while waiting for the LHC) · LHC School Lecce June 2006 Sandra Leone, INFN Pisa More details on Jets A jet is a complicated object : measured by calorimeter towers defined by a clustering

Sandra Leone, INFN PisaLHC School Lecce June 2006

Top Physics at CDF Top Physics at CDF ……(while waiting for the LHC)(while waiting for the LHC)

Sandra LeoneSandra LeoneINFN Pisa

Italo-Hellenic School of Physics 2006The Physics of LHC: Theoretical Tools and Experimental Challenges

Martignano, Lecce, June 12-18, 2006


OutlineOutline

� Motivations for studying top � A brief history� Top production and decay� The Tevatron & CDF� Detector issues� Identification of final states� Cross section measurement� Single top production� Mass determination� Study of top properties� The lesson for LHC

bscdu

t


Motivations for Studying TopMotivations for Studying Top

� Only known fermion with a mass at the natural electroweak scale.

� Similar mass to tungsten atomic # 74 35 times heavier than b quark.⇒Why is Top so heavy?⇒Is top involved in EWSB?

�(Does (2 √ 2 GF)-1/2 ≈ Mtop mean anything?)⇒Special role in precision electroweak physics?⇒Is top, or the third generation, special?

� New physics BSM may appear in production (e.g. topcolor) or in decay (e.g. Charged Higgs).


A Brief History of TopA Brief History of Top� 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 for the third family of quarks

(weak isospin of b can be inferred from the forward-backward asymmetry in e+e- � bb)

� Anomaly free SM requires the sum of the family charges to be zero: given the b (and the tau lepton) there should be a 2/3 charge quark

• 1977-1994: increasing lower top mass limits


A Brief History of TopA Brief History of Top� First top evidence in 1994 in CDF

data, 19 pb-1, 15 events on a background of 6, ⇒ 2.8 σ excess, not enough to claim

discovery

� Confirmed in 1995 by CDF and D0 in first ~70 pb-1 of run 1 data (4.8 σ ).

� Final Tevatron Run 1 top analyses based on ~110 pb-1.

⇒Production σσσσ in many channels.⇒Mass: 178.0 ± 4.3 GeV (CDF/DØ) ⇒Study of several aspects of

event kinematics.⇒Limits on single top production,

rare/non-SM decays.� Overall consistency with the SM � But only ~100 analyzable top events

⇒analyses statistics-limited.


Why Why TevatronTevatron Top results in a school on LHC Top results in a school on LHC physics?physics?

� Tevatron is the only place until the LHC turns on, to study the top quark.

�LHC will be a top factory, producing ∼ 2800 ttbar events per hour at low luminosity (1033)

�Top quark will be one of the major subject of study at LHC

�Moreover will be a background to many other processes -> it will be important to have it under control

�It’s not easy: looking for relatively rare events -> accurate determination of background necessary

�The LHC environment will be a difficult one as well


A more cultural perspective of TopA more cultural perspective of Top……

About 5 orders of magnitude range in quark masses!

�Top analyses as playground to learn how to optimize the cuts to reduce the bckgnd contamination, optimize the simulation, and realize that you’ll have to use real data in order to study all the instrumental effects

LHC?⊙


Production and Decay BasicsProduction and Decay Basics

85%

15%

NB: qq, gg fractions reversed at LHC

t W+

b

tW

-

b

SM predicts: BR( t → Wb) ≈ 100%

σtheory ≈ 7 pb

Event topology

determined by the decay

modes of the 2 W’s (W+W-) in final state

b-jet: identify via secondary vertex or soft lepton tag

At the Tevatron top quarks are mainly pair produced via

strong interaction:


Top Decay : add. Motivation for Studying TopTop Decay : add. Motivation for Studying Top

� In the SM, assuming V-A coupling with a CKM matrix parameter

|Vtb| = 1 for the t → bW decay vertex, one gets (LO):

Γ(t → bW ) ≈ 175 MeV (MT/MW)2 (MT,MW >> Mb)

⇒⇒⇒⇒ Γ(t → bW ) ≈ 1.5 GeV ⇒⇒⇒⇒ τ(top) ≈ 4 x 10-25 s� Non-perturbative QCD hadronization takes place in a time of order:

Λ-1QCD ∼ (100 MeV)-1 ∼ 10-23 s

⇒ top decays before hadronizing, as free quark (no top hadrons, no toponium spectroscopy)

⇒the top quark provides the first opportunity to study the decay characteristics of a “bare” quark.

� t → Ws, t → Wd allowed but suppressed by factors of ∼ 10-3 and ∼ 5 x 10-5 respectively


tt--ttbarbar Final StatesFinal States� Dilepton (ee, µµ, eµ)

⇒BR = 5%⇒2 high-PT leptons + 2 b-jets + large missing-ET

� Lepton (e or µ) + jets⇒BR = 30%⇒single lepton + 4 jets (2 from b’s) + missing-ET

� All-hadronic⇒BR = 44%⇒six jets, no missing-ET

� τhad +X⇒BR = 21%

Most favorable channels for top

physics

More challenging backgrounds, but

measurements still possible

e-e (1/81)

mu-mu (1/81)

tau-tau (1/81)

e -mu (2/81)

e -tau (2/81)

mu-tau (2/81)

e+jets (12/81)

mu+jets (12/81)

tau+jets (12/81)

jets (36/81)Dilepton

L+Jets


The The TevatronTevatronRun II: √s = 1.96 TeV

36 p and pbar bunches �396 ns between bunch crossing

Started in spring 2001

The Fermilab Tevatron has been the only place, and will be until the LHC turns on, to study the top quark.


Tevatron Peak LuminosityTevatron Peak Luminosity

In may 2004 Typical stores: 5 – 6 x1031

1.6 x 1032

Peak Luminosities above 1 x 1032 cm-2 s-1 are common

Record: initial lum ~ 1.8 x 1032 cm-2 s-1 on 11/10/2005After a commissioning period, data “good for physics’’ since Feb. 2002


A Brief History of CDFA Brief History of CDF

� 1985: First collisions with partial detector

� 1987: Core detector in place. Jet Physics

� 1988-89: “Run 0” 4x the expected data, seen lots of W/Z’s

� 1992-1995 : “Run I” -added silicon detector. Top quark discovered!

� 2001-present: Run II begins with essentially a new detector, higher collisions energy and more data.

