R - PowerPoint PPT Presentation

1 / 21
About This Presentation
Title:

R

Description:

Probe for New Physics. R gis Lef vre, QCD 06, July 3rd 2006, Montpellier, ... 21. PERP axis // axis (bisector) Transverse Plan. PTJET2. PTJET1. Bisector Method ... – PowerPoint PPT presentation

Number of Views:20
Avg rating:3.0/5.0
Slides: 22
Provided by: reg9150
Category:
Tags: perp

less

Transcript and Presenter's Notes

Title: R


1
Inclusive Jet Production _at_ CDF
  • Régis Lefèvre
  • IFAE Barcelona
  • on behalf of the CDF Collaboration

QCD 06 Montpellier, France July 3rd-7th 2006
2
The 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

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
  • Latest results based on 1 fb-1

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 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

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 ?
    RSEPto emulate experimental merging/splitting
  • Arbitrary parameter RSEP prescription RSEP
    1.3 (based on parton level approximate arguments)

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

7
Results from ZEUS / D0 Run I
D0 Run I
  • Disagreement at low pT
  • Suggests Underlying Event not properly
    accounted for

8
Framework / 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

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

10
Energy 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
11
Calorimeter 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

12
kT 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)
13
kT Jets vs. D (0.1 lt y lt 0.7)
D 0.5
D 1.0
14
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
15
kT 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

16
kT Jets with 1 fb-1 Data / Theory
17
Midpoint Jets with 1 fb-1 Data / Theory
18
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

19
Backup Slides
20
The kT Algorithm Step-by-Step
Longitudinally invariant kT algorithm
(Ellis-Soper inclusive mode)
21
Bisector Method
0.1 lt y lt 0.7
  • ?// ? ISR
  • ?PERP ? ISR ? Detector Resolution
  • Assuming ISR democratic in ?
  • ?D ? (?2PERP - ?2//) / ? 2 ? Detector
    Resolution
Write a Comment
User Comments (0)
About PowerShow.com