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Page 1: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

Physics of Hadron CollidersLecture 2: Top Physics at CDF

Joseph Kroll

University of Pennsylvania

[email protected]

Page 2: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 2

Fermilab Collider Accelerator Complex

• There are 8 accelerators in the chain

• Proton source (3)– Cockroft-Walton

– Linac

– Booster

• Antiproton source (2)– Debuncher

– Accumulator

• Main Injector (1)

• Recycler (1)

• Tevatron (1)

see www-ad.fnal.gov/public/index.html

Drawing courtesy of Fermilab

Page 3: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 3

Fermilab Aerial View

Photo courtesy of Fermilab

Main Injector

Tevatron

DØCDF

Fixed Target

n.b., objects not to scale

Page 4: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 4

Fermilab Site (cont)

Photo courtesy of Fermilab

AccumulatorDebuncher

Booster

Linac

Cockroft-Walton

Photo courtesy of Fermilab

Page 5: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 5

Proton Source

Cockroft-Walton750 kV DCAccelerates H¯

Linac805 MHz130 m length3 MV/meter accel.400 MeV on outputalso H¯

Booster1 GHz475 m circumference400 MeV acc. to 8 GeVaccelerates protonsbeam to MiniBoone too

Beam from Boostergoes to Main Injectoraccelerated to 120 GeVto make antiprotons

Photo courtesy of Fermilab

Photo courtesy of Fermilab

Photo courtesy of Fermilab

Page 6: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 6

Antiproton Source – Three Components

Target• 120 GeV p’s hit Ni target• 106 p make » 20 8 GeV “pbars”• focused by Li lens• pbars filtered out by mag. spec.

Debuncher• trade E for t• pbars easier to accept in Accum.

Accumulator• 8 GeV pbars cooled (stacked)• Stochastic cooling• holds pbar “stack” for hours• large stack = 200mamps

Accumulator

DebuncherPhoto courtesy of Fermilab

Page 7: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 7

Stochastic Cooling

I said I wouldtry to find outthe answers to questions I couldnot answer.

Here’s an answerfrom Paul Derwent(FNAL) on why wesay “stochastic”

Page 8: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 8

Main Injector and Recycler

Main Injector

RecyclerMain Injector• Biggest change for Run II• 3.3 km circumference• replaced “Main Ring”• commissioned 98-99• increases pbar prod by 3• fixed target @ 120 GeV• collider @ 150 GeV• FT & collider simultaneous

Recycler• 8 GeV pbars from Acc• allows faster stacking• permanent magnets •1.5kG dipole, 3.7kG/m Quad

Photo courtesy of Fermilab

Page 9: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 9

Tevatron

After MIBefore MI

Tevatron

Main Ring

• 1st superconducting synchrotron• 6.28 km in circumference• commissioned 1983• 1000 4.4 T dipoles, 6.4 m long, 4.2o K• Run I: 900 GeV Run II: 980 GeV

1989 NASMedal ofTechnology:Alvin TollestrupHelen Edwardsof Fermilab

AT HE

Photo courtesy of Fermilab Photo courtesy of Fermilab

Page 10: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 10

Tevatron Collider Runs and CDF

• Run -2 (October 1985) “Engineering” Run– 28 collisions recorded with VTPC

• Run -1 (1987-1988)– first physics (» 30 nb^{-1}): W’s, jets, incl. particle distributions,…

• Run 0 (1988-1989)– » 5 pb-1 data: Z0 mass, limits on top, EWK, QCD, B’s, exotics,…

• Run 1 (1992-1996)– DØ’s first run

– peak L = 2.4 £ 1031 cm-2s-1, 6 £ 6 (3.6 sec)

– » 120 pb-1 data: top discovery, W mass, sin2,…

• Run 2 (2001-2009?)– to date: 500 pb-1 delivered, 400 recorded by CDF

– peak L = 7.2 £ 1031 cm-2s-1, 36 £ 36 (396 nsec)

