Why Studying n-DVCS ?Eric Voutier

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~)()()()( 22211 tF

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n

n-DVCS gives access to the least known and constrained GPD, E

0 because F1(t) is small

0 because of cancelation of u and d quarks

Sensitivity of the difference of polarized cross sections to the angular momentum of quarks

How to Measure n-DVCS ?Eric Voutier

E03-106 experiment in Hall A is an exploratory measurement ofn-DVCS in the valence region

Triple Coincidence Experiment (e,e’n)

Neutron detection is a very involved matter : in-situ efficiencies and contaminations should be mastered large efficiencies should be achieved…

Possible opportunity for target spin asymmetries

Double Coincidence Experiment (e,e’)

Separation of coherent and incoherent channels

Triple Coincidence Experiment (e,e’(A-1))

Neutron tagging via detection of the recoiling residual system

E03-106 @ JLab.Hall_AEric Voutier

M. Mazouz, Doctorat Thesis, Grenoble (2006)

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Neutron contribution

Deuton contribution

Ids1Ids2

Twist-2 (BH.DVCS Interference)

Twist-3 (BH.DVCS Interference)DVCSds1 Twist-3 (DVCS.DVCS)

Ins1Ins2

Twist-2 (BH.DVCS Interference)

Twist-3 (BH.DVCS Interference)DVCSns1 Twist-3 (DVCS.DVCS)

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Experimental ResultsEric Voutier

Data taking under similar background conditionsInterchange regularly LH2 and LD2 targets (1-2 h)

P R E L I M I N A R Y

Possible observation of 2 contributions of opposite signsBUT

Results are dominated by systematics originating from the relative calibration of the calorimeter between LH2 and LD2 data

M. Mazouz, Doctorat Thesis, Grenoble (2006)

xB = 0.36Q2 = 1.91 GeV2

Eric Voutier

The mass of the target particle (nucleon or nucleus) is reconstructed taking advantage of the energy/angle correlation of DVCS .

Experimental spectra

A calorimeter energy resolution better than 2% would allow to disentangle n-DVCS and d-DVCS in

order to access the real parts

Simulated shapes

Current energy resolution allow separation of imaginary parts as long as n-DVCS and d-DVCS signals are opposite signs

Going Further ?

Going Further ?Eric Voutier

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A

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Kinematical separation Better separation at high t

2

A

Going Further ?Eric Voutier

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Many possible configurations giving access to different GPDs’ combination.

Technical issues regarding the feasibility of polarized 3He cells with thin windows

Unpolarized beam, transverse target polarization

Unpolarized beam, perpendicular target polarization

Unpolarized beam, longitudinal target polarization

Combined with similar combinations for protonsa flavor separation can be achieved

Target Spin Asymmetry

Questions ?Eric Voutier

Flavor Separation

Limits of the quasi-elastic description of the reaction ?

Double Coincidence Experimental Method

Imaginary parts can be separatedSeparating the real parts is very challenging

Existence & magnitude of nuclear corrections ?

Measurement of the same observable for proton and neutronyields a combination of GPDs with same flavor

Separating flavor GPDs would require 4 different observables