Prospects for $${K_L \rightarrow \pi ^0\nu \bar{\nu }}$$, $$K_S\rightarrow \mu ^+\mu ^-$$, $$K_L\rightarrow \pi ^0 \ell ^+\ell ^-$$ and $$\varepsilon '/\varepsilon $$ after the new $${K^+ \rightarrow \pi ^+\nu \bar{\nu }}$$ result from NA62
Year: 2026
Type: article
Abstract: The recently announced NA62 measurement of the $${K^+ \rightarrow \pi ^+\nu \bar{\nu }}$$ K + → π + ν ν ¯ branching ratio, based on 2016–2024 data, is fully consistent with its very accurate Standard Model (SM) prediction. While it is not excluded that the final result based on 2016–2026 data will deviate from the SM prediction, the question arises whether a similar fate awaits the $${K_L \rightarrow \pi ^0\nu \bar{\nu }}$$ K L → π 0 ν ν ¯ decay. This decay is currently being searched for by the KOTO experiment, with the present upper bound roughly two orders of magnitude above its very precise SM prediction. The proposed KOTO II experiment aims to provide the first discovery of the $${K_L \rightarrow \pi ^0\nu \bar{\nu }}$$ K L → π 0 ν ν ¯ decay and measure its branching ratio. Building on the findings of several previous papers we demonstrate that in the presence of suitably chosen large new complex phases and of a small amount of new right-handed $$\bar{s} d$$ s ¯ d couplings, in addition to the left-handed ones, the $${K_L \rightarrow \pi ^0\nu \bar{\nu }}$$ K L → π 0 ν ν ¯ branching ratio can still be enhanced by one order of magnitude with respect to the SM prediction while keeping both $${K^+ \rightarrow \pi ^+\nu \bar{\nu }}$$ K + → π + ν ν ¯ and $$\varepsilon _K$$ ε K SM-like. Simultaneously the decays $$K_S\rightarrow \mu ^+\mu ^-$$ K S → μ + μ - , studied by LHCb, and
Source: The European Physical Journal C
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
Awards: G1897041155, TRR 257: Phänomenologische Elementarteilchenphysik nach der HiggsEntdeckung, G2645866196, G2946282769, EXC 2118: Precision Physics, Fundamental Interactions and Structure of Matter (PRISMA+), G4066435496, EXC 2094: ORIGINS: Vom Ursprung des Universums bis zu den ersten Bausteinen des Lebens, G9001171362
OpenAlex ID: W7170091301