Recent Measurements of the Top Quark from Fermilab

Kevin Lannon

The Ohio State University

For the CDF and D0 Collaborations

Note to Slide Readers

This presentation makes heavy use of animations. Several slides to do make sense unless viewed in animated form. I recommend viewing this presentation as a slide show.

APS 4-15-07 K. Lannon 2

The Top Quark and the Standard Model

  Top quark discovery     Late 1970’s: Existence suggested by discovery of b quark 1980’s: Existence required for consistency of Standard Model Eluded experimental observation for two decades 1995: Observed at Tevatron Top quark needed to complete the “period table” of the Standard Model Properties of top quark that made discovery difficult also make study interesting!

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Top Quark is Special

  Top is really massive  Comparable to gold nucleus!

  In Standard Model: Mass related to coupling to Higgs (Yukawa coupling)  Top Yukawa coupling near unity (natural value?)  Why are couplings for other quarks so small in comparison?

Special relationship between top and Higgs?

Top quark decays very quickly (10 -24 seconds)    Decays before hadronization No hadron spectroscopy Momentum and spin transferred to decay product

1000 100 10 1 0.1

0.01

0.001

GeV/c 2 u d Quark Masses s c b 5 orders of magnitude between quark masses!

t

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The Tevatron Accelerator

   Highest energy accelerator in the world (E

cm

= 1.96 TeV) World record for hadron collider luminosity (L

inst

= 2.86E32 cm -2 s -1 ) Only accelerator currently making top quarks   Run I (1992-1995)   Integrated 105  4 pb -1 luminosity Discovery of the top quark Run II (2001-present)   Integrated > 2.5 fb -1 and counting!

Precision study of top quarks APS 4-15-07 K. Lannon 5

Tevatron Performance

Peak Luminosity Integrated Luminosity Today’s Presentation: ~1 fb -1 Analyzed by Summer    Integrated luminosity at CDF and D0  Total delivered: ~2.7 fb -1 to each experiment    Total recorded: ~2.2 fb -1 (~ 20  Run I!) at each experiment So far for top analyses, used up to ~1 fb -1 More analyses with 1.2-2.0 fb -1 in progress for summer Doubling time currently ~1 year Future: ~4 fb -1 by end of 2007, ~8 fb -1 by 2009 APS 4-15-07 K. Lannon 6

CDF and D0 Detectors

CDF   General purpose detectors capable of many different physics measurements Top physics uses almost all detector systems D0 APS 4-15-07 K. Lannon 7

Top Quark Production at Tevatron

 QCD pair production    NLO = 6.7 pb First observed at Tevatron in 1995 ~85% ~15% t-channel  EWK single-top production    s-channel:  NLO t-channel:  NLO First evidence!

= 0.9 pb = 2.0 pb  Other?:

X

0 

t t

,

t t H

???

APS 4-15-07 K. Lannon s-channel 8

SM Top Quark Decays

BR(

t



Wb

) ~ 100%    Particular analyses usually focus on one or two channels New physics can impact different channels in different ways Comparisons between channels important in searching for new physics APS 4-15-07 K. Lannon 9

Top Signatures

Electron or muon Neutrino: Missing E

T

Dilepton Lepton + Jets

Jet: shower of particles b-jet: identified with secondary vertex tag

All Hadronic

t t

        

b b e

,  APS 4-15-07

t t

    

qqb b e

,  K. Lannon

t t



qqqqb b

10

Top Production Rates

Needle in haystack (approx.)    Like finding a needle in a haystack . . . .  (

p p



t t

@

M top

 175

GeV

)  6 .

