generalized parton distributions
DESCRIPTION
Generalized Parton Distributions. Duality'05, 08/06/05. M. Guidal, IPN Orsay. 1/ Generalized Parton Distributions. H,E( x , x , t ) H,E( x , x , t ). ~. ~. GPDs. (Ji, Radyushkin, Muller, Collins, Strikman, Frankfurt). t= D 2. g*. g,M,. -2x. x+ x. x- x. p - D /2. - PowerPoint PPT PresentationTRANSCRIPT
Generalized Parton DistributionsGeneralized Parton Distributions
1/ Generalized 1/ Generalized Parton Parton DistributionsDistributions
p-/2 p’(=p+2)
H,E(x,,t)H,E(x,,t)
~~
x-
t=2
x+
GPDsGPDs
(Ji, Radyushkin, Muller, Collins, Strikman, Frankfurt)
light-cone dominance, nμ (1, 0, 0, -1) / (2 P+)
p-/2 p’(=p+2)
H,E(x,,t)H,E(x,,t)
~~
x-
t=2
x+
GPDsGPDs
Vector Ms : H,E
Large Q2, small t
PS Ms : H,E~ ~
(Ji, Radyushkin, Muller, Collins, Strikman, Frankfurt)
: T lead. twist
Mesons : L
light-cone dominance, nμ (1, 0, 0, -1) / (2 P+)
{{[[Hq(x,,t)N(p’)N(p’)++N(p)N(p) + + Eq(x,,t)N(p’)iN(p’)i++N(p)]N(p)]
5 5 [[Hq(x,,t)N(p’)N(p’)+ + 5 5 N(p) +N(p) + Eq(x,,t)N(p’)N(p’)N(p)]N(p)]}}2M2M_ ~~
2M2M
_
_
_
H,E(x,,t)H,E(x,,t)
~~
x-
t=2
x+
{{[[Hq(x,,t)N(p’)N(p’)++N(p)N(p) + + Eq(x,,t)N(p’)iN(p’)i++N(p)]N(p)]
5 5 [[Hq(x,,t)N(p’)N(p’)+ + 5 5 N(p) +N(p) + Eq(x,,t)N(p’)N(p’)N(p)]N(p)]}}2M2M_ ~~
2M2M
_
_
_
Vector Ms : H,E
Large Q2, small t
PS Ms : H,E~ ~
(Ji, Radyushkin, Muller, Collins, Strikman, Frankfurt)
: T lead. twist
Mesons : L p-/2 p’(=p+2)
GPDsGPDs
light-cone dominance, nμ (1, 0, 0, -1) / (2 P+)
H, H, E, E (x,ξ,t)~ ~
“Ordinary” parton distributions
H(x,0,0) = q(x), H(x,0,0) = Δq(x) ~
x
Elastic form factors
H(x,ξ,t)dx = F(t) ( ξ)
x
Ji’s sum rule
2Jq = x(H+E)(x,ξ,0)dx
gq LGL 21
21
(nucleon spin)
x+ξ x-ξ
tγ, π, ρ, ω…
-2ξ
: do NOT appear in DIS NEW INFORMATION
xξ-ξ +
1-1 0anti-quark distribution
quark distribution
q q distribution amplitude
Cross-section measurementand beam charge asymmetry (ReT)
integrate GPDs over x
Beam or target spin asymmetrycontain only ImT,
therefore GPDs at x = and
(M.
Va
nde
rhae
gh
en)
1
1
1
1
),,(),,(
~),,(
~ tHidxx
txHPdx
ix
txHT DVCS
p p’
H,E,H,E~ ~x
tx
ExtensionsExtensions
RCS : p->p (intermediate t) (Radyushkin, Dihl, Feldman, Jakob, Kroll)
VCS : ep->e (Frankfurt, Polyakov, Strikman, Vanderhaeghen)
tDDVCS : ep->ep* (e+e-) (M.G., Vanderhaeghen, Belitsky, Muller,...)
IDVCS : pp->(Freund, Radyushkin,Shaeffer,Weiss)
tDVCS : p->p* (e+e-) (Berger, Pire, Diehl,...)
N-DVCS : eA->eA(Scopetta, Pire, Cano, Polyakov, Muller, Kirschner, Berger....)
Hybrids, pentaquarks,... (Pire, Anikin,Teryaev,...)
sDDVCS : ep->ep (Vanderhaeghen, Gorschtein,...)
_
- “Trivial” kinematical corrections
- Quark transverse momentum effects (modification of quark propagator)
- Other twist-4 ……
DES: finite Q2 corrections(real world ≠ Bjorken limit)
DES: finite Q2 corrections(real world ≠ Bjorken limit)
GPD evolution
O (1/Q)
O (1/Q2)
Dependence on factorization scale μ :
Kernel known to NLO
- Gauge fixing term- Twist-3: contribution from γ*L may be expressed in terms of derivatives of (twist-2) GPDs.
