GPDs @ JLab12 & EIC QCD workshop, 15/12/06

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

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

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

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

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/0607029

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

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

P.Y. Bertin, C.E. Hyde-Wright, F. Sabatié, E. Voutier et al. E03-106 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)

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

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

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

Sensitivity to GPD models A 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

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

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 : JLab@12 GeV (valence quark region) and EIC (gluons and sea quarks region)