# Presentation: 253744

## Régis Lefèvre
IFAE Barcelona
on behalf of the CDF Collaboration

*IFAE Barcelona*
*on behalf of the CDF Collaboration*

- Inclusive Jet Production @ CDF

- QCD 06
*Montpellier, France*
* **July 3**rd**-7**th** 2006*

##  Proton-antiproton collisions
 s = 1.96 TeV
 36 bunches: crossing time = 396 ns 
 Peak luminosity ~ 1.2 1032 cm-2 s-1

-  Proton-antiproton collisions
-  s = 1.96 TeV
-  36 bunches: crossing time = 396 ns
-  Peak luminosity ~ 1.2 1032 cm-2 s-1

- The Tevatron in Run II

-  Collecting ~ 20 pb-1 / week
-  About 1.6 fb-1 delivered

## CDF

-  Highly upgraded for Run II
-  New silicon tracking
-  New drift chamber
-  Upgraded muon chambers
-  New plug calorimeters
-  New TOF

-  Data taking efficiency ~ 85 %
-  About 1.3 fb-1 on tape
-  Latest results based on 1 fb-1

## Motivations

- Legacy from Run I
- Great interest on apparent excess at high ET
- SM explanation
- Gluon PDF increased at high x
- New PDFs from global fit include CDF and D0 jet data from Run I (CTEQ6, MRST2001)

- Stringent test of pQCD
- Over ~ 8 orders of magnitude
- Tail sensitive to New Physics
- Probing distances ~ 10-19 m
- PDFs at high Q2 & high x
- Production enhanced at high pTthanks to new s

## Cone Jet Algorithms and pQCD

- Infrared and Collinear Safety
- Fixed order pQCD contains not fully cancelled infrared divergences
- Inclusive jet cross section affected at NNLO
- Run I Cone Algorithm: JetClu
- Neither infrared nor collinear safe
- Run II Cone Algorithm: Midpoint
- Uses midpoints between pairs of proto-jets as additional seeds
-   Infrared and collinear safety restored
- Merging/Splitting
- NLO pQCD uses larger cone radius  R’ = R  RSEPto emulate experimental merging/splitting
- Arbitrary parameter RSEP: prescription  RSEP = 1.3 (based on parton level approximate arguments)

## The kT Algorithm

- Inclusive kT algorithm
- Merging pairs of nearby particles in order of increasing relative pT
* *
- D parameter controls merging termination and characterizes size of resulting jets
- pT classification inspired by pQCD gluon emissions
- Infrared and Collinear safeto all orders in pQCD
- No merging/splitting
- No RSEP issue comparing to pQCD

- Successfully used at LEP and HERA
- Relatively new in hadron-hadron collider
- More difficult environment
-  Underlying Event
-  Multiple Interactions per crossing (MI)

## Results from ZEUS / D0 Run I

- D0 Run I

- Disagreement at low pT
-  Suggests Underlying Event  not properly accounted for

## Framework / Related Topics

- Look first at central jets: 0.1 < |y| < 0.7
- Where calorimeter simulation is best
- Use D = 0.5, 0.7 and 1.0
- To make sure that Underlying Event and MI contributions are well under control
- Data fully corrected to particle level
- Requires a good simulation of the detector
- Monte-Carlo generator should be able to reproduce the Jet Shapes
- Jet fragmentation and parton cascades
- NLO pQCD corrected to particle level
- Parton level pQCD calculation correctedfor the Underlying Event and Hadronization
- Requires a Monte-Carlo generator able to   reproduce the Underlying Event

## Underlying Event

- Everything but the hard scattering process
- Initial state soft radiations
- Beam-beam remnants
- Multiple Parton Interactions (MPI)
- Studied in the transverse region
- Leading jet sample
- Back-to-back sample

## Energy Flow Inside Jets

**(1-********)**

-   Jet shapes governed by multi-gluon emission from primary parton
- Test of parton shower models
- Sensitive to underlying event structure
- Sensitive to quark and gluon mixture in the final state

- Phys. Rev. D 71, 112002 (2005)

- 37 < pT < 380 GeV/c

## Calorimeter Response to Jets

- (First set electromagnetic scale using Z  e+e-)
- Absolute jet energy scale
- E/p of isolated tracks used to tune the showering simulation (G-Flash)
- Residual discrepancies taken as systematic errors
- Induced uncertainty on jet energy scale between 1 and 3%
- Reasonable simulation of the pT spectrum of the particles within a jet by PYTHIA and HERWIG fragmentation models (fundamental as non-compensated calorimeters)
- Induced difference on jet energy scale < 1%
- Photon-jet balance
- Data and Simulation agree at 1% to 2% level
- Non uniformity versus 
- Dijet balance
- Relative response known to 0.5% level
- Resolution
- Bisector method
- Jet energy resolutions known within relative uncertainties of few %

## kT Jets: Published Results

- Phys. Rev. Lett. 96, 122001 (2006)

- D = 0.7    0.1 < |y| < 0.7

- PYTHIA-Tune A used as nominal
- HERWIG used for uncertainty

## kT Jets vs. D   (0.1 < |y| < 0.7)

- D = 0.5

- D = 1.0

## Forward Jets

- Essentials to pin down PDFs vs. eventual New Physicsat higher Q2 in central region
- DGLAP gives Q2 evolution
- Expend x range toward low x

- High-x

- Low-x

- “Rutherford type” parton backscattering

## kT Jets: Latest Results

- D = 0.7
- 5 rapidity regions up to |y| = 2.1
- |y| < 0.1
- 0.1 < |y| < 0.7
- 0.7 < |y| < 1.1
- 1.1 < |y| < 1.6
- 1.6 < |y| < 2.1
-  L ~ 1 fb-1

## kT Jets with 1 fb-1: Data / Theory

## Midpoint Jets with 1 fb-1: Data / Theory

## Conclusion

- Inclusive jet production measured with both kT and Midpoint
- Both measurements based on ~ 1 fb-1
- 5 rapidity ranges, up to |y| = 2.1
- Careful treatment of non perturbative effects
- Underlying Event well under control
- Good agreement with NLO
- Stringent test of pQCD over ~ 8 orders of magnitude
- For central jets, pT reach extended by ~ 150 GeV/c with respect to Run I
- To be used in future PDF global fits in orderto better constrain the gluon PDF at high x
- Forward jets essentials

## Backup Slides

## The kT Algorithm Step-by-Step

- Longitudinally invariant kT algorithm (Ellis-Soper inclusive mode)

## Bisector Method

- //   ISR
- PERP  ISR  Detector Resolution
- Assuming ISR democratic in 
-    D  =  (2PERP - 2//) /  2  Detector Resolution

- 0.1 < |y| < 0.7