  Electron behavior in doped Mott systems continues to be a major unsolved
problem in quantum many-electron physics. A central issue in understanding the
universal Mott behavior in a variety of complex systems is to understand the
nature of their electron-hole pair excitation modes. Using high resolution
resonant inelastic x-ray scattering (RIXS) we resolve the momentum dependence
of electron-hole pair excitations in two major classes of doped copper oxides
which reveals a Mott pseudogap over the full Brillouin zone and over the entire
phase diagram. The pair bandwidth and zone-boundary pair velocity renormalize
on either sides of the phase diagram at very different rates indicating strong
particle-hole doping asymmetries observed for the first time.
