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Single Top Productionat the Tevatron

Top Quark SymposiumUniversity of MichiganApril 7, 2005Gordon Watts

for D and CDF

Searches

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Gordon Watts Top Quark Symposium - Single Top at the Tevatron April 7, 2005 2

A Lonely Production

Too small for theTevatron (LHC?) Tait hep-ph/990352

s-channel t-channel

s NLO = 0.88pb 8% s NLO = 1.98pb 11%hep-hp/207055 (Harris, Laenen, Phaf, Sullivan, Weinzierl)

Pair Production

Weak Decay VertexVtb , unitarityExotic Models (FCNC, Top

Flavor, 4th Gen)SM Higgs BackgroundW+Jets Proving Ground

Discovery First!

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Signature & Backgrounds

Signal for s and t channel mostly similar

Lepton + Missing ET + Jets

t-channel extra b tends tobe forward Similar to top pair

production, but with less jetsHarder Signal To Find

Backgrounds

W/Z + jets ProductionFake LeptonsTop Pair Production

WW, WZ, Ztt , etc.

Anything with a lepton + jets + ET signature

(t-channel)

Much worse than for pair productionbecause of lower jet multiplicity

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The MC SituationZTOP single top generator is most often used as bench mark

http://home.fnal.gov/~zack/ZTOP/ZTOP.htmlNot an event generator, so

Re-weights MADEVENT to fit the ZTOP distributions

The trick is in getting the t- channel correct

Generate bq,gq t+b+q separately

Modified version of CompHEPMatch 2 2 and 2 3 process using b p T for cross overComparison with ZTOP shows no difference

(single top)

CDF

D

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The MC Situation(background)

W+Jets with Heavy Flavor is most important Jet Double Counting issues HF factions both b and c

CDF and D use ALPGENFull Event SimulationHF fraction (b, c) from ALPGEN

Wbb from NLO calculation

Bowen, Ellis, Strassler :understand W(b,c) as itaffects shape variables!

(charm tagging not measured!)

Steve: There is more than one R
http://www-d0.fnal.gov/Run2Physics/top/public/winter05/singletop/figures/input_variables/Add_njets.eps

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Search StrategyCommon Analysis Strategy

Basic SelectionCuts

Final Cuts

Limit Fitting

Clean up the data, removedetector backgrounds. Does not

maximize S:B.

Apply btagging, understandshape variables (s, t channel),multivariate analysis, etc.

Use binned maximum likelihood(fit distributions to maximizelimit)

CDF D

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D

The Approach

CDF Improve S/B to maximize separation in onedistribution (Qx h)

Basic Selection Cuts More Restrictive

Use Multiple distributions, combined with aNeural Network, to maximize separation

Basic Selection are efficient, but let in agreat deal more background.

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Basic Selection Cuts

Lepton (e, m) PT > 20 GeV PT > 15 GeVJet E T > 15 GeV,

| h| 15 GeV(Jet 1: E T >25

GeV), |h| 20 GeV ET > 15 GeV

CDF D

Along with other clean-up cuts

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Final Cuts IB-Tagging Both apply a secondary Vertex

Reconstruction Algorithm(Lxy)

B

Decay Length ( Lxy)Hard Scatter

Eff on bs

Fake On lights

CDF Recently released improved version of tagging(15%), but it isnt used in blessed single top results.Ds is a comparable to what is shown here.

Charm Tagging Rates ~ 30% of bBoth experiments classify events by

single or more than one tag

CDF D
http://www-cdf.fnal.gov/physics/new/top/public/btag/gen4/efficiency_et.epshttp://www-cdf.fnal.gov/physics/new/top/public/btag/gen4/efficiency_et.epshttp://www-cdf.fnal.gov/physics/new/top/public/btag/gen4/mistag_et.epshttp://www-cdf.fnal.gov/physics/new/top/public/btag/gen4/mistag_et.epshttp://www-cdf.fnal.gov/physics/new/top/public/btag/gen4/mistag_et.epshttp://www-cdf.fnal.gov/physics/new/top/public/btag/gen4/efficiency_et.eps

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Final Cuts IITop Mass Cut

140 GeV Mlbn 210 GeV CDF:

Mlbn Lepton, b-tagged jet, neutrino (Missing E

D: Input to MultivariateAnalysis tt

W+JetsQCDt-channel (x10)s-channel (x10)

CDF D

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Final Sample StatisticsLuminosity D: 230 pb-1

CDF: 162 pb-1

Acceptance(%) s-channel 2.7 0.2 1.06 0.08

t-channel 1.9 0.2 0.89 0.07

D CDF

S/ Bs-channel 0.32 0.25

t-channel 0.28 0.48

D CDF

These Are Small Numbers!CDF: Expects ~2 events on ~34D: Expects ~5 events on ~280

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Straight Cut AnalysisHow Well Can We Do With a Straight Cut Analysis?

