the top quark yesterday and today hugh montgomery jefferson lab irfu-cea saclay february 4, 2010

The Top Quark Yesterday and Today

Hugh MontgomeryJefferson Lab

IRFU-CEA SaclayFebruary 4, 2010

2

OutlineWhy do we need the top quark?

A virtual life

Observation of the Top Quark

Properties of the Top Quark

Electroweak Coupling of the Top Quark

The Top Quark and the Future

3

Elementary Particle Physics

4

Elementary Particle Physics

Fermicentric Dates

Major Discoveries b quark

1977 t quark

1995 nt (tau neutrino)

2000

Critical measurements t and W mass 1998 proton structure

1984-95 using neutrinos and muons

QCD at highest 1988-now energies

9

Upsilon Discovery- 1977

bound state of bottom quarks

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The Virtual Life of the Top Quark

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Premature Single Top Production

Schwienhorst – Fermilab W&C 4/1/2005

An ephemeral existenceUA1 at the SppS

1984:– Using isolated high transverse momentum lepton

– 2 or 3 hadron jets– Observed 5 events (e+ >=2 jets); 4 events (μ+ >=2 jets)– Expected background: 0.2 events

• fake leptons dominate

• bb & cc production negligible– Conclude: results consistent with M top = 40 ±10 GeV

1988:– x6 the data– much better understanding of backgrounds– M top > 44

Yagil – Top Turns Ten 12

For a top mass less than the W mass UA2 (88/89) was competitive with CDF


14

Mass Predictions and Limits

Quigg, Langacker

16

Fermilab Antiprotons

17

19pb

57pb

Tevatron Run I and Top

Au

g 9

3

Dec 9

4

Yagil – Top Turns Ten

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CDF - The Experiment

Urgency

CDF

D0

Glenzinski – Top Turns Ten 19

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DZero

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A First Hint for CDF


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A DZero Top Quark?

23Grannis– The Antitop Quark at the Antiproton celebration, LBL

Profile of the Top Quark

Top Production and decay

DIL - both W decay to leptons

Low rate, Very clean

SVX - one of the b-jets is identified using a displaced vertex tag

SVX detector

SLT - one of the b-jets is identified using a leptonic decay product

lepton I.D. in jets


25Grannis– The Antitop Quark at the Antiproton celebration, LBL

Dilepton Observations 1995

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Single Lepton & Jets

Grannis– The Antitop Quark at the Antiproton celebration, LBL

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Discovery : Observation


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List of Institutions on Dzero at time of discovery

(Grannis), Hadley – Top Turns Ten

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Dzero Author List

Thanks to all

Abachi to Zylberstejn

(Grannis), Hadley – Top Turns Ten

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Top Mass

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Constraints/Observables 18 fermion 3-vector components Use constraints

W mass (twice) (2) Mass of top = mass of antitop (1) Assume mass for top Fit using measurement errors

Measure 1 lepton(3) and 4 jets (12) and Missing Transverse Energy (2) 20 constraints plus measurements (20-18 2C)

Measure 2 leptons(6) and 2 jets (6) and Missing Transverse Energy (2) 17 constraints plus measurements (17-18 -1C)

Further constraints The parton distributions (poor man’s beam

energy) Internal characteristics Full matrix element

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Top Mass: Methodologies Choose any characteristic of the event

which is related to the top mass Lepton transverse momentum B quark decay length Mass reconstructed by constrained fit

To lepton plus jets events (2C) using just kinematics Using full matrix element Reducing combinations with b tagging

To dilepton events (<~0C!!!) using all the approaches above

To All jets events Using all the different approaches above

WITH (IN)Efficiencies properly treated!! Lots of MC studies

WITH BACKGROUNDS properly treated!!

The Mass of the Top QuarkCDF 1994


CDF measured:1994 Mtop = 174 +- 10 +-

13 GeV1995 Mtop = 176 +- 8 +- 10

GeV33

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Top Mass


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D0 Run I – Full Matrix Element For each event estimate probability for a top mass value using all

measured quantities compared to distribution of t-tbar production matrix element.

(Need to integrate over measurement resolutions)

Contemporary Top Mass

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Tevatron (Winter 09):mt=173.1 ± 0.6 (stat) ± 1.1 (syst) GeVmt=173.1 ± 1.3 (stat+syst) GeV

Florencia Canelli, LP2009

CDF (4.3 fb-1):mt(l+j)=172.6±0.9(stat)±0.7(JES) ±1.1(syst)GeV

Single Experiment Uncertainty~1 GeV!!!!

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Implications of the Top Quark Mass

The total width of the top quark is 1- 1.5 GeV ( proportional to m3 ) The top quark decays in 0.5 * 10-24 seconds

Before it can form a hadronNo top mesonsNo toponiumNo hadronisationHadronisation does not modify the spin orientationThe observed mass is that of the quark

The top quark is our only bare quark!

