A simulation study on the measurement of D^0-D^0mixing parameter y at BES

We established a method on measuring the D^0-D^0 mixing parameter y for BESIII experiment atthe BEPC II e^＋e^- collider. In this method, the doubly tagged 4（3770） D^0-D^0 events, with one D decaysto CP-eigenstates and the other D decays semileptonically, are used to reconstruct the signals. Since this analysis requires good e/π separation, a likelihood approach, which combines the dE/dx, time of flight and the electromagnetic shower detectors information, is used for particle identification. We estimate the sensitivity of the measurement of y to be 0.007 based on a 20 fb^-1 fully simulated MC sample.