B,Bs→Kform factors: An update of light-cone sum rule results

Abstract

We present an improved QCD light-cone sum rule (LCSR) calculation of the B{yields}K and B{sub s}{yields}K form factors by including SU(3)-symmetry breaking corrections. We use recently updated K meson distribution amplitudes which incorporate the complete SU(3)-breaking structure. By applying the method of direct integration in the complex plane, which is presented in detail, the analytical extraction of the imaginary parts of LCSR hard-scattering amplitudes becomes unnecessary and therefore the complexity of the calculation is greatly reduced. The values obtained for the relevant B{sub (s)}{yields}K form factors are as follows: f{sub BK}{sup +}(0)=0.36{sub -0.04}{sup +0.05}, f{sub B{sub s}}{sub K}{sup +}(0)=0.30{sub -0.03}{sup +0.04}, and f{sub BK}{sup T}(0)=0.38{+-}0.05, f{sub B{sub s}}{sub K}{sup T}(0)=0.30{+-}0.05. By comparing with the B{yields}{pi} form factors extracted recently by the same method, we find the following SU(3) violation among the B{yields}light form factors: f{sub BK}{sup +}(0)/f{sub B{pi}}{sup +}(0)=1.38{sub -0.10}{sup +0.11}, f{sub B{sub s}}{sub K}{sup +}(0)/f{sub B{pi}}{sup +}(0)=1.15{sub -0.09}{sup +0.17}, f{sub BK}{sup T}(0)/f{sub B{pi}}{sup T}(0)=1.49{sub -0.06}{sup +0.18}, and f{sub B{sub s}}{sub K}{sup T}(0)/f{sub B{pi}}{sup T}(0)=1.17{sub -0.11}{sup +0.15}.