Study the feasibility of an electron-nucleon collider (ENC) as a future extension of the HESR at the FAIR facility.

Description of work and role of partners
Detailed physics simulations of benchmark channels represent the strattegy in this proposal to define the physics potential of the ENC.

A research program using double polarized electron-nucleon scattering will be proposed to address the most important questions of contemporary hadron structure physics:

  1. How is the angular momentum of a nucleon shared among the constituents of a nucleon?
  2. How do the flavours including gluons and sea quarks share linear and angular momen┬Čtum?
  3. What are the transverse dependencies of these distributions?

The participating groups bring in complementary expertise, necessary for the ambitious study proposed here: The first group (UBO, UMainz, GSI, CEA-IRFU, CNRS/IN2P3/IPNO, INFN-LNF, UTorino/INFN-TO, and UGlasgow) brings a long-standing experimental expertise in the field of hadron structure physics and analysis into this study. They are highly visible groups, which are involved in experiments at ELSA, MAMI, JLAB, COMPASS, HERMES, and BESSIII. They will be mainly responsible for the physics simulations.

The second group (UMainz, UREG, CNRS/CPHT, UTorino/INFN-TO, and SINS) provides the theory contribution that is necessary for the physics simulations. The calculation of the GPDs, TMDs and TMAs within a phenomenological framework or from lattice QCD will serve as an important input to the studies proposed here.

The participating accelerator physicists (UBO, UMainz, and FZJ) will study the electron storage ring design in the HESR tunnel. The participating institutions have a well-established reputation in the field of polarized particle accelerators, storage rings of electrons and protons, polarized electrons sources and accelerator design and operation.

Task 1: Physics simulations of benchmark channels: The experimental groups will perform detailed physics simulations of benchmark channels as the strategy to define the physics potential of the ENC. Physics simulations of exclusive and semi-inclusive doubly polarized lepton-proton scattering will be the main focus of this work package. UBO, UMainz, GSI, CEA-IRFU, CNRS/IN2P3/IPNO, INFN-LNF, UTorino/INFN-TO, and UGlasgow will perform physics simulations and benchmark channel analysis. UMainz, UREG, CNRS/CPHT, UTorino/INFN-TO, and SINS provide necessary theoretical input. While the PANDA central detector is particularly well suited to detect photons and electrons with high efficiency and resolution, the detection of forward going recoil protons has to be compromised due to the final focus elements of the collider. Studies of combined dipole and quadrupole elements have to be performed. The present PANDA detector target region, which is based on a frozen pellet target, needs to be adapted to the collider geometry including the silicon micro-vertex detector.

Task 2: Electron ring design study: The planned physics programme at the ENC requires high luminosity and polarized beams with longitudinally oriented high beam polarization. The demands on the electron ring are challenging (approx. 2A of circulating beam current, spin manipulation under strong influence of spin diffusion caused by synchrotron radiation). The suitability of different lattice designs, ranging from simple FODO structures to DBA subsections, combined with a full snake setup or solenoid based spin rotators have to be WT3: Work package description 283286 HadronPhysics3 - Workplan table - 2011-07-11 09:43 - Page 25 of 151 investigated. In order to preserve the beam polarization and quality (emittance, stability) in collision mode, detailed studies of spin and beam dynamics have to be performed. Lattice and rotator design have to be optimized accordingly.