# Presentation: 601441

## TOP QUARK PHYSICS AT THE TEVATRONresults and prospects

- Krzysztof Sliwa
- CDF Collaboration
- Tufts University
- Department of Physics and Astronomy
- Medford, Massachusetts 02155, USA
- Cracow Epiphany Conference on Heavy Flavours
- 3-6 January 2003, Krakow, Poland

## TOP QUARK

- Top quark was expected in the Standard Model (SM) of electroweak interactions as a partner of b-quark in SU(2) doublet of weak isospin in the third family of quarks
- First published evidence for top quark by CDF in 1994
- 		CDF	: F. Abe *et al*. Phys. Rev. Lett. **73** (1994) 225
-  Observation (discovery) by CDF and D0 in 1995
- CDF	: F. Abe *et al*. Phys. Rev. Lett. **74 **(1995) 2626
- D0	: S. Abachi *et al*. Phys. Rev. Lett. **74** (1995) 2632
- With all data from Run-0 and Run-I analysed (~110 pb-1) a summary of results and a perspective view on the status quo of top physics is given
- In anticipation of much increased statistics in Run-IIa (2 fb-1) the fact that top quark physics is one of the best windows to the new physics beyond the SM is emphasised; prospects are discussed

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## TOP  QUARK  PRODUCTION

-      production of top-antitop quark pairs
-      single top quark production

- (Drell-Yan)

- (W-gluon fusion)

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## TOP MASS AND CROSS SECTION - methodology

- 	MEASUREMENT OF CROSS SECTION (CDF and D0)
- 		i.   search for events with top signature
- 		ii.  calculate expected SM background
- 		iii. count events above backgrounds
- 		iv. apply corrections for acceptance and reconstruction inefficiencies 	and  biases
- 		tt pair-production cross section
- 		single top production cross section

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## TOP MASS AND CROSS SECTION - methodology

- 	MEASUREMENT OF CROSS SECTION (CDF and D0)
- 	One should remember two important details:
- 	It is *assumed** *that the selected sample of events contains just the *tt events*
- 	and the *SM background*. This is the simplest and the most natural hypothesis since top quark is *expected* in the SM.
- 	Some of the acceptance corrections are ***strongly*** varying functions of top quark mass, Mt. The measured cross section depend on the adopted value of Mt, which has to be determined independently.

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## TOP MASS AND CROSS SECTION - methodology

- 	DIRECT MEASUREMENT OF TOP MASS (CDF and D0)
- 	All mass measurement techniques assume that each selected event contains a pair of massive objects of the same mass (top and anti-top quarks) which subsequently decay as predicted in SM. A variety of fitting techniques use information about the event kinematics. A one-to-one mapping between the observed leptons and jets and the fitted partons is assumed.
- 	Two things to remember:
- 	It is *assumed** *that the selected sample of events contains just the *tt events* and the *SM background*. This is the simplest and the most natural hypothesis since top quark is *expected* in the SM.
- 	The combinatorics, i.e. the problem that only one out of a large number of jets-lepton(s) combinations is correct, adds to the complexity of the problem.

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## TOP MASS AND CROSS SECTION - methodology

- 	Production of tt pairs via strong interactions from qq or gg initial state is the dominant production mechanism at s=1.8 TeV; for top quark masses above      Mt  120 GeV the qq fusion process dominates and the SM top quarks are expected to decay into real W and b quarks.
- 	Assuming SM, there will be three classes of final states, all with 2 b-quark jets:
- 	di-leptons, when both W decay leptonically, with 2 jets and missing transverse energy (MET):	 BF 4/81 for e, (~5%)
- 	lepton+jets, when one W decays leptonically and the other into quarks, with 4 jets and MET:	 BF 24/81 for e, (~30%)
- 	all-hadronic, when both W decay into quarks, with 6 jets and no MET:
- 			 BF 36/81 (~45%)

****

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## TOP MASS AND CROSS SECTIONDIRECT SEARCHES - methodology

- All CDF and D0 searches impose stringent identification, selection and transverse energy, Et, cuts on leptons and jets to minimize background
- Except for the di-lepton sample, where backgrounds are expected to be small, various techniques of b-tagging are employed. “Soft-lepton” tagging is used by both CDF and D0, and the secondary vertex tagging using a silicon vertex detector (SVX) by CDF
- D0, not equipped with a SVX makes greater use of various kinematic variables to reduce backgrounds
- The largest SM background is QCD W+jets production. Both CDF and D0 use VECBOS calculations to estimate the shapes of background distributions due to this process
- Presently available samples of top candidates are small, and the measurements of the cross section and the top quark mass is still dominated by statistical errors. THIS WILL NO LONGER BE TRUE IN RUN-II

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## TOP MASS AND CROSS SECTIONresults of D0 and CDF searches :  Run-I (~110 pb-1)