Page 11: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 11

The CDF II Upgrade (1996-2001)*

• Actually there have been many CDF upgrades• CDF II refers to the detector built after Run I• Essentially the entire detector rebuilt

– Only the Central EM and HAD calorimeter remained

• new bunch separation (132 nsec) all new electronics• new drift chamber (COT) & silicon tracker (L00, SVXII, ISL)• Time of Flight for particle id• new end plug calorimetry & lumi monitor• more muon coverage• new fully digital trigger system with new capabilities (SVT)• new DAQ

* Actually the CDF II upgrade began well before 1996 and is still taking place

Page 12: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 12

Silicon trackingDrift chamber

Lumi monitor

Hadronic Calorimetry

Muon systems

Iron shielding

Solenoid and TOF

ElectromagneticCalorimetry

CDF II

Page 13: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 13

Running Conditions (Run I versus Run II)

Higher luminositysame number of bunches more interactions/crossing

Average number ofinteractions/crossingabout the same at Lmax

in Run 1 and Run 2

n.b.,We will not run with 99 bunches (132 nsec)

Example of a slide fromthe days before powerpoint

Page 14: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 14

CDF Run II Data Taking

Integrated luminosity deliveredand acquired by CDF

Integrated luminosityacquired by CDFper fiscal year (e.g., FY03 is Oct. 2002 to Sep. 2003)

Day since beginning of yearTevatron Store Number

Page 15: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 15

CDF Run II Data Taking (continued)

Initial Luminosity vs. Store Number CDF Data Taking Efficiecny vs. Store #

80%

Not at the LEP orB Factory Level (yet)

Blue is running averageover 20 Stores

CDF Averages and Records

Page 16: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 16

The CDF II Silicon Tracker

3 Parts:Layer 00SVX IIISL

Page 17: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 17

Insertion of the Central Outer Tracker

Page 18: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 18

Tracking System Assembly (continued)

Page 19: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 19

Roll-in of Central Detector

Page 20: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 20

CDF II Trigger System

Detector

L1 trigger

L2 trigger

L3 trigger

tape

46 L1buffers

1.7 MHz bunchcrossing rate

30 kHz L1 accept

300 Hz L2 accept

70 Hz L3 accept

Hardware tracking for pT 1.5 GeV

Muon-track matching

Electron-track matching

Missing ET, sum-ET

Silicon tracking

300 CPU’s

Jet finding

Full event reconstruction

Refined electron/photon finding

>100Hz with datacompression

4 L2 buffers

courtesy E. Thomson (OSU/Penn)

Page 21: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 21

Run II Physics @ CDF II

• Top physics (center piece of Run II physics program)– top is discovered measure properties (mass, production, decays)

– does it have non-standard model decays, production?

• Exotic Physics (new particle searches)– at the energy frontier until LHC turns on

• Electroweak Physics– W mass, Higgs search, WW, WZ, ZZ production

• QCD– inclusive jet cross-section, W/Z + jets, jet correlations, heavy flavor

– soft physics (diffraction, double pomeron scattering, etc.)

• Heavy Flavor Physics (b and c)– B hadron weak decays: B0

s flavor oscillations is the center piece

– Charm physics program (completely new for Run II – SVT)

Page 22: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 22

10 Years Ago

Aside: Have we directlyobserved all 12fundamental fermions?

