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 1

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 2

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 3

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 4

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 5

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 6

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 7

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 8

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 9

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 10

Experimental side Measurement Di-jet well-balanced events with Mjj=80-600 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 11

Momentum correlations (cont’d) hadron correlations follow the pattern expected for partons 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) 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 14

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 15

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 16

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=80-600 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=80-600 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 17