  We report an investigation of criticality in QCD at finite isovector chemical
potential, mu_3, and at zero temperature. At the critical point, mu_3^c = m_pi,
we find that an uncharged scalar and pseudoscalar and a charged pseudoscalar
meson become massless within the resolution of our measurement. The effective
long distance theory therefore breaks O(4) symmetry by charged pion
condensation. This results in a rising quark number susceptibility. The baryon
remains massive, as indicated by a vanishing baryon number susceptibility.