Page 23: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 23

Top Pair Production

The dominant source of top is strong (QCD) production

quark-antiquarkannihilation

gluon fusion

top is massiveat Tevatronproducedcentrally

Page 24: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 24

Predicted Cross-section M. Cacciari et al., hep-ph/0303085

Central valueis “CTEQ6”structure fcns= 175 GeV

Variation from• pdf’s• s,

GeV cross-section in picobarns (pb)

30% increase s = 1.8 to 1.96 TeV

pdf uncertainty:from high-x g- see later slide

Page 25: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 25

Comment on Parton Distribution Functions

CTEQ is an acronym for a set of structure functions producedby a collaboration called :

There are others: e.g., MRST

“Coordinated Theoretical-Experimental Project on QCD” see www.phys.psu.edu/~cteq

Martins, Roberts, Stirling, Thorne, hep-ph/0207067

There are many sets of pdf’s based on global fits of various data

n.b., excellent summer schooltransparencies available there

check out www.durpdg.dur.ac.uk/hepdata/pdf3.html

Page 26: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 26

Which Process Dominates?

Depends on mt and s

Center of mass energy Ecm of partons 1 and 2

Parton 4-vectors are (E,pz):

Need at least

For x1 ¼ x2 x > 0.2 Tevatron x > 0.03 LHC

Aside: really need more (phase space)mean pT(top) » mt/2

Page 27: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 27

Quarks at Tevatron, Gluons at LHC

Tevatron

LHC

(uncertainty in g at high x ~ 10% uncertainty on

LHC

Tevatron

g

u

d

u

Page 28: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 28

Single Top Production

Electroweak top production also important

0.88 § 0.10 pb-1 1.98 § 0.24 pb-1 negligible @ Tevatron

Harder to observe than

Difficult background for SM Higgs search

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

Page 29: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 29

Standard Model Top Anti-Top Signature

Vtb ¼ 1* BF(t ! Wb) = 100%

* assuming unitarity 0.9990 < Vtb < 0.9993 @ 90% CL (PDG2002)

mt = 175 GeV real W

t! Wb) = 1.5 GeV, t = 4£10-25 s no top hadrons

Classify topologies according to W decay

dilepton both W decays leptonic (means e or , not

lepton + jets One W decay leptonic, other hadronic

all hadronic both W decays hadronic

dilepton and lepton + jets are the discovery modes

Page 30: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 30

Three tt Signatures

Dilepton

2 high pT leptons, ET, 2 b-jets

Lepton + jets

1 high pT lepton, ET, 2 b-jets, 2 light quark jets

All hadronic

2 b-jets, 4 light quark jets

W!, ! hadrons treated separately

4.6% (6.4%)

33.6% (37.6%)

61.8% (56.0%)

Use W! e, 10.7% each(add W! 10.7%, !e, 35.2% total)

Page 31: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 31

Three Signatures (continued)

All hadronic

QCD multijet production several orders of magnitude higher ► need b-jet identification ► must reconstruct top invariant mass ► still very challenging (for trigger too)

Remember

most probable topology

Lepton+jet also a probable topology

Real W production still orders of magnitude higher ►several approaches – described later ►much cleaner than hadronic – especially with b-tag

see next slide

Dilepton least probably topology

Real WW production comparable see next slide

Page 32: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 32

Aside: W and Z Production at the Tevatron

Dilepton and Lepton+jets signature contain W! e,

(for s=1.96 TeV, about 10% lower for s=1.8 TeV)

WW production is comparable to top production

e.g., see J.M. Cambell & R.K. Ellis, Phys. Rev. D 60, 113006 (1999)

Page 33: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 33

Dilepton Signature

Pair of opp. charge, high pT leptons: e+e-, e+- & e-+, +-

Substantial ET from two ’s Two high pT b-jets

Background from real high pT lepton pairs (“physics backgrounds”)• Drell-Yan and Z0! ee, (no real ET)• Z0! (real ET too)• WW production (real ET too)

Jet requirement greatly reduces these backgrounds

Background from “fake” leptons too• W + jets, W! e, & jet! fake lepton

Page 34: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 34

Lepton + Jets Signature

High pT lepton: e or

Substantial ET from

Two high pT b-jets

Two high pT light quark jets

Physics background• W + jets

Reduce backgrounds with• kinematic criteria• identifying b jets (b-tags)