� 2004: First Run II physics papers published


The CDF Run II DetectorThe CDF Run II Detector– new front-end,DAQ

– trigger• new L1 track trigger

• new L2 secondary vertex tracker (SVT)

– new silicon tracker• 7 layers |η|<2

• 3-D reconstruction

– new central tracker• Nstereo=Naxial=48

� ∆∆∆∆pt/pt<0.001pt

– Time of flight

– new forward calorimeter

– µ,e id to |η|η|η|η|=2

Inherited from Run I:• Central Calorimeter• Muon System (some new)• Solenoid


CDF Run II DetectorCDF Run II Detector

Central tracking

|η| < 1.0

Muon Chambers

|η| < 1.5

Central+Plug

Calorimetry

|η| < 3.6

Silicon tracking

|η| < 2.0

10m


CDF Integrated LuminosityCDF Integrated Luminositydelivered ~1.6 fb-1

on tape ~1.3 fb-1

Taking data efficiency L(recorded)/L(delivered)

commonly > 85%

Running stably since Feb. 02 Physics on 0.9 – 1.2 fb-1

Start of physics-quality

data

Error on luminosity is ± 6%�1.6% due to CerenkovLuminosityCounter systematic error on rate�4.0% due to CLC acceptance sys�3.8% due to limited knowledge of pp inelastic cross section.


Principles for Particle IdentificationPrinciples for Particle Identification

Beam direction



Corresponding energy deposition in calorimeter consistent with MIP

Extrapolated track matching signal in muon chambers

Corresponding energy deposition in EM calorimeter

Small Had/EM

shower shape consistent with that expected for an electron

A track in the Central Outer Chamber

A track in the Central Outer Chamber

Muons: (|η| < 1)Electrons: (|η| < 2.8)



No associated track

Projective tower geometry.

Fixed cone algorithm in η−φ, ∆∆∆∆R = 0.4

Missing Transverse energy:

ET = Σi ETi • ni

ET = - ET

Energy deposition in em calorimeter

Energy deposition in em and had calorimeter

No interaction seen in the detector

Photon:Jet: Neutrino:


More details on JetsMore details on Jets

A jet is a complicated object:

�measured by calorimeter towers �defined by a clustering algorithm

�Doing analysis with jets requires the energy of the measured jet to be converted to the energy of the parent parton or particle jet.

�From measured jet energies to parton energies we need to correct for:

�Instrumental effects�Physics effects�Jet Algorithm effects


“Physics at a Physics at a hadronhadron collidercollider……

…Is all about the trigger!” High pT leptonHigh ET jet, photonHigh Missing ET (MET)

Examine each pp collision Select few interesting events (<70 Hz)

Store for further offline analysis Keep 1 out of 25,000

0.0000015 Hz15 fbpp→WH→ℓνbb (if MH=120GeV)

0.0002 Hz2 pbpp→tt→WWbb→ℓνbbX

0.04 Hz0.5 nbpp→ZX→ℓℓX

0.4 Hz5 nbpp→WX→ℓνX

1 kHz10 µbpp→bb (b pT>6 GeV, |η|<1)

6 MHz60 mbInelastic pp

Event RateCross-sectionProcess

Assume L =100x1030 cm-2s-1, ℓ=electron or muon


Comparison of Cross SectionsComparison of Cross Sections

� In 1 fb-1 of data, ~ 1.4 x 1014 total collisions, one in every 1010 producing a ttbarevent (c.f. one every 2.5 x 106 producing a W event)

Note: LHC will be a top factory, producing ∼ 2800 ttbar events per hour at low luminosity (1033)

with 1 fb-1

1.4 x 1014

1 x 1011

6 x 106

6 x 105

14,0005,000

1000 ~ 100100 ~ 10

σσσσ Tevatron @ NLO: 6.7 ± 1.2 pb

σσσσ LHC @ NLO: ~830 ± 100 pb


Method to identify a top signalMethod to identify a top signal� Start from “counting events” passing cuts in all decay

channels

⇒Optimization of signal region with respect to SM background processes (control region)

� Background dominates the production of ttbar pairs by several orders of magnitude

� How to separate signal from background:

⇒Top events have very distinctive signatures

�Decay products (leptons, neut., jets) have large pT’s

�Event topology: central and spherical

�Heavy flavor content: always 2 b jets in the final state!


DileptonDilepton ChannelChannel

ℓ

ℓ

jet

jet

b

b

νννν

νννν

p p

ET

+

-

jet

jet

b

b

νννν

νννν

pp p

ET

ET

Signature:� Two high pT Isolated leptons

opposite sign

� Veto Z, cosmic, conversion

� ∆Φ(ET,l/j)>20o, or ET>50 GeV

� ET > 25

� Two jets with ET>10 GeV

� Total ET > 200 GeV (HT = Scalar summed ET of jets, leptons, and ET )

Expect: S/B ~ 9

Dominant backgrounds: Drell-Yan, W+jets (“fakes”)

Relatively clean:

�Top and a small amount of SM bkgds

�Down side is small event samples


DileptonDilepton Channel: Channel: eeee, , eeµµµµµµµµ, , µµ (750 µµ (750 µµ (750 µµ (750 µµ (750 µµ (750 µµ (750 µµ (750 pbpb−−11))))))))

64 events on 19 ± 4 background12 ee, 24 µµ, 28 eµ ttbar

signal bin

Jet MultiplicityPT


DileptonDilepton KinematicsKinematicsHt:Scalar summed ET of jets,

leptons, and missing ET

Leptons transverse energy

With higher statistics in Run IIData follow SM expected

distribution of top + bkgd

RunI: had seen hints of discrepancy in kinematic distributions

Missing ET


DileptonDilepton background overviewbackground overview�Instrumental backgrounds

�Drell-Yan (ee, µµ)

�False ET from mismeasured leptons, jets

�Fake leptons

�W+jets with jet misidentified as lepton

�Use data whenever possible

�Physics backgrounds

�Diboson (WW/WZ/ZZ) and Z � ττττττττ

�Real leptons, ET, jets

�Evaluate using MC

�Determine bkgd in 0j, 1j bins to give confidence in signal bin prediction


DileptonDilepton: DY (: DY (eeee, , µµµµ) background) background• Large cross section but no intrinsic

ET

� False Et

� Detector coverage isn’t 4π� Reconstruction isn’t perfect

� Tails of ET resolution critical� Simulation doesn’t accurately model

this� Extra cuts in “Z window”� Estimate residual contamination:

� Use loose Z data to normalize (subtract expected non-Z’s)

� Use MC to distribute inside -outside Z window, across jet bins

ET > 25

ET > 25


DileptonDilepton: Fake lepton backgrounds: Fake lepton backgrounds

114 +/- 3169j100

65 +/- 975j70

49 +/- 651j20

PredObsvDIL

� Determine lepton fake rate from jets in j50 sample

� Cross-check fake rates in other samples with jets

� Apply fake rates to jets in W+jets data sample

ET of observed (predicted) fake tracks in green (black)

# o

bserv

ed (

pre

dic

ted)

fakes

Jet20

Jet70


Dilepton:ZDilepton:Z --> > ττττ, , dibosondiboson bkgdsbkgds� In both cases:

⇒Real missing energy⇒Jets from decays or

initial/final state radiation

� Estimates derived using PYTHIA, ALPGEN+HERWIG MC, normalized to theoretical xsecs

� Correct for underestimation of extra jets in MC⇒Determine jet bin reweighting

factors for Z � ττ from Z�ee, µµ data

⇒Reweight WW similarly


Why Measure the ttbar Cross Section?Why Measure the ttbar Cross Section?� Basic engineering number, absolute measurement (→ very

difficult!) , prior step to any top property study.

