1. JLab12 & EIC
QCD workshop, 15/12/06

2. 1/ GPDs are a beautiful/rich theoretical tool
but are very difficult to access/extract experimentally
2/ Very encouraging first experimental results coming out
from JLab 6 GeV (and HERMES) where we develop/test
the analysis techniques
3/ GeV and EIC are the ultimate facilities
for a full study/definite extraction of GPDs

3. t x H,E,H,E g* x~xB g,M,... ~ p p’ Beam or target spin asymmetries
Cross sections and
charge asymmetries measurements (ReT)
Integral of GPDs over x
Beam or target spin asymmetries
contain only ImT,
i.e. GPDs at x = x and -x
Intro

4. ep epg Global (polarized and unpolarized) data analysis,
X-sec, asym., (p,n), (g,M), to extract the GPDs
ep epg
x = xB/(2-xB)
k = -t/4M2
A = Ds 2s
s+ - s-
s+ + s- =
DsLU ~ sinf{F1H + x(F1+F2)H +kF2E}df ~
Polarized beam, unpolarized target:
H(x,x,t), H(x,x,t), E(x,x,t)
Kinematical suppression
(BSA)
Unpolarized beam, long. pol. target:
DsUL ~ sinf{F1H+x(F1+F2)(H + … }df ~
H, H
(l)TSA
Unpolarized beam, trans. pol. target:
DsUT ~ sinf{k(F2H – F1E) + ….. }df
H, E
(t)TSA

5. 1/ GPDs are a beautiful/rich theoretical tool
but are very difficult to access/extract experimentally
2/ Very encouraging first experimental results coming out
from JLab 6 GeV (and HERMES) where we develop/test
the analysis techniques
3/ GeV and EIC are the ultimate facilities
for a full study/definite extraction

6. ep epg Hall A 6 GeV DVCS Bethe-Heitler
GPDs
Difference of polarized cross sections
Unpolarized cross sections
Thesis C. Muñoz-Camacho (Saclay), A. Camsonne (Clermont) : arXiv:nucl-ex/

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

8. PRELIMINARY DVCS + BH cross sections and comparison to theoritical BH
Hall B 6 GeV
Thesis H.S. Jo (Orsay)
0.09<-t<0.2
0.2<-t<0.4
0.4<-t<0.6
PRELIMINARY
0.6<-t<1
1<-t<1.5
1.5<-t<2

9. P.Y. Bertin, C.E. Hyde-Wright, F. Sabatié, E. Voutier et al.
E n-DVCS
P.Y. Bertin, C.E. Hyde-Wright, F. Sabatié, E. Voutier et al.
en eng
Strong sensitivity to E
PRELIMINARY
Thesis M. Mazouz (Grenoble)

10. 1/ GPDs are a beautiful/rich theoretical tool
but are very difficult to access/extract experimentally
2/ Very encouraging first experimental results coming out
from JLab 6 GeV (and HERMES) where we develop/test
the analysis techniques
3/ GeV and EIC are the ultimate facilities
for a full study/definite extraction

11. JLab 12 GeV : valence quarks region EIC : gluons and sea quarks
Large phase space (x,t,Q2)
JLab 12 GeV :
valence quarks
region
EIC : gluons
and sea quarks
High luminosity
Valence region
JLab12
Sea/gluon region
EIC

12. Beam GeV
IC in standard position – 80 days – 10^35 Lum – VGG model

13. Sensitivity to GPD modelsA LU
BSA
<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
TSA
<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

14. Exclusive r0 prod. with transversely polarized target
2D (Im(AB*))/p T
AUT = -
A ~ (2Hu +Hd) r0
|A|2(1-x2) - |B|2(x2+t/4m2) - Re(AB*)2x2
B ~ (2Eu + Ed)
Q2=5 GeV2
Asymmetry depends
linearly on the GPD E,
which enters
Ji’s sum rule. r0
Goeke, Polyakov,
Vdh, (2001)
L=1035cm-2s-1
2000hrs

15. Summary GPDs depend on3 variables (x,x,t) and only 2 are
experimentally accessible (x,t) : convolution issue and
inevitable model dependence
Need to measure over a large phase space several channels
and observables which mutually constrain the GPDs
parametrizations
Very encouraging first experimental results coming out
from JLab 6 GeV (twist-2 dominance, first constraints
on GPD models, first –very preliminary- extractions of
Ju, Jd,…)
Ultimate facilities : GeV (valence quark region)
and EIC (gluons and sea quarks region)