, 1, 2 b-tagged jets

Estimate Ntt in 0-tag sample
Within standard model Vtb vB(t?Wb)
h.o. 0.9990ltVtblt0.9992 at 90 C.L.
CDF Published 160 pb-1 PRL 95, 102002, 2005
B(t?Wb) 1.120.27 -0.23 (stat syst)
Vtbgt0.61 _at_95C.L. DØ 240 pb-1 hep-ex/0603002
(submitted to PRL) B(t?Wb)1.030.19-0.17
(statsyst) Vtbgt0.61 _at_95C.L.
April 11, 2006
C.Clément FPCP 2006
6/18
7
Top Quark Decay W helicity
If right handed W then 1) angular momentum is
not conserved OR 2) b is right handed
(suppressed) ? no WR
f-30
f070
f0
April 11, 2006
C.Clément FPCP 2006
7/18
8
W helicity
70 W0 30WL
W rest frame
WL
W0
v
t
W
b
WR
?
l
? angle between the l and the direction of t

• Longitudinal polarization W0
• leptons emitted ? to W boost
• Left handed polarization WL
• leptons emitted antiparellelle to W boost
• ?lower lepton pT

April 11, 2006
C.Clément FPCP 2006
8/18
9
W helicity
Measurement of f by DØ in leptonjets and
dilepton events fit cos ? templates to data
DØ 370 pb-1 preliminary f0.08
0.08(stat)0.05(syst) (for f00.7)
CDF f and fo in ljets and dilepton i) fit
cos ? templates ii) use lepton pT
CDF 200 pb-1 (hep-ex/0511023) f00.740.22-0.34 f
lt0.27 _at_ 95 C.L.
April 11, 2006
C.Clément FPCP 2006
9/18
10
Top Quark Charge
OR
?
DØ 370 pb-1 preliminary Qtop is not 4e/3 at 94CL
April 11, 2006
C.Clément FPCP 2006
10/18
11
The Mass of the Top Quark
Quadratric dependence in mtop
Log dependence in mH

• Originally used EW measurements to predict mtop
• Derive mHiggs from EW
  measurements and mtop
• Future (if we know mHiggs) does EW, mHiggs and
  mtop fit together

Why mtop is hot
April 11, 2006
C.Clément FPCP 2006
11/18
12
Template Method in situ calibration
Largest systematic error
Idea Constrain jet energy scale using the known
W mass and the observed mjj

• Split leptonjet sample in 4 depending on 0/1/2
  tags and jets pT
• Extract mrecot and mjj for each event by
  minimizing ?2
• Compare observed mrecot and mjj to templates at
  various mass and JES

l, jet resolutions
CDF 680 pb-1 Mtop173.42.5(statJES) 1.3(syst)
GeV
April 11, 2006
C.Clément FPCP 2006
12/18
13
Matrix Element Method in situ calibration

• Attempts to use maximum of information

• Constrain jet energy scale using the
• known W mass and the observed mjj
• Combine 0, 1 and 2 tag events

yParton kinematics
Vector of kinematic observables
Transfer from parton to measured kinematics
Probability of the parton config y (ME)
DØ 370 pb-1 Mtop170.6 4.0-4.7(statJES)
1.4(syst)
Jet energy scale
Main systematics on top quark mass b-jet energy
scale Jet energy scale ISF FSR Background
shapes Signal fraction
Top quark mass
April 11, 2006
C.Clément FPCP 2006
13/18
14
More on Top Quark Mass

• Many mass analyses techniques, various
• channels,
• Dilepton mass low statistics but promising
• because less sensitive to JES and smaller
• background.
• Consistent with precision EW?

April 11, 2006
C.Clément FPCP 2006
14/18
15
Electroweak Top Production
t-channel, tqb st2.0 pb
s-channel, tb ss0.9 pb

• Measure directly the Vtb CKM matrix element, ss,
  st ?Vtb2
• Experimentally challenging because not too
  different from W2 jets
• Use events with W?ev or W? ?v
• Signature 1 isolated lepton, MET, 2 or more jets
• s-channel 1,2 b-tagged jets t-channel 1
  b-tagged jet 1 light jet
• Major backgrounds Wjets, top anti-top pairs,
  fake leptons
• Not yet observed!

April 11, 2006
C.Clément FPCP 2006
15/18
16
Search for Single Top

• Precuts
• 1 isolated electron/muon,
• high MET,
• 1 or 2 b-jets, (s channel)
• 1 b- and 1 light-jet (t-channel)
• 2. Discriminate against
• Wjets and
• 3. Build 4 discriminants
• Wjets / s-channel
• ttbar / s-channel
• Wjets / t-channel
• ttbar / t-channel

e.g. used in tqb/Wbb and tqb/ttbar discriminant
DØ Preliminary 370 pb-1 exp/obs s-channel
3.3/5.0 pb t-channel 4.3/4.4 pb Published 230
pb-1 (Phys. Let. B 622) s-channel 4.5/6.4
pb t-channel 5.8/5.0 pb
April 11, 2006
C.Clément FPCP 2006
16/18
17
Search for Single Top

• On 695 pb-1 CDF carries out 2 analyses
• likelihood discriminant based
• ANN based

Eg. of variable used in discriminant , here
top-mass like variable
Extrapolation to larger dataset
April 11, 2006
C.Clément FPCP 2006
17/18
18
Conclusions

• Now an order of magnitude more data is available
  thanks to run II, CDF and DØ are providing a
  series of precision measurements of the top quark
  properties,
• Precision tests of SM prediction for production
  (pQCD), decay vertex
• (V-A, Vtb), electric charge, single top
  production are performed
• Many more measurements not mentionned here
  search for t quark, t?Wb, Z? , anomalous
  couplings, FCNC decays, decays with
  tau-leptons...
• Single top searches are getting closer to
  expected cross sections
• Precise measurement of the top quark mass,
  already
• outperforming expected performance of 3 GeV,
• Put constraints on the SM,
• realistically aiming at ?mtop2 GeV for
  entire Run II

April 11, 2006
C.Clément FPCP 2006
18/18