� Requires detailed understanding of backgrounds and selection efficiencies.

� Test of SM

⇒Departures from QCD prediction could indicate nonstandard production mechanisms, i.e. production through decays of SUSY states.

∫××

−=

LdtA

NNtt backobs

εσ )(

_


DileptonDilepton: : tttt acceptance and efficiencies acceptance and efficiencies

Acceptance:� Determine from PYTHIA MC

(mt=175 GeV)� Apply trigger efficiencies, lepton

ID MC correction factors, luminosity weights for different detector categories

22%

25%53%

Lepton efficiencies:� Determined in Z -> ℓ ℓ using second leg of Z’s

� Get efficiency for data and MC, estimate difference and derive scale factor ( 90%, 79%, 83% for ee, µµ, eµ respectively)

Final acceptance x eff = 0.732 %


Dilepton:SignalDilepton:Signal acceptance acceptance systematicssystematics

2.4Monte Carlo Generators- compare acceptance of PYTHIA to HERWIG

4.4Initial- and Final-state radiation- ISR: difference from no-ISR sample

- FSR: parton-matching method, different PYTHIA tune

1Parton Distribution Functions (PDF’s)- default CTEQ5L vs MRST PDF’s, different αs samples

3.1Jet Energy Scale- vary jet corrections by ±1σ, for evts w/≥2 jets

4Lepton ID efficiency- Variation of data/MC SF with isolation

DIL(%)Systematic

Must take into account many effects potentially contributing to the acceptance uncertainty:


DileptonDilepton: Systematic Uncertainty on Background : Systematic Uncertainty on Background EstimateEstimate

30-50Fake Estimate- J20, J50, J70, J100 x-check

42Drell-Yan Estimate- Absolute scale (data driven), Monte Carlo shape

~20WW, WZ, ZZ estimate- Compare WW+0p+(njet scaling) to WW+2p

13-30Jet Energy Scale – same procedure on bkgnd acc.

4Lepton efficiency – same as signal

DIL(%)Systematic


DileptonDilepton: Cross section results : Cross section results

∫××

−=

LdtA

NNtt backobs

εσ )(

_

SM: σ = 6.7 pb (mt = 175 GeV/c2)

~750 pb-1

σσσσ(tt) = 8.3 ± 1.5 (stat) ± 1.0 (syst) + 0.5 (lumi) pb


DileptonDilepton Channel: lepton + track (LTRK) Channel: lepton + track (LTRK)

Signature: looser requirements for second lepton:

� 1 lepton+1 isolated track opposite sign

�pT>20 GeV

�|ηηηη| < 1

� Et > 25 GeV

� ≥ 2 central jets (|ηηηη| < 2, ET>20)

�Sensitive also to ττττ lepton final states (~20% from ττττ)

46 events on 14.6 ± 3.6 background30 e+track, 16 µ+track ttbar

signal bin

Jet Multiplicity

σσσσ(Mtop=178) = 9.9 ± 2.1(stat) ± 1.3(syst) ± 0.6(lum) pb


DileptonDilepton event displayevent display

jet

jet

ννννe1

e2

•2 electrons (ET1=73 GeV, PT2=63 GeV)

• Missing ET = 59 GeV

• 2 central jets + 1 forward jet

e1

e1e1

e2

jetjet


ee--µµ eventeventCDF Run II Preliminary (360 pb-1)MET: 91 GeV, ϕ = 2.8

CEM electron: E

T= 61 GeV,

ϕ = 4.8

tl (= CMX muon): p

T= 102 GeV,

ϕ = 0.8

Jet 1: E

T= 43 GeV,

tagged

Jet 2: E

T= 37 GeV,

tagged

Jet 3: E

T= 36 GeV


tttt DileptonDilepton decays with decays with ττhadhad�We look for anomalously large or small τ τ τ τ lepton rate in top decay

�One W decays into ττττ , the other into µµµµ or e

� ττττ decay mode: semileptonic, 1 charged hadron (~50%) or 3 charged hadrons (~15%)

�Signature: high PT e or µµµµ, large ET, ≥ 2 jets and a object passing ττττ identification cuts:

⇒ PTτ > 15 GeV/c

⇒Isolated Σ PT < 1 GeV/c

⇒electron and muon removal

�HT>205 GeV is requested to reduce the background.

�Use W-> τ ντ ντ ντ ν to understand τ τ τ τ ID


tttt DileptonDilepton decays with decays with ττhadhad

32Obs. Data

0.92 ± 0.05stat1.32 ± 0.05stat ttbar

1.32 ± 0.301.43 ± 0.31Bckground

Muon+ τhadEle + τhadSample In ~360 pb -1 expect ~2.2

signal events. Background dominated by jets faking τ’s.

Results:


Single lepton channel (Lepton + jets)Single lepton channel (Lepton + jets)Signature:

�One high pT Isolated lepton

�Veto Z, cosmic, conversion, dilepton

�ET > 20 GeV

�3 or more jets with ET>15 GeV|η| < 2.0

�S/B ~ 1/6

4028461064768183Secondary vertex sample (~700 pb -1)

W+>=4 jetsW + 3 jetsW + 2 jetsW + 1 jet

ℓ

ℓ

l

b

b

νννν

p p

E T

l

jet

jet

jet


Lepton + jets Channel: HLepton + jets Channel: HTT cutcut� HT is the scalar sum of ET of jets, leptons, and ET

� HT is a powerful discriminator for Top signal

� HT > 200 GeV keep 96% of signal and reject 38% of background

An HT cut increases the systematics due to Top mass dependence, Energy scale and Heavy flavor fraction, but still small compared with other syst(SF, lum)


Lepton +jets channel: counting eventsLepton +jets channel: counting events� Require ≥ 1 jet to be identified as a b-jet

(“b-tagged”)

� Motivation of using b-tags:⇒Reduce the backgrounds, especially W + light flavor jets

events while keeping good efficiency on ttbar signal

⇒B tag improves S/B from 1/6 �3/1

� Count ttbar candidate events

� Predict rates for SM non-top processes in tagged W+jets, excess in ≥3 jets is top

� Use data as much as possible to determine background contamination (non-W QCD, fake tags)

� Use MC when necessary (diboson, W+heavy flavor)


Tagging Tools: Tagging Tools: VertexingVertexing and Soft and Soft MuonsMuons

B hadrons in top signal events:

are long-lived and massive may decay semileptonically

Top Event Tag EfficiencyFalse Tag Rate (QCD jets)

