Moriond 2001Jets at the TeVatron1 QCD: Approaching True Precision or, Latest Jet Results from the TeVatron Experimental Details SubJets and Event Quantities Cross Sections Presented by John Krane Iowa State University

Moriond 2001Jets at the TeVatron2 Changing Paradigms in QCD Inclusion of error estimates in the PDFs Progress toward NNLO predictions More rigorous treatment of experimental errors More consistent E T calculations between experiments covariance matrices jet algorithms workshop calculation of virtual corrections hope for better underlying event

Moriond 2001Jets at the TeVatron3 Jet Definition Cone Definition R =0.7 in  merge/split K T Definition cells/clusters are combined if their relative k T 2 is “small” (D=1.0 or scaling parameter) For subjets, also define “large” (y cut, =10 -3 ) Iteration vs ratcheting 0.5 vs 0.75 Centroid found with 4-vector addition vs Snowmass addition D  uses Ellis and Soper’s definition

Moriond 2001Jets at the TeVatron4 Central Tracking EM Calorimeter Hadronic Calorimeter Muon A-Layer Magnet Muon B&C e  jet  noise Jet Cuts Typical cuts on EM fraction, hotcells, missing E T, vertex position, etc. > 97% efficient > 99% pure

Moriond 2001Jets at the TeVatron5 Jet Energy Corrections Response functions Noise and underlying event “Showering” Resolutions Estimated with dijet balancing or simulation the symmetric part d 2  dE T d  ETET d 2  dE T d  ETET no distinction between jets of different kinds

Moriond 2001Jets at the TeVatron6 Jet and Event Quantities Subjet Multiplicity Underlying event structure Low E T Multijet studies New !

Moriond 2001Jets at the TeVatron Subjet Multiplicity Linear Combination: = f g M g + (1-f g ) M Q Assume M g, M Q independent of √s Measure M at two √s energies and extract the g and Q components Largest uncertainty comes from the gluon fractions in the PDFs Mean Jet Multiplicity Quark Jet FractionGluon Jet Fraction Subjet Multiplicity M D0 Preliminary Coming soon as a PRD no attempt to develop a likelihood function HEWIG prediction =1.86 ± 0.08(stat) Using the k T algorithm

Moriond 2001Jets at the TeVatron8 Underlying event structure Counting charged particles in azimuthal sectors Improve modeling of underlying event

Moriond 2001Jets at the TeVatron9 Low E T Multijet events At high-E T, QCD does quite well. But try counting jets at low-E T …compare to Pythia Each jet’s E T >20 GeV. For 2 jets or more, normalization is off, so correct to >40 GeV spectrum.

Moriond 2001Jets at the TeVatron10 Low E T Multijet events Strong p T ordering in DGLAP suppresses “spectator jets” BFKL has diffusion in log(p T ) Looking also at Jetrad and Herwig

Moriond 2001Jets at the TeVatron11 Cross Sections R32 630/1800 ratio of jet cross sections Forward cross sections Two PRDs K T central inclusive Published! Submitted New !  2 analysis

Moriond 2001Jets at the TeVatron12 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

Moriond 2001Jets at the TeVatron13 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*H T is most robust (As minimum E T threshold climbs, the “hardness” of the event is less well- represented by E T max ?) PRL 86, 1955 (2001)

Moriond 2001Jets at the TeVatron14 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*E T (7%) and 0.25*E T (23%). PDF Variations  f  R Variations

Moriond 2001Jets at the TeVatron15 A few words on  2 10 MC simulations of systematic errors 100 trials The calculations work great, root-diagonal elements alone not sufficient for plots

Moriond 2001Jets at the TeVatron16  d 2  dE T d  (fb/GeV) E T (GeV) Rapidity-dependent Inclusive D  ’s most complete cross section measurement Uncertainty in theory is larger than uncertainty is data! PRL 86, 1707 (2001)

Moriond 2001Jets at the TeVatron17 Jets PRD #1: CDF’s Run 1b inclusive jet Has discussion of  2 technique. Includes comparisons to Run 1a data D  ’s run 1b data

Moriond 2001Jets at the TeVatron18 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 2001Jets at the TeVatron19 K T 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 2001Jets at the TeVatron20 K T Comparison Normalization differs by 20% or more p T dependence D  has an error matrix expect  2 numbers soon “No significant deviations of predictions from data” D  Preliminary

Moriond 2001Jets at the TeVatron21 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 2001Jets at the TeVatron22 Backup slides

Moriond 2001Jets at the TeVatron23 Large H T Sum of jet E T ’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}

Moriond 2001Jets at the TeVatron24 Energy Scale “Offset” : noise, pileup, multiple interactions, underlying event “Response” : observed energy vs. True energy “Showering” : removes edge-effects at the jet cone boundary

Moriond 2001Jets at the TeVatron25 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 2001Jets at the TeVatron26 Cross Section Uncertainties: The Covariance Matrix separate errors into categories based on degree of E T correlation determine change in cross section at each data point from each error repeat for each uncertainty

Moriond 2001Jets at the TeVatron27 Jet Cross Section at 1800 GeV Comparing D  and CDF / /

Moriond 2001Jets at the TeVatron28 Simulation of Jet Cross Sections using CTEQ4M

Moriond 2001Jets at the TeVatron29 Backup Slides

Moriond 2001Jets at the TeVatron30 NLO QCD Glossary Parton Distribution Function (PDF) Factorization Scale (  f ) Renormalization Scale (  ) R sep ff PDF 2R 1.3R

Moriond 2001Jets at the TeVatron31 Uncertainties in the Theory

Moriond 2001Jets at the TeVatron32 The D  Calorimeter Liquid Argon Uranium absorber Full coverage to |  | =  x 0.1 segmentation 6+ nuclear interaction lengths

Moriond 2001Jets at the TeVatron33 Luminosity 1800 GeV: 630 GeV: …as determined by World Average

Moriond 2001Jets at the TeVatron34 Luminosity Determined with a fit between 1800 and 546 GeV

Moriond 2001Jets at the TeVatron35 Total Efficiency Correction also...Vertex efficiency ~90%

Moriond 2001Jets at the TeVatron36 The MPF method

Moriond 2001Jets at the TeVatron37 Other Systematics Jet selection (cuts) Event selection (missing E T cut, vertex cut) 630: < 1% 1800: 1-2% Unsmearing: full covariance (qg fractions are correlated) scaling to dimensionless variables ~ 0.8%

Moriond 2001Jets at the TeVatron38 Energy Scale Uncertainty (A toy Monte Carlo Study) Generate Monte Carlo Jets with appropriate E T spectrum, weight Generate lum, number of interactions, vertex Call energy scale correction to get errors component-by-component

Moriond 2001Jets at the TeVatron39 Energy Scale Uncertainties

Moriond 2001Jets at the TeVatron40 Classifying Uncertainties The error correlations:  =  Completely Correlated no symbol = Uncorrelated (independent)

Moriond 2001Jets at the TeVatron41 Total Ratio Correlation

Moriond 2001Jets at the TeVatron42 Augmented QCD