Polarized light ions and spectator nucleon tagging at EIC

Abstract: An Electron-Ion Collider (EIC) with suitable forward detection capabilities would enable a unique experimental program of deep-inelastic scattering (DIS) from polarized light nuclei (deuterium 2H, helium 3He) with spectator nucleon tagging. Such measurements promise significant advances in several key areas of nuclear physics and QCD: (a) neutron spin structure, by using polarized deuterium and eliminating nuclear effects through on-shell extrapolation in the spectator proton momentum; (b) quark/gluon structure of the bound nucleon at x > 0.1 and the dynamical mechanisms acting on it, by measuring the spectator momentum dependence of nuclear structure functions; (c) coherent effects in QCD, by exploring shadowing in tagged DIS on deuterium at x << 0.1. The JLab MEIC design (CM energy sqrt{s} = 15-50 GeV/nucleon, luminosity ~ 10^{34} cm^{-2} s^{-1}) provides polarized deuterium beams and excellent coverage and resolution for forward spectator tagging. We summarize the physics topics, the detector and beam requirements for spectator tagging, and on-going R&D efforts.