We have searched for the decay ${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$ in data from the Fermilab charm photoproduction experiment E691. The resulting upper limit is B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$)<0.45B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$). Since the branching fraction for ${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$ can be calculated from the measured branching fraction B(${\mathit{D}}^{+}$→K¯ ${}_{}{}^{\mathrm{*}0}{}_{}{}^{}$${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$) to be (1.7±0.3)%, this implies a 90%-confidence-level lower limit on B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$) of 3.4%.

• Received 12 February 1990

DOI:https://doi.org/10.1103/PhysRevLett.64.2885