DVCS at JLab

DVCS at JLab

Como, 11/06/2013

JLab published 6 GeV results

JLab 6GeV analysis in progress

JLab 12 GeV program



JLab 12 GeV program

JLabDuty 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 ADVCS@JLab

ep epg

H(e,e’g)X

H(e,e’gp)

H(e,e’g)X - H(e,e’gg’)X'

H(e,e’g)N

DVCS : exclusivity

• Good resolution : no need for the proton array• Remaining contamination 1.7%

HRS+calorimeterep -> epgep -> ep0 0->ggep -> ep0gep -> ep0N…

HRS+calorimeter + proton array

DVCS Bethe-HeitlerGPDs

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 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


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


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.

+


beam charge asym.

+

beam spin asym

+

…

linearization

unpol.sec.eff.

+

beam pol.sec.eff.

c2 minimization

beam spin 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 minimizationlinearization

VGG model

Moutarde 10 model/fitKM10 model/fit

Nucleon tomography

The axial charge (~Him) appears to be more « concentrated » than the electromagnetic charge (~Him)

~

c2 minimizationlinearization

VGG model



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 :


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


CLAS :



« eg1dvcs » (2008)Analysis of the long.pol. target asymmetries


CLAS :



« eg1dvcs » (2008)Analysis of the long.pol. target asymmetries


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 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

Documents

DVCS at JLab