ee’

GPDsN N’

Deeply virtual Compton scattering on the nucleon at 6

and 11 GeV

Silvia Niccolai

Soutenance HDRIPN Orsay – November 27th 2014

p

p

n

N 'NGPDs

sud

Technical project: polarized target for electron scattering experiments at CLAS

Few-body interactions among nucleons:three-body photodisintegration of 3He at CLAS

Baryon spectroscopy: pentaquark searchin d(3He)→+(p) Phys. Rev. Lett. 97, 032001 (2006)

Nucleon structure: GPDsPAC proposal: DVCS with polarized target at CLAS

Nucleon structure: strange form factors → parity violationRadiative corrections for G0 (Hall C), forward anglesEur. Phys. J. A26, 429 (2005)

GENOVA

9/97-10/98

CV: Experimental hadronic physics at JLab (junior years)

1/99-2/03

3/03-9/03

10/03-9/06

Phys. Rev. C 70, 1 (2004)

CV: Structure of the nucleon at CLAS (senior years)

e1-dvcs experiment (2005):• cross sections for ep→e’p’0

→ sensitivity of this channel to transversity GPDs (chiral-odd)Phys. Rev. Lett. 109, 112001 (2012)Phys. Rev. C 90, 039901 (2014)

• 3 PhD theses at IPN: H.S. Jo (DVCS cross section) B. Moreno (DVCS asymmetry) A. Fradi (ep→e’n+ c. s.)

e1-dvcs2 experiment (2008):• 2 PhD theses: B. Guegan (DVCS c.s.) N. Saylor (DVCS c.s.)

e1-6 experiment (2001):• 1 PhD thesis, underway: B. Garillon (ep→e’p’f0 (f2) c.s.)

3 « encadrements de stagiaires »

Part 1: DVCS on longitudinally polarized

protons at 6 GeV

x

e e’

Xp

(Q2)

Electron-proton scattering: yesterday

e e’

p p’

(t=Q2)

1950: Elastic scattering ep→e’p’ (Hofstadter, Nobel prize 1961)

1967: Deep inelastic scattering (DIS) ep→e’X (Friedman, Kendall, Taylor, Nobel prize 1990)

• Discovery of the quarks (or “partons”)• Measurement of the momentum and spin distributions of the partons: q(x), q(x)

• The proton is not a point-like object• Measurement of charge and current distributions of the proton: form factors (F1(t), F2(t))

LowQ2

HighQ2

x

Electron-proton scattering: today

?Form factors:

transverse quark distribution in

coordinate space

Parton distributions:longitudinal

quark distributionin momentum space

F1(t), F2(t) q(x), (x)

x

Electron-proton scattering: today

GPDs: H, E, H, EFully correlated quark

distributions in both coordinate and momentum space

~ ~

Form factors: transverse quark distribution in

coordinate space

Accessible inhard exclusive processes

Parton distributions:longitudinal

quark distributionin momentum space

q(x), (x)F1(t), F2(t)

pNm

pNtxEpNpNtxH

pypedyP

pNm

ipNtxEpNpNtxH

pypedyP

N

qq

yyqq

yixP

N

qq

yyqq

yixP

2',,

~',,

~

)()0('2

,2

',,',,

)()0('2

55

0

5

0

Deeply Virtual Compton Scattering and GPDse’

t

(Q2)

e*

x+ξ x-ξ

H, H, E, E (x,ξ,t)~~

N(p) N(p’)

« Handbag » factorization validin the Bjorken regime:

high Q2 , (fixed xB), t<<Q2

• Q2= - (e-e’)2

• xB = Q2/2M=Ee-Ee’

• x+ξ, x-ξ longitudinal momentum fractions• t = 2 = (p-p’)2

• xB/(2-xB)

GPDs: Fourier transforms of non-local, non-diagonal QCD operators

P = (p+p’)/2

Light-cone: a± = (a0 ± a3 )/ √2

factorization

Deeply Virtual Compton Scattering and GPDs

Vector: H (x,ξ,t)

Tensor: E (x,ξ,t)

Axial-Vector: H (x,ξ,t)

Pseudoscalar: E (x,ξ,t)

~

~conserve nucleon spin

flip nucleon spin

At leading order QCD, twist 2, chiral-even (quark helicity is conserved), quark sector→ 4 GPDs for each quark flavor

Properties and “virtues” of GPDs

X. Ji, Phy.Rev.Lett.78,610(1997)

tGdxtxE

tGdxtxH

tFdxtxE

tFdxtxH

P

A

,,~

,,~

,,

,,

2

1

)()0,0,(~

)()0,0,(

xqxH

xqxH

Link with FFs Forward limit: PDFs

(not for E, E)~

Nucleon tomography

Nucleon spin: ½ = ½ + L + G JLJtxEtxHxdx 2

1))0,,()0,,((

2

1 1

1

Intrinsic spin of the quarks ≈ 25% Intrinsic spin on the gluons G ≈ 0 (??) Orbital angular

momentum of the quarks L ?