60%0.5%

15%~2%

Identify low-pt muon from decayVertex of displaced tracks


Double bDouble b--tagged tagged Lep+TrkLep+Trk event at CDFevent at CDF


Vertex Tagging AlgorithmVertex Tagging Algorithm

� Take advantage of the long lifetime of B hadrons: τ(b) ∼ 1 ps(cτ ≈ 450 µm) ⇒ B hadrons travel Lxy ∼ 3mm before decay

� Select good quality tracks with large impact parameter.� Try to reconstruct a vertex with ≥ 2 traks

⇒ first pass searches for at least 3 tracks with loose kin and Pt >2 GeV/c

⇒ second pass looks for 2 tracks vertices with tighter cuts on tracks qualityand Pt> 3 GeV/c

� A jet containing a vertex is considered b-tagged if has large (positive) decay length significance: Lxy/σLxy > 7.5 (typically σLxy ∼ 150 µm)


Vertex bVertex b--Tagging EfficiencyTagging Efficiency� Use events with back-to-back jets,

non-isolated electron, require away jet to be tagged (enriched in heavy flavor)

� The efficiency of b-tagging determined by the ratio of the number of double tagged to single tagged events, in data and MC

� Define a Scale Factor between data and MC tagging efficiency (usually

εεεεDATA < εεεε MC) SF ≈ 0.91 ± 0.07⇒ SF < 1 due to # of good vertex tracks

higher in MC

� Check in generic jets the ET

dependence of the b-tagging efficiency

�Efficiency for tagging at least one jet in a ttbarevent (L+>=3 jets, including data-MC scaling):

ε ≈ 60 ± 4 %


Vertex Tagging BackgroundVertex Tagging Background� Most from W+heavy flavor and W+mistags

� W+mistags: from generic jet data

� In generic jets heavy flavor pairs are produced by both direct production and gluon splitting. In W+jets by gluon splitting only.

⇒The fraction of Wbb, Wcc events is determined from MC and scaled to the observed number of W events in each jet multiplicity bin

� The (smaller) QCD (non-W) background is evaluated from data: lepton isolation vs Missing ET method (standard)


W + W + mistagsmistags backgroundbackground

� “Fake tags” background:⇒The fake background is measured from generic jet data

using negative decay-length tags �Assume that positive mistag rates are well described by negative

(Lxy <0) tag rates. �Probability to have a negative Lxy (~ 0.5% per jet)

– it is parametrized as a function of the jet ET, jet silicon track multiplicity, η

– it is used to estimate the mistag rate:» Negative- non-physical tags = positive mistags

⇒This probability matrix is then applied to W+jets events to obtain the background estimate in our sample

�


NonNon--W W ““QCDQCD”” Background: Background: ““IsoIso vsvs METMET””

The simplest and most discriminating difference between an “isolated” electron as the one coming from the W decay and a jet is the Isolation.There is NO correlation between Missing Transverse Energy and Isolation for dijet events faking a W->eνννν candidate.→”Isorel vs MET” method


Lepton + jets with Lepton + jets with ≥≥ 1 vertex tag: results1 vertex tag: results

≥ 1 SecVerteX = 314 events on 70 ± 8 bkgnd

Mis tag from

Generic jet data

Method II:

based on MC

MET vs Isolation

method: data driven

top signal region

Number of jets per event:


Tagged Jets PropertiesTagged Jets Properties

The tagged events contain b quarks, as

seen by the decay length Lxy distribution


Tagged Jets PropertiesTagged Jets Properties

The tagged jets are kinematicallyconsistent with the expectation from top, as seen by their ET distribution


Summary of secondary vertex countingSummary of secondary vertex counting

1581565141029Observed positive tags

463329-Observed double tags

1.9 ±0.57.2±1.324 ± 5-Double tags backg

53±6 17±2408 ±53921 ± 113Total background

4028461064768183Events before tagging

W + ≥ 4 jW + 3 jW + 2 jW + 1 j

Require HT > 200 GeV for 3, ≥ 4 jets bins only,

~700 pb-1


Lepton +jets cross section Lepton +jets cross section

� High pt lepton plus missing ET

� N(jet) 3 � 1 jet SEC(ondary) VTX� HT>200 GeV

∫⋅⋅

−≥+=

LdtA

BKGNjetsWNtt

εσ

)()3()(

A: ttbar acceptance : b-jet eff. for ttbarε

≥

8.2 ± 0.6 (stat) ± 1.0 (syst) pb=)(ttσ

≥

Assuming a top mass of 178 GeV/c2

~700 pb-1


Lepton +jets with Lepton +jets with ≥≥ 2 vertex tag2 vertex tagssLower statistics but low background: 79 events observed in top region, 9.1 ± 1.8 bkgd expected

b-tagging efficiency and its uncertainty enters twice here

2 jet bin:29 events observed, ~ 24±5 bkg.~ 7 ttbar expected

# of jets per event:

top signal region

=)(ttσfor a top mass of 178 GeV/c2

8.8+1.2-1.1(stat.)+2.0

-1.3 (sys.) pb


Soft Lepton TaggingSoft Lepton Tagging� Leptons from semi-leptonic decays of B have a softer pT

spectrum than W/Z leptons and are less isolated

� Soft Muon Tagger based on a “Global χ2” to identify low-pt muons: “Global χ2” combines information from muon matching variables There is no calorimetry or isolation requirements

� b-tagging with SLTµ: Track with dR slt-jet<0.6,

|dZ slt-Zvtx|<5cm & pT>3 GeV/c

are considered by the SLTµ tagger An event is tagged if at least

one SLTµ tag is found


Lepton + jets: Soft Lepton Tag countingLepton + jets: Soft Lepton Tag counting

Number of jets per event

MET vs isolation method

Predicted by data in/out

of Z-mass window.

From MC and theory

Alternative way to secondary vertex b-tag

(b→µν→µν→µν→µνX, b→→→→c →→→→ µνµνµνµνX)

top signal region

Predicted by fake rate

matrix made by photon

+ jets sample.


Lepton + Jets: Soft Lepton Tag ResultsLepton + Jets: Soft Lepton Tag Results

Tagged Events: 139 48 13 7 20



Soft Lepton Tag PropertiesSoft Lepton Tag Properties

Jet ET distribution in W + ≥≥≥≥ 3 jets for SLtagged events and expectations from background and ttbar (scaled to the measured cross section of 5.2 pb).

Comparison of the SLTµ pT distribution in W + ≥≥≥≥ 3 jets for SLtagged events and for expectations from background and ttbar (scaled to the measured cross section of 5.2 pb).


All All HadronicHadronic channelchannelVery difficult channel!!

Signature:

• 6 or more jets

• kinematical selection

• ≥≥≥≥ 1 vertex tag.

Background estimate based on data.

