Heavy ion beam loss mechanisms at an electron-ion collider

There are currently several proposals to build a high-luminosity electron-ion collider, to study the spin structure of matter and measure parton densities in heavy nuclei, and to search for gluon saturation and new phenomena like the colored glass condensate. These measurements require operation with heavy nuclei. We calculate the cross sections for two important processes that will affect accelerator and detector operations: bound-free pair production and Coulomb excitation of the nuclei. Both of these reactions have large cross sections, 28–56 mb, which can lead to beam ion losses, produce beams of particles with altered charge:mass ratio, and produce a large flux of neutrons in zero degree calorimeters. The loss of beam particles limits the sustainable electron-ion luminosity to levels of several times ${10}^{32}/{\mathrm{cm}}^2/\mathrm{s}$.

Figure 1

(Top) Per-photon cross section for bound-free (blue line) and Coulomb excitation (red line) for gold beams at eRHIC, as a function of photon energy, in the target rest frame. (Bottom) Flux-weighted cross sections for $eA$ production of Coulomb excited gold and BFPP. The photon spectrum scales as $1/k$, so the reactions are concentrated at low photon energies.