Summay of Session 2

1

• Summay of Session 2
• QCD spin structure of nucleons

2
Summary Session 2

• Introduction
• Helicity distributions
• Gluon polarisation
• transversity

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Summary of Session 2

• six excellent plenary talks
• Metz, Barone, Garçon, Hasch, Bressan, Saito
• 55 talks in parallel sessions, 16 h
• half experiment / half theory
• exp. talks about 2/3 lp, 1/3 pp
• theo. talks about 1/3 on transversity and SSA
• Apologies for not being able to cover everything
  appropriately

4

• HELICITY DISTRIBUTIONS

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Final g1 for p, d, n
Riedl

• quasi final data set for p and d
• corrected for smearing (radcor, detector)

6
Quark helicity distributions
Rubin
7
Inclusive asymmetries
Peshekhonov
inclusive

• COMPASS deuteron data 2002 2003
• most precise data for xlt3x10-2
• 2004 similar precision
• kaon/pion asymmetries to come

ve hadrons
8
?q - Theory

• method using A? and moments to determine
• model-independent determination of from incl.
  and semi-incl. asym. in LO and NLO.
  Fragmentations functions cancel in
• needs very precise data (?Jlab)

Shevchenko
Christova
remark A? exp. diffcult with magnetic
spectrometers
9
?q - JLAB
Jiang
Semi-SANE E04-113

• under construction (2006-2007)
• expect very precise data for x gt 0.1
• apply method

10
Evolution

• role of higher twist in the determination of PDF.
  HT cancels largely in A1
• .
• small-x evolution double logarithm resummation
  important for g1 for x 10-3 -10-4

Stamenov
Ermolaev

• parametrisation-independent matrix solution of
  DGLAP
• estimates of ?G/G and Lq ranges

Goshtasbpour
Ramsey
11

• GLUON POLARISATION

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?G/G - Photon-Gluon Fusion
measured
aLL calculable partonic asymmetries R
Monte-Carlo (Lepto for Q2 gt 1 GeV2)
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?G/G - SMC
Rondio

• event selection high-pT pairs
• Q2 gt 1 GeV2
• neural network
• SpT2 gt 2.5 GeV2
• RPGF 0.32

Hermes (all Q2)
SMC
pT12pT22
NN
xg
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?G/G - COMPASS
Schill

• Analysis a la SMC
• SpT2 gt 2.5 GeV2, Q2 gt 1 GeV2
• open charm signal

10 of statistics
2002/3
PGF cc ?open charm
Hermes
Compass 2002/3
SMC
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?G/G RHIC pp
p0
16
?G/G - Phenix ALL for p0
Fukao
Outlook 2005/7
2003/4
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?G/G Star ALL jets (2005)
Sowinski
2005
pT (GeV)
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NLO and NLL
Vogelsang

• Resummation of NLL important for single-inclusive
  processes ( ,
  )
• Crucial for lower energy fixed target
• Excellent agreement of NLO NNL calculations
  with collider data!
• prompt photons good probe for ?G/G at RHIC

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Prompt photons/p0
Vogelsang, Okada
20
RHIC detector upgrades

• important enlargement of xg coverage ? first
  moment

Kinney
Togawa

• Tungsten-Silicon sampling calorimeter

Silicon vertex barrel detector
2007-2008
2009
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Proposals

• Spintransfer in Hyperon production in pp
• Xu, Rykov
• Polarised DY p? p?at GSI (transversity)
• Efremov

22

• TRANSVERSE SPIN

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AN for pp -gt p0X
Ogawa
Makdisi
xF 0
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SSA and intrinsic kT
Murgia, DAlesio

• A generalized pQCD approach to SSA and unpol.
  cross sections LO.pQCD spin and new
  kT-dependent PDF and FF
• AN (p?p?pX)
• Sivers effect contributes, Collins effect
  suppressed
• suppressed for xFlt0 for all mechanisms
• good agreement with STAR data AN (p?p?p0X)

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Intrinsic kT (continued)
Boglione

• In the same model it was shown that
• AN(p?p?DX) is an ideal process to study the
  Sivers distribution functions of quarks and
  gluons
• The Hermes data can be
  described as well as the unpolarised Cahn
  asymmetries from EMC using

Prokudin
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p? p? cross section in NLO
Mukherjee

• first NLO calculation
• example prompt photon at Phenix
• scale dependence significantly reduced
• study of K-factors for DY

Ratcliffe
27
Hermes Collins Sivers
Schnell
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COMPASS Collins Sivers
Pagano
Collins
Sivers
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Dihadron fragmentation
Bacchetta

• New quark polarimeter

• simpler, no kT convolution, cf

van der Nat
Joosten
30
More Asymmetries
Gamberg

• Boer-Mulders function
• AUL
• Model for transversity and intrinsic motion of
  quarks
• Chiral-odd twist-3 DF e(x)
• New observables from color gauge invariance

Kinney
Zavada
Wakamatsu
Pijlman
31
Spin transfer to ?
Alexakhin

• Spin transfer to ?

• transverse ? polarisation

Friedrich
Belostotski
32
Exclusive ? production

• SDME
• Model

Neyret
Goloskokov
33
GPDs

• DVCS Beam Charge Asymmetry new deuteron
• Hard exclusive pp
• Exclusive p and vector mesons
• Hermes recoil detector

Marukyan
Fabbri
Rostomyan
Stewart
34
More from theory
Leader

• Spin sum rule revisited
• problem in derivation of
• rigorous treatment yields miraculously same SR
• new sum rule for transverse spin
• Higher twist resummation
• Asymmetries in SIDIS

Teryaev
Di Salvo
35
Fragmentation functions

• Determination of polarised fragmentation from
  Belle data in progress
• Possible difficulties with LUND fragmentation at
  low energies
• Q2 dependence of GDH

Seidl
Kotzinian
Nagaitsev
36
Personal Impression

• Two new facilities are working perfectly
• RHIC and COMPASS
• Enormous progress on theory of transverse spin
  and SSA
• Is ?G/G small?
• Exciting times ahead