DVCS at JLab
Como, 11/06/2013
JLab published 6 GeV results
JLab 6GeV analysis in progress
JLab 12 GeV program
JLab published 6 GeV results
JLab 6GeV analysis in progress
JLab 12 GeV program
JLab
Duty cycle 100% Emax6 GeV Pmax80%
22 '' qkpkM X LH2 / LD2 target
Polarized Electron Beam
Scattered Electron
g
N
Nucleon Detector
Left HRS
Charged ParticleTagger Electromagnetic Calorimeter
HALL AHALL ADVCS@JLab
ep epg
H(e,e’)X
H(e,e’p)
H(e,e’)X - H(e,e’’)X'
H(e,e’)N
DVCS : exclusivity
• Good resolution : no need for the proton array• Remaining contamination 1.7%
HRS+calorimeterep -> epep -> ep0 0->ep -> ep0ep -> ep0N…
HRS+calorimeter + proton array
DVCS Bethe-Heitler
GPDs
Using the (first version) of the BKM formalism, one can extract a combination of the “Im” CFFs and their Q2-dependence
e’
p
epa epg
g
420 PbWO4 crystals : ~10x10 mm2, l=160 mm Read-out : APDs +preamps
JLab/ITEP/Orsay/Saclaycollaboration
HALL BHALL B
DVCS@JLab
CLAS DVCS ALU
x~0.16,-t~0.31,Q2~1.82
CLAS DVCS AUL
Given the well-established LT-LO DVCS+BH amplitude
DVCS Bethe-Heitler
GPDs
Can one recover the 8 CFFs from the DVCS observables?
In general, 8 GPD quantities accessible (Compton Form Factors)
with
Given the well-established LT-LO DVCS+BH amplitude
DVCS Bethe-Heitler
GPDs
Obs= Amp(DVCS+BH) CFFs
Can one recover the 8 CFFs from the DVCS observables?
Two (quasi-) model-independent approaches to extract, at fixed xB, t and Q2 (« local » fitting),
the CFFs from the DVCS observables (leading-twist formalism)
1/ «Brute force » fitting
c2 minimization (with MINUIT + MINOS) of the available DVCS observables at a given xB, t and Q2 pointby varying the CFFs within a limited hyper-space (e.g. 5xVGG)
M.G. EPJA 37 (2008) 319 M.G. & H. Moutarde, EPJA 42 (2009) 71
M.G. PLB 689 (2010) 156 M.G. PLB 693 (2010) 17
The problem can be (largely) undersconstrained:JLab Hall A: pol. and unpol. X-sectionsJLab CLAS: BSA + TSA
2 constraints and 8 parameters !
However, as some observables are largely dominated bya single or a few CFFs, there is a convergence (i.e. a well-definedminimum c2) for these latter CFFs.
The contribution of the non-converging CFF entering in the error bar of the converging ones.
DsUL ~ sinfIm{F1H+x(F1+F2)(H + xB/2E) –xkF2 E+…}df~ ~DsLU ~ sinf Im{F1H + x(F1+F2)H -kF2E}df~
2/ Mapping and linearization
If enough observables measured, one has a system of 8 equations with 8 unknowns
Given reasonnable approximations (leading-twist dominance, neglect of some 1/Q2 terms,...), the system can be linear(practical for the error propagation)
K. Kumericki, D. Mueller, M. Murray, arXiv:1301.1230 hep-ph, arXiv:1302.7308 hep-ph
unpol.sec.eff.
+
beam pol.sec.eff.
c2 minimization
unpol.sec.eff.
+
beam pol.sec.eff.
c2 minimization
beam spin asym.
+
long. pol. tar. asym
unpol.sec.eff.
+
beam pol.sec.eff.
c2 minimization
beam spin asym.
+
long. pol. tar. asym
beam charge asym.
+
beam spin asym
+
…
linearization
unpol.sec.eff.
+
beam pol.sec.eff.
c2 minimization
beam spin asym.
+
long. pol. tar. asym
beam charge asym.
