Moriond 2001Jets at the TeVatron1 QCD: Approaching True Precision or, Latest Jet Results from the...

Moriond 2001 Jets at the TeVatron 1

QCD: Approaching True Precisionor, Latest Jet Results from the TeVatron

Experimental Details

SubJets and Event Quantities

Cross Sections

Presented by John Krane

Iowa State University


Changing Paradigms in QCD

Inclusion of error estimates in the PDFs

Progress toward NNLO predictions

More rigorous treatment of experimental errors

More consistent ET calculations between experiments

covariancematrices

jet algorithmsworkshop

calculation of virtual corrections

hope for better underlying event


Jet Definition

Cone DefinitionR=0.7 in merge/split

KT Definition

cells/clusters are combined if their relative kT

2 is “small”(D=1.0 or 0.5 -- scaling parameter)

For subjets, also define “large”

(ycut, =10-3)

2

2

222 ),min(

Ti

ii

ijT

jT

iij

Ed

DEEd

R

Iteration vs ratcheting

0.5 vs 0.75Centroid found with4-vector addition vsSnowmass addition

D uses Ellis and Soper’s definition


Central Tracking

EM Calorimeter

HadronicCalorimeter

Muon A-Layer

Magnet

Muon B&C

e jet noise

Jet Cuts

Typical cuts on EM fraction, hotcells, missing ET, vertex position, etc.

> 97% efficient

> 99% pure


Jet Energy Corrections

Response functions Noise and underlying event “Showering”

ResolutionsEstimated with dijet balancing or simulation

the symmetric part

d2dET d

ET

d2dET d

ET

no distinction between jetsof different kinds


Jet and Event Quantities

Subjet Multiplicity

Underlying event structure

Low ET Multijet studies New !


1 2 3 4

0.5

0.4

0.3

0.2

0.1

Subjet Multiplicity

Linear Combination:

<M> = fg Mg + (1-fg) MQ

Assume Mg, MQ independent of √s

Measure M at two √s energies andextract the g and Q components

Largest uncertainty comes fromthe gluon fractions in the PDFs

Mean Jet Multiplicity

Quark Jet FractionGluon Jet Fraction

jetsjets dM

dN

N

1

Subjet Multiplicity M

D0 Preliminary

Coming soon as a PRD

no attempt to developa likelihood function

1

1

q

g

M

MR

(sys) 0.19

0.23(stat) 04.091.1 R

HEWIG prediction =1.86±0.08(stat)

Using the kT algorithm


Underlying event structure

Counting charged particles in azimuthal sectors

Improve modeling of underlying event


Low ET Multijet events

At high-ET, QCD does quite well.

But try counting jets at low-ET…compare to Pythia

Each jet’s ET>20 GeV.

For 2 jets or more, normalization is off, so correct to >40 GeV

spectrum.


Low ET Multijet events

Strong pT ordering in DGLAP suppresses “spectator jets”

BFKL has diffusion in log(pT)

Looking also at Jetrad and Herwig


Cross Sections

R32 630/1800 ratio of jet cross sections Forward cross sections

Two PRDs

KT central inclusive

T

smearTT

Eversus

CEL

N

ddE

d

2

Published!

Published!

Published!

Submitted

New !

2 a

nalys

is


Inclusive R32

A study of soft jet emission rate

Ratios exploit error correlations

We observe lack of PDF sensitivity

Investigate R scale sensitivity with Jetrad

TJets 2

Jets 3 Hσ

σvs


Inclusive R32

several formulae for R

R not always same for jets in the same event (yet agreement not improved)

single-scales seem better than mixed-scales,

0.3*HT is most robust

(As minimum ET threshold climbs, the “hardness” of the event is less well-represented by ET

max?)

PRL 86, 1955 (2001)


Inclusive Ratio

Published yesterday in PRL

2 probabilities fall between 30% and 60%

D has tried a “normalization-only” test, which yields generally poor agreement (<1%), except for 2*ET (7%) and 0.25*ET (23%).

22

23

s

Exversus

ddE

dE TT

T

T

PDF Variations

fR Variations

1800

630


A few words on 2

10 MC simulations of systematic errors

100 trials

The calculations work great,root-diagonal elements alonenot sufficient for plots


d2 d

ET

d

(fb

/GeV

)

ET (GeV)

Rapidity-dependent Inclusive

D’s most complete cross section measurement

Uncertainty in theory is larger than uncertainty is data!

