M.Garçon, M. Guidal, C. Hadjidakis,

K. Lukashin, L. Morand, S. Morrow,

J. Santoro, E. Smith

Exclusive Exclusive 00,, electroproduction electroproduction on the proton @ CLASon the proton @ CLAS

S. Morrow et al., Eur.Phys.J.A39:5-31,2009 (0@5.75GeV)

J. Santoro et al., Phys.Rev.C78:025210,2008 (@5.75GeV)

L. Morand et al., Eur.Phys.J.A24:445-458,2005 (@5.75GeV)

C. Hadjidakis et al., Phys.Lett.B605:256-264,2005 (0@4.2 GeV) K. Lukashin, Phys.Rev.C63:065205,2001 (@4.2 GeV) } e1-b

(1999)

} e1-6(2001-2002)

e1-6 experiment (Ee =5.75 GeV)(October 2001 – January 2002)

ep ep +(-)

Mm(epX)

Mm(ep+ X)

e

p

+

-)

MC Acceptance calculation in 7DVariable Range No.

Bins Bin Width

Q2(GeV2) 1.6-3.1 3.1-5.6

5 5

0.3 0.3

xB 0.16-0.7 9 0.06

t(GeV2) 0.1-1.9 1.9-4.3

6 3

0.3 9.8

0-360 9 40

cosHS+ -1.0 - +1.0 8 0.25

HS+ 0-360 8 45

MM[epX] (GeV)

0.22-1.87 15 0.22 200 million simulated events 100 days

Comparison DATA-SIMULATION

Determine & from comparison to data

Nacc+(*Nacc+(*Nacc

Ngen+(*Ngen+(*Ngeneff =Determine acceptance as;

1) Ross-Stodolsky B-W for 0(770), f0(980) and f2(1270)with variable skewedness parameter,2) ++(1232) +- inv.mass spectrum and +- phase space.

Background Subtraction (normalized spectra)

(*p p0) vs W

d/dt (*p p0)

Fit by ebt

Large tmin ! (1.6 GeV2)

Angular distribution analysis, cos cm

Relying on SCHC (exp. check to the ~25% level)

Longitudinal cross section L(*Lp pL

0)

Interpretation “a la Regge” : Laget model

*p p0

*p p

*p pFree parameters:*Hadronic coupling constants: gMNN

*Mass scales of EM FFs: (1+Q2/2)-2

Regge/Laget

L (*Lp pL0)

Pomeron ,f2

LO (w/o kperp effect)

Soft overlap (partial)

Handbag diagram calculation has kperp effects to account for preasymptotic effects

LO (with kperp effect)

Interpretation in terms of GPDs ?

GPDs parametrization based on DDs (VGG/GK model)

VGG GPD model

VGG GPD model

GK GPD model

H, H, E, E (x,ξ,t)~ ~

x+ξ x-ξ

tγ, π, ρ, ω…

-2ξ

xξ-ξ +

1-1 0

Quark

distribution

q q Distribution amplitude

Antiquark

distribution

“ERBL” region “DGLAP” region

W~1/

ERBL DGLAP

Double Distributions parametrizationDouble Distributions parametrization (Radyushkin)

Hq(x,)~ d dxDDq()

With : andDDq()=h) q() h()=[(1-||)2-2]

DDq(,t)=q () h)-’(1-)t

Reggeized t dependenceReggeized t dependence (M.G.,Polyakov,Vanderhaeghen,Radyushkin)

xξ-ξ +

1-1 0

Add new D-term in ERBL region :

Hq(x,t)= d dxDDq(t)+ d dxDD’(t)

DD’(,t)= h) b’t/||b’t+1With: Which reduces to a D-term-like form as t->0Normalization arbitrary: fitted to data!

DDs + “meson exchange”

DDs w/o “meson exchange” (VGG)

“meson exchange”

“DDs” GPDs +“meson exchange”

Laget Regge

dL/dt (*p p0)

ep->ep

cos(cm) distribution

cm distribution

Cross section (*p p

Laget T+L

Laget L VGG L

(H&E)

Laget Regge model

for *p p

Issue with GPD approach if0 exchange dominant :

0->E

E subleading in handbag for VM production

~

~while

Cross section (*p p –Comparison with GPD calculation (VGG)-

ep->ep

GK L

L

Laget T+L

W=2.9 GeV

W=2.45 GeV

W=2.1 GeV

Largest set Largest set everever of data for VM of data for VM ((00,,)) production production in the valence region in the valence region ((L,TL,T, d, d/dt,…)/dt,…)

Laget Regge model describes well most of the featuresLaget Regge model describes well most of the featuresof of cross sections cross sections (total and diff., L and T)(total and diff., L and T) up to up toQQ22~3.5 GeV~3.5 GeV22..

GPD handbag approach, GPD handbag approach, though with large corrections (kthough with large corrections (kperpperp),),

gives good description of data for gives good description of data for W>~5 GeV W>~5 GeV for the for the 33 channels. channels.

Summary

For For channel: continues to work for channel: continues to work for W<~5 GeVW<~5 GeV

For For channel: fails by large for channel: fails by large for W<~5 GeV W<~5 GeV (can potentially be (can potentially be cured by adding new contribution to GPD DD parametrisation) cured by adding new contribution to GPD DD parametrisation)

For For channel: fails by large for channel: fails by large for W<~5 GeV W<~5 GeV (won’t be cured by (won’t be cured by the same ansatz than the the same ansatz than the vs H&E VM GPD dominancevs H&E VM GPD dominance) )

W~1/

GPDs/handbag

GPDs/handbag ???

IM(p+)

IM(p-)