Quark angular momentum (Ji’s sum rule)

M. Burkardt, PRD 62, 71503 (2000)

),0,(~

)2()b,(

~

),0,()2(

)b,(

2b

02

2

2b

02

2

xHed

xH

xHed

xH

i

i

Accessing GPDs through DVCS

1

1

1

1

),,(),,(

~),,(

~ tGPDsidxx

txGPDsPdx

ix

txGPDsT DVCS

Only and tare accessible

experimentally

IDVCSBH

BHDVCSIA

BHDVCSI

TT BHDVCS

22

2

2

~

dxxx

txHtxHPRe qq

1

0

q

11),,(),,(

2

qe H

),,(),,(q tHtHIm qq 2qe H

DVCS allows access to 4 complex GPDs-related quantities:

Compton Form Factors (,t)

Im{Hn, En, En}

= xB/(2-xB) k=-t/4M2)

leptonic planehadronic

planeN’

e’

e

Unpolarized beam, longitudinal target:

sI1,UL ~ sinIm{F1H+(F1+F2)(H + xB/2E) –kF2 E+…}~ Im{Hp, Hp}

~

sI1,unp ~ sin Im{F1H + (F1+F2)H -kF2E}~

Polarized beam, unpolarized target: Im{Hp, Hp, Ep}~

Sensitivity to GPDs of DVCS spin observables

Polarized beam, longitudinal target:

cILP ~ (A+BcosRe{F1H+(F1+F2)(H + xB/2E)…}~ Re{Hp, Hp}

~

Im{Hn, Hn, En}

~

Proton Neutron

~

Re{Hn, En, En}~

Im{Hn}

~

cos)(

cos)(

cos)(

sin

,1,1,0,0

,1,1,0,0

,1,1,0,0

)(,1)(

Iunp

BHunp

Iunp

BHunp

ILP

BHLP

ILP

BHLP

LL

Iunp

BHunp

Iunp

BHunp

IULunp

ULLU

cccc

ccccA

cccc

sA

Unpolarized beam, transverse target:

UT ~ cossinsIm{k(F2H – F1E) +… } Im{Hp, Ep}

Twist 2

sI1,unp ~ sin Im{F1H + (F1+F2)H -kF2E}~

Polarized beam, unpolarized target: Im{Hp, Hp, Ep}~

= xB/(2-xB) k=-t/4M2)

leptonic planehadronic

planeN’

e’

e

Unpolarized beam, longitudinal target:

sI1,UL ~ sinIm{F1H+(F1+F2)(H + xB/2E) –kF2 E+…}~ Im{Hp, Hp}

~

Sensitivity to GPDs of DVCS spin observables

Polarized beam, longitudinal target:

cILP ~ (A+BcosRe{F1H+(F1+F2)(H + xB/2E)…}~ Re{Hp, Hp}

~

Im{Hn, Hn, En}

Proton Neutron

~

~

cos)(

cos)(

cos)(

sin

,1,1,0,0

,1,1,0,0

,1,1,0,0

)(,1)(

Iunp

BHunp

Iunp

BHunp

ILP

BHLP

ILP

BHLP

LL

Iunp

BHunp

Iunp

BHunp

IULunp

ULLU

cccc

ccccA

cccc

sA

Twist 2

DVCS experiments worldwide

Jefferson Lab(Halls A&B)

HERMES

COMPASS

The CLAS eg1-dvcs experiment ep→epγ→→

Analysis team composed of:E. Seder, U Connecticut (CEA Saclay)S. Pisano, INFNFRA. Biselli, Fairfield US. Niccolai

Also: ongoing BSA and TSA for nDVCS(D. Sokhan, Glasgow U)

• Target: longitudinally polarized NH3 (polarization ~80%)

• Experiment approved by PAC28 (2005) with A rating• Data taken from February to end of August 2009• Beam energy ~5.9 GeV• CLAS + IC to detect forward photons

IC (inner calorimeter): 424 lead-tungstate

crystals + APD readout(built at IPNO)

