SU(3) Breaking Effects in Charmed Meson Decays

Abstract

The decay rates of $D^{+}\to {\pi }^{+}{\pi }^0$ and $D^0\to K^{+}{\pi }^{-}$ recently measured by CLEO give the ratios $R_1=2|V_{cs}/V_{cd}{|}^2\Gamma (D^{+}\to {\pi }^{+}{\pi }^0)/\Gamma (D^{+}\to {\bar{K}}^0{\pi }^{+})=3.29\pm 1.16$ and $R_2=|V_{cs}^{\ast }{V}_{ud}/(V_{cd}^{\ast }{V}_{us}){|}^2\Gamma (D^0\to K^{+}{\pi }^{-})/\Gamma (D^0\to K^{-}{\pi }^{+})=2.92\pm 1.34$. Both are about three times of those expected from SU(3) symmetry. We show that, in the large-$N_c$ factorization approach, such large SU(3) violations can be accounted for by the accumulations of several small SU(3)-breaking effects. An important requirement is the relative magnitude of the form factors, $f_{+}^{D\pi }(0)>f_{+}^{DK}(0)$.

Comments: 10 pages, ITP-SB-93-49, UCD-93-31