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![Page 1: Delia Hasch](https://reader036.fdocuments.net/reader036/viewer/2022062304/56813300550346895d99bec3/html5/thumbnails/1.jpg)
Delia Hasch
DVCS & hard exclusive meson prod.-- experimental review --
TRANSVERSITY 2011, Losinj, Croazia, Aug 29 - Sep 02, 2011
a very brief introduction
prerequisites and methods
from low to high x : selected results
perspectives
all details tomorrow: F. X. Girod S. Yaschenko N. D’Hose V. Burkert
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[slide by L. Pappalardo]
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3D imaging of the nucleon & OAM
TMD (x,kT)spin-orbit
correlations
GPD(x, x,t)2+1D imaging; access to OAM
W(x,r,kT)
rd 3 dzkd T2
Wigner distribution (‘mother function’):
(model dependent) relations between TMDs & GPDs:
)0,0,(~)( )n()n(1 xExf qqT
[Burkardt 2002][Burkardt, Hwang 2003][Diehl, Haegeler 2005] ecc.
C. Lorce [tomorrow]
FT
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nucleon tomography[transversely polarised nucleon]
TMDs GPDs[model calculation by B. Pasquini, F. Yuan] [model calculation by M. Burkardt]
model dependent relation Sivers TMD--in transverse momentum coordinates--
GPD E--in impact parameter coordinates--
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relations to OAM
GPDs TMDs[plot: courtesy B. Musch]
proton helicity flipped while quark helicity is conserved
0qE requires orbital angular momentum
1
1
0),,(),,(2
1t
qqq txEtxHxdxJ
DL=1
DL=1 DL=2 require interference of nucleon wave
fct.s with different units OAM
spin-orbit correlation
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Q2
t
Q2>>, t<<
appear in factorisation theorem for hard exclusive processes
x x
),,( txH Bjxx Bjx~
how to measure GPDs ?
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Q2
t
Q2>>, t<<
appear in factorisation theorem for hard exclusive processes
x x
),,( txH Bjxx Bjx~
how to measure GPDs ?
spin ½ target:
4 leading-tw, chiral even q & g GPDs: H, H conserve nucleon helicity
E, E involve nucleon helicity flip
+ 4 chiral odd GPDs connection to transversity
~
~
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Q2
t
Q2>>, t<<
appear in factorisation theorem for hard exclusive processes
x x
),,( txH Bjxx Bjx~
how to measure GPDs ?
DVCS: most clean process, (some) flavour
dependent info from p & n target H, H, E, E~ ~
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Q2
t
Q2>>, t<<
appear in factorisation theorem for hard exclusive processes
x x
),,( txH Bjxx Bjx~
how to measure GPDs ?
DVCS: most clean process, (some) flavour
dependent info from p & n target H, H, E, E~ ~
DVMP: flavour decomposition; gluons: VM H, E
PS H, E~ ~
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Q2
t
Q2>>, t<<
appear in factorisation theorem for hard exclusive processes
x x
),,( txH Bjxx Bjx~
how to measure GPDs ?
DVCS: most clean process, (some) flavour
dependent info from p & n target H, H, E, E~ ~
DVMP: flavour decomposition; gluons: VM H, E
PS H, E~ ~ factorisation only for sL
meson distribution amplitude needed large NLO & power corrections
BUT:
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form factors:
Q2
t
constraints of GPDs
Q2>>, t<<
appear in factorisation theorem for hard exclusive processes
x x
),,( txH Bjxx
Bjx~)(),,( 1 tFtxHdxe q
q q )()0,0,(, xqxH gq
)()0,0,(~ , xqxH gq
:~
,EE nucleon helicity flip don’t appear in DIS
+ Lorentz invariance: polynomiality
+ lattice calculations
... ecc. )()0,0,( 1 xhxH qT
PDFs :
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x xextracting GPDs: caveats
x is mute variable (integrated over), needs deconvolution
apart from ‘cross over’ trajectory (x=±x) GPDs not directly accessible
cross section & beam charge asymmetry ~ Re(TDVCS)
beam or target spin asymmetries ~ Im(TDVCS)
x scan of GPDs from Q2 evolution: EIC
Compton Form Factor (CFF)
extrapolation t 0 model dependent
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Q2
t
Q2>>, t<<
the ideal experiment for measuring hard exclusive processes
high & variable beam energy ensure hard regime
wide kinematic range
L/T separation for ps meson prod.
high luminosity small cross sections
fully differential analysis
hermetic detectors ensure exclusivity
… doesn’t exist (yet)…
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experimental prerequisites polarised 27GeV e+/e- unpolarised 920GeV p ≈full event reconstruction
polarised 27GeV e+/e- long+transv polarised p, d targets unpolarised nuclear targets missing mass technique 2006/7 data taken with recoil det.
