Soft QCD Phenomena in High-ET Jet Events at CDF

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Soft QCD Phenomena in High-ET Jet Events at CDF
Andrey Korytov
(for the CDF Collaboration)

• Abstracts covered in this talk
• A356 Fragmentation Differences of Quark and
  Gluon Jets at CDF
• A362 Measurement of Jet Shapes and Energy Flows
  in Dijet Production at the Tevatron
• A353 Jet Evolution and the Underlying Event in
  Run 2 at CDF
• Official Title
• Studies of Jet Shapes and Fragmentation
  Differences
• of Quark and Gluon Jets with the CDF Detector
• (note Underlying Event fell out from the title)
• Better Title
• Studies of Soft QCD Phenomena in High-ET Jet
  Events
• with the CDF Detector

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Soft QCD Phenomena in High-ET Jet Events

• Anatomy of events with high ET jets
• hard scattered partons
• final state radiation
• initial state radiation
• multi-parton interactions
• proton/antiproton remnants
• ? Note separation between sub-processes is not
  clean
• due to entangled color connections
• Soft QCD Phenomena
• Jet fragmentation is largely driven by soft QCD
• So is the UE physics
• Tools available
• re-summed pQCD approximations
• (analytic, but only for limited number of
  observables)
• Monte Carlo generators (generic, but have many
  tunable ad-hoc knobs)

JETS
UNDERLYING EVENT
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Why bother?

• Jet Fragmentation
• Jet development physics
• Parton shower stagechallenge for pQCD
  calculations at the very soft limit (kTLQCD)
• Hadronization stagestill remains a mystery
• Many high-ET physics analyses depend on good
  understanding of jet properties
• Underlying Event
• UE physics is poorly understood
• MC Generators implement UE differently and often
  with many (too many?) parameters
• Even when tuned to match the accessible data, MC
  predictions for LHC vary wildly
• UE pollutes many analyses
• ? source of systematic errors

kT1 GeV/c
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Results presented in this talk

• Jets
• Momentum distribution of charged particles in
  jets vs. NLLA
• Multiplicities of charged particles in g- and
  q-jets vs. NLLA
• Energy flow in jets (jet shapes) vs. MC
• Underlying Event
• Energy flow away from jets vs. MC
• Charged particle multiplicity flow away from
  jets vs. MC
• Momentum distribution of away-from-jet charged
  particles vs. MC

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Jets doing fragmentation analytically
CDF Charged particle momentum spectra
(?cone0.47) and MLLALPHD fit

• Jet fragmentation
• parton shower development MLLA
• Modified Leading Log Approximation
  with one kT-cutoff parameter QeffQcutoffLQCD
• hadronization LPHD
• Hypothesis of Local Parton Hadron Duality with
  one parameter KLPHDNhadrons/Npartons
• MLLALPHD
• cannot describe all details
• but all analytical
• and works surprisingly well
• Momenta of charged particles in jets
• Qeff 230 ? 40 MeV
• KLPHD(?) 0.56 ? 0.10

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Jets gluon vs quark jet differences

• Ratio r Nhadrons(gluon jet) / Nhadrons(quark
  jet)
• recent calculations (for partons) extensions of
  NLLA, r1.4-1.7 (Q10-100 GeV)
• lots of results from LEP, not all
  self-consistent r 1 to 1.5
• jet-ID biased, model-dependent, few
  unbiased/model-independent

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Jets gluon vs quark jets at CDF

• di-jet events (60 gluon jets) and g-jet events
  (80 quark jets)
• di-jet or g-jet center of mass frame Ejet ½Mjj
  or ½Mgj
• Nch multiplicity in cones with opening angle q
  from 0.3 to 0.5 rad
• Energy scale QEjetq
• Results
• Ratio r1.6?0.2, almost energy scale independent
• multiplicities in quark and gluon jets see plot

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Jets Energy flow inside jets (vs MC)

• Jet shape fractional energy flow Y(r)
  ET(0r) / ET(0R), where R1
• In central region, do it with
• Calorimeter towers (?)
• Charged tracks (?)
• Either wayshapes are nearly identical
• Herwig and Pythia practically coincide and agree
  with data

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Jets Energy flow inside jets (vs MC)

• In forward region, do it with
• Calorimeter towers only
• Data vs MC discrepancy
• ? the higher jet h and
• ? the smaller jets ET,
• the larger the disagreement
• Is it real or do we have simulation problems with
  the new plug calorimeter?
• expand tracker analysis to higher h region
• any D0 data?

