1/ 1/ GPDsGPDs are a are a beautiful/richbeautiful/rich theoretical tool theoretical tool but are very but are very difficultdifficult to access/extract experimentally to access/extract experimentally

2/ Very encouraging first experimental results coming out2/ Very encouraging first experimental results coming outfrom from JLab 6 GeVJLab 6 GeV (and (and HERMESHERMES) where we develop/test ) where we develop/test the analysis techniques the analysis techniques

3/3/ JLab@12 GeV JLab@12 GeV and and EICEIC are the ultimate facilities are the ultimate facilities for a full study/definite extraction of GPDsfor a full study/definite extraction of GPDs

Cross sections and charge asymmetries measurements (ReT)

Integral of GPDs over x

Beam or target spin asymmetriescontain only ImT,

i.e. GPDs at x = and

1

1

1

1

),,(),,(

~),,(

~ tHidxx

txHPdx

ix

txHT DVCS

p p’

H,E,H,E~ ~x

tx

= xB/(2-xB)

k = -t/4M2 A =

=ep ep

LU~ sin{F1H + (F1+F2)H +kF2E}d~

Polarized beam, unpolarized target:

H(,t), H(,,t), E(,,t)

Kinematical suppression

~

(BSA)

Unpolarized beam, long. pol. target:

UL~ sin{F1H+(F1+F2)(H + … }d~ H, H

~

(l)TSA

Unpolarized beam, trans. pol. target:

UT~ sin{k(F2H – F1E) + …. }d H, E

(t)TSA

Global (polarized and unpolarized) data analysis,Global (polarized and unpolarized) data analysis,X-sec, asym., (p,n), (X-sec, asym., (p,n), (,M), to extract the GPDs,M), to extract the GPDs

1/ 1/ GPDsGPDs are a are a beautiful/richbeautiful/rich theoretical tool theoretical tool but are very but are very difficultdifficult to access/extract experimentally to access/extract experimentally

2/ Very encouraging first experimental results coming out2/ Very encouraging first experimental results coming outfrom from JLab 6 GeVJLab 6 GeV (and (and HERMESHERMES) where we develop/test ) where we develop/test the analysis techniques the analysis techniques

3/3/ JLab@12 GeV JLab@12 GeV and and EICEIC are the ultimate facilities are the ultimate facilities for a full study/definite extractionfor a full study/definite extraction

Difference of polarized cross sections

Unpolarized cross sectionsUnpolarized cross sections

Thesis C. Muñoz-Camacho (Saclay), A. Camsonne (Clermont) : arXiv:nucl-ex/0607029

Hall A 6 GeV DVCS Bethe-Heitler

ep ep GPDs

Twist-2 terms dominate the cross section and are independent of Q2 in the explored kinematical domain The contribution to the cross section of twist-3 terms is small and is independent of Q2 in the limit of error bars

Strong indication in favor of factorization already from Q2=2 GeV2

in the valence region

0.09<-t<0.2 0.2<-t<0.4 0.4<-t<0.6

0.6<-t<1 1<-t<1.5 1.5<-t<2

PRELIMINARY

Thesis H.S. Jo (Orsay)

DVCS + BH cross sections andDVCS + BH cross sections andcomparison to theoritical BHcomparison to theoritical BH

Hall B 6 GeV

E03-106 n-DVCSP.Y. Bertin, C.E. Hyde-Wright, F. Sabatié, E. Voutier

et al.

Thesis M. Mazouz (Grenoble)

PRELIMINARY

en en

Strong sensitivity to E

1/ 1/ GPDsGPDs are a are a beautiful/richbeautiful/rich theoretical tool theoretical tool but are very but are very difficultdifficult to access/extract experimentally to access/extract experimentally

2/ Very encouraging first experimental results coming out2/ Very encouraging first experimental results coming outfrom from JLab 6 GeVJLab 6 GeV (and (and HERMESHERMES) where we develop/test ) where we develop/test the analysis techniques the analysis techniques

3/3/ JLab@12 GeV JLab@12 GeV and and EICEIC are the ultimate facilities are the ultimate facilities for a full study/definite extractionfor a full study/definite extraction

JLab 12 GeV : valence quarks region

EIC : gluons and sea quarksregion

Large phase space Large phase space ((,t,Q,t,Q22))

High luminosityHigh luminosity

Valence regionValence region

Sea/gluon regionSea/gluon region

JLab12JLab12

EICEIC

IC in standard position – 80 days – 10^35 Lum – VGG model

Beam asymmetry@12 GeVBeam asymmetry@12 GeV

ALU

<xB> =0.2<Q2> = 3.3 GeV2

<-t> = 0.45 GeV2

<xB> =0.2<Q2> = 3.3 GeV2

<Q2> =3.3 GeV2

<-t> = 0.45 GeV2

<xB> =0.36<Q2> = 4.1 GeV2

<-t> = 0.52 GeV2

<xB> =0.36<Q2> = 4.1 GeV2

<Q2> =4.1 GeV2

<-t> = 0.52 GeV2

BSA

TSA

Sensitivity to GPD modelsSensitivity to GPD models

2 (Im(AB*))/ T

t/4m2) - ReUT

Asymmetry depends linearly on the GPD E, which enters Ji’s sum rule.

A ~ (2Hu +Hd)

B ~ (2Eu + Ed)0

Goeke, Polyakov,Vdh, (2001)

0

Q2=5 GeV2

L=1035cm-2s-1

2000hrs

Exclusive Exclusive 00 prod. with transversely polarized target prod. with transversely polarized target

GPDs depend on3 variables GPDs depend on3 variables (x,(x,,t),t) and only and only 22 are are experimentally accessible experimentally accessible ((,t),t) : convolution issue and: convolution issue andinevitable model dependenceinevitable model dependence

Very encouraging first experimental results coming outVery encouraging first experimental results coming outfrom JLab 6 GeV (from JLab 6 GeV (twist-2twist-2 dominance, first constraints dominance, first constraints on GPD models, first on GPD models, first –very preliminary-–very preliminary- extractions of extractions ofJJuu, , JJdd,…),…)

Need to measure over a large phase space several Need to measure over a large phase space several channelschannelsand and observablesobservables which mutually constrain the GPDs which mutually constrain the GPDs parametrizationsparametrizations

SummarySummary

Ultimate facilities : Ultimate facilities : JLab@12 GeVJLab@12 GeV ( (valence quarkvalence quark region) region)and and EICEIC ( (gluonsgluons and and sea quarkssea quarks region) region)