top results at cdf yen-chu chen/ 陳彥竹中央研究院物理所 institute of physics, academia...

Top Results at CDF

Yen-Chu Chen/陳彥竹

中央研究院物理所Institute of Physics, Academia Sinica

Taiwan, ROC

For the CDF collaboration

ICFP 20052005/10/03-08

Yen-Chu Chen ICFP 2005 2

Outline• The Top quark

• CDF experiment– Current (2005:1 fb-1)

– Future (2009: 5 fb-1 up to 8 fb-1 or more)

• Top quark production

• Top quark mass measurement – Implication to Higgs search

• Search for resonance in t t pairs

• Future prospects

• Other Top physics

• Conclusion

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The last of the 6 quarks.

Discovery was announced in 1995 by CDF and D0.

The Top Quark


The Top quark

• Properties

– Standard Model

• Charge : + 2/3

• Spin : 1/2

• Mass : ? → A free parameter in the model

• Higgs mass (mt, MW)


Top quark physics

P Pt

tX

b

b

W

W

l

q

l

q

q'_

q'

__

Production Cross section

Top massTop polarization

Decay modes, rare decays, etc.

W helicity Top charge


CDF detector


Integrated luminosity

Stacking rate of the p.

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Data for Physics

QCD

Top

Recorded2002 → Aug. 2004 Recorded: 530 pb-1

Physics: 320 - 470 pb-1

2002 → Aug. 2005 Recorded: 950 pb-1

Physics: 620 ~ 880 pb-1

Store Number (Aug.23,2005)

Exceed 1 fb-1 recorded in Sep. 2005!

100 pb-1 in RUN I


Top quark production• p p → t t

~ 6.7 pb at √S = 1.96 TeV: 85% qq → t t15% gg → t t

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t t decay modes

• Di-lepton: t t → W+bW–b → l+b l–b – Two high pt leptons, high missing energy, b-tagging

• Lepton + jet: t t → W+bW–b → lb qqb– One high pt lepton, high missing energy, b-tagging

• All jet: t t → W+bW–b → qqb qqb

– b-tagging, number of jets, small missing energy, n

o high pt lepton, kinematical requirement, etc.

_ _ _

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_

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69.7

Top di-lepton event candidate


(t t ) di-lepton channel

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Number of events

• Ntop = L • is included in the MC

(tt) = 9.85 ± 2.13(stat) ± 1.30(sys) ± 0.5(lumi) pb

• Assuming mt = 178 GeV/c2

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Checking kinematics


(t t ) lepton+jet channel

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• Needs b-tagging– Second vertex (SVX) tagging


The result

= 8.7 0.9 (stat) +1.2 -0.9 (syst) pb

– Assuming mt = 178 GeV/c2

= 8.9 0.9 (stat) +1.2 -0.9 (syst) pb

– Assuming mt = 175 GeV/c2


Needs update


Top mass


Top mass measurement - di-lepton -

• The challenges:– ’s not measured.– Combinatory of l + jet.

• Solutions:– Additional constraints– Matrix element– …


Top mass measurement - lepton-jet -

• Challenges:– Finding l + jet pair

– b-jet tagging

– Jet energy

– …

• One of the solutions:– The W→j j mass was used as constraint.

– Fit the Top mass and the jet energy scale (JES) simultaneously.

The world best Top mass measurement from single channel and single experiment: 173.5 +4.1/-4.0 GeV/c2


JES and top mass


mt = 173.5 +2.7/-2.6 3.0 GeV/c2


SM Higgs mass = ?


Indication of new physics?


Search for X0 → t t_


m (t t) _


Consistent with the SM?


Test the m(tt) spectrum with X0 of various masses

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A fit with SM + X0(500)


Projection (BR)


Projection (mt)

• Approaching 1.5 GeV uncertainty.


Projection (single Top)• Single Top discovery could be next year!


More on Top properties• W helicity in the Top decay

– Current result supports the V-A theory.• cos and pt :

– F0 = 0.74 +0.22 -0.34 (stat. + syst.) , F+ = 0.00 +0.20 -0.19 (stat. + syst.)

