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Positron Beam for Measurements of Generalized Parton Distributions

e+ @ JLab Generalized parton distributions Polarized positron production Polarization transfer physics PEPPo Perspectives ConclusionsInstitut de Physique NuclaireOrsay, FranceEric Voutier Trento, June 8-12, 2015New Directions in Nuclear Deep Inelastic Scattering?

Eric VoutierXXVth International Workshop on Nuclear Theory1

Generalized Parton Distributions

GPD conceptElectro-production of photonsExperimental observablesTrento, June 8-12, 2015Eric VoutierXXVth International Workshop on Nuclear Theory2GPD concept GPDs are the appropriate framework to deal with the partonic structure of hadrons and offer the unprecedented possibility to access the spatial distribution of partons.Parton Imaging

M. Burkardt, PRD 62 (2000) 071503 M.Diehl, EPJC 25 (2002) 223GPDs can be interpreted as a 1/Q resolution distribution in the transverse plane of partons with longitudinal momentum x. GPDs = GPDs(Q2,x,x,t) whose perpendicular component of the momentum transfer to the nucleon is Fourier conjugate to the transverse position of partons.

GPDs encode the correlations between partons and contain information about the dynamics of the system like the angular momentum or the distribution of the strong forces experienced by quarks and gluons inside hadrons.X. Ji, PRL 78 (1997) 610 M. Polyakov, PL B555 (2003) 57 A new light on hadron structureEric Voutier

Trento, June 8-12, 20153/31Eric VoutierXXVth International Workshop on Nuclear Theory3

GPDs enter the cross section of hard scattering processes via an integral over the intermediate quarks longitudinal momenta


Deep Exclusive ScatteringGPDs can be accessed via exclusive reactions in the Bjorken kinematic regimeQ2 >> M2 -t 50%dp/p = 10-2ex = 1.6 mm.mradey = 1.7 mm.mradEric Voutier

Trento, June 8-12, 201528/31Eric VoutierXXVth International Workshop on Nuclear Theory28Positron beam at CEBAFe+ Production ScenariiCEBAF INJ (10-100 MeV)FEL (100 MeV)CEBAF (12 GeV)

Eric Voutier

Trento, June 8-12, 201529/31Eric VoutierXXVth International Workshop on Nuclear Theory29Technological challengesTowards a Polarized Positron BeamHigh Intensity Polarized Electron SourcePolarized electron gun at JLab did demonstrate high intensity capabilities, though the polarization at high current was not measured. The path from a sketched concept to a full design is a correlated multi-parameter problem requiring to adress and solve several technical/technological challenges. High Power Production TargetHigh power absorbers (10-100 kW) are challenging for heat dissipation, radiation management, and accelerator integration. Optimized Positron CollectionProperties of usable beam for Physics (intensity, polarization, momentum spread, emittance) are strongly related to the positron production and collection schemes and strategies (1 or 2 targets).Positron Beam ShapingPre-acceleration (Hadronic Physics) or deccelaration (Material Science) are required to produce a beam suitable for Phyiscs. Eric Voutier

Trento, June 8-12, 201530/31Eric VoutierXXVth International Workshop on Nuclear Theory30ConclusionsSummaryThe merits of polarized and/or unpolarized positron beams for the Physics program at JLab is comparable to the benefits of polarized with respect to unpolarized electrons.

2g physics, GPDs NP @ low energy, Material Science @ very low energy The PEPPo experiment @ the CEBAF injector has been a first step in this process, opening a world-wide access to polarized positrons. An R&D effort is necessary toresolve the several technical and technological challenges raised by the development of a (un)polarized positron beam for Physics.31/31Eric Voutier

Trento, June 8-12, 2015Eric VoutierXXVth International Workshop on Nuclear Theory31


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