Measurement of the form-factor ratios for D+s→φℓ+νℓ

Abstract We have measured the form factor ratios r V = V (0)/ A 1 (0) and r 2 = A 2 (0)/ A 1 (0) for the decay D s + →φ l + ν l , φ→K + K − , using data from charm hadroproduction experiment E791 at Fermilab. Results are based on 144 signal and 22 background events in the electron channel and 127 signal and 34 background events in the muon channel. We combine the measurements from both lepton channels to obtain r V =2.27±0.35±0.22 and r 2 =1.57±0.25±0.19.