Two-color QCD at nonzero quark-number density

We have simulated two-color four-flavor QCD at nonzero chemical potential $\mu$ for quark number. Simulations were performed on $8^4$ and ${12}^3\times 24$ lattices. Clear evidence was seen for the formation of a colorless diquark condensate which breaks quark number spontaneously, for $\mu >{\mu }_c\sim m_{\pi }/2.\mathrm{}$ The transition appears to be second order. We have measured the spectrum of scalar and pseudoscalar bosons which shows clear evidence for the expected Goldstone boson. Our results are in qualitative agreement with those from effective Lagrangians for the potential Goldstone excitations of this theory.