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Why Studying n-DVCS ?Eric Voutier
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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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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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Kinematical separation Better separation at high t
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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