+
beam spin asym
+
…
linearization
VGG modelKM10 model/fit
Moutarde 10 model/fit
Current extractions of CFFs from DVCS
The sea quarks (low x) spread to the periphery of the nucleon while the valence quarks (large x) remain in the center
HIm:the t-slope reflects the size of the probed object (Fourier transf.)
c2 minimization
linearizationVGG model
Moutarde 10 model/fitKM10 model/fit
Nucleon tomography
The axial charge (~Him) appears to be more « concentrated » than the electromagnetic charge (~Him)
~
c2 minimization
linearizationVGG model
JLab published 6 GeV results
JLab 6GeV analysis in progress
JLab 12 GeV program
CLAS :
« e1-dvcs 1» (2005) and « e1dvcs2 » (2008)Analysis of the (pol. and unpol.) DVCS cross-sections
Several DVCS analysis under way with JLab 6 GeV data:
CLAS :
« e1-dvcs 1» (2005) and « e1dvcs2 » (2008)Analysis of the (pol. and unpol.) DVCS cross-sections
Four main analyzers:
H.-S. Jo, F.-X. Girod, B. Guegan, N. Saylorfrom whom I borrowed a lot of material/slides andwhom contribution is greatly acknowledged
Several DVCS analysis under way with JLab 6 GeV data:
CLAS :
« e1-dvcs 1» (2005) and « e1dvcs2 » (2008)Analysis of the (pol. and unpol.) DVCS cross-sections
Four main analyzers:
H.-S. Jo, F.-X. Girod, B. Guegan, N. Saylorfrom whom I borrowed a lot of material/slides andwhom contribution is greatly acknowledged
« eg1dvcs » (2008)Analysis of the long.pol. target asymmetries
Several DVCS analysis under way with JLab 6 GeV data:
CLAS :
« e1-dvcs 1» (2005) and « e1dvcs2 » (2008)Analysis of the (pol. and unpol.) DVCS cross-sections
Four main analyzers:
H.-S. Jo, F.-X. Girod, B. Guegan, N. Saylorfrom whom I borrowed a lot of material/slides andwhom contribution is greatly acknowledged
« eg1dvcs » (2008)Analysis of the long.pol. target asymmetries
Several DVCS analysis under way with JLab 6 GeV data:
Hall A :
Rosenbluth separation of the DVCS cross-section(separation of DVCS and BH contributions)
Samples of CLAS « e1-dvcs2 » analysis
5.88 GeV beam energy
Samples of CLAS « e1-dvcs2 » analysis
5.88 GeV beam energy
Data
MC
Ratio
Acceptances
Elastic cross section from « e1-dvcs2 »
Thanks to I. Akushevich
How to go from momentum coordinates (t) to space-time coordinates (b) ?
(with error propagation)
Burkardt (2000)
From CFFs to spatial densities
Applying a (model-dependent) “deskewing” factor:
and, in a first approach, neglecting the sea contribution
JLab published 6 GeV results
JLab 6GeV analysis in progress
JLab 12 GeV program
JLab Upgrade to 12 GeV
CHL-2
Enhance equipment in existing halls
Add new hall
GPD program at JLab 12 GeV (Halls A, B and C)
DVCS beam asymmetry ALU on proton&neutron
DVCS long. target spin asymmetry AUL on proton&neutron
DVCS long. target spin asymmetry AUT on proton&neutron
DVCS unpolarized cross sections on proton
DVMP: pseudoscalar mesons
DVMP: vector mesons
Simulations Hall A@12GeV
Precision study of the Q2 scaling law
Validation of the GPD formalism,Estimation of the higher twist corrections90 days of DVCS
L~1038cm-2s-1
E12-06-119Similar studies for AUL,AUT,ALL,ALT,… as well
Projections for CLAS12 for HIm
Corresponding spatial densities
f= 60°xB = 0.2Q2 = 2 GeV2
t = -0.2 GeV2
DVCS BSA: sensitivity to Ju,d
DVCS on the proton Ju=.3, Jd=.1
Ju=.8, Jd=.1
Ju=.5, Jd=.1
Ju=.3, Jd=.8
Ju=.3, Jd=-.5
Ee = 11 GeV
f= 60°xB = 0.17Q2 = 2 GeV2
t = -0.4 GeV2
n-DVCS BSA is:• very sensitive to Ju, Jd • can be as strong as for the protonAccording to the kinematics and Ju, Jd
DVCS on the neutron Ju=.3, Jd=.1
Ju=.8, Jd=.1
Ju=.5, Jd=.1
Ju=.3, Jd=.8
Ju=.3, Jd=-.5
Ee = 11 GeV
DVCS BSA: sensitivity to Ju,Jd