Jets at the Jets at the TevatronTevatron

B. Paul PadleyB. Paul Padley

Dept of Physics and Dept of Physics and AstronomyAstronomy

Rice UniversityRice University

Exciting TimeExciting Time

Obviously we have entered an era of Obviously we have entered an era of new energy and luminosity.new energy and luminosity.

Clearly the is a great potential to do Clearly the is a great potential to do new and exciting thingsnew and exciting things

And the old stuff even looks new and And the old stuff even looks new and exciting.exciting.

Probing ~10Probing ~10-19-19 m scale m scale

Highest mass di-jet event so far

ET = 666 GeV

= 0.43

Highest mass di-jet event so far(corrected mass = 1364 GeV/c2):

ET = 633 GeV

= -0.19

r-view

D0 Highest Dijet Mass EventD0 Highest Dijet Mass Event

1206 1206 GeV/c2 dijet GeV/c2 dijet mass eventmass event

ClustersClusters

Use Run II cone algorithmUse Run II cone algorithm Combine particles in a R=0.7 coneCombine particles in a R=0.7 cone Use the four vector of every tower as a Use the four vector of every tower as a

seedseed Rerun using the midpoints between pairs Rerun using the midpoints between pairs

of jets as seedsof jets as seeds Overlapping jets merged if the overlap Overlapping jets merged if the overlap

area contains more than 50% of lower Pt area contains more than 50% of lower Pt jet, otherwise particles assigned to nearest jet, otherwise particles assigned to nearest jet.jet.

Cf. Blazey et al. Hep-ex/0005012v2

JetsJets

Both groups are using E-scheme Both groups are using E-scheme recombinationrecombination

2 2

1

( , ) ( , , , )

( ) ( )

1ln

2

tan

J J J i i i ix y z

i J C

J J JT x y

J JJ z

J Jz

JyJJx

P E E p p p

P p p

E py

E p

p

p

p

Cf. Blazey et al. Hep-ex/0005012v2

Inclusive Jet Cross Inclusive Jet Cross SectionSection

Extending Run 1 reach by ~150 GeV Extending Run 1 reach by ~150 GeV

Run II Data shown taken between Feb 2002 and Run II Data shown taken between Feb 2002 and summer 2003summer 2003

(They are planning on new results using Kt (They are planning on new results using Kt algorithm in May)algorithm in May)

Inclusive Jet Cross Inclusive Jet Cross SectionSection

Excitement Excitement about Run 1 about Run 1 high Ehigh ETT excess excess

SM explanation: SM explanation: gluon PDF not gluon PDF not well well constrained at constrained at high xhigh x

Use EKS pQCD

http://zebu.uoregon.edu/~soper/EKSJets/jet.html

Inclusive Jet Cross Inclusive Jet Cross Section RatioSection Ratio

Both plots the same with extra point on the lower

Inclusive Jet Cross Inclusive Jet Cross SectionSection

Notice forward jets

Inclusive Jet Cross Inclusive Jet Cross SectionSection

Inclusive Jet Cross Inclusive Jet Cross SectionSection

JES uncertainty <7% dominant contributor to systematic uncertainties

Dijet Cross SectionDijet Cross Section

Dijet Cross SectionDijet Cross Section

Dijet Dijet DecorrelationsDecorrelations

In leading order pQCD dijets are back to back

Jet 1

Jet 2

Dijet Dijet DecorrelationsDecorrelations

Three jet events in leading order pQCD

As Kt goes to 0, goes to

If Kt is large

Jet 1

Jet 2

Jet 3

Kt

distribution is directly distribution is directly sensitive to QCD higher sensitive to QCD higher order radiation without order radiation without explicitly measuring the explicitly measuring the third jetthird jet

Dijet Dijet DecorrelationsDecorrelations

Decorrelations, Decorrelations, Compare to LOCompare to LO

Decorrelations, Decorrelations, Compare to LOCompare to LO

Same plots as previous page, just spread out for print visibility

Poor fit to data at Poor fit to data at low Pt. low Pt.