The eg1-dvcs polarized target

Dynamic Nuclear Polarization of NH3

• Free electrons (ṄH2 radicals) are implanted in crystalline beads of ammonia via electron radiation

• Radicals are polarized ( ~100%) at 5 T and 1 K (P=tanh(µB/kT) )

• Microwaves (140 Ghz) drive electron/proton spin-flip transitions and transfer polarization to protons

• Polarization is measured with NMR

Polarized ammonia

Carbon

Empty

Optics

bt

btepbtbt

FC

NBN )1( 0

NNPNNPP

NNPNNPA

ttb

ttLU

UTAttf

UL cNNPNNPD

NNNNA

LTAttbf

LL cNNPNNPPD

NNNNA

Experimental definition of the observablesb: beamt: targetFCbt: charge, from Faraday CupB0: relative 0 contaminationPt: target polarizationPb: beam polarizationDf: dilution factorcAUT, cAUL: transverse corrections

Beam-spin asymmetry

Target-spin asymmetry

Double-spin asymmetry

Im{Hp

}

For each 4-dimensional bin in (Q2, xB, -t,

Charge-normalized DVCS/BH yield

Im{Hp, Hp}~

Re{Hp, Hp}~

« Highlights » of the eg1-dvcs analysis• Selection of the ep final state: exclusivity cuts to reduce nuclear background and ep0→ep() contamination; different strategies to define the cuts for the IC and EC topologies

NH3, before cuts12C, before cuts

NH3, after cuts

12C, after cuts92.01)(

3

12

NH

Cf N

NcepD %10

)90(

0

A

B

Pt : measured during the experiment by NMR.NMR coils surrounded the target → more sensitive to polarization of its outer volume. Risk to overestimate Pt

« Highlights » of the eg1-dvcs analysis

• Extraction of PbPt

theotb A

APP exp

PbPt deduced from elastic BSA (ep→e’p’):

)(exp

NND

NNA

f

Atheo : known function of the kinematics and of the e.m. FFs

Pb measured during the experiment with Moller runs

%74%80 tt PP

Beam-spin asymmetryFit:LUsin/(1+cos) ( constrained: equal for the 3 asymmetries)

Beam-spin asymmetryLU ~ Im{Hp}

Fit:LUsin/(1+cos)

Beam-spin asymmetryLU ~ Im{Hp}

Fit:LUsin/(1+cos)

• VGG: Vanderhaegen, Guidal, Guichon• KMM12: Kumericki, Mueller, Murray• GK: Goloskokov, Kroll • GGL: Gonzalez., Goldstein, Liuti

Target-spin asymmetryUL ~ Im{Hp, Hp}

~Fit:ULsin/(1+cos)

E. Seder et al. arXiv:1410.6615 , submitted to PRL

Target-spin asymmetry

E. Seder et al. arXiv:1410.6615 , submitted to PRL

Fit:ULsin+B sin 2

Agreement with world dataImproved statistics x10 at low -tExtended kinematic coverage

E. Seder et al. arXiv:1410.6615 , submitted to PRL

CLAS: <Q2>= 2.4 (GeV/c)2, <xB>= 0.31HERMES: <Q2>= 2.459 (GeV/c)2, <xB>= 0.096CLAS2006: <Q2>= 1.82 (GeV/c)2, <xB>= 0.28

Target-spin asymmetry

E. Seder et al. arXiv:1410.6615 , submitted to PRLE. Seder et al. arXiv:1410.6615 , submitted to PRL

“This paper presents new data on Generalized Parton Distributions (GPDs) obtained through DVCS. The results obtained are by far (at least one order of magnitude) the most accurate and the most extensive to date on the target-spin asymmetry in DVCS. Together with earlier published data on beam-spin asymmetries they will significantly advance our knowledge about GPDs. As such, this work has indeed significant impact on the field of hadronic structure. The fact that insight in the 3D-structure of the nucleon is pushed forward by experiments and analyses today fully merits the attention of a broader audience than that served by the Physical Review journals, and I support the publication in Physical Review Letters.” PRL referee

Double-spin asymmetryFit:LL+LLcos/(1+cos)

Constant termdominated

by BH

LL~ Re{Hp, Hp}~Fit:LL+LLcos/(1+cos)

cos term small and dominated by BH

Double-spin asymmetry

Extraction of Compton Form Factors from DVCS observables

8 CFF

M. Guidal: Model-independent fit, at fixed Q2, xB and t of DVCS observables8 unknowns (the CFFs), non-linear problem, strong correlations Bounding the domain of variation of the CFFs with model (5xVGG) M. Guidal, Eur. Phys. J. A 37 (2008) 319

Extraction of CFF from DVCS TSA, BSA, DSA

[12] CLAS BSA (Girod et al.)[14] CLAS TSA (Chen et al.)

