Jet Studies at CDF

Anwar Ahmad BhattiThe Rockefeller University

CDF CollaborationDIS03 St. Petersburg Russia

April 24,2003

• Inclusive Jet Cross Section• Di-Jet Mass distribution• Jet shape and energy Flow in the event

Jet Cross Section Measurement

Measure parton distribution functions at high Look for deviations from QCD predictions Backgrounds for various new physics signals A step towards more complicated analyses

2( , )x q

Results from Run I In Run I, CDF found that the jet cross

section is higher than prediction using PDF at that time (1996).

A global fit by the CTEQ collaboration found that gluon distributions at high x are not constrained by other data. (Direct photon data is not precise enough, both due to theoretical and experimental uncertainties.)

They introduced one more parameter.

CDF Run 1b

dσ/d

pt (

nb/G

eV)

D0 Run IThe CTEQ6 set includes, D0 high η (high x, low Q) data. In this fit large gluon density at high x is a natural choice.

Jet Transverse Energy (GeV)

CTEQ4M

CTEQ4HJ

MRST

(Dat

a-T

heor

y)/T

heor

y

10100

610 710 500

Statistical Errors only

Improvements

TeV

Better DAQ/ upgraded trigger, higher statistics.

New plug calorimeter

Better modeling of

calorimeter at low Et and shower spreading (work

in progress)

1.96s

Transverse Energy of Jet (GeV)

1.1 | | 3.6

Ru

n II

/ Run

ITheory predicts x2 higher cross section at 400 GeV

x5 higher cross section at 600 GeV.

CTEQ 6.1 Run II/Run I 0.1< |y|<0.7

Data Set (Feb 2002-Jan 2003) Luminosity

Central Jet

Event vertex

cmCleanup using missing

and visual scan Four triggers, use

data where trigger >99% efficient.

185L pb

0.1 | | 0.7d

| | 60z

TEJet Transverse Energy (GeV)

Eve

nts/

10

GeV

Good match between triggers in overlap region

Trigger Efficiency

Measure trigger efficiency using lower Et threshold trigger

T

rigge

r E

ffic

ienc

y

A High Et Jet Event

569TE GeV 608TE GeV

Jet Clustering and Jet Energy Corrections

Iterative cone clustering with JetClu algorithm R=0.7 Correct calorimeter energy to particle’s energy within a

cone radius R No out-of-cone corrections Calorimeter scale set to Run I scale based on photon

jet balancing results. corrections to raw cal energy.Correct for

underlying event /multiple interactions

calorimeter non-linearity

smearing due to resolution.

(5 5)%

Comparison with NLO QCDCTEQ6.1 PDFs / 2J

TE

Reasonable agreement within large uncertainties

Cro

ss S

ectio

n R

atio

D

ata/

CT

EQ

6.1

Transverse Energy of the jet (GeV)

Comparison with Run I

Higher due to higher

1.8 TeV 1.96 TeV

Systematic errors mostly cancel but RunII jet energy scale uncertainty is dominant.

Reasonable agreement

but more work needed to

understand the details.

s

Jet Transverse Energy (GeV)

( / )II I

Cro

ss S

ectio

n R

atio

Systematic Uncertainties Response

(Test beam and data)Raw Energy ScaleJet Fragmentation (measured

from CDF data) Jet Energy ResolutionUnderlying Event Energy Luminosity

0/

pp

6%

Systematic uncertainty dominated by energy scale of calorimeter in Run II.

Per

cent

unc

erta

inty

in c

ross

sec

tion

Transverse Energy of Jet (GeV)

Jet Cross Section at large pseudorapidity

Determine high x, low PDF’s from CDF data2q

Raw Cross Section

DiJet Mass Spectrum

* Jet1,2| cos | 2 / 3,| | 2.0 2 2

1 2 1 2( ) (P P )M E E ����������������������������

A good place to look for new physicsAntoni Munar’s talk April 25, 2:55 pm

EW and Physics Beyond SM Session

Mass (corrected)= 1364 GeV

Run II extend the range by ~300 GeV due to higher cross section at √s =1.96 TeV

Jet Shape and Energy Flow in an Event

Internal structure of jet Test pQCD/ parton shower

modelsHadronization/fragmentation,

essential for jet energy determination

Compare with Herwig/ Pythia

Previous (PRL70, 1993) measurement, good agreement with pQCD calculations( ).

3s1.3sepR

Energy Distribution within a Jet (differential)

Good agreements with Herwig and Pythia in central region Slightly wider jets in forward region at low TE

Herwig after detector simulation Pythia after detector simulation

CDF II Preliminary r/R

Energy Distribution within Jet

Jets become narrower as their Et increases.Smaller fraction of energy in R=0.4 as η of the jet increases.

Ψ(r

=0.

4)/Ψ

(r=

0.7)

Jet Transverse Energy (GeV)

Energy Flow in an event

•Reconstruct jet using JetClu.• Define

• Measure transverse energy

along φ direction within Δη for various separations between two leading jets.•Compare with Herwig predictionafter detector simulation.

0Jet

Good agreement between data and Herwig (Parton Shower+ Underlying Event)

Jet

1/

/(G

eV/b

in)

TNdE

d

CDFII Preliminary

Detector Level30GeVJetTE

ConclusionsThe Run II inclusive jet cross section extends to jet GeV.The cross section is consistent with NLO QCD predictions The dijet mass spectrum extends to GeV.The energy distribution within a jet measured for GeV.The jet shape and energy flow in event is well modeled by Herwig

Monte Carlo and Pythia Monte Carlo. We are working on Angular Distributions Inclusive jet cross section to higher η Jet Cross section using MidPoint and kt clustering b-jet cross section W/Z + Jet cross sections Photon Production Many and more accurate results in near future.

550TE

30 130JetTE

1364JJM