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M. Contalbrigo, A. Drago and P. Lenisa Università di Ferrara and INFN – ITALY V.Barone

Measuring the sea polarization by Drell-Yan production at moderate energies. M. Contalbrigo, A. Drago and P. Lenisa Università di Ferrara and INFN – ITALY V.Barone Università del Piemonte Orientale and INFN - Italy. XVII International Spin Physics Symposium – Kyoto – October 2006.

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M. Contalbrigo, A. Drago and P. Lenisa Università di Ferrara and INFN – ITALY V.Barone

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  1. Measuring the sea polarization by Drell-Yan production at moderate energies M. Contalbrigo, A. Drago and P. Lenisa Università di Ferrara and INFN – ITALY V.Barone Università del Piemonte Orientale and INFN - Italy XVII International Spin Physics Symposium – Kyoto – October 2006

  2. Helicity distributions of valence quarks (rather) well known • Helicity distributions of polarized sea poorly known • Fits: • Models agree on , disagree on size • Situation more confused for transversity • Models agree within a factor 2 for • Even worse for • Models disagree both on sign of and size. • JPARC: 50 GeV polarized p beam on polarized target: • Double-polarized DY production sensitive to polarized sea (u). Introduction

  3. Std. scenario: Val. scenario: Models: Longitudinal sea M. Glück et al. Phys. Rev. D 63 (2001) 094005

  4. Val. scenario Models: xB xF=x1-x2 D. Dutta et al. LoI for JPARC Std. scenario Double-polarized longitudinal Drell-Yan

  5. Quark and antiquark distribution functions

  6. Formal relation connectingquark and antiquark distribution functions • Antiquark distributions can be computed either: • using this formal relation (cQSM)  semiconnected diagrams ? Jaffe NPB229(1983)205 • directly from the definition of antiquark d.f. (bag models) •  saturation of valence quark sum rule ?

  7. Transverse sea CQSM CDM V. Barone, T. Calarco and A. Drago Phys. Lett. B 390 (1997) 287 M. Wakamatsu and T. Kubota Phys. Rev. D 63 (1999) 034020 • The two models predict different sign for (with comparable amplitude).

  8. 1 1 2 2 xB D. Dutta et al. LoI for JPARC Double-polarized transverse Drell-Yan Asymmetries evoluted with the assumptions: CDM (~CQSM) • Aymmetry is large at JPARC energy (> 0.1) • Sign of the asymmetry will distinguish between the two models. • It will give indications about calculation of sea distributions.

  9. Higher energy p-p machine V. Barone, T. Calarco and A. Drago Phys. Rev. D 56 (1997) 527 Small asymmetries

  10. What about extraction? • Transversity extraction problematic with only p-p scattering • Product of two unknown function. • Summary: Sign of the asymmetries discriminates fits assumption and models • Sinergy with double polarized p-pbar experiment

  11. h1 from pbar-p Drell-Yan at PAX (GSI) Anselmino et al. PLB 594,97 (2004) 10 % precision on the h1u (x) in the valence region

  12. PAX JPARC M2/s=x1x2~0.01-0.3 x1=x2ATTh1u2 Extraction of h1u for x>0.05 Measurement of h1u for 0.15<x<0.5 DY events distribution PAX+JPARC  complete mapping of transversity

  13. Conclusions • Large asymmetries (> 0.10) for d. pol. DY at JPARC • Discrimination between fits assumption and models • Look at the signs of ALL and ATT • Will teach how to calculate antiquark distributions • High complementarity between JPARC and PAX@GSI • Complete mapping of transv. valence + sea polarization

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