HERA till 2007
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experimental prerequisites polarised 27GeV e+/e- unpolarised 920GeV p ≈full event reconstruction
polarised 27GeV e+/e- long+transv polarised p, d targets unpolarised nuclear targets missing mass/energie technique 2006/7 data taken with recoil det.
Hall-A missing mass/energie technique
highly polarised, high lumi 6GeV e- long polarised effective p, n targets
HERA till 2007
CEBAF
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experimental prerequisites polarised 27GeV e+/e- unpolarised 920GeV p ≈full event reconstruction
polarised 27GeV e+/e- long+transv polarised p, d targets unpolarised nuclear targets missing mass/energie technique 2006/7 data taken with recoil det.
Hall-A missing mass/energie technique
highly polarised, high lumi 6GeV e- long polarised effective p, n targets
HERA till 2007
CEBAF
CERN highly polarised, 160GeV m long+transv polarised effective p, d targets
missing mass/energie technique
COMPASS-II with recoil det.
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low high x
xB
10-3 10-1 0.2-0.5
HERA collider HERMES / JLab10-4 < xB < 0.02 0.02 < xB < 0.4 / 0.1 < xB < 0.6
sea quarks & gluons (gluons) (valence) quarks
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low high x
xB
10-3 10-1 0.2-0.5
HERA collider HERMES / JLab10-4 < xB < 0.02 0.02 < xB < 0.4 / 0.1 < xB < 0.6
sea quarks & gluons (gluons) (valence) quarks
COMPASS
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low high x
xB
10-3 10-1 0.2-0.5
HERA collider HERMES / JLab10-4 < xB < 0.02 0.02 < xB < 0.4 / 0.1 < xB < 0.6
sea quarks & gluons (gluons) (valence) quarks
COMPASS
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exclusivity
≈ hermetic detector
p escapes through beam pipe
LPS: p tagged control sample
@ the HERA collider experiments
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exclusivity
LPS: p tagged data sample
e-sample: BH control sample
e+e-, J/ y bg-sample
g-sample: BH+DVCS
(BH+DVCS) - BH
@ the HERA collider experiments
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exclusivity
full data sample
e-sample: BH control sample
e+e-, J/ y bg-sample
g-sample: BH+DVCS
(BH+DVCS) - BH
@ the HERA collider experiments
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exclusivityfixed target: via missing mass / energy
subtractedvery well understood
part of the signal (ep e’ g X)
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exclusivity
(ep e’ g X) with p detection & D+ ID: transition GPDs
talk by S. Yaschenko
fixed target: via missing mass / energy
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exclusivity
subtractedvery well understood
part of the signal (ep e’ g X)
Hall-A
fixed target: via missing mass / energy
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results on (off) the menudata over wide kinematic range: HERA-collider COMPASS HERMES JLab
VM production H, E
low x: gluon imaging
high x: quarks & gluons ; role of NLO & power corrections
low W data from Jlab ( X. Girod, tomorrow)
ps meson production H, E
DVCS H, E, H, E ... the golden channel & most rich plate
role of transverse photons: CLAS p0,p+ ALU, HERMES p+ AUT, cross sec.
relation to transversity: HT h1 from p0 AUT
models & GPDs
hunting the OAM
nuclear modification of DVCS ampllitudes: HERMES
~ ~
~ ~
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VM production @low xW & t dependences: probe transition from soft to hard regime
soft hard
expect d to increase from ~0.2 to ~0.8
b to decrease from ~10 to ~4-5 GeV2
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VM production @low xW dependence: probe transition from soft to hard regime
r fJ/Y
U
two ways to set a hard scale: large Q2
mass of produced VM
universality: r and f at large Q2+M2 similar to J/ Y , Y
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VM production @low xt dependence: probe transition from soft to hard regime
r fJ/Y
U
s ~ e-b|t|
universality of b slope parameter
point like configurations dominate
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gluon imaging: J/y [Frankfurt, Strikman, Weiss (2011)]
FT average impact parameter
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VM production from low high x
xB
10-3 10-1 0.2-0.5
HERA-collider COMPASS / HERMES / Jlab g+(sea) g+(sea)+qv ( ,r w) qv ( ,r w)
NLO corrections to VM production are large: [M. Diehl, W. Kugler (2007)]
r0 cross section @typical kinematics of COMPASS / HERMES / JLab12
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VM production from low high x
xB
10-3 10-1 0.2-0.5
HERA-collider COMPASS / HERMES / Jlab g+(sea) g+(sea)+qv ( ,r w) qv ( ,r w)
... despite, LO GPD model (handback fact.; DD ansatz): [S. Goloskokov, P. Kroll (2007, 2010)]