Selected Variables:Object E T /p T Jet #1HT like (various sums of

the objects E T s) Invariant Mass of

combinations of

masses (like Mlbn)

D

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Relative Sizes OfBackgrounds

(Sum Of Jets In Event)

W+Jets Is LargestBackground!

One of hardest to getright!

Single b-tagrequired for this

plot.

Need to takeadvantage ofother topologiesto improve limit!

CDF D

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b

Getting Clevert-channel

Charge of up quark determines charge of W lepton (p vs p)Recoil against gluon/quark makes for asymmetry

Look at d-quark Jet Rapidity normalized by Charge!

CDF D

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Q X h

Monte Carlo TemplatesCDF Uses thesedistributions as

input to the finallimit calculationfor separate s,t channel limits

Use HT for acombined s+tchannel limit

CDF

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Other Variables

D S/B is worse by design than CDFs

Use a Multivariate analysis to separate the signal frombackground

A multi-dimensional maximum likelihood possible Statistics are prohibitive!

Shape Variable 1

Shape Variable 2Shape Variable 3Shape Variable 4

Neural Net

BinnedMaximumLikelihood

OutputDistribution

D

Basic Selection Cuts: Let in as much signal as possible

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Input Variables IEvent Energy, Object Properties

Cross Check Background Model

MC Shapes

pTjet1 , H, HT

D

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Input Variables IIObject Combinations


MC Shapes

Mtop, Mall jets

D

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Input Variables IIIAngular Variables


MC Shapes

cos(lepton,jet1 untagged) top tagged

D

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Input VariablesEvent Energy

pTtag , pTuntag, pTtopjet , pTjet1,jet2 , H (all jets but tagged), HT (jets), H T (jets-tagged), H(jets-top quark jet), H T (jets-top quark jet)

Object CombinationsM (jets), p T (all jets tagged), Mtop (tagged jet), s,M(jets-tagged) , MT (jets 1&2), pT (jets 1&2), M(jets-topquark jet) M top (best jet)

Angular VariablesDR(jets 1&2), h(untagged)XQ(lep), cos(lepton,untagged)top rest , cos(jets, jet1 tagged) all jets rest ,cos(lepton, Q(lepton)xz) best top rest , cos(jets, jet1 not

best) all jets rest Both s&t, t-only, s-only

D

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Neural Net Design

Neural Net

Wbb

NeuralNettt

l+jets

Two Networks Per Analysis

2d Histogram used inbinned likelihood fit

Trained on signal andWbb as background

Trained on signal andtt lepton + jets as

background

D

We also use Decision Trees in place of NN

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SystematicUncertainties

Fitting Shape Variables Requires Special Handling ofSystematic Errors

1 binCalculate the Systematic Errors For That 1 Bin

Jet Energy Scale, Trigger, BTagging, etc.

Repeat for All BinsShape Fluctuations Will Be Properly Accounted For

DCDF

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Systematics

B-ID: 7%Luminosity: 6%

Top Quark Mass: 4%JES: 4%

D CDF

DCDF

Some will improve withincreased Luminosity

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Final Results

Channel CDF (pb) D (pb) SM

s+t

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Probability Density

s-channel

t-channel

DCDF
http://localhost/var/www/apps/www-d0/WWW/docs/Run2Physics/top/public/winter05/singletop/figures/limit_plots/lim_tb_tqb_posterior.eps

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Beyond The Standard Model

m dataonly

e data only
http://localhost/var/www/apps/www-d0/WWW/docs/Run2Physics/top/public/winter05/singletop/figures/limit_plots/new_2d_posterior.eps

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Theorist talk@ UW inMay, 2003

With this analysisas it stands willstill needs ~2 fb -1for evidence!

Record Store of1.05x1032 last

week!

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Near Future

Upgrade to modern b-quark taggingExplore multivariate methodsIncreased Dataset!

Aggressive Program to Increase AcceptanceB-tagging improvementsNeural Network & Other Technique (DTs) Improvements

Last paper published before evidence! (I suspect)

CDF: PRD is publishedD: Paper in preparation

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Monte Carlo Understanding

From hep-ph/041223(Bowen, Ellis, Strassler)

No ParticularW+Jets

Background Type

is dominate!Production

Mechanismsaffect shapes

How well do we knowCharm Tag RateProduction Fractions?

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SingleTop at TeV4LHCStart of Workshop

Single Top Theory Qing-Hong CaoSingle Top Experiment R. Schwienhorst

Working Group MeetingSingle top: Simulations & Strategies; Zack SullivanSingle top in MCFM; Keith EllisEffective NLO generator SingleTop from CompHEP;

Edward BoosElectroweak & Single Top Plans (Discussion)

BNL

Single Top Production: Ellis

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Conclusions

Channel CDF (pb) D (pb)s+t

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Documents