Direct Measurement Of B(D-S->Phi Pi)

The absolute inclusive branching fraction of D-s(+)-->phi X+ has been measured from data collected by the BES detector at a center-of-mass energy of 4.03 GeV, corresponding to an integrated luminosity of 22.3 pb(-1). At this energy, direct pair production e(+)e(-)-->Ds+Ds- has been observed. We have selected D-s candidate events by reconstructing five hadronic decay modes D-s(+) -->phi pi(+), (K) over bar(0)*K+,(K) over bar(0)K(+), f(0) pi(+) and K(0)K(-)pi(+)pi(+) and have searched for inclusive phi's in the recoiling D-s(-). We observed three recoiling phi's in the 166.4 +/- 31.8 D-s candidate events, which leads to the absolute branching fraction B(D-s(+)-->phi X+) = (17.8+(+15.1)(-7.2) (+0.6)(-6.3)) % and B(D-s(+)-->phi pi(+)) = (3.6(-1.6)(-1.3)(+3.1)(+0.4)) %. [S0556-2821(97)02423-5].