Title: R
1Inclusive Jet Production _at_ CDF
- Régis Lefèvre
- IFAE Barcelona
- on behalf of the CDF Collaboration
QCD 06 Montpellier, France July 3rd-7th 2006
2The Tevatron in Run II
- Proton-antiproton collisions
- ?s 1.96 TeV
- 36 bunches crossing time 396 ns
- Peak luminosity 1.2 ?1032 cm-2 s-1
- Collecting 20 pb-1 / week
- About 1.6 fb-1 delivered
3CDF
- 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
4Motivations
- 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
5Cone 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)
6The 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)
7Results from ZEUS / D0 Run I
D0 Run I
- Disagreement at low pT
- Suggests Underlying Event not properly
accounted for
8Framework / Related Topics
- Look first at central jets 0.1 lt y lt 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
9Underlying 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
10Energy Flow Inside Jets
- 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)
(1-?)
37 lt pT lt 380 GeV/c
11Calorimeter Response to Jets
- (First set electromagnetic scale using Z ? ee-)
- 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 lt 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
12kT Jets Published Results
D 0.7 0.1 lt y lt 0.7
-
- PYTHIA-Tune A used as nominal
- HERWIG used for uncertainty
Phys. Rev. Lett. 96, 122001 (2006)
13kT Jets vs. D (0.1 lt y lt 0.7)
D 0.5
D 1.0
14Forward 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
15kT Jets Latest Results
- D 0.7
- 5 rapidity regions up to y 2.1
- y lt 0.1
- 0.1 lt y lt 0.7
- 0.7 lt y lt 1.1
- 1.1 lt y lt 1.6
- 1.6 lt y lt 2.1
- ? L 1 fb-1
16kT Jets with 1 fb-1 Data / Theory
17Midpoint Jets with 1 fb-1 Data / Theory
18Conclusion
- 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
19Backup Slides
20The kT Algorithm Step-by-Step
Longitudinally invariant kT algorithm
(Ellis-Soper inclusive mode)
21Bisector Method
0.1 lt y lt 0.7
- ?// ? ISR
- ?PERP ? ISR ? Detector Resolution
- Assuming ISR democratic in ?
- ?D ? (?2PERP - ?2//) / ? 2 ? Detector
Resolution