Run I results published in CDF Collaboration,T. Affolder et al., Phys. Rev. D 63, 072003 (2001)

Page 35: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 35

Digression: Jet Reconstruction at CDF

Quarks and gluons do not exist as “free” objects (colored)fragment or hadronize into “jets” of particles

Recall results from UA2 in Lecture 1

jet reconstruction get back to the parton (q or g) 4-vectorto compare to theory or reconstruct mass e.g., W! qq0

CDF: uses fixed cone algorithm in - space

Many possible approaches used at e+e- and hadron colliders

follows UA1

Page 36: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 36

CDF Jet - Cone Algorithm

• Start with calorimeter cells – define energy momentum vector– vector points from origin to centroid of cell: (px,py,pz,E), where E = |p|– ET

2 = px2 + py

2

• Select “seed” cells: ETcell > seed threshold (e.g., 1 GeV)

• Form seed “clusters”– Add vectors of all seed cells within R (ranked in ET)– typical values R: 0.4, 0.7, 1.0 top search uses R = 0.4– centroid of cluster determined by ET weighting– changes as seed clusters added - iterate

• After all seeds merged, add in remaining calorimeter cells– require E_T > noise threshold (e.g., 100 MeV)

• Jets defined this way have mass (partons are massless)

see CDF Collaboration F. Abe et al., Phys. Rev. D 45 1448 (1992)

Page 37: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 37

Azimuthal Energy Flow in 2 Jet Events

CDF Collaboration F. Abe et al., Phys. Rev. D 45 1448 (1992)From CDF two jet data

Distribution of calorimeter energyaround jet axes

leading jet has <ET> » 40 GeV

Cone size 0.4, 0.7, 1.0all reasonable

top: R=0.4 optimal for counting jets

leading jet leading jet

away jet

Page 38: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 38

Jet Energy CorrectionsJets formed from “raw”calorimeter energies

Detector Effects

Physics Effects

• nonlinear calorimeter response to low energy hadrons• B field bends low pT particles out of cone (or do not reach Cal)• cracks and transition regions of calorimeter• different response of EM & Had

• extra E from “underlying event” & multiple interactions• fragmentation effects & soft g rad.• and

Calibrate central calorimeter(||<1) in situ with spectrometer

Balance calorimeter responseout to ||=2.4 using dijet data

Check jet energy scalewith vs. jet data

Typical correction: increase raw ET by 30%

Page 39: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 39

CDF Jet Corrections Have Several Levels

Run II: use absolute E correction from Run I

Top analysis usesLevel 5 jets

Page 40: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 40

Focus 1st on Lepton + Jets Channel

• This was the discovery channel in Run I

• Used to measure top production and mass

• Signature is a leptonic W decay & four jets (2 are b’s)

• Jets not all in detector acceptance 3 or 4 jets

• Discovery relied on identifying at least one b jets– B hadron relatively long lived – use secondary vertex tag

– Exploit B semileptonic decays – soft lepton tag (soft ≠ W decay)

• Can also isolate top signal using kinematic criteria– top is heavy – harder more central jets than initial state parton radiation

– neural nets give even better discrimination

Page 41: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 41

W Selection

Start with event sample collected with inclusive high pT lepton trigger

see e.g., CDF Collaboration F. Abe et al.,Phys. Rev. D 50 p. 2966 (1994)

Lepton (e or ) must be isolated

Electron Selection

ET > 20 GeV, ||<1 (central)

Selection criteria based on• Ehad/EEM

• E/p• Shower shape in Calo.• track match with shower max det.• shape in shower max det.

Efficiency: 80%

Muon Selection

pT > 20 GeV/c, ||<1

Selection criteria based on• minimum ionizing in EM and Had• match chambers and track

Efficiency: 90%

ET > 20 GeV Reject dileptons, Z0! e+e-, +-

Page 42: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 42

Do Selected Events Look Like W’s?

