B_c→J/ψ helicity form factors and the B_c~+→J/ψ+(P, V, l~+ν_l) decays

【摘要】 In this paper,we calculate the B_c→J/ψ helicity form factors（HFFs） up to twist-4 accuracy by using the light-cone sum rules（LCSR） approach.After extrapolating those HFFs to the physically allowable q² region,we investigate the B_c⁺-meson two-body decays and semi-leptonic decays B_c⁺→J/ψ（P,V,l⁺v_l）,where P/V stand for light pseudo scalar and vector mesons,respectively.The branching fractions can be derived using the CKM matrix element and the B_c lifetime from the Particle Data Group,and we obtain B（B_c⁺J/ψπ⁺）=(0.136_-0.002^+0.002)%,B（B_c⁺→J/ψK⁺）=(0.010_-0.000^+0.000)%,B（B_c⁺→J/ψρ⁺）=(0.768_-0.033^+0.029)%,B(B_c⁺→J/ψK^*+)=(0.043_-0.001^+0.001)%,B（B_c⁺→J/ψμ⁺v_μ）=(2.802_-0.675^+0.526)%and B（B_c⁺→J/ψτ⁺v_τ）=(0.559_-0.170^+0.131)%.We then obtain R_π⁺/μ⁺v_μ=0.048_-0.012^+0.009 and R_K⁺/π⁺=0.075_-0.005^+0.005,which agree with the LHCb measured value within 1σ-error.We also obtain R_J/ψ=0.199_-0.077^+0.060,which like other theoretical predictions,is consistent with the LHCb measured value within 2σ-error.These imply that the HFFs under the LC SR approach are also applicable to the B_c⁺ meson two-body decays and semi-leptonic decays B_c⁺→J/ψ+（P,V,l⁺v_l）,and the HFFs obtained using LCSR in a new way implies that there may be new physics in the B_c→J/ψl⁺v_l semi-leptonic decays.更多还原

【Abstract】 In this paper,we calculate the B_c→J/ψ helicity form factors（HFFs） up to twist-4 accuracy by using the light-cone sum rules（LCSR） approach.After extrapolating those HFFs to the physically allowable q² region,we investigate the B_c⁺-meson two-body decays and semi-leptonic decays B_c⁺→J/ψ（P,V,l⁺v_l）,where P/V stand for light pseudo scalar and vector mesons,respectively.The branching fractions can be derived using the CKM matrix element and the B_c lifetime from the Particle Data Group,and we obtain B（B_c⁺J/ψπ⁺）=(0.136_-0.002^+0.002)%,B（B_c⁺→J/ψK⁺）=(0.010_-0.000^+0.000)%,B（B_c⁺→J/ψρ⁺）=(0.768_-0.033^+0.029)%,B(B_c⁺→J/ψK^*+)=(0.043_-0.001^+0.001)%,B（B_c⁺→J/ψμ⁺v_μ）=(2.802_-0.675^+0.526)%and B（B_c⁺→J/ψτ⁺v_τ）=(0.559_-0.170^+0.131)%.We then obtain R_π⁺/μ⁺v_μ=0.048_-0.012^+0.009 and R_K⁺/π⁺=0.075_-0.005^+0.005,which agree with the LHCb measured value within 1σ-error.We also obtain R_J/ψ=0.199_-0.077^+0.060,which like other theoretical predictions,is consistent with the LHCb measured value within 2σ-error.These imply that the HFFs under the LC SR approach are also applicable to the B_c⁺ meson two-body decays and semi-leptonic decays B_c⁺→J/ψ+（P,V,l⁺v_l）,and the HFFs obtained using LCSR in a new way implies that there may be new physics in the B_c→J/ψl⁺v_l semi-leptonic decays.更多还原