6 of the gluon fields are independent linear combinations of the simple gluon fields we enumerated
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 1 Quark and Gluon Jet...
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Transcript of Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 1 Quark and Gluon Jet...
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 1
Quark and Gluon Jet Fragmentation Differences
Abstracts covered in this talk• 5-0081 Fragmentation differences of quark and gluon jets at the Tevatron (CDF)
• 5-0437 Charged particle multiplicities in 3-jet events and two-gluon systems (DELPHI)
Andrey Korytov
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 2
Multiplicity in Gluon and Quark Jets: Theory
CDF
kT=1 GeV/c
kT
Parton shower stage—challenge for pQCD calculations in very soft domain (kT < 1 GeV):
• resummation at LLA and NLLA precision: - start out from color singlet- small opening angles around jet direction- r = Ng/Nq = CA/CF = 9/4 = 2.25
• continues flow of papers since mid-1980 to include corrections going beyond the NLLA accuracy most recent r = Ng/Nq = 1.4-1.7 (Q=20-100 GeV)
Hadronization stage—still a mystery:
• Believed to be local, independent of jet origin:Nhadrons = K Npartons (Local Parton-Hadron Duality)
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 3
Proved to be a hard measurement:• continuous flow of papers from e+e- experiments (15+ papers over
last 15 years): r = Ng/Nq ranged from 1 to 1.5
Multiplicity in Gluon and Quark Jets: Experiment
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 4
Gluon vs. Quark Jets: Historical Perspective
r-measurement history
0.0
0.5
1.0
1.5
2.0
2.5
1980 1985 1990 1995 2000 2005
Year
r = N
g / N
q HRSOPALSLDALEPHDELPHICLEOCDF
NLL extensionsCA /CF =9/4 (LLA, NLLA)
Ratio r = Nch(gluon jet) / Nch(quark jet)
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 5
DELPHI: Theory behind the new analysis Eden et al., 1998: New look at relationship between Ngg and Nqq
multiplicities - Predict Ngg from Nqq (e+e-) data.
- Match Integration constant to reproduce experimental Nch multiplicity in Υ-decays.
Eden et al., 1999: Multiplicity in 3-jet events (e+e- data) can be written as a sum ofa) restricted multiplicity in qq-system (two energy scales)b) half of unrestricted multiplicity in gg-system (single energy scale)
Eden “A” No consensus on proper scales!
Eden “B”
Various scales appearing in formulae above:
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 6
DELPHI: Multiplicity in 3-jet events
DATA
s=91 GeV
Events clustered in 3 jets
Two independent variables:
1 and 3
q- and g-jets are not identified
on event-by-event basis
THEORY (with experimental input):
Eden “A”
Eden “B”
1
Jet 1
Jet 3
Jet 2
3
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 7
DELPHI: Ngg from 3-jet events
Use preferred Eden “A”:
Ngg(kLe) is obtained from
1) Nqqg = N3-jet(1, 3): measured multiplicity
2) Constrained Nqq(Lqq, kLu): evaluated from unconstrained multiplicity in e+e- data, using:
Theory curve for Nggis based on Nqq(s) dataand normalized on this point
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 8
DELPHI: r = (Ngg from 3-jet events) / Nqq
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 9
CDF: Data analysis strategyDijet and -jet events with Mjj and Mj ~80-100 GeV
tracks are not used in jet reconstruction
Dijet events (~60% gluon jets) and -jet events (~80% quark jets) small uncertainties in energy range used (well known range of PDFs)
Dijet or -jet center of mass frame: Ejet = ½Mjj or ½Mj
Nch multiplicity in cones with opening angle from ~0.3 to ~0.5 rad
Energy scale Q = 2Ejettan(cone/2) Ejetcone
Q=11-25 GeV (no controversy on proper scales for small opening angles)
Some leading-order diagrams for dijet events Some leading-order diagrams for -jet events
Jet 1
Jet 2
conep p
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 10
CDF: Nch multiplicities in gluon and quark jets
Multiplicities measured in range of Q=11-25 GeV Tevatron and e+e- data (Q>10 GeV) agree E-scaling observed Tevatron and e+e- data (Q>10 GeV) follow 3NLL trends
two-parameter fit to CLEO (10 GeV) and OPAL (80 GeV) data
e+e- model-dependent results
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 11
CDF: ratio r = Ng / Nq
Ratio measured in range of Q=11-25 GeV: e.g., r=1.640.17 at Q=19 GeV
E-scaling observed Data agrees with the recent NLL extensions
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 12
CDF: Data vs. Monte Carlo
Gluon Jets: Herwig 5.6 & Pythia 6.115 reproduce multiplicity in gluon jets fairly well
Quark Jets:Herwig 5.6 & Pythia 6.115 over-estimate multiplicity in quark jets by ~30%
Side Note on Pythia vs Herwig:Pythia gives ~3-4% higher multiplicity in comparison to Herwig
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 13
CDF: momentum distributions of particles dN/d
Gluon jets: Herwig and Pythia are in reasonable agreement with dataQuark jets: Herwig and Pythia disagree with data
x = p/Ejet = 1 0.5 0.1 0.05
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 14
CDF: momentum-dependent ratio r()Momentum distributions of charged particles in gluon and quark jets
Ratio reaches max and flattens for soft part of spectrum at ~1.80.2
Same pattern was observed at LEP
x = p/Ejet = 1 0.5 0.1 0.05
Andrey Korytov, University of Florida ICHEP2004 August 15-22, 2004, Beijing 15
SummaryCDF:
Multiplicities in gluon and quark jets and their ratio are measured for energy scales Q=11-25 GeV (analysis is model-independent): r = 1.640.17 at Q=19 GeV
Ejetcone-scaling is observed
Multiplicities and their ratio follow recent pQCD calculations pushing resummation precision beyond the Next-to-Leading Log Approximation
DELPHI:
Multiplicities in gluon jets are measured for energy scales Q=13-53 GeV (analysis is model-dependent): r ~ 1.35 ( about 1% error) at Q=20 GeV
Ratio of multiplicities in gluon and quark jets agrees with recent pQCD calculations at Q>20 GeV and is systematically lower at Q<20 GeV
Multiplicities of charged particles in 3-jet events may help to sort out uncertainties with scales to be used for describing events of complicated topologies