We consider the ``second-class current'' decay $τ^-\toπ^-ην_τ$ from several points of view. We first focus on the decay rate as expected within standard weak interaction and QCD due to isospin violation. The decay contributions divide into $P$- and $S$-wave parts. The former can be reliably estimated using the $ρηπ$ coupling inferred from the rates and Dalitz-plot distributions of $η\to 3π$ decays. The somewhat larger $S$-wave part, which was previously computed using chiral perturbation theory, is estimated from a simple $\bar qq$ model. Both estimates of the $S$-wave part depend on whether the $a_0(980)$ scalar particle is a $\bar qq$ or some other (4-quark) state. Finally, we discuss genuinely new, non-$V-A$ scalar weak interactions. The $τ^-\toπ^-ην_τ$ decay provides information on this question, which nicely complements that from precision $β$ decay experiments. % In summary, we discuss the possible implications of putative values of the branching fraction ${\cal B}(τ^-\toπ^-ην_τ)$. In the case of larger values, in particular of the $S$-wave part, not only will detection of the decay be more likely and more reliable, its implications will be more far-reaching and interesting.
Semileptonic decays $Λ_c^+ \to Λ\ell^+ ν_\ell\,\,(\ell=e,μ)$ in the covariant quark model and comparison with the new absolute branching fraction measurements of Belle and BESIII
Measurement of the H to ZZ branching fraction at 350 GeV and 3 TeV CLIC
在本文中，我们调查的前景，测量分支分数的标准模型希格斯玻色子衰变到一对$Z$玻色子在未来的紧凑型线性对撞机（CLIC）在350 GeV和3 TeV的质心能量。使用CLIC探测器的详细模拟进行研究，同时考虑到所有相关的物理和光束诱导的背景过程。结果表明，在质心能量为350 GeV（3 TeV）时，假设积分亮度为1 ab $^{-1}$（5 ab $^{-1}$），用半轻子末态可以测量出Higgs产生截面和分支分数BR的乘积（${H\rightarrow\thinspace ZZ^\ast}$），相对统计不确定度为20%（3.0%）.