CFFs fitting code by M. Guidal

ImH has steeper t-slope than ImH : is axial charge more

“concentrated” than the electromagnetic charge?

~

Some sensitivity to ReH, ReEbut with big uncertainties

→ DSA at CLAS12

~~

Slope of ImH decreasing as xB increases: fast quarks

(valence) more concentrated in the nucleon’s center, slow quarks (sea) more spread out

Part 2:DVCS on the neutron at 11 GeV

JLab upgrade and CLAS12

CHL-2CHL-2

Add new hallAdd new hall

CLAS12

CLAS12

H1, ZEUS

Valence region

Sea/gluon region

Emax(A,B,C) = 11 GeV

CLAS12: high luminosity (1035 cm-2s-1) and large acceptance:• Charged particles, 5o<<135o • Photons: 2.5o<< 5o (Forward Tagger) 5o<<40° (E.m. Calorimeter)

12 GeV

Extensive experimental program for p-DVCS planned: • BSA, lTSA, tTSA (CLAS12)• Cross sections, Q2-scaling tests (Halls A and C)

(H,E)p(ξ, ξ, t) = 4/9 (H,E)u(ξ, ξ, t) + 1/9 (H,E)d(ξ, ξ, t)(H,E)n(ξ, ξ, t) = 1/9 (H,E)u(ξ, ξ, t) + 4/9 (H,E)d(ξ, ξ, t)

A combined analysis of DVCS observables on proton and neutron targets is necessary for the flavor separation of the GPDs

(H,E)u(ξ, ξ, t) = 9/15[4(H,E)p(ξ, ξ, t) – (H,E)n(ξ, ξ, t)](H,E)d(ξ, ξ, t) = 9/15[4(H,E)n(ξ, ξ, t) – (H,E)p(ξ, ξ, t)]

DVCS on the neutron: motivation

GPDs depend on the quark’s flavor: Proton and neutron GPDs are linear combinations of quarks GPDs

The BSA for nDVCS is sensitive to the GPD E, That is the least known and the least constrained of the

GPDs and that appears in Ji’s sum rule → Ju, Jd

We will intiate an experimental program at JLab on neutron DVCS at 11 GeV, by measuring the beam-spin asymmetry (BSA)

LU ~ sin Im{F1H + (F1+F2)H -kF2E}d~ Im{Hn, Hn, En}~

First nDVCS measurement: Hall A@6 GeV

deedneenpeepXeeD ),(),(),(),(

Subtraction of the contributions from the proton using H2 data convoluted with Fermi motion

“Impulse approximation” (no FSI)

Active nucleon identified via

MM(e

M. Mazouz et al., PRL 99 (2007) 242501

Model-dependent extraction of Ju et Jd

Q2 = 1.9 GeV2 xB = 0.36

Im(CIn) compatible with zero (→ too high xB?)

Big statistical and systematic uncertainties(mostly due to the H2 subtraction and 0 background)

S. Ahmad et al., PRD75 (2007) 094003

VGG, PRD60 (1999) 094017

= 60°xB = 0.17Q2 = 2 GeV2

t = -0.4 GeV2

The BSA for nDVCS:• is very sensitive to E• depends strongly on the kinematics→ a large acceptance is necessary → CLAS12

VGG model

Ju=.3, Jd=.1

Ju=.1, Jd=.1

Ju=.5, Jd=.1

Ju=.3, Jd=.3

Ju=.3, Jd=-.1

Ee = 11 GeV

BSA for nDVCS at 11 GeV: sensitivity to E

LU

Hall A

Central Detector

nDVCS@CLAS12: detector requirements

More than 80% of the neutrons have >40°→ Neutron detector in the CD

<pn> ~ 0.4 GeV/c <n> ~ 60°

ed→e’n(p)

