We present a study of the decay BJ/. We obtain the CP-odd fraction in the final state at time zero, R=0.16±0.10(stat)±0.02(syst), the average lifetime of the (B, ) system, (B)=1.39(stat)(syst) ps, and the relative width difference between the heavy and light mass eigenstates, /(L-H)/=0.24(stat)(syst). With the additional constraint from the world average of the B lifetime measurements using semileptonic decays, we find (B)=1.39±0.06 ps and /=0.25. For the ratio of the B and B0 lifetimes we obtain =0.91±0.09(stat)±0.003