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

Double-polarized DY production sensitive to polarized sea (u). Introduction 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).

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

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

Quark and antiquark distribution functions

Formal relation connecting quark 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 ?

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).

Double-polarized transverse Drell-Yan 1 2 Asymmetries evoluted with the assumptions: CDM 1 D. Dutta et al. LoI for JPARC xB 2 (~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.

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

Sign of the asymmetries discriminates fits assumption and models Summary: Model DY Asymmetries Fit symm.sea + ALL< 0 ATT< 0 CQSM ALL> 0 CDM ATT> 0 Sign of the asymmetries discriminates fits assumption and models Transversity extraction problematic with only p-p scattering Product of two unknown function. What about extraction? Sinergy with double polarized p-pbar experiment

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

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

Large asymmetries (> 0.10) for d. pol. DY at JPARC 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