Summay of Session 2 QCD spin structure of nucleons
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Transcript of Summay of Session 2 QCD spin structure of nucleons
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Summay of Session 2
QCD spin structure of nucleons
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SPIN 2004 session 2
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G. Mallot/CERN
Summary Session 2
IntroductionHelicity distributionsGluon polarisation
transversity
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SPIN 2004 session 2
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• 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
Summary of Session 2
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HELICITY DISTRIBUTIONS
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Final g1 for p, d, n
• quasi final data set for p and d
• corrected for smearing (radcor, detector)
Riedl
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Quark helicity distributions
Rubin
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Inclusive asymmetries
• COMPASS deuteron data 2002 – 2003
• most precise data for x<3x10-2
• 2004 similar precision
• kaon/pion asymmetries to come
Peshekhonovinclusive
+ve hadrons
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• 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)
Δq - Theory
Christova
Shevchenko
remark: A exp. diffcult with magnetic spectrometers
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Δq - JLAB
• under construction (2006-2007)• expect very precise data for
x > 0.1
• apply method
JiangSemi-SANE E04-113
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Evolution
Stamenov
Ermolaev
Goshtasbpour
Ramsey
•parametrisation-independent matrix solution of DGLAP
•estimates of ΔG/G and Lq ranges
• 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
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GLUON POLARISATION
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ΔG/G - Photon-Gluon Fusion
measured
aLL: calculable partonic asymmetriesR: Monte-Carlo (Lepto for Q2 > 1 GeV2)
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ΔG/G - SMC
• event selection high-pT pairs– Q2 > 1 GeV2
– neural network
– ΣpT2 > 2.5 GeV2
• RPGF = 0.32
Rondio
SMC Hermes (all Q2)
NN pT12+pT2
2
xg
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ΔG/G - COMPASS
• Analysis a la SMC– ΣpT
2 > 2.5 GeV2, Q2 > 1 GeV2
• open charm signal10% ofstatistics
Schill
Hermes
SMC
Compass2002/3
PGF: cc open charm
2002/3
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ΔG/G – RHIC pp
π0
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ΔG/G - Phenix: ALL for π0
Fukao
Outlook 2005/72003/4
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ΔG/G – Star: ALL jets (2005)
STARSTAR Sowinski
0 5 10 15 20 25 30
0.2
0.4
0.6
0.8
1.0
0.0
gg qq
qg
Inclusive Jets :LOW. Vogelsang
pT (GeV)
2005
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• 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 ΔG/G at RHIC
NLO and NLLVogelsang
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Prompt photons/π0
Vogelsang, Okada
prompt γπ0
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RHIC detector upgrades
Tungsten-Silicon sampling calorimeter
prompt photon central arms
GS95
x
NCC
Kinney TogawaSilicon vertex barrel detector
• important enlargement of xg coverage first moment
2007-20082009
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• Spintransfer in Hyperon production in pp
Xu, Rykov
• Polarised DY p↑ p↑at GSI (transversity)
Efremov
Proposals
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TRANSVERSE SPIN
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AN for pp -> π0X
STARSTAR OgawaMakdisi
xF = 0
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SSA and intrinsic kT
• A generalized pQCD approach to SSA and unpol. cross sections: LO.pQCD + spin and new kT-dependent PDF and FF
• AN (p↑pπX): – Sivers effect contributes, Collins effect suppressed
– suppressed for xF<0 for all mechanisms
– good agreement with STAR data AN (p↑pπ0X)
Murgia, D’Alesio
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Intrinsic kT (continued)
In the same model it was shown that
• AN(p↑pDX) 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
Boglione
Prokudin
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p↑ p↑ cross section in NLO
• first NLO calculation• example: prompt photon
at Phenix• scale dependence
significantly reduced
• study of K-factors for DY
Mukherjee
Ratcliffe
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Hermes Collins & Sivers
Schnell
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COMPASS Collins & Sivers
Pagano
Collins Sivers
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Dihadron fragmentation
• New quark polarimeter
h1
h2
quark
TR
Bacchetta
• simpler, no kT
convolution, cf
van der Nat
Joosten
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More Asymmetries
• 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
Gamberg
Kinney
Zavada
Wakamatsu
Pijlman
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Spin transfer to Λ
Alexakhin • Spin transfer to Λ
• transverse Λ polarisation
Friedrich Belostotski
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• SDME:
• Model
Exclusive ρ production
Neyret
Goloskokov
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• DVCS Beam Charge Asymmetry new: deuteron
• Hard exclusive ππ• Exclusive π and vector mesons• Hermes recoil detector
GPDs
Marukyan
Fabbri
Rostomyan
Stewart
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More from theory
• 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
Leader
Teryaev
Di Salvo
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• Determination of polarised fragmentation from Belle data in progress
• Possible difficulties with LUND fragmentation at low energies
• Q2 dependence of GDH
Fragmentation functions
Seidl
Kotzinian
Nagaitsev
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Personal Impression
• Two new facilities are working perfectly:
RHIC and COMPASS• Enormous progress on theory of
transverse spin and SSA
• Is ΔG/G small?
Exciting times ahead