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偏極核子・反核子衝突における 小横運動量ドレル・ヤン過程 arXiv:0801.0026 [hep-ph] ― QCDの摂動高次項の影響と核子の transversity 分布 ― 田中和廣 ( 順天堂大 ) 川村浩之 ( 理研 ) 小平治郎 (KEK)
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— Transversity Chiral-odd : unmeasurable in inclusive DIS First global fit (LO): SIDIS at HERMES, COMPASS + Collins function from BELLE Anselmino et al. (’07) Lattice study by QCDSF/UKQCD tDY data can provide an direct access to QCD corrections Transversely Polarized Drell-Yan (t DY) process RHIC,J-PARC
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bulk of dileptons produced at small Q T large perturbative corrections from gluon radiations make Q T the relevant scale NLO double-spin asymmetries Martin, Schafer, Stratmann, Vogelsang(’99) “sea-quark region” is probed at the scale double-spin asymmetries at a measured Kawamura, Kodaira, Tanaka, NPB777 (’07) 203 PTP 118 (’07) 581
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Barone, Cafarella, Coriano, Guzzi, Ratcliffe (‘05) Shimizu, Sterman, Yokoya, Vogelsang (’05) directly probe the valence-quark transversity at GSI For Q T unobserved: Large asymmetries ~ 20-40% QCD corrections are rather small We consider the QCD corrections for Q T observed case “threshold resummation’’ at the NNL level Kawamura, Kodaira, Tanaka, arXiv:0801.0026 [hep-ph]
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Next-to-leading logarithmic (NLL) resummation formula Process-indep.: Kodaira, Trentadue (’82) Davies, Stirling,Webber (’85) Collins, Soper, Sterman ( ‘85) Kawamura,Kodaira,Shimizu,Tanaka, PTP 115 (’06) 667
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NLL resummation formula for spin-independent cross section from Altarelli, Ellis, Greco, Martinelli (’84); Collins, Soper, Sterman (’85) is universal ! Gluon distribution participates !
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Gaussian smearing factor:
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Transversity distribution μ-dep.: NLO DGLAP evolution Hayashigaki, Kanazawa, Koike (’97) Kumano, Miyama (’97) Vogelsang(’98) x-dep.: Vogelsang et al (’98) Input PDFs nucleon models, empirical fit
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Shaded area : LO empirical fit Anselmino et al., PRD75 (’07) 054032
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S = 210 GeV 2, Q = 4GeV, y=φ=0 NLL+LO: total (“NLL+Y’’) prediction @ GSI “Soffer bound PDF” flat behavior: universality of soft gluon effects @ J-PARC
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Novel asymptotoic formula Saddle-point formula at the NLL level “degree 0 approximation’’ suggested by CSS (’85)
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“very large prefactor” is universal ! gluon distribution decouples ! extension of LL-level saddle point formula by Parisi, Petronzio (’79) to NLL level
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Most of soft gluon resummation effets cancel out “unconventional scale” a part of NLL-level resummation contribution survives
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“Soffer bound PDF” @ GSI S = 210 GeV 2, y=φ=0
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S = 80 GeV 2, y=φ=0
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y=φ=0 S = 30 GeV 2 S = 45 GeV 2
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φ=0 S = 45 GeV 2, y=0.3S = 210 GeV 2, y=0.5
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Summary: DY at small Q T in QCD
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