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CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 22

RoadmapRoadmap

• The TevatronThe Tevatron• The CDF and DThe CDF and DØ DetectorsØ Detectors• Review of the Top QuarkReview of the Top Quark• Top Branching FractionTop Branching Fraction• Search for Single Top Search for Single Top

ProductionProduction• SummarySummary

TractriciousTractricious

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 33

The TeVatronThe TeVatron

• Proton-antiproton collisions at 1.96 Proton-antiproton collisions at 1.96 TeV (Run I: 1.8 TeV)TeV (Run I: 1.8 TeV)

• Peak Luminosity: > 10Peak Luminosity: > 103232 cm cm-2-2 s s-1-1..

• What’s new for Run II?What’s new for Run II?– Main Injector: 150 GeV proton Main Injector: 150 GeV proton

storage ring.storage ring.– Recycler: Antiproton storage ringRecycler: Antiproton storage ring

• Currently being commissioned Currently being commissioned and working well.and working well.

• Total Integrated luminosity:Total Integrated luminosity:– Currently, over 800 pbCurrently, over 800 pb-1-1..– Should have between 4 fbShould have between 4 fb-1-1

and 9 fband 9 fb-1-1 by 2009. by 2009.

_

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The Run II CDF DetectorThe Run II CDF Detector

• Similar to most colliding detectors:Similar to most colliding detectors:– Inner silicon trackingInner silicon tracking– Drift ChamberDrift Chamber– SolenoidSolenoid– EM and Hadronic CalorimetersEM and Hadronic Calorimeters– Muon DetectorsMuon Detectors

• New for Run II:New for Run II:– Tracking: 8 layer silicon and Tracking: 8 layer silicon and

drift chamberdrift chamber– Trigger/DAQTrigger/DAQ– Better silicon, calorimeter and Better silicon, calorimeter and

muon coveragemuon coverage

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The Run II DThe Run II DØØ Detector Detector

• New central tracking inside 2 T New central tracking inside 2 T solenoidsolenoid– Silicon vertex detectorSilicon vertex detector

• b-taggingb-tagging– Scintillating fiber trackerScintillating fiber tracker

• New forward muon systemNew forward muon system• New readout / trigger electronicsNew readout / trigger electronics

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 66

Top ReviewTop Review

• The top quark was discovered (in The top quark was discovered (in pairs) by CDF and D0 in 1995.pairs) by CDF and D0 in 1995.

• The The GoldenGolden quark ( ~ 180 GeV/c quark ( ~ 180 GeV/c22) ) – Only fermion with mass near Only fermion with mass near

EW scale; 35 times heavier EW scale; 35 times heavier than the bottom quarkthan the bottom quark

• Very Wide (1.5 GeV/cVery Wide (1.5 GeV/c22))– The top quarks decay before The top quarks decay before

they can hadronize.they can hadronize. We can study the decay of We can study the decay of the bare quark.the bare quark.

• From what we already know about From what we already know about CKM matrix, we expect CKM matrix, we expect BR(tBR(tWb) ~ 100%Wb) ~ 100%

tt Pair Lepton + Jet Decaytt Pair Lepton + Jet Decay-

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 77

A Quick Note About ScaleA Quick Note About Scale

Since we’re not all Since we’re not all intimately familiar intimately familiar

with hadron with hadron colliders.colliders.

Top:Top:

1 in 10 billion1 in 10 billion

Cross Sections at 1.96 TeVCross Sections at 1.96 TeV

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Top Branching Fraction: The Data SampleTop Branching Fraction: The Data Sample

• To date, we have only confirmed seeing To date, we have only confirmed seeing top produced in pairs.top produced in pairs.

• For this analysis, we use two distinct For this analysis, we use two distinct samples (classified by W decays):samples (classified by W decays):– Dilepton eventsDilepton events– Lepton + jet eventsLepton + jet events

DileptonsDileptons

• Two high pTwo high pTT leptons (e, leptons (e, ))

• Two high energy jetsTwo high energy jets• Large missing transverse energyLarge missing transverse energy

• Large scalar sum ELarge scalar sum ETT (H (HTT))

Lepton + JetsLepton + Jets

• One high pOne high pTT lepton (e, lepton (e, ))

• Four high energy jetsFour high energy jets• Large missing transverse energyLarge missing transverse energy

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 99

Top Dilepton Event at CDFTop Dilepton Event at CDF

We use these displacementsWe use these displacements

to “tag” b jets to “tag” b jets

(SecVtx b tagging algorithm).(SecVtx b tagging algorithm).