Transverse Mass Distributions CDF Collaboration F. Abe et al.,Phys. Rev. D 50 p. 2966 (1994)

From ‘94 top “evidence” PRD, Run II selection very similar

Page 43: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 43

Jet Requirements and HT

Top signal sample: ≥ 3 Jets ET>15 GeV, ||<2.0

mt measurement: require 4th jet ET>8 GeV, ||<2.4

Run II: may add HT>200 GeV

HT ´ ET of lepton, jets, ET

@ this stage tt efficiency is » 8% 40-60 events in 100 pb-1, S:B»1:4

Top is heavy larger HT on average than W+jets background

Jets

HT

Simulation

R=0.4 contains 70% E

Page 44: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 44

Displaced tracks or secondary vertex

Identifying (tagging) b quark Jets

Semileptonic decays:

Not isolated and softer than W! l “soft lepton tag” or SLT

B hadron lifetime ~ 1.5 psecSignificant Lorentz boost measurable displacement

Simulation: top mass = 160 GeV

CDF Collaboration F. Abe et al.,Phys. Rev. D 50 p. 2966 (1994)

pT(b)

displacement intransverse plane

5 mm

Page 45: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 45

Illustration of Displaced Tracks and Vertex

Page 46: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 46

Illustration of Displaced Tracks and Vertex

d

Interaction point(primary vertex)

Secondary Vertex(displaced vertex)

B decay product

Underlying eventB fragmentation product

Jet Axis

d = impact parameter

in plane transverse to beam axis

Page 47: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 47

Definition of Terms

Impact parameter d: distance of closest approach of track to vertex

Primary vertex: pp interaction point

Primary vertex follows Gaussian distribution in x, y, & z

Unless specified otherwise, “impact parameter” meansin the plane transverse to the beam line (xy or rφ)

† at the most narrow point (waist) – transverse size varies with z

Secondary vertex: decay/interaction point displaced from theprimary vertex by a distance that is experimentally measurable.

Page 48: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 48

from J/ (pT>1.5 GeV)with SVXII inner-most layer

Methods of Identifying Long Lived Particles

• Associate Tracks with jety

– count number of significantly displaced tracks: d/d > parameter

• 1st used at Mark II (SLC) for Z0! bb (R. Jacobsen)

– determine probability tracks originated from PV: “jet probability”• developed at LEP (א – Dave Brown) – later used by CDF

– correlations between “d” and “φ” (used by CDF in “top evidence”)

– reconstruct secondary vertex

d should include• uncertainty in track parameters• uncertainty in vertex position

Rely on impact parameter d & error d

Impact parameter significance: d/d

† jet may be calorimeter jet or track based jet found with - algorithm

includes 30mfrom beamspot

Page 49: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 49

Decay Distance in plane transverse to beam axis

Lxy < 0

Lxy > 0

Generic jets: symmetric distribution around 0 in Lxy

b-jets: very asymmetric distribution, biased towards Lxy>0

Jet axis

Page 50: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 50

CDF Displaced Vertex Algorithm (SECVTX)

Page 51: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 51

CDF Top Discovery

CDF Collaboration, F. Abe et al., Phys. Rev. Lett. 74, p. 2626 (1995)

data sample: 67 pb-1

27 tags in 21 W + ≥ 3 jets evtsexp. # of tags from backgnd: 6.7 ± 2.1

b tag eff. 42§5%for ≥ 1 tag/evt

also found excess of SLTand dilepton events

Page 52: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 52

Run II: Preliminary Version of Same Analysis (162 pb-1)

Page 53: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 53

Run II Top Candidate

Page 54: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 54

Run II: Preliminary Version of Same Analysis (162 pb-1)

Dominantsystematicis background:motivates HT

Page 55: Physics of Hadron Colliders Lecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu.

19 May 2004 J. Kroll University of Pennsylvania 55

Run II: Preliminary Version of Same Analysis (162 pb-1)

Dominant systematic still background: but less so