moriond 2001jets at the tevatron1 qcd: approaching true precision or, latest jet results from the...
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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
Moriond 2001 Jets at the TeVatron 2
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
Moriond 2001 Jets at the TeVatron 3
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
Moriond 2001 Jets at the TeVatron 4
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
Moriond 2001 Jets at the TeVatron 5
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
Moriond 2001 Jets at the TeVatron 6
Jet and Event Quantities
Subjet Multiplicity
Underlying event structure
Low ET Multijet studies New !
Moriond 2001 Jets at the TeVatron 7
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
Moriond 2001 Jets at the TeVatron 8
Underlying event structure
Counting charged particles in azimuthal sectors
Improve modeling of underlying event
Moriond 2001 Jets at the TeVatron 9
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.
Moriond 2001 Jets at the TeVatron 10
Low ET Multijet events
Strong pT ordering in DGLAP suppresses “spectator jets”
BFKL has diffusion in log(pT)
Looking also at Jetrad and Herwig
Moriond 2001 Jets at the TeVatron 11
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
Moriond 2001 Jets at the TeVatron 12
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
Moriond 2001 Jets at the TeVatron 13
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)
Moriond 2001 Jets at the TeVatron 14
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
Moriond 2001 Jets at the TeVatron 15
A few words on 2
10 MC simulations of systematic errors
100 trials
The calculations work great,root-diagonal elements alonenot sufficient for plots
Moriond 2001 Jets at the TeVatron 16
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)
Moriond 2001 Jets at the TeVatron 17
Jets PRD #1: CDF’s Run 1b inclusive jet
Has discussion of 2 technique.
Includes comparisons to Run 1a dataD’s run 1b data
Moriond 2001 Jets at the TeVatron 18
Jets PRD #2:
D’s Run 1b jet results
Tour de Force:
1800 central inclusive,dijet mass,dijet angular distribution,630/1800 inclusive ratio
Moriond 2001 Jets at the TeVatron 19
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
Moriond 2001 Jets at the TeVatron 20
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
Moriond 2001 Jets at the TeVatron 21
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
Moriond 2001 Jets at the TeVatron 22
Backup slides
Moriond 2001 Jets at the TeVatron 23
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
Moriond 2001 Jets at the TeVatron 24
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
Moriond 2001 Jets at the TeVatron 26
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
Moriond 2001 Jets at the TeVatron 27
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//
Moriond 2001 Jets at the TeVatron 28
Simulation of Jet Cross Sections
using CTEQ4M
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Moriond 2001 Jets at the TeVatron 29
Backup Slides
Moriond 2001 Jets at the TeVatron 30
NLO QCD Glossary
Parton Distribution Function (PDF) Factorization Scale (f) Renormalization Scale ()
Rsep
f
2R1.3R
Moriond 2001 Jets at the TeVatron 31
Uncertainties in the Theory
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Moriond 2001 Jets at the TeVatron 32
The DCalorimeter
Liquid ArgonUranium absorber
Full coverage to || = 4.2 0.1 x 0.1 segmentation6+ nuclear interaction lengths
Moriond 2001 Jets at the TeVatron 33
Luminosity
1800 GeV:
630 GeV:
%1.6pb92 -1
%2.3pb54.0 -1
essubprocess;00 ppiAipp
iLL
…as determined by World Average
Moriond 2001 Jets at the TeVatron 34
Luminosity
Determined with a fit between 1800 and 546 GeVTitle:
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Moriond 2001 Jets at the TeVatron 35
Total Efficiency Correction
also...Vertex efficiency ~90%
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Moriond 2001 Jets at the TeVatron 36
The MPF method
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jetT
T
TThad
EE
versus
E
nR
cosh
ˆE1
Moriond 2001 Jets at the TeVatron 37
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%
Moriond 2001 Jets at the TeVatron 38
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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Moriond 2001 Jets at the TeVatron 39
Energy Scale Uncertainties
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Moriond 2001 Jets at the TeVatron 40
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
Moriond 2001 Jets at the TeVatron 41
Total Ratio Correlation
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Moriond 2001 Jets at the TeVatron 42
Augmented QCD
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