Measurements of G

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Measurements of ?G

• Focus on COMPASS data
• ?G from scaling violations
• ?G/G from hadron production
• Open charm
• Hadron pairs
• Single hadrons
• pp RHIC

G. Mallot CERN/COMPASS
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NLO QCD fits

• Several groups performing World Data fits
• Example AAC, new fit 2006
  Hirai, 2a Thu
• Still large uncertainty in ?G, even sign not
  determined
• Extra difficulties in polarized case
• No positivity condition
• No momentum sum rule

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COMPASS QCD fit
Q2 3 GeV2

• New g1d data world data
• ? G gt 0 and ? G lt 0
• Low-x data prefer ? G lt 0
• ? G' 0.20.3
• a0 0.330.030.05
• ?s -0.080.010.02

? G gt 0
? G lt 0
CERN-PH-EP/2006-029, Quintans, Savin
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COMPASS QCD fit

• Not yet included in fits final Hermes g1dDe
  Nardo, Thu

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Photongluon fusion (PGF)

• Gluon polarisation is measurable in PGF

• measure
• calculate and
• using Monte Carlo

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Hadron production

• LO analysis of hadron-pair asymmetries
• open charm single D meson AROMA
• cleanest process wrt physics background
• high-pT hadron pairs with Q2 gt 1 GeV2 LEPTO
• high-pT hadron pairs with Q2 lt 1 GeV2 PYTHIA
• NLO (photo production)
• open charm Bojak, Stratmann
• single incl. high-pT hadron Jaeger. Stratmann,
  Vogelsang
• hadron pairs LO done, Hendlmeier, Stratmann,
  Schäfer
• NLO underway
• All analyses up to now in LO (plus parton showers)

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Open Charm Ds from Ds

• D ? D ps? K p ps slow pion required

20022004
D0 ? K p p0
D0 ? K p
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Open charm MC

• analysis uses event aLL weighting,
• aLL estimated with NN from event kinematics
• indispensible due to large variation of aLL
• good correlation of 0.82 between generated and
  reconstructed aLL

aLL generated
aLL reconstructed (NN)
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Hadron production

• Ratios for processes for Q2 lt 1

Resolved photons
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Example kT tuning
nucleon
photon

• systematic error
• determined using 15 independent MC simulations
• exploring the parameter space
• in kT of nucleon and photon
• fragmentation functions
• parton shower on/off,
• renormalisation scale

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Resolved photons

• More than 50, however assuming a min and
  maxscenario, shows little difference.
• Probing photon at large x, where photon PDF
  rather well determined

? u/u
Glück, Reya, Sieg
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Data versus MC

• excellent to good agreement for all kinematics
  variables

pT
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Gluon polarisation
high-pT pairs Q2gt1GeV2
20022003
high-pT pairs Q2lt 1GeV2
20022004
Open charm
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? G/G from high-pT pairs

• GRSV-max strongy disfavoured

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COMPASS QCD fit
Note New Hermes single hadron analysis analysis
to be presented at SPIN 2006

• Note NLO fits, LO data

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New Hermes analysis
Single inclusive hadrons
P. Liebing, 2A, Tue
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Can we learn more about x?
here Lepto and Q2gt1
All processes
PGF events (MC)
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Splitting in xg bins?
Compass

• Splitting of high-pT, Q2lt1 data in 3 xg bins
  under study
• Optimizing correlation of rec. and true xg (NN)
• More significant with 2006 data

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• pp at RHIC
• looking forward to many talks in 2a Tue

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pp NLO Calculations
In much better shape
Jäger,Schäfer, Stratmann, Vogelsang de Florian
Jäger,Stratmann,Vogelsang Signer et al.
Gordon,Vogelsang Contogouris et al. Gordon,
Coriano
Bojak, Stratmann
Summary by Stratmann, DIS2006
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p0 production at RHIC

• Phenix

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Direct photons

• good agreement ofcalc. and data at collider
  energies

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Towards a global analysis
W.Vogelsang, M. Stratmann (DIS2006, work in
progress)
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Dg from p0 production (RUN05)
Slide from Hirai DIS2006

• 1st moment Dg
• 0.31 ? 0.32 (DISp0)
• 0.47 ? 1.08 (DIS only)
• Significant reduction of the Dg uncertainty

• Sign problem
• gg process dominates
• Ds? Dg(x) 2
• Positive or negative Dg?
• c2p0 11.18(Dggt0) vs. 11.05 (Dglt0)
• (8
  data points)

• Consistent results
• 1st moment (0.1ltxBjlt1)
• Dggt0 0.30 ? 0.30
• Dglt0 0.32 ? 0.42
• DIS p0 data covered
• Large-x is positive

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Inclusive jets at STAR
from Kiryluk, DIS2006
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Summary

• finally data on ?G are coming in!
• all results indicate ?G small comparedto some
  anomaly inspired models
• sign still undefined, ?G still could carry most
  of the nucleons spin
• need data on x-dependence to pin down the shape
• need to include COMPASS and HERMES data in
  starting global analyses (NLO calculations)
• need abs cross sections from COMPASS and HERMES
  to prove that LO/NLO is applicable
• looking forward to 500 GeV/c at RHIC
• Great and exciting harvest since Trieste 2004

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