Detected in forward CLAS12

Detected inEC, FT

Not detected

Detected in CND

In the hypothesis of absence of FSI:pμ

p = pμp’ → kinematics are complete

detecting e’, n (p,,),

pμe + pμ

n + pμp = pμ

e′ + pμn′ + pμ

p′ + pμ

Resolution on MM(en) studied with nDVCS event generator + electron and photon resolutions

obtained from CLAS12 FastMC+ design specs for Forward Tagger

→ dominated by photon resolutions

Resolution on MM(en) studied with nDVCS event generator + electron and photon resolutions

obtained from CLAS12 FastMC+ design specs for Forward Tagger

→ dominated by photon resolutions

The Central Neutron Detector (CND) must ensure:• good neutron/photon separation for 0.2<pn<1 GeV/c → ~150 ps time resolution (obtained from GEANT4 simulations)• momentum resolution below 10%• no stringent requirements for angular resolutions

CTOF can detect neutrons as well (3% efficiency)

Central Tracker (SVT+MM): charged-particles veto

• limited available space (~10 cm radially)

→ limited efficiency

→ no space for light guides in the forward direction (CTOF)

• strong magnetic field (~5 T) → problems for light readout

CND(IPNO)

CTOF

Central Tracker(Micromegas

SPhN)

CND: constraints and early R&D studies

~ 2 years of R&D (IPNO, INFN Genova et Frascati)Three kinds of magnetic-resistant photo-detectors tested

Silicon PMs: too small active surface→ Too few photons → too big Nt 1

APDs:• Too noisy• t ~ 1.5 ns

Micro-channel-plate PMs:• Good resolution t ~ 100 ps• Loss of gain in magnetic field B ~ 1T• Short life time due to radiation damage

Chosen design for the CND

CND design: scintillator barrel3 radial layers, 48 bars per layer

coupled two-by-two by “u-turn” lightguides, light read upstream by

PMTs connected to the bar via 1.5m-long light guides

• Plastic scintillator: compromise between neutron efficiency (~1% /cm) and fast response

• Photon-neutron separation → measurement of β via Time-Of-Flight

cTOF

l

22 hzl

TOF: time from the interaction vertex to the impact point; l: path lenght + PID (m) → momentum

z: hit position along the scintillator bar; h: radial distance of the hit from the vertex → requires radial segmentation

rightlefteff ttvz 2

1 veff : light velocity in the scintillator bar; tleft,right: time measured at the two ends of the bar→ double readoutz → θ

nDVCS@CLAS12 & CND history• Simulations and R&D for detector conception started in 2008 (summer student project…)

• LOI for nDVCS@CLAS12 endorsed by PAC34 (2009)

• Proposal for nDVCS@CLAS12 approved by PAC37 and rated (A) by PAC38 (2011)

• CND project presented at Conseil Scientifique of IN2P3, obtained 300 k€ (fall 2011)

• Partial support also received from the HP3 program of the European 7th Framework

• JLab review of the CND in February 2012

• R&D and choice of all components finalized the same year

• Completion of purchase of all detector components by end of 2013

• Construction started in December 2013, almost complete!

PMT-N

PMT-D

GEANT4 simulations used to evaluate: efficiency PID (neutron/photon separation) momentum and angular resolutions definition of reconstruction algorithms background studiesMeasured t and light loss due to u-turn implemented in the simulation

CND: expected performances

Efficiency ~ 8-9% for a threshold of 3 MeV, TOF<8 nsand pn = 0.2 - 1 GeV/c

pn=0.4 GeV/c

Beam-time requested and obtained: 90 days (80 of production data taking at L = 1035 cm−2s−1/nucleon)• CLAS12 + Forward Calorimeter + Central Neutron Detector (efficiency ~10%)• 85% polarized electron beam• liquid deuterium target

nDVCS: expected accuracy and coverage

ed→ e(p)n

-t0 1.2

BSA

-0.2

0.2

Relative error on the yield: N/N~0.05%-10%

Estimated systematicuncertainties: 8%

Ju=.3, Jd=.1Ju=.1, Jd=.1

Ju=.3, Jd=.3Ju=.3, Jd=-.1

Model predictions (VGG)for different values of

quarks’ angular momentum

JLab PAC: high-impact experiment

E12-11-003

Determination of the detector components

Goal: optimize the time resolution ↔ neutron/photon discrimination

• Components chosen via comparative tests in cosmic rays on prototypes, checking light yield and σt (and costs…)

• Measured σt fed to simulation to verify PID requirements

Shielding PMT Wrapping Scintillator Glue U-turn

- 2.5 mm - R2083 - Mylar Al - BC408 - MBOND 200 - Triangular

- 5 mm - 9954A - VM2000 - EJ200 - BC600 - Semicircular

- R9779 - Al foil

- R10533

Tests on the one-layer prototype

One-layer prototype used to determine:• Wrapping material• PMT• Scintillator

Direct PMT

Trigger detectors

Indirect PMT

Ind PMT

Dir PMTR2083

R9779

(EJ200 scintillator, semicircular U-turn, Al foil wrapping)