?
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UE studies with charged tracks

• Event sample min-bias, jet events (central jets)
• Measure
• Average Number of particles in direction
  transverse to leading jet nd2N / dfdh
• PT spectrum of particles in direction transverse
  to leading jet dn/dPT
• Average Energy summed over charged particles in
  transverse direction d2ET/dfdh
• Confront data and MC
• Identify importance of various MC knobs/parameters

ET(jet)

• Charged tracks
• d2N/dfdh
• d3N/dfdhdPT
• d2ET/dfdh

transverse particles as a probe of the
underlying event
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UE data vs. default Pythia and Herwig

• Default Pythia and Herwig fail to reproduce data
  one way or another, e.g.
• Pythia 6.206 underestimates number of tracks in
  transverse direction
• Herwig 6.4 gives too soft spectrum for particles
  in transverse direction, especially in events
  with small ET jets (missing MPI now have been
  added)

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UE tune Pythia to match CDF data

• Pythia CDF Tune A vs. Default 6.206
• Enhanced initial state radiation
• Smoothed out probability of Multi-Parton
  Interactions (vs. impact)
• MPIs are more likely to produce gluons than
  quark-antiquark pairs
• and MPI gluons are more likely to have color
  connection to p-pbar remnants

PYTHIA 6.206 and CDF Tune A (CTEQ5L) PYTHIA 6.206 and CDF Tune A (CTEQ5L) PYTHIA 6.206 and CDF Tune A (CTEQ5L) PYTHIA 6.206 and CDF Tune A (CTEQ5L)
Parameter Default Tune Description
PARP(67) 1.0 4.0 Scale factor that governs the amount of initial-state radiation.
MSTP(81) 1 1 Turns on multiple parton interactions (MPI).
MSTP(82) 1 4 Double Gaussian matter distribution.
PARP(82) 1.9 2.0 Cut-off for multiple parton interactions, PT0.
PARP(83) 0.5 0.5 Warm Core 50 of matter in radius 0.4.
PARP(84) 0.2 0.4 Warm Core 50 of matter in radius 0.4.
PARP(85) 0.33 0.9 Probability that the MPI produces two gluons with color connections to the "nearest neighbors".
PARP(86) 0.66 0.95 Probability that the MPI produces two gluons either as described by PARP(85) or as a closed gluon loop. The remaining fraction consists of quark-antiquark pairs.
PARP(89) 1,000.0 1,800.0 Determines the reference energy E0.
PARP(90) 0.16 0.25 Determines the energy dependence of the cut-off PT0 as followsPT0(Ecm) PT0(Ecm/E0)PARP(90).

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UE Pythia Tune A describes Data
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Summary

• Jet fragmentation
• Momenta of charged particles in jets are well
  described by NLLA pQCD
• MLLA kT-cutoff Qeff230 ? 40 MeV
• LPHD Nhadrons/Npartons KKLPHD(?) 0.56 ? 0.10
• Multiplicities in gluon and quark jets and their
  ratio r 1.6 ? 02
  agree with extended NLLA pQCD
  and recent LEP data
• Jet shapes mostly agree with PYTHIA and HERWIG,
  but more
  studies/tuning are needed for high-h jets
• Underlying event
• Run II and Run I data agree, Run II analysis is
  being expanded
• MC generators with default parameters do not
  quite work, but can be tuned
  to match data ? insights into UE physics?

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• A few backup slides follow this page

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Tevatron upgrade Run II vs. Run I

• Original Plan Run I ? Run II
• CM energy 1.8 ? 1.96 TeV
• Bx spacing 3.5 ? 0.4 ms
• Max luminosity 2x1031 ? 50x1031
  cm-2 s-1
• Integrated luminosity 0.1 ? 15 fb-1
• (before LHC turn-on)
• As of May 2003
• Peak luminosity so far
  4.5x1031 cm-2 s-1
• Total delivered (incl. commissioning) 0.24
  fb-1
• On tape (CDF, incl. commissioning) 0.18
  fb-1
• Good for physics (CDF)
  gt0.13 fb-1
• CDF current data taking efficiency 90
• Long-term plan (by end of 2008)

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CDF upgrade what is new

• Retained from CDF I
• Solenoid
• Central Calorimeters
• Central Muon System
• Brand new in CDF II
• 5-layer 3D vertex Si detector
• Intermediate Si layers
• Central Drift Tracker
• Plug Calorimeter
• Mini-plug calorimeter
• Time of Flight System
• Expanded Muon Coverage
• TRIGGER, now includes
• displaced vertex
• track pTgt1.5 GeV/c
• Faster Front End Electronics

• 3d vertex coverage hlt2
• Tracking coverage hlt2
• Calorimeter coverage hlt3.6
• Mini-plug calorimeter 3.6lthlt5.1
• Muon coverage hlt1.5

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Jets Gluon vs Quark jets at CDF

• Momentum distributions of charged particles in
  gluon and quark jets
• Ratio reaches max and flattens for soft part of
  spectrum at 1.8?0.2
• Same pattern was observed at LEP