New Directions in Kaon Physics: Interference in $K^0\toμ^+μ^-$ as a New Golden Mode
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arXiv
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| Natura: | Preprint |
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2026
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| _version_ | 1866910187253661696 |
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| author | Kitahara, Teppei |
| author_facet | Kitahara, Teppei |
| contents | The rare decays $K^0_L \toμ^+μ^-$ and $K^0_S \toμ^+μ^-$ have long been regarded as difficult channels to extract short-distance physics because they are dominated by long-distance contributions via two-photon exchanges. A qualitatively new feature arises once the interference between $K_L^0$ and $K_S^0$ is taken into account. The interference term is sensitive to genuine direct $CP$ violation in $s \to d μ^+ μ^-$ processes and turns this channel into a clean probe of the $CP$-violating short-distance physics. In this contribution, I summarize the basic mechanism of the $K_L^0$--$K_S^0$ interference, the flavor-tagging strategy at LHCb-like setup, and the projected sensitivities for a kaon-unitarity-triangle parameter combination $|A^2λ^5\barη|$ and also for the sign ambiguity of the $K_L^0 \to γγ$ three-point amplitude. As a result, it is expected that the CKM parameter $|A^2λ^5\barη|$ could be constrained by LHCb at the level of about $35\%$ of its Standard Model (SM) value, and the discrete ambiguity in $\mathcal{B}(K_L^0 \to μ^+μ^-)_{\rm SM}$ could be resolved at more than $3σ$ by the end of the high luminosity LHC. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_01744 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | New Directions in Kaon Physics: Interference in $K^0\toμ^+μ^-$ as a New Golden Mode Kitahara, Teppei High Energy Physics - Phenomenology High Energy Physics - Experiment The rare decays $K^0_L \toμ^+μ^-$ and $K^0_S \toμ^+μ^-$ have long been regarded as difficult channels to extract short-distance physics because they are dominated by long-distance contributions via two-photon exchanges. A qualitatively new feature arises once the interference between $K_L^0$ and $K_S^0$ is taken into account. The interference term is sensitive to genuine direct $CP$ violation in $s \to d μ^+ μ^-$ processes and turns this channel into a clean probe of the $CP$-violating short-distance physics. In this contribution, I summarize the basic mechanism of the $K_L^0$--$K_S^0$ interference, the flavor-tagging strategy at LHCb-like setup, and the projected sensitivities for a kaon-unitarity-triangle parameter combination $|A^2λ^5\barη|$ and also for the sign ambiguity of the $K_L^0 \to γγ$ three-point amplitude. As a result, it is expected that the CKM parameter $|A^2λ^5\barη|$ could be constrained by LHCb at the level of about $35\%$ of its Standard Model (SM) value, and the discrete ambiguity in $\mathcal{B}(K_L^0 \to μ^+μ^-)_{\rm SM}$ could be resolved at more than $3σ$ by the end of the high luminosity LHC. |
| title | New Directions in Kaon Physics: Interference in $K^0\toμ^+μ^-$ as a New Golden Mode |
| topic | High Energy Physics - Phenomenology High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2605.01744 |