Observe 143 tags excess over 683 expected background in signal region.

pbsyststattt

3.5

4.3

7.4

3.2 8.7)()(5.28.7 +−

+− =±=σ


7.5 ± 1.7 (stat) +3.3- 2.2 (syst) = 7.5 +3.7

-2.8 pb


Top cross section summaryTop cross section summary

√√ss--Dependence:Dependence:

⇒ Main data driven systematics(jet energy scale, ISR, εbtag) scale with 1/√N :

⇒ RunII(2fb-1) δσδσδσδσtt/σσσσtt <10%


22ndnd PartPart

Top Physics at CDFTop Physics at CDFand lessons for LHC and lessons for LHC


OutlineOutline

� Motivations for studying top � A brief hystory� Top production and decay � The Tevatron & CDF� Detector issues� Identification of final states� Cross section measurement� Mass determination� Single top production� Study of top properties� The lesson for the LHC

Yesterday Introductory

Part


You cannot trust MC to predict instrumental effects/backgrounds involving distribution tails

Is our detector/simulation particularly bad?

No! You always have at some level this kind of effects

We are afflicted by very “rare” instrumental

backgrounds

We are looking for very rare events

What can we do?

Optimize the cuts to reduce the bckgndcontamination, optimize with available data

the simulation, but in the end use real datawhenever possible


Cannot rely (completely) on MC when instrumental backgrounds are concerned,

distribution tails are concerned

Are MC useless?Are MC useless?

NO! of course, they are necessary tools!

� Use MC to model the kinematical and geometrical acceptance of signal and physics backgrounds

� Trust ME calculations� Trust basic kinematical description of data� Trust basic description of detector features

� Check MC predictions on control samples

BUT


Final states:Final states:

ℓ

ℓ

jet

jet

b

b

νννν

νννν

p p

ET

+

-

jet

jet

b

b

νννν

νννν

pp p

ET

ET

Dilepton:

b

b

νννν

p p

E T

jet

jet

jet

ℓ

ℓ

Lepton + jets


Once reOnce re--established top established top existanceexistance, , letlet’’s measure its properties. s measure its properties. First property is its First property is its massmass


Top mass is a fundamental SM parameter

• Related through radiativecorrections to other EW observables.

CDF&D0

RUNII

Why is Top Mass so special?Why is Top Mass so special?

• Very important for precision tests of SM.•Together with Mw and other electroweak precision

measurements, it constrains MHiggs

• By far the largest quark mass, largest mass of all known fundamental particles


What is the top mass?What is the top mass?� Particle masses are not “directly measured”

⇒ one can only measure cross sections, decay rates� Measurement of Mtop: at Tevatron, LHC:

⇒kinematic reconstruction, fit to invariant mass distribution⇒Best measurement from lepton +jets

� Experimental accuracy of Mtop :⇒Measurement comparison data from Monte Carlo⇒ you measure the mass that is implemented in your MC

� measured mass is not strictly model independent

� Situation at the Tevatron:⇒δδδδMtop = 2.3 GeV (Tevatron; today)

� Projections at the LHC:⇒δδδδMtop < 1 GeV with 10 fb-1

��Will Tevatron get there first?


Top Mass Measurement ChallengesTop Mass Measurement Challenges

Why so challenging? It is a difficult measurement Many combinations of leptons and jets:

Events are complicated! Measurements are not perfect!Experimental observations are not as pretty as Feynman diagrams!

�Missing neutrino�Confusion in ID assignment (add. Jets from ISR/FSR, b-tag: not 100% correct)

�Link observables to parton-level energies�Large syst uncert. from jet energy scale�Need accurate detector simulation

l

ν

W+

W-

t

t

b-jet

b-

jet

jet

jet

X Constraints

Method: reconstruct Mtop with 2 constraints: M(W+)=M(W-), M(t)=M(tbar)

ℓ


Lepton + Lepton + ≥≥ 4 jets: template method4 jets: template method

Wbb MCData

tt MC

Datasets

Massfitter

Templates

χ2 mass fitter:�Finds top mass that fits event best� All event info into one number � 12 parton/jet matching assignments possible, 2 longit. neutrino possible, use b-tag to reduce permutations � test for consistency with top using kinematic constraints � choose combination with lowest χ2

Likelihoodfit ResultLikelihood fit:

� fit resulting mass distribution to MC background + top signal templates at different values of Mtop

� Best template to fit data gives mass� Constraint on background normalization


The new CDF top mass measurement The new CDF top mass measurement in in

Lepton+Jets channel with 680 pbLepton+Jets channel with 680 pb--11

� Subdivision improves statistical uncertainty.⇒Pure and well reconstructed events contribute more to result.

⇒Adds 0-tag events.

� Subdivision does not improve systematic uncertainty.⇒Most systematics, including jet energy scale, are highly

correlated among the samples.

Improve stat. power of the method dividing the sample in 4 categories of events that have different backg. contamination and different sensitivity to the top mass

0.6:11:14:110:1S:B

ET>2115>ET>8ET>15ET>8j4

ET>21ET>15ET>15ET>15j1-j3

0-tag1-tag(L)1-tag(T)2-tagCateg.


Top Mass reconstruction in Top Mass reconstruction in MontecarloMontecarlo eventsevents


� W+heavy flavor jets(bb,cc,c)⇒Heavy flavor fraction from MC⇒Normalized to data

� W+jets(mistag)⇒Use measured mistag rate,

applied to the data� Multijet:non-W (jet->e, track->µµµµ)

⇒Estimated from data� Single top, diboson (WW,WZ)

⇒Estimated from MC

Mass analysis event selection & BackgroundsMass analysis event selection & Backgrounds

57

4.0±±±±1.3

2tag

75

31.±±±±7.

1tagL

no est22.±±±±5.bkgds

108120Data

1tagT 0tagIn 680 pb-1

360 candidate events used for top mass measurement


3.4TOTAL

0.4MC statistics

0.2b-tagging

0.6b-jet energy scale

1.0Background shape

0.3Generators

0.4PDFs

0.4FSR

0.4ISR

3.1Jet Energy Scale

∆Mtop (GeV/c2)Systematic

Systematic Errors (based on 318pbSystematic Errors (based on 318pb--11))

Can we improve jet systematic?

Dominated by jet energy scale:


3.4TOTAL

0.4MC statistics

0.2b-tagging

0.6b-jet energy scale

1.0Background shape

0.3Generators

0.4PDFs

0.4FSR

0.4ISR

3.1Jet Energy Scale

∆Mtop (GeV/c2)Systematic

0.6Total

0.4Semi-leptonicdecay

0.3Color flow

0.4Heavy quark fragmentation

∆Mtop

(GeV/c2)

B-jet energy

scale

Systematic ErrorsSystematic Errors

Though we find that 70% of JES uncertainty comes from b-jet, b-jet uncertainty is mainly due to generic jet corrections: only 0.6 GeV/c2

additional uncertainty on Mtop due to b-jet-specific systematics


Jet Energy Jet Energy MismeasurementMismeasurement

Precision on the determination of jet energies is necessary for Mtop measurements.Jets may be mismeasured due to a variety of effects:

� Instrumental effects: calorimeter non-linearities non-instrumented regions non-compensating calorimeter

�Physics effectsContribution from underlaying eventmultiple ppbar interactionsthere are different types of jets

�Algorithm effects: might not capture all particles (out of cone)low energy jets might not be possible to define

Non-uniform

response

Diff. resp.

of π0/πi+-

Non-linearity

Shower, frag.