• R2083 gives the best σt but is very expensive

• R9779 σt is ~10% worse but a factor 3 less expensive

)( 22)(

2)()2(1)2(1 scSizetriggerTtriggerT

Shape of u-turn (semicircular) was chosen using a preliminary setup (without long light guides)

Ind PMT

Dir PMTR2083

R9779

(EJ200 scintillator, semicircular U-turn, Al foil wrapping)

PMTs choice: test and simulation

Photons: R2083 R9779Neutrons: R2083 R9779

Gemc simulation of the CND:• measured t used to smear timing• vs p for photons and neutrons• Error bars represent 3• R9779 still meets requirements

Final choice R10533: same price and time performances of R9779, higher gain – no amplifier needed

Tests on three-layer prototype confirmed all choices of components

+ choice of CFDs and splitters

• R2083 gives the best σt but is very expensive

• R9779 σt is ~10% worse but a factor 3 less expensive

45°

<B>=230 G @ PMTsRelative angle B-PMT~70°

Final choice is 5 mm of mild-steel shielding

Magnetic field values

without shielding

Magnetic probe

Position of photocathode

Mild steel

µ-metal

Magnetic field tests (LAL, Orsay)

JLab field simulations confirm the B~0 inside our

5mm shieldings

60°ProbeShielding

Magnet

Also done tests checking PMT signal amplitude vs field angle

Detector construction: gluing

U-turn: yes, it works!

144 scintillators, 144 long light guides, 72 u-turn light guides, 144 « fish-tail » guides, 144 « connection » guides

Gluing started in December 2013Polishing before gluing

The gluing room at IPN OrsayFish-tail guide

Detector construction: wrapping

Wrapping:Al foilBlack tape

Measurement of the thickness to verify clearance requirements

One layer is completed

Detector construction and testing

One block of the CND:end of the light guides

Connecting the guideto the shielded PMT

All PMT bases are ready and mounted

One block of the CND in the cosmic-raystest room

Direct light

Indirect light

U turn drop

TOP layer

MIDDLE layer

BOTTOM layer

Raw data: TDC vs ADC

Characterization of the blocksOne week of data taking to characterize each block, right after assembly (same 6 PMTs used):

• Light collection• Effective light velocity in scintillator+light guides• Light attenuation • Time resolution

E.S. Smith et al. NIM A 432 (1999) 265-298Measurement of time resolution with cosmic rays (following the method described by R.T. Giles et al. NIM A 252 (1986) 41-52)

SPMT PMTAPMT PMT

BPMT PMT

Time resolution with cosmic rays, trigger from triple coincidence

Support structure and installation tests

6 stainless steel brackets

6 aluminum arches

Mock up of the solenoid

Mock up of the solenoid support ring

21 blocks constructed: only 3 more to go! Shipping to JLab in April ‘15

We arrived at this stage thanks to (alphabetic order): Julien Bettane, Jean-Luc Cercus, Brice Garillon, Giulia Hull, Miktat Imre, Michael Josselin, Alain Maroni, Gilles Minier, Thi Nguen-Trung, Joel Pouthas, Daria Sokhan, Claude Thèneau.

Conclusions and outlook GPDs are a unique tool to explore the internal landscape of the nucleon:

• 3D quark/gluon imaging of the nucleon• orbital angular momentum carried by quarks

Their extraction from experimental data is very difficult: • there are 4 GPDs for each quark flavor• they depend on 3 variables, only two (, t) experimentally accessible• they appear as integrals in cross sections

Recently-developed fitting methods allow to extract CFFs from DVCS observables•We need to measure several p-DVCS and n-DVCS observables over a wide phase space

Our new measurement of 3 spin observables for p-DVCS allows the extraction of ImHp and ImHp → spatial distribution of electric and axial charge in the proton

The 12-GeV-upgraded JLab will be the only facility to perform DVCS experiments in the valence region, for Q2 up to 11 GeV:

• DVCS experiments on both proton (L/T polarized and unpolarized) and deuteron targets are planned for 3 of the 4 Halls at JLab@12 GeV

• The CND is ready to go! nDVCS@CLAS12 experiment foreseen for the year 2018

• Work ongoing on PAC proposal for nDVCS with a longitudinally-polarized target (TSA and DSA): sensitivity to ImHn and ReHn → flavor separation!

~