Within the standard model,we have investigated rare Z-boson decays into double heavy quarkonia,Z→VV and Z→VP,with V and P denoting vector and pseudo scalar quarkonia,respectively.It is assumed that the leading-order...Within the standard model,we have investigated rare Z-boson decays into double heavy quarkonia,Z→VV and Z→VP,with V and P denoting vector and pseudo scalar quarkonia,respectively.It is assumed that the leading-order QCD diagrams would give the dominant contributions to these processes,and the corresponding branching fractions,for instance,B(Z→J/ΨJ/Ψ),have been estimated to be approximately 10^(-13)in literature.However,these decays could also happen through electromagnetic transitions Z→Vγ^(*)and Z→Pγ^(*),with the virtual photon transforming into V.Interestingly,the smallness of the vector quarkonium mass can give rise to a large factor m_(Z)^(2)/m_(V)^(2)relative to the QCD contributions,which thus counteracts the suppression from the electromagnetic coupling.We systematically include these two types of contributions in our calculation to predict branching fractions for these decays.Particularly,owing to the virtual photon effects,it is found that B(Z→J/ΨJ/Ψ)will be significantly enhanced,up to 10^(-10).展开更多
Belle Collaboration reported a new observed value of K＊- （892） mass by studying τ^- → Ksπ^-vτ decay, which is significantly different from the current world average value given by Particle Data Group 2006. Moti...Belle Collaboration reported a new observed value of K＊- （892） mass by studying τ^- → Ksπ^-vτ decay, which is significantly different from the current world average value given by Particle Data Group 2006. Motivated by this new data, we revisit the issue on the K^＊0（892）- K^＊±（892） mass splitting. Our theoretical estimation favors the new measurement by Belle Collaboration. Therefore further experimental efforts are urgently needed to improve our understanding of these issues.展开更多
基金Supported in part by the National Natural Science Foundation of China(11575175,12047502)National Research and development Program of China(2020YFA0406400)。
文摘Within the standard model,we have investigated rare Z-boson decays into double heavy quarkonia,Z→VV and Z→VP,with V and P denoting vector and pseudo scalar quarkonia,respectively.It is assumed that the leading-order QCD diagrams would give the dominant contributions to these processes,and the corresponding branching fractions,for instance,B(Z→J/ΨJ/Ψ),have been estimated to be approximately 10^(-13)in literature.However,these decays could also happen through electromagnetic transitions Z→Vγ^(*)and Z→Pγ^(*),with the virtual photon transforming into V.Interestingly,the smallness of the vector quarkonium mass can give rise to a large factor m_(Z)^(2)/m_(V)^(2)relative to the QCD contributions,which thus counteracts the suppression from the electromagnetic coupling.We systematically include these two types of contributions in our calculation to predict branching fractions for these decays.Particularly,owing to the virtual photon effects,it is found that B(Z→J/ΨJ/Ψ)will be significantly enhanced,up to 10^(-10).
基金Supported by NSFC (10275059, 10775124, 90403021)CAS (KJCX2-SW-N10)
文摘Belle Collaboration reported a new observed value of K＊- （892） mass by studying τ^- → Ksπ^-vτ decay, which is significantly different from the current world average value given by Particle Data Group 2006. Motivated by this new data, we revisit the issue on the K^＊0（892）- K^＊±（892） mass splitting. Our theoretical estimation favors the new measurement by Belle Collaboration. Therefore further experimental efforts are urgently needed to improve our understanding of these issues.