- Other contributions such as small (but measureable effect).
(here for DVCS)
2/ Study on the2/ Study on the(x,t) correlation of the GPDs(x,t) correlation of the GPDs
(in coll. with M. Vanderhaeghen,
A. Radyushkin & M. Polyakov)
H(x,0,b )=FT H(x,0,t)
(Burkhardt)
y
xpz
b
x
f x b( , )
1
0
xz
b
The The GPDGPDs contains contain information information on the on the longitudinallongitudinal ANDAND transversetransverse distributions ofdistributions ofthethe partons partons in the nucleonin the nucleon
GPDs in impact parameter spaceGPDs in impact parameter space
N 'N
3-D picture of the nucleon3-D picture of the nucleon (femto-graphy of the nucleon)(femto-graphy of the nucleon)
(Belitsky)
GPDsGPDs : : tt dependence ( dependence ( small –small –t t ))
evaluate for ξ = 0 : model and
t = 0 :
t ≠ 0 :
2 free parameters : ’1,’2 Fit 4 form factors : G E,M p,n
LOW -t ( -t < 1 GeV2
) : Regge model Goeke, Polyakov,
Regge trajectory :
valence model for
E
Vanderhaeghen (2001)
proton proton & & neutron neutron charge radiicharge radii
GPV Regge model
Regge slope
experiment
F1u = uv(x)1/(x ’t)dx
1
0
r 21,p =-6’ lnx(euuv+eddv)dx
proton proton electromagnetic form electromagnetic form factorsfactors
GPV Regge model
forward parton distributions
at = 1 GeV2 (MRST2002 NNLO)
neutron neutron electromagnetic form electromagnetic form factorsfactors
GPV Regge model
Large t power behavior is fixed by large x (->1) behavior
GPDsGPDs : : tt dependence ( dependence ( large –t large –t )) modified Regge model : M.G., Polyakov, Radyushkin, Vanderhaeghen (2004)
Hq(x,,t)=q(x)x-t=q(x)e-t ln(x)
F1(t)->1/t2, F2(t)->1/t4 (t>>)
if q(x) ~ (1-x) then FF->1/t(+1)
2/ Large x behavior of E should be different from H :
extra (1-x) power q for q(x)
if q(x)->(1-x) then FF->1/t(+1)/2 (Drell-Yan-West relation)
exp(- α΄ t lnx) -> exp(- α΄ (1 – x) t lnx)
M. Burkardt (2002)
1/
proton proton electromagnetic form electromagnetic form factorsfactors
GPRV modified Regge
modelGPV Regge model
’ = 1.105 GeV-2
u = 1.713
d = 0.566
neutron neutron electromagnetic form electromagnetic form factorsfactors
GPRV modified Regge
model
GPV Regge model
proton proton Dirac & Pauli form factorsDirac & Pauli form factors
GPRV modified Regge
model
GPV Regge model
x
b (fm)
N -> N -> ΔΔ transition form factorstransition form factors
GPRV modified
Regge model
GPV Regge
model
in large Nc limit
PROTON M2q 2 Jq
valence model M1
(GPV 01)
2 Jq
valence model M2
(GPRV 04)
2 Jq
Lattice
QCDSF 03
u 0.40
0.69 0.63 0.734 ± 0.135
d 0.22 -0.07 -0.06 -0.085 ± 0.088
s 0.03 0.03 0.03
u + d + s
0.65 0.65 0.60 0.65 ± 0.16
quark contribution to quark contribution to proton proton spinspin
with
valence models for eq(x) :
M1 :
M2 :
PROTON 2 Jq
valence model M2
(GPRV 04)
ΔqHERMES
(1999)
2 Lq
u 0.63 0.57 ± 0.04 0.06 ± 0.04
d -0.06 -0.25 ± 0.08 0.19 ± 0.08
s 0.03 -0.01 ± 0.05 0.04 ± 0.05
u + d + s
0.60 0.30 ± 0.10 0.30 ± 0.10
orbital angular momentum orbital angular momentum carried by quarkscarried by quarks
evaluated at μ2 = 2.5 GeV2
SummarySummary
Generalized Parton Distributions (GPDs)
x-t correlations and nucleon form factors 3 parameters (’,u,d) GPDs
describe all existing data (GE,Mp,n)
spin of nucleon / lattice QCD
The actorsThe actors
JLab
Hall A Hall B Hall C
p-DVCS
n-DVCS
Vector mesons
p-DVCS
d-DVCS
Pseudoscalar mesons
DESYHERMES ZEUS/H1
Vector & PS mesons
DVCS
CERNCOMPASS
Vector mesons
DVCS
+ theory (almost) everywhere
JLab(Ee=6 GeV):CLAS/Hall B (2001+2005) and Hall A (2004)
HERA (Ee=27 GeV) : HERMES and ZEUS/H1 (up to 2006)
CERN (E=200 GeV) : COMPASS (2007 ?)