- 		References:
- 		CDF:	F. Abe et al. Phys. Rev. Lett. 80 (1998) 2773
- 			F. Abe et al. Phys. Rev. Lett. 79 (1997) 3585
- 		D0:	S. Abachi et al. Phys. Rev. Lett. 79 (1997) 1203
- 			S. Abachi et al. Phys. Rev. D 58 (1998) 052001

| Channel | D0 sample | D0 background | CDF sample | CDF background |
| --- | --- | --- | --- | --- |
| di-leptons |     5 |   1.4  0.4 |     9 |   2.4  0.5 |
| lepton+jets SVX tagged |     |  |    34 |   9.2  1.5 |
| lepton+jets soft-lepton tagged |    11 |   2.4  0.5 |    40 | 22.6  2.8 |
| lepton+jets topological cuts |    19 |   8.7  1.7 |  |  |
| all-jets |    41 | 24.8  2.4 |   187 |  144  12 |
| e |     4 |   1.2  0.4 |  |  |
| e,  |  |  |       4 |         2 |

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## TOP MASS MEASUREMENT IN LEPTON+JETS CHANNEL 

- In the lepton+jets and all-jets final states there is enough kinematical constraints to perform a genuine fit
- Four-momenta of the measured lepton and jets are treated as the corresponding input lepton and quarks’ four-momenta in the kinematical fitting procedures.
- Leptons are measured best, jets not as well (in Run-I better in D0 than in CDF), while the missing transverse energy (MET) has the largest uncertainty
- In the lepton+jets final state one may, or may not, use MET as the starting point for the transverse energy of the missing neutrino. In their published analyses CDF and D0 make use of MET.
- D0 use two multivariate discriminant analyses to select their top enriched and background samples of events that are basis of their top mass and cross section analyses.

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## CDF Top Mass in lepton+jets channel

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## CDF Top Mass in lepton+jets channel

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## D0 Top Mass in lepton+jets channel

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## D0 Top Mass in lepton+jets channel

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## TOP MASS MEASUREMENT IN DI-LEPTON CHANNEL

- In the di-lepton mode situation is much more complicated, as the problem is underconstrained (two missing neutrinos). Several techniques were developed. All obtain a probability density distribution as a function of Mt whose shape allows identifying the most likely mass which satisfies the hypothesis that a pair of top quarks were produced in an event and that their decay products correspond to a given combination of leptons and jets.
- MET may, or may not, be used.
- D0 developed two methods, the Neutrino Phase Space weighting technique (WT) and the Average Matrix Element technique (MWT), a modified form of Dalitz-Goldstein and Kondo methods
- Three measurements of top quark mass have been “blessed” in CDF. Two use MET (WT and “Minuit” fitting); one does not (a modified Dalitz-Goldstein, which instead includes information about parton distribution functions, transverse energy of the tt system and angular correlations among top decay products in the definition of likelihood - in the Bayesian way)

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## CDF Top Mass in di-lepton channel

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## CDF/D0 Top Mass in di-lepton channel

- CDF: 167.4±10.3±4.8 GeV/c2

- D0: 168.4±12.3±43.6 GeV/c2

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## CDF/D0 Top Mass in di-lepton channel

- 	Likelihood distributions for individual D0 (left) and CDF (right) events

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## CDF and D0 systematic errors in di-lepton channel

- Dominant uncertainties (in GeV/c2)

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## CDF Top Mass in all-jets channel

- There is enough kinematical contraints for a 3C fit. Huge backgrounds from QCD multi-jet production. B-quark tagging required.
-              	   Mt  = 186±10.0(stat)±5.7(syst) GeV/c2

- Systematic errors in all-jets channel (GeV/c2)

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## COMBINED TOP MASS MEASUREMENTS

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## CDF AND D0 TOP MASS MEASUREMENTS

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##  TOP PAIR PRODUCTION CROSS SECTION

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## TOP PAIR PRODUCTION CROSS SECTION

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##  TOP PAIR PRODUCTION CROSS SECTION

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##  TOP PAIR PRODUCTION CROSS SECTION

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## SUMMARY OF TEVATRON RUN-I RESULTS

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## SINGLE TOP PRODUCTION

- Electroweak process. Standard Model cross sections:
-        (ppWgt+X) = 1.70±0.20 pb  (Stelzer at al)
-        (ppW*t+X) = 0.72±0.04 pb  (Smith at al)
- Direct access to Wtb vertex, one could determine the |Vtb| element of Cabibbo-Kobayashi-Maskawa matrix
- Search for anomalous couplings - large production rates or anomalous angular distributions

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## SINGLE TOP PRODUCTION

- CDF:  < 13.5 pb at 95% CL

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## SINGLE TOP PRODUCTION

- Using an array of neural nets:
- D0 : s-channel  < 17 pb at 95% CL
-        t-channel  < 22 pb at 95% CL

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## RUN-II AT TEVATRON 2001-?

