Recent Results Addressing the KARMEN Timing Anomaly
  Recent resuls from experiments at Fermilab and the Paul Scherrer Institute have constrained the parameter space available for a hypothetical particle $Q^0$ produced in the decay $\pi^+ \to \mu^+ Q^0$. This decay has been invoked to explain a peculiar feature of an event arrival time distribution observed in the KARMEN neutrino experiment. 
E. D. Zimmerman