« DES » in the world« DES » in the world
e
p
e’
p’
The epThe ep ep ep process process
DVCSDVCS
e
p
e’
p’
e
p
e’
p’
Bethe-HeitlerBethe-Heitler
GPDs
...
2
1''
5
dt
d
dt
d
dtddkd
d LTV
ee
1
1V
Vete
B ECxQ 1,2
Energy dependenceEnergy dependence
BH
DVCS
Calculation (M.G.&M.Vanderhaeghen)
e
p
e’
p’
The epThe ep ep ep process process
DVCSDVCS
e
p
e’
p’
e
p
e’
p’
Bethe-HeitlerBethe-Heitler
Interference between the 2 processes : if the electronbeam is polarised => beam spin asymmetry
GPDs
First experimental signaturesFirst experimental signatures
Magnitude and Q2 dependence of DVCS X-section (H1/ZEUS)
First observations of DVCS beam asymmetries
CLAS HERMES
DVCS
First observations of DVCS charge asymmetry (HERMES)
All in basic agreement with theoretical predictions
2 2
2
1.25 GeV
0.19
0.19 GeV
B
Q
x
t
Phys.Rev.Lett.87:182002,2001
4.8 GeV data (G. Gavalian)
PRELIMINARY
0.15 < xB< 0.41.50 < Q2 < 4.5 GeV2
-t < 0.5 GeV2
PRELIMINARY
PRELIMINARY
5.75 GeV data (H. Avakian &L. Elhouadrhiri)
CLAS/DVCS at 4.8 and 5.75 GeVCLAS/DVCS at 4.8 and 5.75 GeV
γ*Lρ
Handbag diagram calculation (frozen s) can account for CLAS and HERMES data on σL(ep->ep)
Q2(GeV2)
CLAS 4.2 GeV data (C. Hadjidakis, hep-ex/0408005)
W=5.4 GeV
HERMES (27GeV)A. Airapetian et al., EPJC 17
σL(ep->ep)
Regge (Laget)
GPD (MG-MVdh)
Mesons
proton proton & & neutron neutron charge radiicharge radii
GPV Regge model
Regge slope
experiment
F1u = uv(x)1/(x ’t)dx
1
0
r 21,p =-6’ lnx(euuv+eddv)dx
<x ><x >00
<x ><x >-1 -1
t=0t=0
<x ><x >11
DDsDDs
« D-term »« D-term »kk
GPDsGPDs
Pion cloudPion cloudTrans. Mom. of partonsTrans. Mom. of partons
F (t), G (t)F (t), G (t)1,21,2 A,PSA,PS
q(x),q(x),q(x)q(x)
R (t),R R (t),R (t)(t)AA VVJJqq
(z)(z)
Deconvolution needed !Deconvolution needed !x : mute variable
p p’
H,E,H,E~ ~
x
tx
Hq(x,,t) but only and t accessible experimentally
d
dQ d dt2
B
~ AH (x,,t,Q )2q
x-idx +BE (x,,t,Q )2
q
x-idx +….
1 1
-1 -1
2
= xB1-x /2B t=(p-p ’)2
x = xB !
/2
Compton ScatteringCompton Scattering
“ “DVCS” (Deep Virtual Compton Scattering)DVCS” (Deep Virtual Compton Scattering)
GPDs probe the nucleon at GPDs probe the nucleon at amplitudeamplitude level level
q(x)~<p|q(x)~<p|(x)(x)(x)|p ’>(x)|p ’> H(x,H(x,)~<p|)~<p|(x-(x-))(x+(x+)|p ’>)|p ’>
pp p’p’
x+x+ x-x-
zz00 1100 11 zz
pp p’p’
x+x+ x-x-x<x<::x>x>::
DIS :DIS : DES :DES :
pp p’p’
xx xx
pp p’p’
x+x+ x-x-
( )b
0 b
y
xz
b
Transverse Transverse localisation of the localisation of the partons partons in the nucleonin the nucleon(independently(independently of their of their longitudinallongitudinal momentum) momentum)
Form FactorsForm Factors
N 'N
'ee
x
)(xf
1
0
y
xpz
xz
LongitudinalLongitudinal momentum distributionmomentum distribution(no (no information information on the on the transversetransverse localisation) localisation)
Parton DistributionParton Distribution
N
'ee
(Belitsky et al.)(Belitsky et al.)
F1s (t)= [s(x)-s(x)]/ (x ’t)dx=0
1
-1
Nucleon strangeness : FNucleon strangeness : F11ss
_
[s(x)-s(x)]dx=01
-1
But : /
_