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• According to what we know about the CKM matrix, BR(t According to what we know about the CKM matrix, BR(t Wb) ~ 100%.Wb) ~ 100%.

•

• We can measure We can measure RR by looking at the by looking at the relativerelative rates of top candidate events with rates of top candidate events with zero, one, or two b-tagged jets.zero, one, or two b-tagged jets.

• Assuming no background and that b-jets Assuming no background and that b-jets

are identified with efficiency are identified with efficiency bb,,– NN00 = N = Ntttt (1 – R (1 – R bb))22 NNtttt 00,,– NN11 = 2 N = 2 Ntttt R R bb (1 – R (1 – R bb ) ) N Ntttt 11,,– NN22 = N = Ntttt (R (R bb ) )2 2 N Ntttt 22..

• The R measurement is therefore:The R measurement is therefore:– Sensitive to RSensitive to R bb,,– Over determined, andOver determined, and– Largely independent of NLargely independent of Ntttt and and (tt).(tt).

• bb is measured separately (40%). is measured separately (40%).

??

Assuming no background:Assuming no background:

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Our LikelihoodOur Likelihood

• We first need to estimate the total number of tt candidates:We first need to estimate the total number of tt candidates:

Efficiency to have Efficiency to have ii jets b-tagged. jets b-tagged.

CalculatedCalculated

1 when we loop over1 when we loop over

0, 1, and 2 b- tags0, 1, and 2 b- tags

MeasuredMeasured

• Our likelihood is:Our likelihood is:

wherewhere

• Remember:Remember:

ii and therefore N and therefore Ntttt depend on Rdepend on R bb. .

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 1212

CDF Dilepton and L+J NumbersCDF Dilepton and L+J Numbers

• In addition to using In addition to using a prioria priori background background estimates, we also use an artificial neural estimates, we also use an artificial neural net in the L+J sample.net in the L+J sample.– Our best 0-tag estimateOur best 0-tag estimate

• We see very good agreement bin by We see very good agreement bin by bin.bin.

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 1313

The CDF MeasurementThe CDF Measurement

• We use both the Dilepton and the We use both the Dilepton and the Lepton + Jets data samples.Lepton + Jets data samples.

•

• We use a Feldman-Cousins We use a Feldman-Cousins construction find our final answer:construction find our final answer:

• Assuming three generations of Assuming three generations of quarks:quarks:

• All uncertainties are stat. + syst.All uncertainties are stat. + syst.

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 1414

The DThe DØØ Measurement Measurement

• Uses 160 pbUses 160 pb-1-1

• DDØØ has two results, each from has two results, each from different tagging methodsdifferent tagging methods– SVT – Displaced secondary SVT – Displaced secondary

vertices (same as CDF)vertices (same as CDF)– CSIP – Counts the number of CSIP – Counts the number of

displaced tracks (displaced tracks (i.e.i.e., |d, |d00| > x cm)| > x cm)

•

•

• Results not independent of top cross Results not independent of top cross section.section.

tttt vs. R vs. R

DDØ PreliminaryØ Preliminary

tttt vs. R vs. R

DDØ PreliminaryØ Preliminary

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 1515

Our ReachOur Reach

• Quick-and-Dirty back of Quick-and-Dirty back of the envelop calculation.the envelop calculation.

• Assume R = 1.Assume R = 1.– Assumed 3 Assumed 3

generations of quarks generations of quarks for |Vfor |Vtbtb| limits| limits((|V|Vtbtb| = 1).| = 1).

• If we keep systematic If we keep systematic uncertainties down, can uncertainties down, can be a very promising be a very promising measurement.measurement.

• Ignores innovationIgnores innovation

95% lower limit95% lower limit

of 0.99 at 20 fbof 0.99 at 20 fb-1-1!!

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t-channel production (Wg fusion)

Search for Single Top at CDFSearch for Single Top at CDF• Why look for single top?Why look for single top?

– Direct measurement of |VDirect measurement of |Vtbtb||22..– SM cross section is still too small to seeSM cross section is still too small to see**, but could be enhanced by new , but could be enhanced by new

physics.physics.– This decay is a background to the Higgs search (WH production, HThis decay is a background to the Higgs search (WH production, Hbb) bb)

and must be understood. and must be understood.

• How do we look for single top?How do we look for single top?– Signature is a lepton, MET and two jets (require at least one be tagged as a Signature is a lepton, MET and two jets (require at least one be tagged as a

b jet).b jet).– Much harder than simple counting experiments used in tt.Much harder than simple counting experiments used in tt.