+ power corrections:
ZeusH1
LO GPD
+ power correction
r0 W = 90 GeV
W = 75 GeV
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VM production from low high x
xB
10-3 10-1 0.2-0.5
HERA-collider COMPASS / HERMES / Jlab g+(sea) g+(sea)+qv ( ,r w) qv ( ,r w)
+ power corrections:
r0 ZeusH1
CompassHermes
W = 90 GeV
W = 10 GeV
W = 5 GeV
... despite, LO GPD model (handback fact.; DD ansatz): [S. Goloskokov, P. Kroll (2007, 2010)]
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VM production from low high x
xB
10-3 10-1 0.2-0.5
HERA-collider COMPASS / HERMES / Jlab g+(sea) g+(sea)+qv ( ,r w) qv ( ,r w)
+ power corrections:
r0 ZeusH1
CompassHermes
W = 90 GeV
W = 10 GeV
W = 5 GeV
... despite, LO GPD model (handback fact.; DD ansatz): [S. Goloskokov, P. Kroll (2007, 2010)]
H1, ZEUSE665HERMESCLAS
Q2 = 3.8 GeV2
f
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Deeply Virtual Compton Scattering
I |τ||τ|dσ 2DVCS
2BH
DVCS cross sections @ low x
||tbedt
d t slope provides absolute normalisation
FT average impact parameter
EEHH~
,,~
,
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DVCS cross section [PLB659(2008)]
t slope measurement provides
absolute normalisation
||tbedt
d
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DVCS cross section
t slope measurement provides
absolute normalisation
||tbedt
d
universality of slope parameter:
pointlike configurations dominate
[PLB659(2008)]
Zeus(p’ tagged events)[JHEP05(2009)]
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DVCS cross section
t slope measurement provides
absolute normalisation
||tbedt
d
universality of slope parameter:
pointlike configurations dominate
[PLB659(2008)]
Zeus(p’ tagged events)[JHEP05(2009)]
fm)02.065.0(2 Tb
@ xB=10-3
FT average impact parameter
@ xB=10-3
[courtesy of C. Weiss]
<Q2>=8.0 GeV2
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sea quark & gluon imaging
@ xB=10-3
[courtesy of C. Weiss]
universality of slope parameter:
pointlike configurations dominate
FT average impact parameter
fm)02.065.0(2 Tb
@ xB=10-3
remember J/y
<Q2>=8.0 GeV2
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DVCS interference term Hall-A
)τττ(τ |τ||τ|dσ BH*DVCSDVCS
*BH
2DVCS
2BH
x x
bilinear in GPDs linear in GPDs
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DVCS interference term Hall-A
)τττ(τ |τ||τ|dσ BH*DVCSDVCS
*BH
2DVCS
2BH
isolate interference term:
bilinear in GPDs linear in GPDs
different beam charges: e+ e- (only @HERA, upcoming @COMPASS)
polarisation observables
DsUT
beam target
U, L U, L, T
Unpolarised, Longitudinally, Transversely polarised
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DVCS interference term Hall-A
)τττ(τ |τ||τ|dσ BH*DVCSDVCS
*BH
2DVCS
2BH
isolate interference term:
bilinear in GPDs linear in GPDs
different beam charges: e+ e- (only @HERA, upcoming @COMPASS)
polarisation observables
DsUT
beam target
U, L U, L, T
H
H
H, E
~DsC, DsLU
DsUL
DsUT, DsLU
neutron
@kinematics of current fixed target exp.
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A LU
first DVCS signals-- interference term --
[PRL87(2001)]
sinf dependence indicates dominance of handback contribution
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call for high statistics
cos1
sinLU c
aA
JLab-e1: DVCS beam-spin asymmetry [PRL100(2008)]
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call for high statistics
cos1
sinLU c
aA
JLab-e1: DVCS beam-spin asymmetry [PRL100(2008)]
<-t> = 0.18 GeV2 <-t> = 0.30 GeV2 <-t> = 0.49 GeV2 <-t> = 0.76 GeV2
3D analysis in x, Q2, t
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call for high statistics
)Im( 1HF
JLab-e1: DVCS beam-spin asymmetry [PRL100(2008)]
... cross section from
interference term
talk by X. Girod
Hall-A
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call for new analysis methodscombined analysis of charge & polarisation observables
separation of interference & DVCS2 amplitudes
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GPD models: DD [VGG(1999)]
minimal-dual [GT(2007)]
call for new analysis methodscombined analysis of charge & polarisation observables
separation of interference & DVCS2 amplitudes
beam-spin asymmetry [JHEP11(2009)]
talk by S. Yaschenkomore, recent results
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GPD models: DD, no D-term [VGG(1999)]
minimal-dual [GT(2007)]
call for new analysis methodscombined analysis of charge & polarisation observables
separation of interference & DVCS2 amplitudes
beam-charge asymmetry [JHEP11(2009)]
talk by S. Yaschenkomore, recent results
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call for completeness
Hall-A
charge asymmetry
beam-spin asymmetry
transverse target spin asymmetry
transverse-target double-spin
longitudinal target spin asymm.