- New Main Injector  CM energy (s) increased from
- 1800 GeV to 1960 GeV  (tt cross section increases by ~35%)
- Different beam crossing time (396 ns and 132 ns later, instead
- of 3.5 s in Run-I) - fewer multiple interactions
- Significant upgrades to both detectors:
- D0 :    addition of SVX to allow better b-tagging
-           addition of a solenoid to allow track momentum reconstruction
- CDF : new calorimeter for 1.1< ||<3.5 (much better energy resolution)
-           new (longer) SVX with double the Run-I tagging efficiency

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## RUN-II AT TEVATRON 2001 - ?

- Aerial view of Fermi National Accelerator Laboratory

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## RUN-II AT TEVATRON 2001 - ?

- D0 detector in its current configuration

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## RUN-II AT TEVATRON 2001 - ?

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## PROSPECTS FOR RUN-II

|  | RUN-I | RUN-IIa CDF | Run-IIa D0 |
| --- | --- | --- | --- |
| “typical” L(cm-2s-1) |  1.6x1030 |      8.6x1031 |    8.6x1031 |
| integrated luminosity | ~110 pb-1 |         2 fb-1 |       2 fb-1 |
| dilepton events | ~10/exp |         140 |       200 |
| lepton+≥4jets | ~20/exp |       1500 |     1800 |
| lepton+≥3jets+≥ 1b tag | ~30/exp |       1400 |     1400 |
| lepton+≥4jets+2 b tags |  ~5 |         610 |       450 |
| ∆Mtop | 7 GeV/c2 |    2-3 GeV/c2 |   2-3 GeV/c2 |
| ∆(tt) | ~30% |       ~8% |      ~8% |

- Run-II a:   2001-2005
- Run-II b: >2005 ( L*dt* =15 fb-1,”typical” L=5.2x1032 cm-2s-1)

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## IS IT ONLY TOP ?

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##  SM consistency checks: W mass vs Mtop

-  SM consistency checks: W mass vs Mtop

- The precision measurements of various electroweak parameters  can be used to check the consistency of the Standard Model and to infer bounds and constraints on its basic parameters. The leading order top quark corrections and quadratic in mass, which allows quite precise “determination” of Mtop indirectly from other electroweak measurements. The dependence of leading order corrections to Higgs mass is logarithmic, and the bounds on Higgs mass are weaker with current errors.

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

##  1996 SM consistency checks: W mass vs Mtop

-  1996 SM consistency checks: W mass vs Mtop

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##  1997 SM consistency checks: W mass vs Mtop

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##  1998 SM consistency checks: W mass vs Mtop

-  1998 SM consistency checks: W mass vs Mtop

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##  SM consistency checks: W mass vs Mtop

- Two comments:
- The value of top mass in the range of about 170 GeV could be obtained indirectly from LEP electroweak measurements but only after assuming Higgs mass of 300 GeV !! This was true from 1993-1996, but not emphasized when claims were made that LEP “measured” the top quark mass of about 170 GeV before CDF and D0.
- Interestingly, fits to electroweak data in which top mass and Higgs mass were left as free parameters were pointing to a low Higgs mass (80-150 GeV) and lower top mass (157-169 GeV). With all the excitement around search for a light Higgs at LEP-II this fact that was not at all emphasized.

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

##  SM consistency checks: W mass vs Mtop

- Results of LEP EWWG
- SM consistency fits
- (Spring 2002)
- Measurements of W and top mass constrain Higgs mass. Fundamental consistency tests of Standard Model

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## IS IT ONLY TOP ?

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## IS IT ONLY TOP ?

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## IS IT ONLY TOP - cross section methodology ACCEPTANCE VARIATION WITH TOP MASS

- Acceptance corrections for the di-lepton and the lepton+jets final states as a function of top quark mass. Notice significant variation in top quark mass  range 140-180 GeV

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## IS IT ONLY TOP ?

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## IS IT ONLY TOP ?

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## IS IT ONLY TOP ?

- Epiphany 2003   January 3-6, 2003  Krakow, Poland

## IS IT ONLY TOP ?

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## IS IT ONLY TOP ?

- CDF and D0 distributions of mass of the tt system

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## IS IT ONLY TOP ?

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## IS IT ONLY TOP ?

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## IS IT ONLY TOP ?

- Rapidity (CDF) and pseudorapidity (D0) distributions of  tt system

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## PHYSICS WITH LARGE STATISTICS TOP SAMPLES

- top quark mass measurements (within 2-3 GeV/c2)
- tt pair production cross section (within 8%)
- single top production cross section
- top-antitop spin correlations, studies of top polarization
- rapidity of tt system
- mass of tt system
- W helicity in top decays
- |Vtb|
- 	NEW PHYSICS ?
- 		any anomalies in the above studies
- 		rare decays....
- CAN’T WAIT FOR MORE DATA IN 2003 !!

- Epiphany 2003   January 3-6, 2003  Krakow, Poland