Jet Energy CorrectionJet Energy Correction

Determine true “parton” E from measured jet E in a cone 0.4

The correction factor depends on jet ET and η and is meant to reproduce the average jet ET correctly, (not to reduce the jet fluctuations around this mean)

A set of corrections was developed for generic jets:⇒Absolute corrections (photon-jet balancing)⇒Relative corrections (central-forward calorimeters, dijet balancing)

Out-of-Cone: correction to partonUnderlying event”top-specific correction” to light quark jets and b-jets separately

Non-uniform

response

Diff. resp.

of π0/πi+-

Non-linearity

Shower, frag.


Jet Energy Jet Energy SystematicsSystematics

A lot of work has been done to reduce the syst. from jet-energy scale (a factor of two improvement compared to start of RunII). The new Run II systematic uncertainties are now better than Run I.

RunII

RunII 2004

RunI

Frac. Syst. uncert. vs Pt

Central region

�What is jet energy scale “JES”?

�Measures how incorrect is our nominal jet energy measurement.�Units of σσσσ: correspond to one s.d. of jet energy uncertainty

⇒ Accounts for ET, η dependence.


WorldWorld’’s Best Top Quark Mass:s Best Top Quark Mass:MMtoptop+ JES simultaneous fit+ JES simultaneous fit

� Measure JES in situ.� Perform simultaneous fit.

⇒ Extend 1-D template (only on reconstructed Mtop) to maximize sensitivity to Jet Energy Scale:⇒ Mtop and JES are simultaneously determined in likelihood fit using shape comparisons ofReconstructed Mtop and, Reconstructed Mjj

distributions, taking correlations between them


l

n

W+

W-

t

t

b-jet

b-jet

jet

jet

JES and JES and MtopMtop measurementsmeasurements-- 2D Template Analysis 2D Template Analysis --

Simultaneous fit to JES and Mtop using top mass and W mass templates:

Mt ( true Mtop, JES), Mjj ( true Mtop, JES)

� Identify jets coming from W• All non-btagged jets pairs are taken

into account equally.• 1/3/6 Mjj per event with 2/1/0 b-tag

� Reconstruct their invariant mass Mjj

� Mjj strongly dependent on JES• Make Mjj templates by varying JES • Fit data with Wjj to measure JES!

� MW uncertainty is negligible (< 50 MeV)

� Mjj mostly independent of Mtop

� This scale is applied to b-jets and light-quark jets

JES from W→jj is mostly

statistical → luminosity scale !

Mjj(W)


2D Top Mass Result with 680 pb-12D Top Mass Result with 680 pb2D Top Mass Result with 680 pb--11

2

top GeV/ (syst) 3.1(stat) 5.24.173 cM ±±=

mtreco in data w/ global best fit overlaid

± 1.7 (stat) ± 1.8 (JES)

Using 360 candidates in 680 pb-1 we measure:

Mtop = 173.4 ± 2.8 GeV/c2

Best single measurement in the world!

Better than TevatronSummer 2005 average!


JES Results with 680 pb-1JES Results with 680 pbJES Results with 680 pb--11

• Combined W→jj and prior

JES yield 40% improvement

Reconstructed dijet (W) mass:

Black curve from global best fit.

∆∆∆∆JES = -0.3 ± 0.6 (stat. + Mtop) σσσσc


Systematic Uncertainty in 680 pbSystematic Uncertainty in 680 pb--11

0.4Bkgd JES

0.7Residual JES

0.1B-tagging

0.2FSR

0.3Generators

0.5Bkgd Shape

0.5ISR

1.3TOTAL

0.3MC stats

0.3PDFs

0.6B-jet energy scale

∆∆∆∆Mtop

(GeV/c2)Systematic

Systematics are largely due to uncertainties in modeling.

From pT and η dependence of modeling uncertainties

Model constrained by Z+jets data


Top mass: matrix element (ME) methodTop mass: matrix element (ME) method� Optimizes the use of kinematic and dynamic information� Calculate a probability per event to be signal or background as a

function of the top mass� Signal probability for a set of measured jets and lepton (x)

� Likelihood simultaneously determines Mtop, Jet Energy Scale, and signal fraction:

� All jet-parton assignments and neutrino solutions are considered, weighted.

� Select events with exactly 4 jets, well described by LO ME.

P(x; M top ,JES) =

1

σdq 1dq 2 f(q 1) f(q 2 ) d σ (y; M top )∫ W(x, y, JES)

L ( f top, M top , JES ) ∝ ∏i

Nevents

f top Ptop ,i ( M top , JES ) + (1 − f top ) Pbkgd ,i (JES )( )

Differential cross sectionDifferential cross sectionDifferential cross sectionDifferential cross section:

LO ME (qq->tt) only

Transfer function: Transfer function: Transfer function: Transfer function: probability

to measure x when parton-level

y was produced


Matrix Element (L+J) ResultsMatrix Element (L+J) Results——680 pb680 pb--11

� Exactly 4 jets with ≥ 1 b tags

� JES here is a constant multiplicative factor.⇒Edata = EMC/JES

� JES = 1.02 ± 0.02.

⇒Consistent with template method

� Virtually identical sensitivity with fewer events!

2

top GeV/ (syst) 4.1(stat) 5.21.174(ME/LJ) cM ±±=Using 118 candidates in 680 pb-1


Top Mass: Top Mass: DileptonDilepton channel, ME techniquechannel, ME technique

~1 27≥1 b tags

19.4 ± 3.464≥0 b tags

BackgroundEvents� Harder to reconstruct Mtop in dilepton events: two neutrinos make system underconstrained.

� Likelihood is similar to L+jets.

� No W reson. → no fit for JES

�Add ME for dominant bkgds:DY+jets, WW+jets, fakes

2

top GeV/ (syst) 1.3(stat) 5.45.164 cM ±±=

Restrict sample to b-tagged events:Mtop = 162.7 ± 4.6 ± 3.0 GeV/c2

750 pb-1

probability density as a function of top pole mass


Top mass summaryTop mass summary

CDF April 2006: 172.4± 1.5 ± 2.2

Tevatron March 2006: 172.5± 1.3 ± 1.9


Keep an eye onKeep an eye on……

� Discrepancy btw L+jets, Dilepton ch. measurements…?

� Is it statistical?� Is there a missing

systematic?� Is our assumption of

SM ttbar incorrect??

