Working Group C: Hadronic Final States

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David Milstead
The University of Liverpool
Working Group C Hadronic Final States
27 experiment and 11 theory contributions
Review of Experiments
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A few questions
Is perturbative QCD in good shape ?
Current measurements of as
Jet rates at high pT and mass
QCD dynamics at low x

What does this mean for LHC ? QCD uncertainties

• HERA/Tevatron towards the LHC
• Parton evolution BFKL/DGLAP are we further
  forward than 1994 ?
• What can we do in HERA 2 ?
• Alpha_s ?
• Non/perturbative QCD
• How useful is our knowledge ?
• Experimental measurements that need no QCD model
  to interpret them.
• a

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Jet Production at CDF
Increase in CM energy to 1.96 TeV extends high pT
sensitivity
Next steps forward jet cross-sections and
improved energy scale uncertainty (1)
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Jet Production at D0
Large energy scale uncertainty under study
Study angular correlations between jets to probe
higher orders
Good agreement by NLO except at extreme Df values
5
Multi-jet Rates at HERA
Direct test of QCD at O(as2) Measure ratio of
3-jets/2-jets and cancel correlated
uncertainties Multijet NLO calculations
available (Phys. Rev. Lett.87082001,2001)
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3-jet/2-jet Ratio at HERA
Invariant kT jet algorithm ETjetgt 5 GeV -1 lt h
lt 2.5 Mass2,3jet gt 25 GeV
Towards an extraction of as ..
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Event shapes Fit and as with NLONLLPC
Resummed calculations (see Dasgupta talk) lead to
improved consistency for both experiments
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Measurements of Jet Substructure
Extract as and separate quark/gluon jets
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Perturbative QCD is in good shape
Selected as measurements presented this week
H1
Event shapes in DIS
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Azimuthal Asymmetries at HERA
Use energy flow to measure over a wider phase
space with reduced systematic errors
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Azimuthal Asymmetries at HERA
100ltQ2lt8000 GeV2 0.2ltylt0.8 0.01ltxlt0.01
Most precise measurement yet
NLO fails to describe data
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Parton Dynamics at low x

• High precision measurements of forward jets
• Sensitive to QCD evolution

DGLAP kTngtgt kTn-1
CCFM
BFKL xngtgtx n-1
Failure of NLO calculations fail away from DGLAP
region
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kT unordering at low x ?
Trigger low x events with hard forward p0
H1
Shorter range transverse momentum compensation
than predicted by DGLAP
Looking forward to HERA-2 and improved forward
acceptance
14
Dijet Production in DIS
Look for jets with DF lt 120o
Sensitive to incoming parton virtuality,
Unintegrated gluon density, higher orders
Significant difference between data and NLO at
low x Extend to forward region with HERA-2
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Strange Pentaquarks
Results from ZEUS HERMES CDF ALEPH
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Searching for ?3/2- and ?03/2
ZEUS
No sign of cascade pentaquark Large statistics
for ?(1530) NA49 measurement in forward region
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New Results on the Qs
ZEUS
ALEPH
HERMES
1521.51.5 2.8 1.7 MeV s 9.2 2 MeV Evidence
for antipentaquark
1527 2.3 MeV s 9.2 2 MeV
Nothing seen Fundamentally different in ee?
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ALEPH Charmed Pentaquark Search

• LEP1 Data at Z-pole
• 1991-1995
• 4.6 M hadronic Z0
• No resonance observed
• Upper limit of
• 6 x 10-4 pq/had.Z0

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Anti-Deuterons at High Energy
Fit to coalescence model
PHENIX
B2 gt interaction size
Structure dependence at the highest energies
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Workshop work (T. Sloan)H1 pentaquark vs ALEPH
limit
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Two Proton Production in gg Collisions
Extend range in W Diquark model supported
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Looking ahead.
Substantial QCD uncertainties at the LHC
Large phase space for QCD radiation
Appropriate modelling of MEPS Large theory
disagreements
Health warning for current LHC studies
Much work ongoing by MC builders (see Dasguptas
talk) Need close experimental/theory collaboration
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Summary
QCD studied in hadronic final states in
pp,ep,ee-,NN Perturbative QCD in good shape
Higher orders needed for low x parton evolution
and azimuthal asymmetries Non-pQCD probed by
identified particle production Pentaquarks,
Deuterons challenge theorists and
experimentalists HERA-2 and Run II necessary to
make progress
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Testin
pQCD tests with jets, event shapes.. Latest as
low x dynamics
Explore npQCD with pentaquarks, deuterons, power
corrections.. Target influence on hadronisation
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Evidence for light pentaquark HERMES
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Colour Reconnection in ee-
R
Measure particle flow between jet systems
C
D
B
A
DELPHI preliminary
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Evidence for light pentaquark ZEUS
First evidence from colliding experiment
First evidence for antipentaquark 9634
Measurement in the central fragmentation region
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Soft Colour Rearrangement in ee-
Rapidity gap signature
Failure of Colour Rearrangement Models
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Jet Production at D0
Jets measured over wide pseudorapidity region but
with large energy scale uncertainty Angular
correlations between jets allow sensitive probe
of QCD
Good agreement by NLO except at extreme Df values
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but no evidence for light pentaquark in ee
Something fundamentally different in baryon
production
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Fragmentation functions in ee-
Use LEP1 and LEP2 data
Good agreement with NLO