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. 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).

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

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

5. Quark and antiquark distribution functions

6. 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 ?

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)
The two models predict different sign for (with comparable amplitude).

8. Double-polarized transverse Drell-Yan1 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.

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

10. 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

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. 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~
PAX+JPARC  complete mapping of transversity

13. 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
Complete mapping of transv. valence + sea polarization