A Z-Tagging Mini-DIRC at the Downstream Ion Focus of an Electron Ion Collider 2nd Detector

The proposed beamline for a 2nd detector at the Electron Ion Collider (EIC) includes a high dispersion focus approsimately 45 m downstream of the Interaction Point (IP). This enables the tagging of any beam fragment or secondary particle with a magnetic rigidity up to 99% (or greater than 101%) of beam rigidity. I will discuss simulations of a proposed absolute intensity (quartz) Cherenkov counter to be included with the Roman Pot tracking detectors. With the Cherenkov light yield scaling as Z² (the ion fragment charge squared), the Poisson statistics fluctuations in photon statistics are sufficiently small to resolve the ion charge to better than ±1e precision from protons to uranium. I will discuss issues of light collection uniformity, photo-sensor saturation, and beam backgrounds. Research topics that would be enabled by this capability will also be summarized.