• Mlb2: f(V+A) = -0.21 +0.42 -0.24

< 0.61 at 95% CL (RUN I data) => F+ < 0.18 at 95% CL

• Br(t→Wb)/Br(t→Wq) = 1.12 +0.21-019 (stat) +0.17

-0.13 (sys)

> 0.62 at 95% CL

• Br(t →q)/BrSM(t →q) < 5.0 at 95% CL

• Searching for charged Higgs in the Top decay

• Is it really Top?– Study on the Top charge in progress

• …


A bit more on Top charge

• Possibility– Q = –4/3; true mt = 271 +33

-38 GeV/c2

• Top charge study in progress

• More data on t t resonance

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Conclusion

• A lot of excitements will come out next year with 1 fb-1 or more data!

• The FNAL will run through 2009! Up to 8 fb-1 could be delivered!

• There could be more discoveries!

The best is yet to come!


BACKUP SLIDES


ILC at the FNAL?


Jet reconstruction


• Second vertex (SVX) tagging– Long life time of the b quark

• Soft muon tagging– Semi-leptonic decay of the b quark

b tagging


SVX b tagging


Single Top• Top quark may also be produced as single

~ 3 pb (t: 1.98 0.25; s: 0.88 0.11)

t-channel s-channel


Q

• Q: charge of the lepton.

: pseudo-rapidity of the b jet.


Compared to data

• The non-top background includes:– miss tagged– W bb– W cc– W c– di-boson– non-W

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The Mlb


• Set upper limit:– t channel: < 10.1 pb at 95% CL– s channel: < 13.6 pb at 95% CL– combined: < 17.8 pb at 95% CL

6.2 times higher than SM!


Projection of searching


Is it really Top?• The “Top” quark discovered has a mass of 17

4 GeV or so, assuming SM.

• Can’t exclude the possibility of having a particle from SUSY model which could have a similar mass but with charge of –4/3.


Top Charge


To obtain the Top charge- di-lepton -

• Jet charge calculation– Track quality

– Jet track selection• Jet charge cone size

• Min. and max. number of tracks in a jet

• Track pt

– Jet charge formula

• Lepton-Jet pairing– Mlb

2 pairing

– Top mass as input


• Charge of b jet:– Use jet charge to identify which jet is b and which one is b.

– Soft lepton (muon) tagging.

• Calculate the charge sum of lepton and b in a pair.

• Count the difference between the |2/3| and |4/3| bins.

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Top charge studyMC, signal

Pythia 175 GeV , di-lepton, 2 jets only

Top Q diff. between the |2/3| and |4/3| bins using 100 events.

About 1 effect could be expected with 100 events.


Top charge studyMC, background

WZ, di-lepton, 2 jets only

The WZ background has negligible effect on the Top charge.

Top Q diff. between the |2/3| and |4/3| bins using 100 events.


Top charge estimation from - lepton + jet -

• Jet charge calculation– Similar to di-lepton case

• Lepton-Jet pairing– Top mass fitter

• Current study shows 3 effect could be achieved with 1fb-1 data.


W helicity in the Top decay

W

t

l

*

* is the angle between the charged lepton and the boost direction of W in the W rest frame from the Top rest frame.

• Due to V-A the polarization of W decay from the Top could be only longitudinal and left-handed.

• The branching fractions from the SM (longitudinal and right-handed):– F0 = 0.7 (mt = 175 GeV/c2)

– F+ = 0.


• F0 = 0.99 +0.29 -0.35 (stat.)

0.19 (syst.)

• F+ = 0.23 0.16 (stat.)

0.08 (sys

t.)

From cos

2 Mlb2

cos – ──── – 1 mt

2 – Mw2


From lepton PT

• F0 = 0.31 +0.37-0.23 (stat.)

0.17 (syst.)

• F+ = -0.18 +0.14-0.12 (stat.)

0.12

(syst.)


• Combine both cos and PT :

– F0 = 0.74 +0.22 -0.34 (stat. + syst.)

– F+ = 0.00 +0.20 -0.19 (stat. + syst.)

• The current results are consistent with the V-A !


W helicity from Mlb2

• V-A and V+A predict different Mlb2 distritions.

l+j single tagl+j double tag

di-leptong


• From RUN I data it appears that the fraction of V+A is consistent with 0!

• For RUN II with 2 fb-1 data, the expected uncertainty is 0.1 (stat.) 0.11 (sys) .

top results at cdf yen-chu chen/ 陳彥竹 中央研究院物理所 institute of physics, academia...

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top results at cdf yen-chu chen/ 陳彥竹中央研究院物理所 institute of physics, academia...