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Why Studying n-DVCS ?

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

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Why Studying n-DVCS ?

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

  2. Eric Voutier Possible opportunity for target spin asymmetries Triple Coincidence Experiment (e,e’g(A-1)) Neutron tagging via detection of the recoiling residual system Double Coincidence Experiment (e,e’g) Separation of coherent and incoherent channels How to Measure n-DVCS ? Triple Coincidence Experiment (e,e’gn) Neutron detection is a very involved matter : in-situ efficiencies and contaminations should be mastered large efficiencies should be achieved… E03-106 experiment in Hall A is an exploratory measurement of n-DVCS in the valence region

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

  4. Eric Voutier Experimental Results M. Mazouz, Doctorat Thesis, Grenoble (2006) P R E L I M I N A R Y xB = 0.36 Q2 = 1.91 GeV2 Possible observation of 2 contributions of opposite signs BUT Results are dominated by systematics originating from the relative calibration of the calorimeter between LH2 and LD2 data Data taking under similar background conditions Interchange regularly LH2 and LD2 targets (1-2 h)

  5. Eric Voutier Going Further ? The mass of the target particle (nucleon or nucleus) is reconstructed taking advantage of the energy/angle correlation of DVCS g. 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

  6. Eric Voutier Better separation at high t Going Further ? Kinematical separation

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

  8. Eric Voutier Questions ? Double Coincidence Experimental Method Imaginary parts can be separated Separating the real parts is very challenging Limits of the quasi-elastic description of the reaction ? Existence & magnitude of nuclear corrections ? Flavor Separation 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

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