同位旋的反击
Isospin strikes back
AI总结：
本文基于同位旋守恒论证$ψ(2S)\toΛ\barΣ^0+\mathrm{c.c.}$应为纯电磁过程，并通过2024年新数据证实此前异常大分支比系测量不可靠，修正值降低逾七倍。
摘要：
假设同位旋守恒，一个$c\bar c$矢量介子衰变到$Λ\barΣ^0+\mathrm{c.c.}$末态的过程是纯电磁的。在领头阶，$c\bar c$矢量介子首先转化为一个虚光子，然后该虚光子产生$Λ\barΣ^0+\mathrm{c.c.}$末态。此外，这种机制，即虚光子耦合到$Λ\barΣ^0+\mathrm{c.c.}$，是在玻恩近似下反应$e^+e^-\toΛ\barΣ^0+\mathrm{c.c.}$得以进行的唯一中间过程。由此可知，在$c\bar c$质量处，过程$c\bar c\toΛ\barΣ^0+\mathrm{c.c.}$与$e^+e^-\toΛ\barΣ^0+\mathrm{c.c.}$的振幅之间若存在任何显著差异，都必须归因于$c\bar c$衰变中的同位旋破坏贡献。在Eur. Phys. J. C $\boldsymbol{80}$, 903 (2020)中，我们研究了$ψ(2S)$矢量介子衰变到$Λ\barΣ^0+\mathrm{c.c.}$的过程，并根据2018年版《粒子物理评论》Phys. Rev. D $\boldsymbol{98}$, 030001 (2018)中发表的大分支比${\rm BR}_{18}(ψ(2S)\toΛ\barΣ^0+\mathrm{c.c.})=(1.23\pm0.24)\times 10^{-5}$，我们声称要么存在显著的同位旋破坏贡献，要么以较低强调程度提出“唯一可用数据并不完全可靠”。无论如何，我们提议进行新的测量。显然，我们的第二个且被认为较不严重的假设是正确的，事实上2024年版《粒子物理评论》Phys. Rev. D $\boldsymbol{110}$, 030001 (2024)中发表的分支比为${\rm BR}(ψ(2S)\toΛ\barΣ^0+\mathrm{c.c.})=(1.6\pm0.7)\times 10^{-6}$，降低了七倍多，误差从约$20\\%$增加到约$45\\%$。
英文摘要：
Assuming isospin conservation, the decay of a $c\bar c$ vector meson into the $Λ\barΣ^0+\mathrm{c.c.}$ final state is purely electromagnetic. At the leading order, the $c\bar c$ vector meson first converts into a virtual photon that, then produces the $Λ\barΣ^0+\mathrm{c.c.}$ final state. Moreover, such a mechanism, i.e., the virtual photon coupling to $Λ\barΣ^0+\mathrm{c.c.}$, is the solely intermediate process through which, in Born approximation, the reaction $e^+e^-\toΛ\barΣ^0+\mathrm{c.c.}$ does proceed. It follows that any significant difference between the amplitudes of the processes $c\bar c\toΛ\barΣ^0+\mathrm{c.c.}$ and $e^+e^-\toΛ\barΣ^0+\mathrm{c.c.}$ at the $c\bar c$ mass must be ascribed to an isospin-violating contribution in the $c\bar c$ decay. In Eur. Phys. J. C $\boldsymbol{80}$, 903 (2020) we studied the decay of the $ψ(2S)$ vector meson into $Λ\barΣ^0+\mathrm{c.c.}$ and, on the light of the large branching fraction ${\rm BR}_{18}(ψ(2S)\toΛ\barΣ^0+\mathrm{c.c.})=(1.23\pm0.24)\times 10^{-5}$, published in the 2018 edition of the Review of Particle Physics Phys. Rev. D $\boldsymbol{98}$, 030001 (2018), we claimed either the presence of a significant isospin-violating contribution or, with a lesser emphasis, a "not complete reliability of the only available datum". In any case, we propose a new measurement. Apparently, our second and considered less serious hypothesis was the right one, indeed the branching fraction published in the 2024 edition of the Review of Particle Physics Phys. Rev. D $\boldsymbol{110}$, 030001 (2024) is $ {\rm BR}(ψ(2S)\toΛ\barΣ^0+\mathrm{c.c.})=(1.6\pm0.7)\times 10^{-6}$, more than seven times lower with the error that increased from $\sim 20\%$ to $\sim 45\%$.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
