working group c: hadronic final states david milstead the university of liverpool review of...
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Working Group C: Hadronic Final States
David MilsteadThe University of Liverpool
Review of Experiments
27 experiment and 11 theory contributions
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A few questionsIs perturbative QCD in good shape ?Current measurements of s
Jet rates at high pT and massQCD dynamics at low x …
Power correctionsPentaquarksHadronisation universalityColour reconnections
Progress in npQCD ?
What does this mean for LHC ? QCD uncertainties
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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 D0Large energy scale uncertainty – under study
Study angular correlations between jets to probe higher orders
Good agreement by NLO except at extreme values
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Multi-jet Rates at HERA
Direct test of QCD at O(s
2)
Measure ratio of 3-jets/2-jetsand cancel correlated uncertainties
Multijet NLO calculations available (Phys. Rev. Lett.87:082001,2001)
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Invariant kT jet algorithm
ETjet> 5 GeV-1 < 2.5 Mass2,3jet > 25 GeV
Towards an extraction of s ……..
3-jet/2-jet Ratio at HERA
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Event shapesFit and swith NLO+NLL+PC
Resummed calculations (see Dasgupta talk) lead to improved consistency for both experiments
0
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Measurements of Jet Substructure
Extract s and separate quark/gluon jets
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Selected s measurements presented this week
Perturbative QCD is in good shape
ZEUS
Event shapesin radiative/non-radiative e+e-
OPAL H1
Event shapesin 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
Most precise measurement yet
NLO fails to describe data
100<Q2<8000 GeV2
0.2<y<0.80.01<x<0.01
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Parton Dynamics at low x• High precision
measurements of forward jets
• Sensitive to QCD evolution
Failure of NLO calculations fail away from DGLAP region
DGLAP kTn>> kTn-1
BFKL xn>>x n-1
CCFM
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kT unordering at low x ?
Shorter range transverse momentum
compensation than predicted by DGLAP
0
Trigger low xevents with hard forward 0
kT unordered 0 2 4
kT orderedH1
Looking forward to HERA-2 and improved
forward acceptance
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Dijet Production in DIS
Significant difference between data and NLO at low x
Extend to forward region with HERA-2
Look for jets with 120o
Sensitive to incoming parton virtuality, Unintegrated gluon density,higher orders…
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Strange Pentaquarks
Results from
ZEUSHERMESCDFALEPH
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Searching for Ξ3/2–- and Ξ0
3/2
No sign of cascade pentaquark
Large statistics for Ξ(1530)
NA49 measurement in forward region
ZEUS
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ALEPH
New Results on the s
HERMES
1527 ± 2.3 MeV
= 9.2 ± 2 MeV
1521.5±1.5 +2.8 – 1.7 MeV
= 9.2 ± 2 MeV
Evidence for
antipentaquark
Nothing seen…Fundamentally different in e+e?
ZEUS
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ALEPH
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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deuterons anti-deuterons
B2
pT /GeV
Anti-Deuterons at High Energy
D cross-section presented by H1 andPHENIX
Fit to coalescence model
B2 –> interaction size
heavy ions
pp p
Structure dependence at the highest energies
PHENIX
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Workshop work (T. Sloan)H1 pentaquark vs ALEPH limit
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Two Proton Production in Collisions
Extend range in W Diquark model supported
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Looking ahead….
Substantial QCD uncertainties at the LHC
= 776 pb(Cacciari et al.)
Large phase space for QCD radiation Appropriate modelling of ME+PS Large theory disagreementsHealth warning for current LHC studies
Much work ongoing by MC builders (see Dasgupta’s talk)Need close experimental/theory collaboration
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Summary
QCD studied in hadronic final states in pp,ep,e+e-,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
e+
e-p
p
N
N
pQCD tests with jets, event shapes..Latests low x dynamics…Explore npQCD with pentaquarks, deuterons, power corrections..Target influence on hadronisation
p
e
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Evidence for light pentaquark HERMES
Peak at:
1527 ± 2.3 MeV
= 9.2 ± 2 MeV
Significance: 4.3
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Colour Reconnection in e+e-
Measure particle flow between jet systems
8.0
2.0
8.0
2.0
DB regions
CA regions
rr
rr
dddn
dddn
R
R
C
A
D B
DELPHI preliminary
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Evidence for light pentaquarkZEUS
First evidence from colliding experiment
Measurement in the central fragmentation region
First evidence for antipentaquark
96±34
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Soft Colour Rearrangement in e+e-
Rapiditygap signature
Failure of Colour Rearrangement Models
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Jet Production at D0Jets measured over wide pseudorapidity regionbut with large energy scale uncertaintyAngular correlations between jets allow sensitive probe of QCD
Good agreement by NLO exceptat extreme values
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… but no evidence for light pentaquark in ee
ALEPHSomething fundamentally different in baryon production
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Fragmentation functions in e+e-
Good agreement with NLO
Use LEP1 and LEP2 data