Stay tunedStay tuned……


Consequences on the Higgs MassConsequences on the Higgs Mass

Preferred MHiggs

MHiggs = 89 +42-30 GeV

MHiggs < 175 GeV @ 95% CL

This limit increases to 207 GeVwhen including the LEP-2 direct search limit of 114 GeV shown in yellow


The Future Prospects for top massThe Future Prospects for top massThe Future Prospects for top mass

� Using W→jj: JES uncertainty becomes mostly statistical

So we can reach JES uncert. < 1 GeV/c2 in Run II

� Reaching total δδδδMtop < 1.5 GeV/c2 can be possible with full Run II dataset

Now !

Achieved 1.3% precision of the Mtop measurement


SingleSingle--Top Quark ProductionTop Quark Production

Theoretical cross section predictions at √s = 1.96 TeV

0.88 ±±±± 0.11 pb 1.98 ±±±± 0.25 pb

Top quark production via the weak interaction

B.W. Harris et al. Phys. Rev. D 66 054024 (2002)

Vtb Vtb

s-channel t-channel


Single Top EWK ProductionSingle Top EWK Production

s –channel (W*)

btWqq * →→→→→→→→

t -channeltqqb '→→→→

tW associated production−−−−→→→→ tWbg

< 14 pb< 13 pb< 18 pbCDF

< 22 pb<17 pbD0

62+17 -4 pb247 ±±±± 25 pb10.6 ±±±± 1.1 pbLHC σσσσNLO

~ 0.1 pb1.98 ±±±± 0.25 pb0.88 ±±±± 0.11 pbTevatron σσσσNLO

Combined

(s+t)Associated tWt-channels-channel

B.W. Harris et al.:Phys.Rev.D66,054024 T.Tait: hep-ph/9909352

Z.Sullivan Phys.Rev.D70:114012 Belyaev,Boos: hep-ph/0003260

RunI

95% C.L.

(mtop=175 GeV/c2)


Cross section smaller than top pair production, but ➡Observation of single top allows direct access to Vtb CKM matrix element: cross section ∝ |Vtb|

Test non-SM phenomena� 4th generation, FCNC couplings like t →→→→ Z/γγγγ c, anomalous Wtbcouplings

Potentially useful for Higgs searches� single top has same final state as Higgs+W (associated) production

Why Single Top? Why Single Top?

only indirectly

known

Direct measurement

only via single-top quark production


Single Top Signature & BackgroundSingle Top Signature & Background

ss--channelchannel

tt--channelchannelb quark produced WITH the top

b quark from the top decay

lepton + Missing ET

b quark from the top decay

lepton + Missing ET

extra light quark

at NLO an additional b from gluon splitting (difficult to measure)

Backgrounds:⇒ W/Z + jets production

⇒ Top pair production

⇒ Multijet events


CDF Single Top Search StrategyCDF Single Top Search Strategy

� W selection:

� - ET > 20 GeV/c (central and forward electrons)

� - pT > 20 GeV/c (central muons)

� - Missing ET > 20 GeV

� Jets selection:

� - Exactly 2 jets, at least one is b-tagged

� - Jet ET > 15 GeV, lηl < 2.8

696 pb-1

Separate Channel Search

2D Neural Network discriminant

+ likelihood fit

Combined Channel Search

1D Neural Network discriminant

+ likelihood fit (Bayesian approach))


Separate Channel searchSeparate Channel search

(syst)pb(stat)0.6σ0.10.1

1.90.6cht

++++−−−−

++++−−−−−−−− ====

t-channel:

σσσσ < 3.1 pb @ 95% C.L.

s-channel:

σσσσ < 3.2 pb @ 95% C.L.

CDF applies a maximum likelihood fit to the network 2D output and the best fits for t- / s-channel are:

t-channel:

s-channel:

The resulting upper limits are:

pb (syst)(stat)0.3σ0.5

0.3-2.20.3chs

++++++++−−−−−−−− ====


� Best fit value:

Combined channel searchCombined channel search

The resulting upper limit

on the cross section is:

σσσσsingle-top < 3.4 pb

at 95% C.L.

(syst)pb(stat)0.8σ0.20.3

1.30.8st

++++−−−−

++++−−−−++++ ====


Measurement of Top Quark Production Measurement of Top Quark Production and Decay Propertiesand Decay Properties

� Let’s continue on the natural path of measuring top quark properties in order to confirm SM or find deviations from it

⇒ Is top quark adequately described by the Standard Model?

Top spin polarization

Production Cross Section

Resonance production ?

Production kinematics


� Several theoretical scenarios:⇒Heavy 4th generation quark

(He et. Al. Hep-ph/0102144) � Consistent with EWK data

⇒ “beautiful mirrors”models (Wagner et. Al. Hep-ph/0109097)�Accomodates LEP b forward-backward asymmetry result

� CDF performs 2D fit: HT = ΣjetsET + ET,l + MET and Mreco from χ2 mass fit in Lepton + Jets channel

� Uses binned likelihood fit and Bayesian limit:⇒Rule out at 95% CL a t’ with

m(t’) < 258 GeV/c2

Search for Heavy Quark Search for Heavy Quark tt’’→→WqWq


Searches for Searches for ttbarttbar ResonancesResonances

pp → X0 → tt

� Various exotic models predict the existence of particles decaying to ttbar: Topcolor-Assisted Technicolor

(Hill, Phys Lett. B345, 483 (1995); Hill and Parke PRD49, 4454 (1994))

� Extends technicolor models and attempts to explain EWSB by introducing a new strong interaction

� Predicts new massive bosons “topgluons” and a topcolor Z’


History: Previous MeasurementsHistory: Previous Measurements

� Observed quite intriguing excess around 500 GeV� Had a similar although smaller excess in Run 1

CDF

Run 1

� Lepton + jets:CDF

Phys.Rev.Lett. 85, 2062 (2000)


Latest CDF measurement (682pbLatest CDF measurement (682pb--11))

With about twice more data the excess disappeared!

95% CL upper limits for the cross section for resonance production

Mtt distribution from data vsexpected SM background in the >400 GeV search region

>725


Top LifetimeTop Lifetime� The SM predicts a top lifetime of

~ 4 x 10-25 s ⇒A measured deviation from

“zero lifetime” could mean:�A much larger top lifetime�New Physics?o Anomalous top production by a long-

lived parent particle, oro A long-lived background to SM top.

•Use Lepton+Jets top pair sample with a b tagged jet.

•Measure signed lepton impact parameter (d0)

•Calibration:

•Used Drell-Yan events near Z resonance to understand the d0resolution.

•Confirmed technique correctly measures tau lifetime in Z → ττ


Top Lifetime (2)Top Lifetime (2)� Backgrounds:

⇒Prompt: W+jets, Drell-Yan, Diboson

⇒Displaced lepton: W/Z decaying to τ, semileptonic b & c decays, photon conversions

� Results:⇒Using 157 events

�32 expected background

First Direct LimitFirst Direct Limit

On Top LifetimeOn Top Lifetime

Data compared to fit result


W Helicity Measurement in top decayW Helicity Measurement in top decay� Top decays before it can hadronize, because width Γt ~ 1.5 GeV > ΛQCD.⇒Decay products preserve information about parent particles.