PDF 2 2dof ProbCTEQ3M 121.56 1.35 0.01CTEQ4M 92.46 1.03 0.41CTEQ4HJ 59.38 0.66 0.99MRST 113.78 1.26 0.05MRSTgD 155.52 1.73 <0.01MRSTgU 85.09 0.95 0.63

PRL 86, 1707 (2001)


Jets PRD #1: CDF’s Run 1b inclusive jet

Has discussion of 2 technique.

Includes comparisons to Run 1a dataD’s run 1b data


Jets PRD #2:

D’s Run 1b jet results

Tour de Force:

1800 central inclusive,dijet mass,dijet angular distribution,630/1800 inclusive ratio


KT Inclusive Jet Cross Section

-0.5 < < 0.5

D = 1.0

Predictions IR and UV safe

Merging behavior well-defined for both exp. and theory

D Preliminary


KT Comparison

Normalization differs by 20% or more

pT dependence

D has an error matrix expect 2 numbers soon

“No significant deviations of predictions from data”

D Preliminary


Summary

TeVatron stopped running in 1996 but several results are still in the queue

Jet substructure Event structure Cross sections

Growing sophistication in results

Greater consistency between experiments Error matrices Better corrections


Backup slides


Large HT

Sum of jet ET’s > 500 GeV

Shape of the cross section limits compositness scale

Limits on Quark Compositeness from High Energy Jets in pbarp Collisions at1800 GeV

Phys. Rev. D Rapid Comm. {62} 031101 2000


Energy Scale

“Offset” : noise, pileup, multiple interactions, underlying event

“Response” : observed energy vs. True energy

“Showering” : removes edge-effects at the jet cone boundary

SR

OEE

measT

T

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Finite jet energy resolution has the effect of inflating the cross section, especially where the

cross section is steepest.

The correction (‘unsmearing’) is determined with dijet asymmetry measurements.

Observed

Cross

Section

Jet Resolution and Smearing Effects


Cross Section Uncertainties: The Covariance Matrix

separate errors into categories based on degree of ET correlation

determine change in cross section at each data point from each error

repeat for each uncertainty

jj

ii

ijij xx

xx

V

correlated

correlated

correlated

0

1,1

1

n Correlatio

un

partially

completely


Jet Cross Section at 1800 GeV

Comparing D and CDF

2 prob. 2 prob.63.2 0.002% 24.7 42.2%

DO Error Only DO and CDF Errors//


Simulation of Jet Cross Sections

using CTEQ4M

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Backup Slides


NLO QCD Glossary

Parton Distribution Function (PDF) Factorization Scale (f) Renormalization Scale ()

Rsep

f

PDF

2R1.3R


Uncertainties in the Theory

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The DCalorimeter

Liquid ArgonUranium absorber

Full coverage to || = 4.2 0.1 x 0.1 segmentation6+ nuclear interaction lengths


Luminosity

1800 GeV:

630 GeV:

%1.6pb92 -1

%2.3pb54.0 -1

essubprocess;00 ppiAipp

iLL

…as determined by World Average


Luminosity

Determined with a fit between 1800 and 546 GeVTitle:

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Total Efficiency Correction

also...Vertex efficiency ~90%

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The MPF method

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jetT

T

TThad

EE

versus

E

nR

cosh

ˆE1


Other Systematics

Jet selection (cuts) Event selection (missing ET cut, vertex cut)

630: < 1% 1800: 1-2%

Unsmearing: full covariance (qg fractions are correlated)

scaling to dimensionless variables ~ 0.8%


Energy Scale Uncertainty(A toy Monte Carlo Study)

Generate Monte Carlo Jets with appropriate ET spectrum, weight Generate lum, number of interactions, vertex Call energy scale correction to get errors component-by-component

b

jTb

jT

ja

iTa

iT

iabijij x

x

Rx

x

RC

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Energy Scale Uncertainties

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Classifying Uncertainties

The error correlations:

=Completely Correlated

no symbol = Uncorrelated (independent)

Error Correlation in Ös energy Jet E

Energy ScaleZsp error sys

response fit partiallyout-of-cone

response background sys bias

MPF accept underlying event cryostat match

Luminosity partially Event cuts Selection cutsResolution fits quark/gluon fractions closureUnsmearing fits filter match Et**3


Total Ratio Correlation

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Augmented QCD

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Moriond 2001Jets at the TeVatron1 QCD: Approaching True Precision or, Latest Jet Results from the...

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