Inclusive Jet Cross Section Jet Energy Corrections. Anwar Ahmad Bhatti DOE Meeting December 2, 2004. QCD and Jet Physics. All production processes are “QCD related” Optimal understanding is basic for all analyses: - Main parameters (ex: gluon PDFs in high x)
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Anwar Ahmad Bhatti
December 2, 2004
Optimal understanding is basic for all analyses:
- Main parameters (ex: gluon PDFs in high x)
- Non perturbative regime (ex: underlying event studies)
- Studies of specific processes where QCD is important
Probe higher energy scales:
- Precise test of perturbative QCD at NLO
- Look for deviations due to new physics
Run I studies were at 10-20%. Aim to improve them to 5%
a) Requires better understanding of relation between experimental measurements and theory (NLO QCD) predictions, kinematic variables clustering, etc.
b) Non-perturbative corrections, underlying events, hadronization
c) Jet energy scale, but improvements limited by detector, jet fragmentation
Run I with CTEQ6.1
CDF Run II
Add seed at middle of two clusters to remove infra red/collinear singularities
Less detector dependence at clustering stage.
Different/better kinematic variables (4-vector and rapidity, instead of Et and η )
New method to correct for energy scale and smearing
Data Corrected to hadrons
Data Corrected to partons
Pt of the Jet (GeV)
Same trend in PYTHIA and HERWIG
The comparison is not fair as data is not corrected for underlying event .
Dynamical Likelihood Method
b-tagging, lepton+4 jets, 162 pb-1
22 events 4 background
(Anwar, Florencia Canelli, Tommaso Dorigo)
a) generic, b-jet corrections
b ) improving di-jet mass resolution geared for dijet/b\bar b resonances.
a) single particle response, measured in data (test beam) and used by simulation
b) particle spectrum in the jets.
Use photon-jet and Z-jet as a cross check.
1. η-dependent corrections, scale all jets in the event to equivalent jets in central calorimeter. (Ken Hatakeyama will talk about it.)
2. Subtract energy from additional p\bar p interactions
3. Correct calorimeter-level jets energy to hadron-level jets for central calorimeter non-linearity.
4. Subtract “underlying event”
5. Add energy outside the clustering cone to recover parton energy.
Hadron Momentum (GeV)
Jet 20,50,70, 100
Tracks in cone R=0.7 around calorimeter jet axis
No tracking efficiency corrections
Fraction of Jet Energy
Fraction of Jet Pt carried by particles
With Pt<400 MeV
Track Pt Max (GeV)
A large fraction of jet energy is carried by low Pt particles
Cal-Pt distributions for fixed Had-Pt Jets
Number of Events
Em Objects agree to 1%
Very good agreement up to 20 GeV.
For p> 20 relies on 1990 test beam. Test beam uncertainty ~2%. Not easy to check with data.
It affects higher Pt jets.
Measurement limited to central 36% of the tower. Need to check φ/η crack simulation further.
0 < p < 12 GeV 2%
12 < p < 20 GeV 3%
p> 20 GeV 4%
After background subtraction
Track momentum (GeV)
π0, photon, electron E/p=1.0
Charged particles using Soon’s E/p curve on page 11.
0 < p < 12 GeV 2 %
5 < p > 20 GeV 3 %
p > 20 GeV 4 %
(Run I-Run II understood to ~2%,
1990 Test Beam 2%, CHA response)
Photon/π0/electrons <1%, ignore.
p<15 GeV 5% difference between in situ calibration and test beam
p>15 GeV 2% test beam calibration
Change in Jet Energy scale
Loss (ΣPt- ΣPt●Response(p))/PtCalJet
Compare energy loss in calorimeter between in data and MC
Pythia Tune A 00,…500
Pythia “loss” 1% lower for Pt<250 GeV
Correcting back to parent parton
Compare energy just outside the cone in data/Pythia/MC
W+Jet data HERWIG MC
Hard Δφ cuts/DiJet background not important/Quarks/gluons
New method: Compare fully corrected jet with photon
Jet Isolation Cut , mainly gluons
Reorganization of jet corrections group, di-jet mass, zb\bar b groups
E/p measurement/modeling <2% (10 GeV) to 2.6% (600 GeV)
Fragmentation (need further studies/HERWIG) ~1-2%