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Jet Studies at CDF

This study at CDF Collaboration delves into inclusive jet cross section, di-jet mass distribution, and jet shape and energy flow in events. The findings show deviations from QCD predictions and investigate new physics signals. With improvements in data acquisition and analysis techniques, the research provides valuable insights into parton distribution functions, gluon distributions, and jet energy corrections.

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Jet Studies at CDF

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  1. 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

  2. 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

  3. Results from Run I CTEQ4M • 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. Statistical Errors only CTEQ4HJ (Data-Theory)/Theory MRST Jet Transverse Energy (GeV) 100 10 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. CDF Run 1b D0 Run I dσ/dpt (nb/GeV) 500

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

  5. 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. Events/ 10 GeV Jet Transverse Energy (GeV) Good match between triggers in overlap region

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

  7. A High Et Jet Event GeV GeV

  8. 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.

  9. Comparison with NLO QCDCTEQ6.1 PDFs Cross Section Ratio Data/ CTEQ6.1 Transverse Energy of the jet (GeV) Reasonable agreement within large uncertainties

  10. 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. Cross Section Ratio Jet Transverse Energy (GeV)

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

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

  13. 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 Run II extend the range by ~300 GeV due to higher cross section at √s =1.96 TeV Mass (corrected)= 1364 GeV

  14. 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( ).

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

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

  17. Energy Flow in an event Detector Level • 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. CDFII Preliminary Good agreement between data and Herwig (Parton Shower+ Underlying Event)

  18. 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.

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