longitudinal-target double-spin
Re (H)
Im (H)
Im (H-E)
Re (H-E)
Im (H)
Re (H)~
~
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towards GPDsrecent developments (beyond VGG(1999)...)
Goloskokov, Kroll (2007):
LO GPD model using DD, regge t dep., power corrections
fit to exclusive meson production data
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towards GPDsrecent developments (beyond VGG(1999)...)
Goloskokov, Kroll (2007):
LO GPD model using DD, regge t dep., power corrections
fit to exclusive meson production data
Kumericki, Müller (2010):
partial wave expansion of GPDs, regge t dep., dispersion relations
fit to DVCS data
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towards GPDsrecent developments (beyond VGG(1999)...)
Goloskokov, Kroll (2007):
LO GPD model using DD, regge t dep., power corrections
fit to exclusive meson production data
Kumericki, Müller (2010):
partial wave expansion of GPDs, regge t dep., dispersion relations
fit to DVCS data
Goldstein, Hernandez,Liuti (2010):
quark-diquark model of GPDs, Regge ansatz for low x region & t dep.
fit to DVCS data talk by S. Liuti [tomorrow]
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towards GPDsrecent developments (beyond VGG(1999)...)
Goloskokov, Kroll (2007):
LO GPD model using DD, reggezised t dep., power corrections
fit to exclusive meson production data
Kumericki, Müller (2010):
partial wave expansion of GPDs, reggezised t dep., dispersion relations
fit to DVCS data
Goldstein, Hernandez,Liuti (2010):
quark-diquark model of GPDs, Regge ansatz for low x region & t dep.
fit to DVCS data talk by S. Liuti [tomorrow] Guidal (2011):
model independent extraction of CFF (GPD extr. requires model ansatz)
kinematic fitting of DVCS data (per experiment)
Guidal 2011
VGG 1999
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towards global analysis of GPDs-- employ all available exclusive data (DVCS & meson production) --
GK (2007) comparison to KM09,10
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hunting the OAM attempts to constrain Jq
1
1
0),,(),,(2
1t
qqq txEtxHxdxJ
GPD models: Jq free parameter in ansatz for E
observables sensitive to E : pDVCS: AUT HERMES
nDVCS: ALU HallA
meson prod. AUT: r0 HERMES, COMPASS
...also , , w f r+, K*0
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hunting the OAM-- pDVCS : transverse target-spin asymmetry --
[JHEP06(2008)]
[VGG]
GPD models: Jq free parameter in ansatz for E
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hunting the OAM-- nDVCS : beam-spin cross section difference --
GPD models: Jq free parameter in ansatz for EHall-A
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hunting the OAM-- r0 : transverse target-spin asymmetry --
:)( 0L
*L
after the full glory of SDME extractions
[formalism by M. Diehl (2007)]
''
n
0
*
10 ,μ,νlong.pol: 0transv.pol: ±1
[PLB679(2009)]
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hunting the OAM-- r0 : transverse target-spin asymmetry --
:)( 0L
*L
after the full glory of SDME extractions
[formalism by M. Diehl (2007)]
''
n
0
*
10 ,μ,νlong.pol: 0transv.pol: ±1
[PLB679(2009)]
[GPD model: Ellighaus et al. (2004)]
more data coming: COMPASS, JLab12 with transv. Target
more models: Goloskokov, Kroll
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conclusions & perspectives
xB
10-3 10-1 0.2-0.5
HERA collider HERMES / JLab10-4 < xB < 0.02 0.02 < xB < 0.4 / 0.1 < xB < 0.6
sea quarks & gluons (gluons) (valence) quarks
COMPASS
increasing amount and precision of experimental data
progress in model calculations, plenty of room for more work...
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conclusions & perspectives
xB
10-3 10-1 0.2-0.5
HERA collider HERMES / JLab
increasing amount and precision of experimental data
progress in model calculations, plenty of room for more work...
JLab12GeVCompass
EIC
bright future for GPD studies:
JLab12
COMPASS-II with recoil
EIC/ENC (mapping of GPDs from Q2 evolution)
talks by V. Burkert, N. D’Hose, F. Maas