7 pb    Distinctive final state Heavy top mass Advanced analysis techniques  Artificial Neural Networks One top pair each 10 10 inelastic collisions at  s = 1.96 TeV APS 4-15-07 K. Lannon 11

Top Quark Physics is Rich

Parallel Sessions C14, F1, X13 J14, R14 F1, J14, K14, R14, T14 K13, K14, J14   J14, R14  Systematically limited measurements   Cross section (~12% precision) Mass (~1% precisions) Statistically limited measurements    Most other measurements of top quark properties Top quark charge Top quark production mechanism Searches    Single top production Resonant production Top to charged Higgs APS 4-15-07 K. Lannon 12

Measuring the Top Cross Section

    Agreement between theory and experimental important test of top quark properties (spin, couplings, mass) Techniques form basis for top properties measurements Key: separating top from backgrounds Two main techniques: Event Kinematics: central, spherical events with large transverse energy

H T

 scalar sum of lepton, jet, and missing E

T

APS 4-15-07 Presence of b-jets: Detected through long life-time of the B hadrons. Decays at displaced vertex K. Lannon 13

Recent Cross Section Results

Individual Measurements

-1

approaching same precision as theoretical calculation Excess of events with  3 energetic jets +  1 b-tag Dilepton Channel 

t t

 8 .

3   0 0 .

6 .

5   0 1 .

9 .

0  0 .

5 pb    15 %

L=900pb -1



t t

 9 .

0  1 .

3  0 .

5  0 .

5 pb APS 4-15-07   Excess of events with  Excess of events with 4 energetic jets and “top-like” kinematics (determined by a multivariate discriminant technique  15 % 

t t

K. Lannon  6 .

3   0 0 .

9 .

8  0 .

7  0 .

4 pb    19 % 14

Cross Section Summary

CDF Run II Preliminary

   Several cross section talks in Session R14 (Monday) APS 4-15-07 K. Lannon 15

Why Measure the Top Mass?

    It’s the most striking feature of the top quark!

Consistency of mass and cross section  Standard Model Top?

Related to the Higgs mass through radiative corrections to the W mass   Provides indirect constraint on Higgs mass More precision constraint  Tighter Tevatron Run II goal  Uncertainty < 3 GeV/c 2 with 2 fb -1 data  New Goal: Uncertainty ~ 1 GeV/c 2 by end of Run II  M W  M 2 top  M W  ln M Higgs Summer 2006 APS 4-15-07 K. Lannon 16

Measuring the Top Mass is Challenging

What a theorist sees: What an experimentalist sees:    Measure jets, not partons   Account for bias and resolution  Jet Energy Scale Determine which jet should be assigned to which parton  Combinatorics (up to 720 permutations for all hadronic decay!) Don’t measure neutrino momentum  Infer p

T

Extra jets from radiation confuse things indirectly APS 4-15-07 K. Lannon 17

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Jet Energy Scale

    Determine parton energy from measurements in calorimeter Correct for    Detector effects Fragmentation/Hadronization Underlying event Energy scale determined from data and MC Uncertainties in jet energy scale directly affect top mass uncertainties  Leading uncertainty without special treatment!

K. Lannon 18

In-Situ Jet Energy Scale Calibration

  W mass known very precisely from other measurements Use W mass reconstructed from jets to constrain jet energy scale   Uncertainty decreases as data increases Key reason why we’re doing better than originally projected!

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Results: Lepton + Jets Channel

170.9 ± 2.2 (stat+JES) ± 1.4 (syst) GeV/c 2

World’s best  Both use  Matrix element technique  In-situ JES calibration Session T14 (Monday)

170.5 ± 2.4 (stat+JES) ± 1.2 (syst) GeV/c 2

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Results: All-Hadronic

   Session T14 (Monday)

171.1 ± 3.7 (stat+JES) ± 2.1 (syst) GeV/c 2

Combines matrix element and template techniques First incorporation of in-situ JES calibration in all-hadronic channel This measurement more precise than expected based on past performance!

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Tevatron Combination

   Top mass measurements in Sessions F1 (Saturday), J14, K14 (Sunday), and T14 (Monday) Many more measurements than can be discussed here Combine for better precision   Best individual measurement: 1.5% Combination: 1.1% uncertainty!

See next talk for impact on indirect Higgs constraints

170.9 ± 1.1 (stat) ± 1.5 (syst) GeV/c 2

K. Lannon 22

  Are we observing Standard Model top?

