Régis LefèvreAnalysis done with Mario Martínez and Olga Norniella
IFAE Barcelona
Inclusive Jet Production using the kT Algorithm at CDF
IMFP2006XXXIV International Meeting
on Fundamental Physics
April 2nd-7th 2006, Madrid, Spain
HRPN-CT-2002-00292
E.U. ResearchTraining Network
Probe for New Physics
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 2
• 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
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 3
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 – New results based on 1 fb-1
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 4
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 order of magnitudes
• Tail sensitive to New Physics– Probing distances ~ 10-19 m
• PDFs at high Q2 & high x
• Production enhanced at high pT
thanks to new s
Run I CDF Inclusive Jet Data(Statistical Errors Only)JetClu RCONE=0.7 0.1<||<0.7R=F=ET /2 RSEP=1.3
CTEQ4M PDFsCTEQ4HJ PDFs
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 5
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 RSEP
to emulate experimental merging/splitting• Arbitrary parameter RSEP: prescription RSEP = 1.3
(based on parton level approximate arguments)
below threshold(no jets)
above threshold(1 jet)
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 6
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
2
222
D
ÄR)p,(pmind jT,iT,ij =
2iT,ii pd =
– 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 ID0 Run I
Disagreement at low pT
Suggests Underlying Event not properly accounted for
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 8
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 hadron level– Parton level pQCD calculation corrected
for the Underlying Event and Hadronization •Requires a Monte-Carlo generator able to
reproduce the Underlying Event
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 9
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
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 10
Energy Flow Inside Jets
(1-)
∑=jets T
T
jets R)(0,P
r)(0,P
N
1Ø(r)
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
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 11
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 %
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 12
Theoretical Predictions
• NLO pQCD: JETRAD
– Scale: R = F = max (PTJET) / 2
– PDFs: CTEQ6.1M package
– Main uncertainty comes from PDFs
•Gluon PDF at high x
• CHAD = parton-to-hadron correction factor– Accounts for non perturbative contributions
•Underlying Event (U.E.)
•Hadronization
– PYTHIA-Tune A used as nominal
•HERWIG used for uncertainty
(parton level no U.E.)
(hadron level with U.E.)CHAD =
PDF uncertainty
CHAD
D=0.7 and 0.1 < |y| < 0.7
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 13
Published Results
Phys. Rev. Lett. 96 122001 (2006)
D = 0.70.1 < |y| < 0.7
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 14
kT Jets vs. D (0.1 < |y| < 0.7)
D = 0.5 D = 1.0
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 15
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
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 16
New 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
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 17
Data / Theory
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 18
Conclusion
• Good agreement with NLO
– Stringent test of pQCD over ~ 8 orders of magnitude
•pT reach extended by ~ 150 GeV/c with respect to Run I
• Careful treatment of non perturbative effects
– Underlying Event well under control
• To be used in future PDF global fits in orderto better constrain the gluon PDF at high x
– Forward jets essentials
• Prospect
– cos * vs. dijet invariant mass
•Limit on contact interactions
Backup Slides
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 20
kT Algorithm Step-by-Step
jet
jet
jet
jet jet
jet jet
jet
2
222
D
ÄR)p,(pmind jT,iT,ij =
2iT,ii pd =
Longitudinally invariant kT algorithm (Ellis-Soper inclusive mode)
Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain 21
PT//
PTPERP
PERP axis
// axis (bisector)
Transverse Plan
PTJET2
PTJET1
Bisector Method
// ISR
PERP ISR Detector Resolution
• Assuming ISR democratic in D = (2
PERP - 2//) / 2 Detector Resolution
0.1 < |y| < 0.7