Direct measurements of the branching fractions for D0→K-e+ve and D0→π-e+ve and determinations of the form factors fK+(0) and fπ+(0)

The absolute branching fractions for the decays D-0 --> K(-)e(+)v(e) and D-0 --> pi(-)e(+)v(e) are determined using 7584 +/- 198 +/- 341 singly tagged (D) over bar (0) sample from the data collected around 3.773 GeV with the BES-II detector at the BEPC. In the system recoiling against the singly tagged (D) over bar (0) meson, 104.0 +/- 10.9 events for D-0 --> K(-)e(+)v(e) and 9.0 +/- 3.6 events for D-0 --> pi(-)e(+)v(e) decays are observed. Those yield the absolute branching fractions to be BF(D-0 --> K(-)e(+)v(e)) = (3.82 +/- 0.40 +/- 0.27) % and BF(D-0 --> pi(-)e(+)v(e)) = (0.33 +/- 0.13 +/- 0.03) %. The vector form factors are determined to be \f(+)(K) (0)\ = 0.78 +/- 0.04 +/- 0.03 and \f(+)(pi) (0)\ 0.73 +/- 0.14 +/- 0.06. The ratio of the two form factors is measured to be \f(+)(pi) (0)/f(+)(K) (0)\ = 0.93 +/- 0.19 +/- 0.07. (C) 2004 Elsevier B.V. All rights reserved.