Luminosity Helps

38Florencia Canelli, LP2009

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Top Quark Pair Production Cross Section

Quadt– Top Quark Physics at Hadron Colliders- Habilitationschrift

Top Quark Pair Production Cross Section

6% precision!

~ 6% Precision


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ttbar production spectra


ttbar Production

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Single Top Production

Schwienhorst – Fermilab W&C 4/1/2005

Single Top Production

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Tevatron (3.2 fb-1), PRD66 054024, 2002:|Vtb|=0.91 ± 0.08 (stat+syst)

Tevatron (3.2 fb-1):

st =2.76 +0.58 -0.47 (stat+syst) pb


Top Quark Properties

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Top Quark Properties

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Top Quark Decays

Quadt– Top Quark Physics at Hadron Colliders- HabilitationschriftBuescher- D0 Report to PAC, December 2005

R = B(tWb)/B(tWq)Related to Vtb

Determined from the relative numbers of 0, 1 and, 2 b quark tags

D0 Result (CDF similar)

R = 1.03+/-0.19/0.17 Vtb >~ 0.8

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Top Quark Decayst H+b?

Different possible decays of the H+

Quadt– Top Quark Physics at Hadron Colliders- Habilitationschrift

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W-Helicity in top Decay

Grannis– The Antitop Quark at the Antiproton celebration, LBLQuadt– Top Quark Physics at Hadron Colliders- Habilitationschrift

Correlations between the lepton and b jet direction in the W rest frame.

lepton pT spectrum depends on W helicity

Effective mass of lepton and b jetFit to full matrix element

κ = N(↑↑) + N(↓↓) − N(↑↓) − N(↑↓)N(↑↑) + N(↓↓) + N(↑↓) + N(↑↓)

Top-antitop spin correlations

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κ = N(↑↑) + N(↓↓) − N(↑↓) − N(↑↓) SM predicts κ = 0.78 N(↑↑) + N(↓↓) + N(↑↓) + N(↑↓)

D0 (4 fb-1): κ =-0.17 +0.64 -0.53

CDF (2.8 fb-1): κ =0.32 +0.55-0.78


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Use jet charge algorithms to attempt to determine the b and bbar jets.

Use event fit to make associations between the W and the b jetConstruct a top charge: compare with the MC of SM and Exotic

D0 AnalysisData favor charge 2/3, excluding 4/3 with 93.7%

cl.

The Charge of the top Quark


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Top Quark Spin


Top and anti-top spins are correlatedAnalysis looks at relative orientation of the leptons in

the top-antitop decays

Correct spin ½ favored

Search for CPT Violation

53D0 (1 fb-1): Dmt=3.8 ± 3.7 GeV

Release constraint on mt = mtbar, measured in lepton + jets events usingmatrix element technique

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Electroweak Relationships

http://lepewwg.web.cern.ch/LEPEWWG/

The top contributes as mt2 to the boson

masses The Higgs contributes as ln mh

2 to the boson masses

Electroweak Parameters

55Florencia Canelli, LP2009

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Future PromisesTheory

SUSY see-saw mechanisms suggest mstop lowest of SUSY masses

Higgs as a top condensate compositeTevatron

DM <~ 1 GeVConstraints on the Higgs

AnomaliesLHC

Signals pointing to EWSB mechanismVtb from single top productionHiggs – top coupling ttg, ttZ couplingsRare decays

ILC DM <~ 20 MeV

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Future Promises

Standard Model Electroweak Relations

MW=(1/2)gv , MZ = (1/2) sqrt(g2+g’2)v Mf = Lf v/sqrt(2)

Arithmetic

v = 246 GeV, v/sqrt(2) = 174 GeV

Mt ~ 173 GeV

Lt =1!!!!

Just a coincidence???

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SummaryThe top quark was conceived more than thirty

years ago.

Some of us are surprised that it is already fifteen years since we helped at its birth.

Even as born it was a giant, helping us to target the Higgs.

Top is still a big baby.

Maybe, it is very close to the Higgs.

Its next ten years promise further greatness.

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AcknowledgementsThis talk depended almost 100% on the

work of others:The colleagues on CDF and D0 with whom I

shared the experience of experimental discovery.

Juan Estrada FNAL W&C – Matrix Element workThe speakers at Top Turns Ten, October 2005: Jim

Cochran, Bogdan Dobrescu, Doug Glenzinski, Nick Hadley, Paul Langacker, Aldo Menzione, Meenakshi Narain and Avi Yagil.

Paul Grannis: Talk at the celebration for the AntiProton.

Arnulf Quadt, whose Habilitation thesis provided one re-education on the subject and some of the figures for the talk.

Florencia Canelli whose summary talk at LP2009 I used for some recent plots

Giorgio Chiarelli, Rencontres de Blois, 2009The beautiful work done by CDF and D0

collaborations during Run II when I have been an anxious spectator.

The Tevatron

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the top quark yesterday and today hugh montgomery jefferson lab irfu-cea saclay february 4, 2010

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