Kinematically wedged in between tt and non-top (W + jets) backgrounds.Kinematically wedged in between tt and non-top (W + jets) backgrounds.

s-channel production (W*)

|V|Vtbtb||22

|V|Vtbtb||22|V|Vtbtb||22

theorytheory ~ 1 pb ~ 1 pb theorytheory ~ 2 pb ~ 2 pb

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 1717

CDF Single Top in Run IICDF Single Top in Run IIMC templatesMC templates

t-channel only: quark tends t-channel only: quark tends to follow proton direction, to follow proton direction,

antiquark follows antiproton antiquark follows antiproton directiondirection

Both channels: single top Both channels: single top busier than non-top BG, but busier than non-top BG, but

not as busy as ttnot as busy as tt

Fit data distributions for these componentsFit data distributions for these components

lepton forward jet

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 1818

CDF Single Top Fit ResultsCDF Single Top Fit Results

B.W. Harris et al.: Phys. Rev. D 66, 054024B.W. Harris et al.: Phys. Rev. D 66, 054024Z. Sullivan hep-ph/0408049Z. Sullivan hep-ph/0408049

1.981.98±0.25 pb±0.25 pbt-channelt-channel

0.880.88±0.11 pb±0.11 pbs-channels-channel

NLO Cross-sectionsNLO Cross-sections√√s s =1.96TeV=1.96TeV

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• 230 pb230 pb-1-1

• Using several neural nets, Using several neural nets, DDØØ has has drastically reduced both s and t channel drastically reduced both s and t channel limits:limits:

• The limits are extracted from a binned The limits are extracted from a binned likelihood fit to the 2D distribution of likelihood fit to the 2D distribution of NN(single top vs. tt) andNN(single top vs. tt) andNN(single top vs. Wbb). NN(single top vs. Wbb).

• Theory is 1 and 2 pb, for s and t channel Theory is 1 and 2 pb, for s and t channel respectively. Recall, CDF’s limits are respectively. Recall, CDF’s limits are 10pb (s-channel) and 13 pb (t-channel).10pb (s-channel) and 13 pb (t-channel).

DDØØ Single Top Results Single Top Results

BRAND NEW RESULTSBRAND NEW RESULTSJust Days Old!Just Days Old!

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CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 2020

Looking ForwardLooking Forward

• Lots of exciting top physics Lots of exciting top physics happening at the Tevatron.happening at the Tevatron.

• Top branching fractionTop branching fraction– CDF measurement is the best CDF measurement is the best

direct limit to date:direct limit to date:

– Assumption about number of Assumption about number of generations.generations.

• Single topSingle top– DDØØ has the best limits to date has the best limits to date– Direct measurement of VDirect measurement of Vtbtb..– Need more data for observation, Need more data for observation,

but Dbut DØØ and CDF are getting and CDF are getting close.close.

Backup SlidesBackup Slides

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 2222

Top Production at the TevatronTop Production at the Tevatron

• Pair productionPair production

– pair- theorypair- theory = 6.7 pb. = 6.7 pb.

q

q

t

t

t

t

gg

gg

s channels channel

~ 15%~ 15%~ 85%~ 85%

t channelt channel

• Single topSingle top– Not yet observedNot yet observed

– s-channel - theorys-channel - theory = 0.88 pb. = 0.88 pb.

– t-channel - theoryt-channel - theory = 1.98 pb. = 1.98 pb.

All of these theoretical values assumeAll of these theoretical values assume

a top quark mass of 175 GeV/ca top quark mass of 175 GeV/c22

at a center of mass energy of 1.96 TeV.at a center of mass energy of 1.96 TeV.

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 2323

Calibrating the b-tagging EfficiencyCalibrating the b-tagging Efficiency

Measure ratio of single- and double-tagged eventsin b-enriched sample with soft (pT>8 GeV) electrons

“Scale factor” measured on this sample is appliedto other samples, even if the efficiencies differ

CKM 2005, March 17, 2005CKM 2005, March 17, 2005Charles PlagerCharles Plager VVtbtb at the Tevatron at the Tevatron 2424

Other VOther Vtbtb Results Results

• J. Swain and L. Taylor (hep-ph/9712420) looked at VJ. Swain and L. Taylor (hep-ph/9712420) looked at V tbtb by by

looking at EW corrections to Z looking at EW corrections to Z bb (no assumption of bb (no assumption of unitarity):unitarity):