Lauri Kaldamäe | Searcharxiv

arXiv2023

Identical particle and lepton mass effects in the decay $H\to Z^\ast(\toτ^+τ^-)+Z^\ast(\toτ^+τ^-)$

We consider identical particle and lepton mass effects in the cascade decay $H\to Z^\ast(\toτ^+τ^-)+Z^\ast(\toτ^+τ^-)$. Since the scale of the problem is set by the off-shellness $p_a^2$ and $p_b^2$ of the respective gauge bosons in the limits ($4m_τ^2\le p_a^2,p_b^2\le (m_H-2m_τ)^2$) and not by $m_H^2$, lepton mass effects are nonnegligible in particular close to the threshold of the off-shell decays. We calculate the rates and single angle decay distributions and compare them with the corresponding rates and single angle decay distributions for the nonidentical particle decays $H\to Z^\ast(\to e^+e^-)+Z^\ast(\toμ^+μ^-)$ involving negligible lepton masses.

hep-ph↗

arXiv2015

Lepton-mass effects in the decays $H \to ZZ^{\ast} \to \ell^{+} \ell^{-} τ^{+} τ^{-}$ and $H \to WW^{\ast} \to \ell ντν_τ$

We consider lepton-mass effects in the cascade decays $H\to Z(\to \ell^{+} \ell^{-})+Z^{\ast}(\to τ^{+}τ^{-})$ and $H\to W^{-}(\to \ell^{-}\bar ν_{\ell})+W^{+\ast}(\to τ^{+}ν_τ)$. Since the scale of the problem is set by the off-shellness $q^{2}$ of the respective gauge bosons in the limits $(m_{\ell}+m_{\ell'})^{2} \le q^{2} \le (m_{H}-m_{W,Z})^{2}$ and not by $m_{W,Z}^{2}$, lepton-mass effects are non-negligible for the $τ$ modes in particular close to the threshold of the off-shell decays. Lepton-mass effects show up e.g.\ in the three-fold joint angular decay distribution for the decays. Nonzero lepton masses lead to leptonic helicity-flip contributions which in turn can generate novel angular dependencies in the respective three-fold angular decay distributions. Lepton-mass effects are more pronounced in the $H \to Z(\to \ell\ell)Z^{\ast}(\toττ)$ mode which, in part, is due to the fact that the ratio of lepton helicity flip/nonflip contributions in the decay $Z^{\ast} \to \ell^{+}\ell^{-}$ is four times larger than in the decay $W^{+\ast}\to \ell^{+}ν$. We also briefly consider the corresponding off-shell -- off-shell decays $H\to Z^{\ast}(\to \ell^{+}\ell^{-})+Z^{\ast}(\to τ^{+}τ^{-})$ and $H\to W^{-\ast}(\to \ell^{-}\bar ν_{\ell})+W^{+\ast}(\to τ^{+}ν_τ)$.

hep-ph↗