1. Jet fragmentation results at CDF
Andrey Korytov
(for CDF Collaboration)
1.2 fb-1 on tape
CDF
p-pbar collisions
sqrt(s) = 1.96 TeV
peak L = 1032 cm-2s-1 D0
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

2. Jet Fragmentation vs Analytical pQCD
Momentum distributions of particles in jets
Multiplicity of charged particles in jets, including g/q-jet differences
Momentum correlations of particles in jets
Forthcoming results (not yet public)
kT-distribution of particles in jets (kT with respect to jet axis)
Global Event Shapes
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

3. Partons, Hadrons, Jets Pick two partons and their momenta
phenomenological parton density functions, PDF
Hard Scattering: 2  X
pQCD exact matrix element at LO, some at NLO,...
Soft final state radiation
pQCD approximate resummation in all orders: LLA (leading log approximation), NLLA
Underlying event
phenomenological models
Hadronization
Calorimeter response
electromagnetic shower for photons
hadronic shower for “stable” hadrons
Jet identification
jet finding algorithms
Hadronic showers EM
showers ?
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

4. Parton momenta and average multiplicities
Partons: NLL resummation
Mueller (1983)
Dokshitzer, Troyan (1984)
Malaza, Webber (1984)
plus subsequent corrections
dN/dx = D(Y, x)
x = ln(1/x) = ln(Ejet/pparton)
Y = ln(Q/Qeff), Q = Ejetqcone
Qeff = Qcutoff = LQCD
From partons to hadrons: Local Parton-Hadron Duality
Azimov, Dokshitzer, Khoze, Troyan (1985)
Hadron observables follow patterns predicted for partons
Nhadrons ~ Npartons ?
Momentum distributions?
Momentum correlations? …
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

5. Particle momenta and average multiplicity
CDF
cone opening angle q=0.47
Momentum distribution
of charged particles in jets
dijet events with well-balanced ET
15-30 cone around dijet axis
Two parameter fit (MLLA+LPHD)
works surprisingly well in
wide range of dijet masses
MLLA Qeff = 23040 MeV
kT-cutoff can be set as low as LQCD
KLPHD( ) = 0.56  0.10
Nhadrons  Npartons
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

6. Gluon-Quark Jet Differences
Charged particle multiplicities in gluon and quark jets:
di-jet and g-jet events have very different quark/gluon jet mix
~60% of gluon jets at Mjj~100 GeV
~20% of gluon jets at Mjj~100 GeV
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

7. Gluon-Quark Jet Differences
Charged particle multiplicities in gluon and quark jets:
measured multiplicities in di-jet and g-jet events
can be resolved for multiplicities in quark and gluon jets
Results agree with NNLLA
ratio r = 1.64  0.17
at Q~20 GeV
Most recent LEP result (OPAL)
ratio r = 1.51  0.04
at Q~90 GeV
Ratio = Ng-jet / Nq-jet
Q = Ejet  qcone
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

8. Two-particle momentum correlations
consider all particle pairs in cone q=0.5 around jet axis
x=ln(Ejet/pparticle)
theory: C. Fong and B. Webber (1990)
To decouple momentum correlations from multiplicity fluctuations, we use distributions normalized to unity
and binominal moments
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

9. Two-particle momentum correlations
consider all particle pairs in cone q=0.5 around jet axis
theory:
Expansion around the peak: Dx=x-x0
normalized to unity
Dx=x-x0
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

10. Two-particle momentum correlations
theory:
D depends on point of expansion
c0 is not independent from c1 and c2:
why is D not zero?
c0(Ejet) is always >1
c1(Ejet) is always positive
c2(Ejet) is always negative
Constants D, a0, a1, a2 depend on Nc, Nf, and whether the jet originates from a quark or a gluon
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

11. Experimental side Measurement
Di-jet well-balanced events with Mjj= GeV
Central, dijet axis |h|<0.7
Only one vertex
Charged particles around dijet axis in cone q=0.5
Remove secondaries (Ks, conversions, etc.)
Unfold small underlying event contribution
Check that correction for efficiency cancels out
Theory: to be able to compare to experiment,
make correlation function from a mix of quark and gluon jets
take fractions of quark/gluon jets from Pythia (defined by PDFs)
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

12. Momentum correlations (cont’d)
hadron correlations follow the pattern expected for partons
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

13. Momentum correlations (cont’d)
hadron correlations follow the pattern expected for partons
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

14. Momentum correlations (cont’d)
fit to c2 coefficients gives kT cutoff Qeff ~ 130 ± 80 MeV
Q = Ejet  qcone (GeV)
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

15. Momentum correlations (cont’d)
fit to c1 coefficient gives kT cutoff Qeff ~ 150 ± 80 MeV
Q = Ejet  qcone (GeV)
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

16. Momentum correlations (cont’d)
c0 coefficient is inconsistent with the theory, it is too small
However, it does not show much trend with energy, as expected
theoretically, this coefficient has some issues…
Q = Ejet  qcone (GeV)
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba

17. Summary Momentum distributions of particles in jets
Consistent with the parton distribution predicted in pQCD (MLLA)
Qeff = 230±40 MeV for the entire range Mjj= GeV/c2
Multiplicity of charged particles in jets:
Particle multiplicity is proportional to that of partons: Nhadrons = KLPHD Npartons
KLPHD=0.56±0.10 for the entire range Mjj= GeV/c2
Ratio of multiplicities in gluon and quark jets rLPHD=1.6±0.2 is consistent with pQCD
Momentum correlations of particles in jets
Particle momentum correlations follow pQCD predictions for partons
Qeff = 140±80 MeV for parabolic and linear terms
The constant (momentum-independent) term is much smaller than predicted…
Forthcoming results (will become public by summer conferences)
kT-distribution of particles in jets (kT is with respect to jet axis)
Global event shapes
Andrey Korytov, University of Florida DIS 2006, 22 April 2006, Tsukuba