Limits on the abundance of millicharged particles bound to matter
  Millicharged particles (mCPs) are hypothesized particles possessing an
electric charge that is a fraction of the charge of the electron. We report a
search for mCPs with charges $\gtrsim 10^{-4}~e$ that improves sensitivity to
their abundance in matter by roughly two orders of magnitude relative to
previous searches. This search is sensitive to such particles over a wide range
of masses and charges for which they can form stable bound states with matter,
corresponding to a gap in parameter space that is beyond the reach of previous
searches from accelerators, colliders, cosmic-ray experiments, and cosmological
constraints.
