M.Garçon, M. Guidal, C. Hadjidakis, K. Lukashin, L. Morand, S. Morrow, J. Santoro, E. Smith Exclusive  0,  electroproduction on the CLAS on the CLAS S. Morrow et al., Eur.Phys.J.A39:5-31,2009 (  J. Santoro et al., Phys.Rev.C78:025210,2008 ( L. Morand et al., Eur.Phys.J.A24: ,2005 ( C. Hadjidakis et al., Phys.Lett.B605: ,2005 (  GeV) K. Lukashin, Phys.Rev.C63:065205,2001 ( GeV) } e1-b (1999) } e1-6 ( )

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

ep  ep  + (  - ) Mm(epX) Mm(ep  + X) e p ++  - )

MC Acceptance calculation in 7D 200 million simulated events 100 days

Comparison DATA-SIMULATION Determine  &  from comparison to data Nacc  +(  *Nacc   +(  *Nacc   Ngen  +(  *Ngen   +(  *Ngen   eff = Determine acceptance as;

1) Ross-Stodolsky B-W for  0 (770), f 0 (980) and f 2 (1270) with variable skewedness parameter, 2)  ++ (1232)  +  - inv.mass spectrum and  +  - phase space. Background Subtraction (normalized spectra)

   (  * p  p  0 ) vs W

d  /dt (  * p  p  0 ) Fit by e bt Large t min ! (1.6 GeV 2 )

Angular distribution analysis, cos  cm Relying on SCHC (exp. check to the ~25% level)

Longitudinal cross section  L  (  * L p  p  L 0 )

Interpretation “a la Regge” : Laget model  *p  p  0  *p  p   *p  p  Free parameters: *Hadronic coupling constants: g MNN *Mass scales of EM FFs: (1+Q 2 /  2 ) -2

Regge/Laget  L (  * L p  p  L 0 ) Pomeron ,f 2

LO (w/o kperp effect) Soft overlap (partial) Handbag diagram calculation has k perp 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

GK GPD model

H, H, E, E (x,ξ,t) ~~ x+ξx-ξ t γ, π, ρ, ω… -2ξ x ξ-ξ-ξ +1 0 Quark distribution q q Distribution amplitude Antiquark distribution “ERBL” region“DGLAP” region W~1/  ERBLDGLAP

Double Distributions parametrization (Radyushkin) H q (x,  )~ d  d  x  DD q (  ) With : and DD q (  )=h  ) q(  )h(  )=[(1-|  |) 2 -  2 ] DD q ( ,t)=q (  ) h  )  -  ’(1-  )t Reggeized t dependence (M.G.,Polyakov,Vanderhaeghen,Radyushkin) x ξ-ξ-ξ +1 0 Add new D-term in ERBL region : H q (x,  t)= d  d  x  DD q (  t) +  d  d  x  DD ’ (  t) DD’( ,t)=  h  ) b’t/|  | b’t+1 With: Which reduces to a D-term-like form as t->0 Normalization arbitrary: fitted to data!

DDs + “meson exchange” DDs w/o “meson exchange” (VGG) “meson exchange”

“DDs” GPDs + “meson exchange” Laget Regge d  L /dt (  * p  p  0 )

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 if  0 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L Laget  T +  L W=2.9 GeV W=2.45 GeV W=2.1 GeV

  

Largest set ever of data for VM (  0,  ) production in the valence region (  L,T, d  /dt,…) Laget Regge model describes well most of the features of    cross sections (total and diff., L and T) up to Q 2 ~3.5 GeV 2. GPD handbag approach, though with large corrections (k perp ), gives good description of data for W>~5 GeV for the 3 channels. Summary For  channel: continues to work for W<~5 GeV For  channel: fails by large for W<~5 GeV (can potentially be cured by adding new contribution to GPD DD parametrisation) For  channel: fails by large for W<~5 GeV (won’t be cured by the same ansatz than the    vs H&E VM GPD dominance)

W~1/  GPDs/handbag GPDs/handbag ???

IM(p  + )

IM(p  - )