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M. Contalbrigo, A. Drago and P. LenisaM. Contalbrigo, A. Drago and P. Lenisa Università di Ferrara and INFN – ITALYUniversità di Ferrara and INFN – ITALY

V.BaroneV.BaroneUniversità del Piemonte Orientale and INFN - ItalyUniversità del Piemonte Orientale and INFN - Italy

XVII International Spin Physics Symposium – Kyoto – October 2006

Measuring the sea polarization Measuring the sea polarization by Drell-Yan production by Drell-Yan production

at moderate energiesat moderate energies

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IntroductionIntroduction

•Helicity distributions of valence quarks (rather) well known

•Helicity distributions of polarized sea poorly known

•Fits:

•Models agree on , disagree on size

0,0 uu

0u

•Situation more confused for transversity

•Models agree within a factor 2 for

•Even worse for

•Models disagree both on sign of and size.

uh1

uh1

uh1

JPARC: 50 GeV polarized p beam on polarized target:

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

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Longitudinal seaLongitudinal sea

M. Glück et al.Phys. Rev. D 63 (2001) 094005

Models:

ouu CDMCQSM

ux

ux

dx

dx

sx

Gx

Val. scenario: 0;

),(

),(2

2

ss

d

u

xu

xd

ssdduuQxq seasea ),( 2

Std. scenario:

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Val. scenario

Std. scenarioxF=x1-x2

q q

q q

LLDYLL

xqxqxqxqe

xqxqxqxqeaA

21212

21212

Double-polarized longitudinal Drell-Double-polarized longitudinal Drell-YanYan

GeVs 10Models:

oAA CDMCQSM

LLLL

D. Dutta et al.LoI for JPARC

xB

5

Quark and antiquark distribution functions

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Formal relation connectingquark and antiquark distribution functions

Antiquark distributions can be computed either:

• using this formal relation (QSM) semiconnected diagrams ? Jaffe NPB229(1983)205• directly from the definition of antiquark d.f. (bag models) saturation of valence quark sum rule ?

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Transverse seaTransverse sea

M. Wakamatsu and T. KubotaPhys. Rev. D 63 (1999) 034020

V. Barone, T. Calarco and A. Drago

Phys. Lett. B 390 (1997) 287

CDM CQSM

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

uh1

dh1

),(1 initu

Qxh),(

1 evoluQxh

),(1 initd

Qxh),(

1 evoldQxh

uh1

8

CDM

(~CQSM)

2

1

q i

q qqqqqTT

DYTT

xqxqxqxqe

xhxhxhxheaA

21212

211121112

Double-polarized transverse Drell-Double-polarized transverse Drell-YanYan

•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.

),(),( 2201 0QxqQxh

q

),(),( 2201 0QxqQxh

q

1

2Asymmetries evoluted with the

assumptions:GeVs 10

D. Dutta et al.LoI for JPARC

xB

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Higher energy p-p machineHigher energy p-p machine

GeVs 100

V. Barone, T. Calarco and A. Drago

Phys. Rev. D 56 (1997) 527

Small asymmetries

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Model DY Asymmetries

Fit symm.sea +ALL< 0 ATT< 0

CQSM ALL> 0 ATT< 0

CDM ALL> 0 ATT> 0

),(),( 2201 0QxqQxh

q

Sign of the asymmetries discriminates fits assumption and models

•Sinergy with double polarized p-pbar experiment

•Transversity extraction problematic with only p-p scattering

•Product of two unknown function.

What about extraction?

•Summary:

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h1 from pbar-p Drell-Yan at PAX (GSI)

Anselmino et al. PLB 594,97

(2004)

)()(

)()(ˆ

)()()()(

)()()()(ˆ

21

2111

21212

211121112

xuxu

xhxha

xqxqxqxqe

xhxhxhxheaA uu

TT

q q

q qqqqq

TTTT

10 % precision on the h1u (x) in the valence region

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PAXPAX

DY events distributionDY events distribution

PAX+JPARC complete mapping of transversity

JPARCJPARC

Extraction of h1u for x>0.05x1=x2 ATTh1u2

Measurement of h1u for 0.15<x<0.5

M2/s=x1x2~0.01-0.3

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ConclusionsConclusions

•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