Semileptonic D Decays from Cleo and Belle

Semileptonic D meson decays are of great physics interest because their description is relatively simple. The decay matrix for semileptonic D meson decay decouples into a weak current component (describing the Wlνl vertex), and a strong current term (for the Wcq̄ vertex) that is parameterized through form factor functions of the invariant mass (q) of the W exchanged. The form factors can not be easily computed in quantum chromodynamics (QCD) since they are affected by significant nonperturbative contributions. That is the main source of uncertainty in the extraction of the CKM matrix element from the simple decay processes. Precise experimental measurements are needed to guide theoretical progress in this area. Charm semileptonic decays allow a measurement of the form factors and CKM matrix elements Vcs and Vcd. Using Heavy Quark Effective Theory (HQET) or lattice gauge techniques, the measured charm form factor can be related to those needed to interpret b → u transition and the measurement of the CKM matrix element Vub. While measurements of form factors in all charm exclusive semileptonic decays are important, those in pseudoscalar-topseudoscalar transitions are the easiest to perform. The differential decay rate for the exclusive semileptonic decay D → Plν (P stands for a pseudoscalar meson) with the electron mass effects neglected can be exc q − l ν