m.garçon, m. guidal, c. hadjidakis, k. lukashin, l. morand, s. morrow, j. santoro, e. smith...
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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-)
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