The perspective of high energy and high duty cycle polarized positron beams in complement to the existing CEBAF (Continuous Electron Beam Accelerator Facility) electron beams is attracting a lot of interest. Following the proof-of-principle PEPPo (Polarized Electrons for Polarized Positrons) experiment demonstrating a new scheme for producing highly polarized positrons, the Jefferson Lab (JLab) Positron Working Group (PWG) engaged in the thorough development of the experimental program that would be achieved at JLab with such beams. It encompasses the determination of the physics quantities that characterize nucleons and nuclei structure: electromagnetic form factors, generalized polarizabilities, parton distributions, and generalized parton distributions. It also concerns some of the hottest questions of the field as the charge radius of the proton and the occurrence of physics beyond the standard model through the search of low mass dark matter particles, the measurement of weak neutral-current couplings, and the investigation of charged lepton flavour violation.
This special issue published in EPJ A presents a coherent collection of experimental and/or theoretical works detailing the experimental program and physics accessible to positron beams at JLab. This program, which represents already several years of actual beam running, should not be understood as exhaustive but more surely as the minimal impact of future CEBAF positron beams on the nuclear physics science.
All articles of the special issue “An Experimental Program with Positron Beams at Jefferson Lab” are available here and are freely accessible until 22 May 2022. For further information, please read the Editorial.