Jet Studies at CDF Anwar Ahmad Bhatti The Rockefeller University CDF Collaboration DIS03 St. Petersburg Russia April 24,2003 Inclusive Jet Cross Section Di-Jet Mass distribution Jet shape and energy Flow in the event

Jet Cross Section Measurement  Measure parton distribution functions at high  Look for deviations from QCD predictions  Backgrounds for various new physics signals  A step towards more complicated analyses

Results from Run I  In Run I, CDF found that the jet cross section is higher than prediction using PDF at that time (1996).  A global fit by the CTEQ collaboration found that gluon distributions at high x are not constrained by other data. (Direct photon data is not precise enough, both due to theoretical and experimental uncertainties.)  They introduced one more parameter. CDF Run 1b dσ/dpt (nb/GeV) D0 Run I The CTEQ6 set includes, D0 high η (high x, low Q) data. In this fit large gluon density at high x is a natural choice. Jet Transverse Energy (GeV) CTEQ4M CTEQ4HJ MRST (Data-Theory)/Theory Statistical Errors only

Improvements  TeV  Better DAQ/ upgraded trigger, higher statistics.  New plug calorimeter  Better modeling of calorimeter at low Et and shower spreading (work in progress) Transverse Energy of Jet (GeV) Run II/ Run I Theory predicts x2 higher cross section at 400 GeV x5 higher cross section at 600 GeV. CTEQ 6.1 Run II/Run I 0.1< |y|<0.7

Data Set (Feb 2002-Jan 2003)  Luminosity  Central Jet  Event vertex cm  Cleanup using missing and visual scan  Four triggers, use data where trigger >99% efficient. Jet Transverse Energy (GeV) Events/ 10 GeV Good match between triggers in overlap region

Trigger Efficiency Measure trigger efficiency using lower Et threshold trigger Trigger Efficiency

A High Et Jet Event GeV

Jet Clustering and Jet Energy Corrections  Iterative cone clustering with JetClu algorithm R=0.7  Correct calorimeter energy to particle’s energy within a cone radius R  No out-of-cone corrections  Calorimeter scale set to Run I scale based on photon jet balancing results.  corrections to raw cal energy.  Correct for underlying event /multiple interactions calorimeter non-linearity smearing due to resolution.

Comparison with NLO QCD CTEQ6.1 PDFs Reasonable agreement within large uncertainties Cross Section Ratio Data/ CTEQ6.1 Transverse Energy of the jet (GeV)

Comparison with Run I  Higher due to higher 1.8 TeV 1.96 TeV  Systematic errors mostly cancel but RunII jet energy scale uncertainty is dominant.  Reasonable agreement but more work needed to understand the details. Jet Transverse Energy (GeV) Cross Section Ratio

Systematic Uncertainties  Response (Test beam and data)  Raw Energy Scale  Jet Fragmentation (measured from CDF data)  Jet Energy Resolution  Underlying Event Energy  Luminosity Systematic uncertainty dominated by energy scale of calorimeter in Run II. Percent uncertainty in cross section Transverse Energy of Jet (GeV)

Jet Cross Section at large pseudorapidity Determine high x, low PDF’s from CDF data Raw Cross Section

DiJet Mass Spectrum A good place to look for new physics Antoni Munar’s talk April 25, 2:55 pm EW and Physics Beyond SM Session Mass (corrected)= 1364 GeV Run II extend the range by ~300 GeV due to higher cross section at √s =1.96 TeV

Jet Shape and Energy Flow in an Event  Internal structure of jet  Test pQCD/ parton shower models  Hadronization/fragmentation, essential for jet energy determination  Compare with Herwig/ Pythia  Previous (PRL70, 1993) measurement, good agreement with pQCD calculations( ).

Energy Distribution within a Jet (differential) Good agreements with Herwig and Pythia in central region Slightly wider jets in forward region at low Herwig after detector simulationPythia after detector simulation CDF II Preliminary r/R

Energy Distribution within Jet Jets become narrower as their Et increases. Smaller fraction of energy in R=0.4 as η of the jet increases. Ψ(r=0.4)/Ψ(r=0.7) Jet Transverse Energy (GeV)

Energy Flow in an event Reconstruct jet using JetClu. Define Measure transverse energy along φ direction within Δη for various separations between two leading jets. Compare with Herwig prediction after detector simulation. Good agreement between data and Herwig (Parton Shower+ Underlying Event) CDFII Preliminary Detector Level

Conclusions  The Run II inclusive jet cross section extends to jet GeV.  The cross section is consistent with NLO QCD predictions  The dijet mass spectrum extends to GeV.  The energy distribution within a jet measured for GeV.  The jet shape and energy flow in event is well modeled by Herwig Monte Carlo and Pythia Monte Carlo.  We are working on Angular Distributions Inclusive jet cross section to higher η Jet Cross section using MidPoint and kt clustering b-jet cross section W/Z + Jet cross sections Photon Production  Many and more accurate results in near future.