⇒Unique opportunity to study the weak interactions of a bare quark, with a mass at the natural electroweak scale!

� SM Prediction:⇒W helicity in top decays is fixed by Mtop, MW, and V-A structure

of the tWb vertex.

⇒W helicity reflected in kinematics of W decay products


W Helicity Measurement, contd.W Helicity Measurement, contd.

-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 10

0.5

1

1.5

2

2.5

3

3.5

4

-

φcos

)φw

(co

s

-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 10

0.5

1

1.5

2

2.5

3

3.5

4

0

φcos

)φw

(co

s

-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 10

0.5

1

1.5

2

2.5

3

3.5

4

+

φcos

)φw

(co

s

22

0

2 )cos1(8

3)cos1(

8

3)cos1(

8

3)(cos

blblblblFFFw −−−− +⋅+−⋅+−⋅= +− ϕϕϕϕ

The angular dependence of the semileptonic decay in the W rest frame is given by:

3.021

2≈

+=− ω

ωF 7.0

21

10 ≈

+=

ωF 0=+F

where ω= MW2/Mtop

2

parameter to measure

SM (V-A) predictions (for mb=0):

left rightlong.

[V+A: 70% long., 30% r.h.]


W W HelicityHelicity Measurement: MMeasurement: Mlblb22

Use the invariant mass of the lepton and the b jet, assuming Use the invariant mass of the lepton and the b jet, assuming mmbb = 0,= 0,

Three data samples used:Three data samples used:

�� Single b tagged Single b tagged leplep + jets+ jets

�� Double b tagged Double b tagged leplep + jets+ jets

�� DileptonDilepton

F+ = 0.02 ± 0.07

F+ < 0.09 at 95% C.L.


θ* is the angle between the P of the charged lepton in the W boson rest frame and the W P in the top quark rest frame. In order to determine the cos(θ*) distribution in the data, the kinematics of the ttbar events are fully reconstructed

Lepton+jets sample

W W HelicityHelicity measurement:cosmeasurement:cosθθ**

F0 = 0.85 +0.15-0.22 (stat.) ± 0.06 (syst.)

F+ = 0.05 +0.11-0.05 (stat.) ± 0.03 (syst.)

F+ < 0.26 at the 95% C.L.


Top Branching fractions R=Top Branching fractions R=B(tB(t��Wb)/B(tWb)/B(t��WqWq))

� Cross section measurements assume t→Wbalways, never t→Wq.

� b-tag rates in tt events test that assumption, depend on B(t→Wb) = R, tag efficiency = ε:

� Measure from the ratio of tag rates the product R εεεε: assume ε and measure R or vice-versa.

(Rε) Rε) Rε)

Rε


Measuring Measuring R R

assuming 3 generations

•Integrated luminosity of 162 pb-1


Outlook from the Outlook from the TevatronTevatron

� Run II measurements of cross section & mass are improving rapidly.

� Other analyses (W helicity, single top…) are making excellent progress.

� A program of precision top physics—and hopefully top surprises— is well established.

� Tevatron performing well: experiments very busy in staying after the data and using all of them!

� We still expect 5x more data 5x more data in hand before LHC starts!

DØ / CDF

Run 2a

Goal

Run II with first 2 fb-1 will provide a chance to:

�Measure Mw to < ±40 MeV/c2

�Measure Mtop to < ±2.0 GeV/c2


Extended Extended TeVTeV goalsgoals� Luminosity plan 2002� Goals 2002 - 05 accomplished� Goals 2006 ~ 500 - 890 pb-1

⇒Tevatron is performing very well⇒Up to now accomplished

expectations0.080.08FY02

8.564.41Total

2.421.16FY09

2.371.14FY08

1.530.63FY07

0.890.50FY06

0.670.39FY05

0.380.31FY04

0.220.20FY03

Design plan

Luminosity/yr (fb-1)

Base plan luminosity/yr (fb-1)

Year

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6 7 8 9 10

End FY

fb-1

Base plan

Design plan

Base plan ~ no recycler

LLLLmax = 2-3 x 1032


Top Top ExpectedExpected statisticsstatistics @ LHC@ LHC

≈ 80 000 000100 days : 1001034High luminosity

(> 2010?)

≈ 8 000 000100 days : 101033Low luminosity

(2008)

≈ 80 00010 days : 0.11032Very beginning

(~ 2007?)

Number of inclusivet t events

Integrated luminosity

(fb-1)

Luminosity

(cm-2s-1)

Data taking


Top @ LHC: Top @ LHC: Some Thoughts (from a nonSome Thoughts (from a non--LHCLHC’’erer))

� With the first data: ⇒ understand the detector and trigger

�Many detector-level checks (tracking, calorimetry)

⇒Minimize MC dependency & check detector simulation

⇒Exploit available ‘candle’ physics signals:

�Presence and mass of the W±, Z0, top-quark

⇒Calibrate:�Jet energy scale�b-jets & tagging (require good alignment: cannot

come immediately)�Balance in transverse plane (missing energy)

“Only after full understanding of these the road to discovery starts…”

M. Cobal



The 3 golden suggestions:

� Measure everything ( ….as much as possible….) in data

⇉ But try to have soon a well-tuned simulation available..

� Understand b-tagging:

⇉ learning how to deal with high luminosity and multiple interactions is crucial : efficiency decreases and mis-tag rates rise

� Make sure the calibration triggers are in:

⇉ Low-pT leptons

⇉ Jets at various thresholds

� Likely have to prescale a lot

� Don’t let them get turned off at high luminosity!


l

νννν

W+

W-

t

t

b-jet

b-jet

jet

jet


Yesterday’s discovery could be tomorrow’s calibration

⇉Top events as “tools” to calibrate the “basics”:

�Clean source of b jets: Measure b-tag efficiency (or data/MC scale factor) in top events?

�Invariant mass of jets should add up to W mass: jet energy scale calibration

�Missing energy calibration: 4-momentum of single neutrino in each event can be constrained from event kinematics


The Road Ahead the The Road Ahead the FemptobarnFemptobarn Era!Era!

� The Tevatron program in the pre-LHC era is very exciting & rich

� The standard model top is pretty healthy⇒ We are beginning to have sensitivity to the unexpected

� More data makes us smarter !

⇒ It is not just the luminosity factor

⇒ We become more daring and more creative

⇒New channels open up� For calibrations

� For cross-checks

� For understanding

� Let me advertise the many opportunities to do great physics at the Tevatron!!

� Many opportunities to develop expertise which will be crucial for the LHC physics program

Documents

while waiting for the LHC) · LHC School Lecce June 2006 Sandra Leone, INFN Pisa More details on Jets A jet is a complicated object : measured by calorimeter towers defined by a clustering