At higher Pt’s it At higher Pt’s it gets better, gets better, especially in the especially in the 2.3 to 2.8 regime2.3 to 2.8 regime

Dijet Dijet DecorrelationsDecorrelations

Dijet Dijet DecorrelationsDecorrelations

Pythia Tune A reproduces the data best.

Underlying Event StudiesUnderlying Event Studies

Jet #1 Direction

“Toward”

“Transverse” “Transverse”

“Away”

Jet #2 Direction

Jet #1 Direction

“Toward”

“Transverse” “Transverse”

“Away”

““Back-to-Back”Back-to-Back”((1212>150>150oo,ETj,ETj22/ETj/ETj11>0.8)>0.8)

Transverse Transverse regions are regions are sensitive to sensitive to underlying eventunderlying event

Underlying Event StudiesUnderlying Event Studies

Charged Particle Density: dN/dd

0.1

1.0

10.0

0 30 60 90 120 150 180 210 240 270 300 330 360

(degrees)

Ch

arg

ed

Pa

rtic

le D

en

sit

y

Back-to-Back

Leading Jet

Min-Bias

CDF Preliminarydata uncorrected

Charged Particles (||<1.0, PT>0.5 GeV/c)

30 < ET(jet#1) < 70 GeV

"Transverse" Region

Jet#1

Min-Bias0.25 per unit -

Run 2Run 2

Underlying Event Underlying Event Studies (2)Studies (2)

Shows the Shows the average charged particle densityaverage charged particle density, dN/d, dN/ddd, in the , in the “transverse” region“transverse” region (p(pTT > 0.5 GeV/c, | > 0.5 GeV/c, || < 1) versus E| < 1) versus ETT(jet#1) for (jet#1) for “Leading Jet”“Leading Jet” and and “Back-to-“Back-to-Back”Back” events compared with events compared with PYTHIA Tune APYTHIA Tune A and and HERWIGHERWIG after CDFSIM. after CDFSIM.

"AVE Transverse" Charge Density: dN/dd

0.0

0.2

0.4

0.6

0.8

1.0

0 50 100 150 200 250

ET(jet#1) (GeV)

"Tra

ns

ve

rse

" C

ha

rge

De

ns

ity

CDF Preliminarydata uncorrectedtheory + CDFSIM

1.96 TeV Charged Particles (||<1.0, PT>0.5 GeV/c)

Leading Jet

Back-to-Back

PY Tune A

HW

Current MC with default parameters fail to reproduce data.In Run 1 PYTHIA 6.206 tuned adding multi-parton interactions.

Run 2 data:Run 2 data:

"AVE Transverse" PTsum Density: dPT/dd

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 50 100 150 200 250

ET(jet#1) (GeV)

"Tra

nsv

erse

" P

Tsu

m D

ensi

ty (

GeV

/c)

CDF Preliminarydata uncorrectedtheory + CDFSIM

Charged Particles (||<1.0, PT>0.5 GeV/c)

Back-to-Back

Leading Jet

PY Tune A

HW

1.96 TeV

Underlying Event Underlying Event Studies (3)Studies (3)

PYTHIA tuned (on Run 1 data) reproduces Run 2 data wellHERWIG (with no multi-parton interaction) works only at high ET

j1.

Average charged PTsum densityAverage charged PTsum density, dPT/d, dPT/ddd, in the , in the “transverse” region“transverse” region

(p(pTT > 0.5 GeV/c, | > 0.5 GeV/c, || < 1) versus E| < 1) versus ETT(jet#1) for (jet#1) for “Leading Jet”“Leading Jet” and and ““Back-to-Back-to-Back”Back” events compared with events compared with PYTHIAPYTHIA Tune A and Tune A and HERWIGHERWIG after CDFSIM. after CDFSIM.

ConclusionsConclusions

First results have been shown – no First results have been shown – no surprisessurprises

Highest mass DY events have been Highest mass DY events have been observedobserved

Jet Energy Scale is dominant error in Jet Energy Scale is dominant error in inclusive cross sectionsinclusive cross sections

Pythia Tune A (by Rick Field) on the Pythia Tune A (by Rick Field) on the Run 1 data is reproducing soft data Run 1 data is reproducing soft data well.well.