M.Garçon, M. Guidal, C. Hadjidakis, K. Lukashin, L. Morand, S. Morrow, J. Santoro, E. Smith...
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Transcript of M.Garçon, M. Guidal, C. Hadjidakis, K. Lukashin, L. Morand, S. Morrow, J. Santoro, E. Smith...
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 ([email protected])
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 ([email protected] 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-)