Jets at the Tevatron

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Jets at the Tevatron. B. Paul Padley Dept of Physics and Astronomy Rice University. Exciting Time. Obviously we have entered an era of new energy and luminosity. Clearly the is a great potential to do new and exciting things And the old stuff even looks new and exciting.

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### Jets at the Tevatron

Dept of Physics and Astronomy

Rice University

Exciting Time
• Obviously we have entered an era of new energy and luminosity.
• Clearly the is a great potential to do new and exciting things
• And the old stuff even looks new and exciting.
• Probing ~10-19 m scale
Highest mass di-jet event so far

Highest mass di-jet event so far

(corrected mass = 1364 GeV/c2):

r-fview

ET = 666 GeV

h= 0.43

ET = 633 GeV

h= -0.19

D0 Highest Dijet Mass Event

1206 GeV/c2 dijet mass event

Clusters
• Use Run II cone algorithm
• Combine particles in a R=0.7 cone
• Use the four vector of every tower as a seed
• Rerun using the midpoints between pairs of jets as seeds
• Overlapping jets merged if the overlap area contains more than 50% of lower Pt jet, otherwise particles assigned to nearest jet.

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

Jets

Both groups are using E-scheme recombination

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

Inclusive Jet Cross Section

Extending Run 1 reach by ~150 GeV

Run II Data shown taken between Feb 2002 and summer 2003

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

Inclusive Jet Cross Section
• Excitement about Run 1 high ET excess
• SM explanation: gluon PDF not well constrained at high x

Use EKS pQCD

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

Inclusive Jet Cross Section Ratio

Both plots the same with extra point on the lower

Inclusive Jet Cross Section

Notice forward jets

Inclusive Jet Cross Section

JES uncertainty <7% dominant contributor to systematic uncertainties

Dijet Df Decorrelations

Jet 1

In leading order pQCD dijets are back to back

Df=p

Jet 2

Dijet Df Decorrelations

Three jet events in leading order pQCD

As Kt goes to 0, Df goes to p

If Kt is large Df<<p

Jet 1

Jet 3

Df<p

Kt

Jet 2

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

Df Decorrelations, Compare to LO

Poor fit to data at low Pt.

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

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

Dijet Df Decorrelations

Pythia Tune A reproduces the data best.

Underlying Event Studies

Transverse regions are sensitive to underlying event

“Back-to-Back”

(Df12>150o,ETj2/ETj1>0.8)

Underlying Event Studies

Run 2

Min-Bias

0.25 per unit h-f

• Direction of leading jet to define 3 fregions
Underlying Event Studies (2)

Run 2 data:

Current MC with default parameters fail to reproduce data.

In Run 1 PYTHIA 6.206 tuned adding multi-parton interactions.

• Shows the average charged particle density, dN/dhdf, in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events compared with PYTHIA Tune A and HERWIG after CDFSIM.
Underlying Event Studies (3)

PYTHIA tuned (on Run 1 data) reproduces Run 2 data well

HERWIG (with no multi-parton interaction) works only at high ETj1.

• Average charged PTsum density, dPT/dhdf, in the “transverse” region

(pT > 0.5 GeV/c, |h| < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events compared with PYTHIA Tune A and HERWIG after CDFSIM.

Conclusions
• First results have been shown – no surprises
• Highest mass DY events have been observed
• Jet Energy Scale is dominant error in inclusive cross sections
• Pythia Tune A (by Rick Field) on the Run 1 data is reproducing soft data well.