1. Why Studying n-DVCS ? Eric Voutier n-DVCS gives access to the least known and constrained GPD, E 0 because F 1 (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

2. How to Measure n-DVCS ? Eric Voutier E03-106 experiment in Hall A is an exploratory measurement of n-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

3. E03-106 @ JLab.Hall_A Eric Voutier M. Mazouz, Doctorat Thesis, Grenoble (2006) Neutron contribution Deuton contribution Twist-2 (BH.DVCS Interference) Twist-3 (BH.DVCS Interference) Twist-3 (DVCS.DVCS) Twist-2 (BH.DVCS Interference) Twist-3 (BH.DVCS Interference) Twist-3 (DVCS.DVCS)

4. Experimental Results Eric Voutier Data taking under similar background conditions Interchange regularly LH 2 and LD 2 targets (1-2 h) P R E L I M I N A R Y Possible observation of 2 contributions of opposite signs BUT Results are dominated by systematics originating from the relative calibration of the calorimeter between LH 2 and LD 2 data M. Mazouz, Doctorat Thesis, Grenoble (2006) x B = 0.36 Q 2 = 1.91 GeV 2

5. 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 ?

6. Eric Voutier Kinematical separation Better separation at high t

7.     2        A Going Further ? Eric Voutier Many possible configurations giving access to different GPDs’ combination. Technical issues regarding the feasibility of polarized 3 He cells with thin windows Unpolarized beam, transverse target polarization Unpolarized beam, perpendicular target polarization Unpolarized beam, longitudinal target polarization Combined with similar combinations for protons a flavor separation can be achieved Target Spin Asymmetry

8. Questions ? Eric Voutier Flavor Separation Limits of the quasi-elastic description of the reaction ? Double Coincidence Experimental Method Imaginary parts can be separated Separating the real parts is very challenging Existence & magnitude of nuclear corrections ? Measurement of the same observable for proton and neutron yields a combination of GPDs with same flavor Separating flavor GPDs would require 4 different observables