  Standard Model top has charge +2/3 Alternative hypothesis: exotic quark with charge -4/3 Difficult to measure (“t”  W + b or W b)  W charge measured through the lepton (straightforward)   Bottom charge inferred from jet (difficult) Correctly pair the lepton and b jet (difficult) APS 4-15-07

Top Charge

K. Lannon Exclude top charge of -4/3 with 81% C.L. Session K14 (Sunday) 23

Top Production Mechanism

Session J14 (Sunday) ~85% ~15%   Does ratio of qq  tt and gg 

tt

match theoretical expectation?

  Depends on top mass, pdfs, etc.

Could be modified by non-standard production Exploit correlation between low p

T

track multiplicity and number of gluons   (

gg

(

p p



t t

) 

t t

)  0 .

01  0 .

16  0 .

07 APS 4-15-07 K. Lannon 24

t-channel

The Search for Single Top

s-channel    Standard Model  Rate  |V

tb

| 2   Spin polarization probes V-A structure Background for other searches (Higgs) Beyond the Standard Model  Sensitive to a 4 th generation   Flavor changing neutral currents Additional heavy charged bosons  W ’ or H + New physics can affect s-channel and t-channel differently

Tait, Yuan PRD63, 014018(2001)

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Signal and Backgrounds

Single-top Signature Other EWK

tt

 : MET High p

T

e or  Backgrounds Multi-jet QCD W + Heavy Flavor W + Light Flavor (Mistags) 2 High E

T

jets,  1 b-tagged Must use multivariate, kinematic techniques to separate signal from background APS 4-15-07 K. Lannon Signal / Background ~ 1/20 Signal size ~ background uncertainty 26

Multivariate Analysis Techniques

Combine information from several variables into a single, more powerful discriminant    Six separate analyses Used many different multivariate analysis techniques: Decision tree, matrix element, multivariate likelihood, neural network Only moderate correlations among discriminants combine results for greater sensitivity  Can APS 4-15-07 K. Lannon 27

Matrix Element Normalized to fit

Single Top Results

Neural Network deficit Expected Signal Significance: 2.5

  APS 4-15-07  2 .

7   1 1 .

5 .

3 pb Session X13 (Tuesday) Expected Signal Significance: 2.6

 K. Lannon   0 .

0   1 0 .

2 pb Session F1 (Saturday) 28

Single Top Results

Expected Signal Significance: 2.1

   4 .

9  1 .

4 pb Session X13 (Tuesday) APS 4-15-07 Expected Signal Significance: 1.8

   4 .

6   1 1 .

8 .

5 pb Session X13 (Tuesday) K. Lannon 29

All Single Top Results

Session X13 (Tuesday) APS 4-15-07 K. Lannon 30

Limit on V

tb      (single top)  |V tb | 2 First direct limit on V tb  No assumption about number of quark generations Assuming Standard Model production:   Pure V-A and CP conserving interaction |V  td | 2 + |V ts | 2 << |V tb | 2 B(t  Wb) ~ 100% Bayesian limits with flat prior between 0 and 1 Session X13 (Tuesday)

0.68 < |V tb | < 1 at 95%CL (f 1 L = 1)

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Summary

    Many more top physics results available than could be covered here See public webpages for CDF and D0:   http://www-cdf.fnal.gov/physics/new/top/top.html

http://www-d0.fnal.gov/Run2Physics/WWW/results/top.htm

Very exciting times in top physics at the Tevatron      Top mass uncertainty 1.1%!

First evidence for single top production: > 3  !

Cross section: Uncertainty on measurements approaching theoretical uncertainties Just beginning to gain sensitivity to many top quark properties Great place to search for new physics!

Stayed tuned for new results this summer APS 4-15-07 K. Lannon 32

Backup Slides

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Weights in the Combination

CDF and D0 both crucial for best precision Better than expected performance from all hadronic measurement  In-situ JES calibration APS 4-15-07 K. Lannon 34