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A new CP violation mechanism generated by the standard neutral Higgs boson : the $η\to π+ π$ case

X. Y. Pham·M. Gourdin
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Abstract

Strictly within the standard electro-weak interaction, CP violation in the flavour conserving process $η\rightarrow π+ π$ could originate from the mixing of the $η$ meson with the virtual scalar Higgs boson $ H^{0}$ via $W$ and top quark exchange. The parity-violation carried by weak gauge bosons makes the mixing possible by quantum effect at two-loop level. Nowhere the Kobayashi-Maskawa (KM) phase mechanism is needed. The phenomenon reveals an unexpected new role of the Higgs boson in the CP symmetry breaking. For the Higgs mass between 100-600 GeV, the $η\rightarrow π+π$ branching ratio is found to be $3.6 \cdot 10^{-26} - 2.4 \cdot 10^{-29}$ , hence CP violation mechanisms beyond the Standard Model are the only ones that could give rise to its observation at existing or near future $η$ factories, unless the Higgs mass is improbably as light as 550 $MeV$.

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X. Y. Pham, M. Gourdin. 1996-06-11. A new CP violation mechanism generated by the standard neutral Higgs boson : the $η\to π+ π$ case. https://doi.org/10.1016/0370-2693(96)00891-x

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