Abstract
We analyze the New Physics sensitivity of a recently proposed method to measure the CP-violating mathcal{B} (KS → μ+μ−)ℓ=0 decay rate using KS− KL interference. We present our findings both in a model-independent EFT approach as well as within several simple NP scenarios. We discuss the relation with associated observables, most notably mathcal{B} (KL → π0 nu overline{nu} ). We find that simple NP models can significantly enhance mathcal{B} (KS → μ+μ−)ℓ=0, making this mode a very promising probe of physics beyond the standard model in the kaon sector.
Highlights
Within the SM, the prediction for KS → μ+μ− involves a large CP-conserving contribution, dominated by long-distance physics, and a much smaller CP-violating contribution, dominated by short-distance physics
We find that simple NP models can significantly enhance B(KS → μ+μ−) =0, making this mode a very promising probe of physics beyond the standard model in the kaon sector
Following the recent understanding that short-distance parameters of the SM can be cleanly extracted from a measurement of interference effects in K → μ+μ− [1, 2], we have addressed the question of what can be learned from such a measurement beyond the SM
Summary
The 2020 LHCb bound on KS → μ+μ− reads [4] B(KS → μ+μ−) < 2.1 · 10−10 ≡ B(KS → μ+μ−)lim. Within the SM, the prediction for KS → μ+μ− involves a large CP-conserving contribution, dominated by long-distance physics, and a much smaller CP-violating contribution, dominated by short-distance physics. Since these two contributions result in final states of opposite CP, they do not interfere and we have. The bound of eq (2.1) can be read as a conservative bound on the CP-violating (CPV) short-distance contribution alone, B(KS → μ+μ−)CPV < B(KS → μ+μ−)lim. [2], within the SM, the decay KL → μ+μ− is CP-conserving, and involves only the (μ+μ−) =0 final state. Which implies that the KS − KL interference term involves only = 0, Γint. Suggesting that a direct measurement of the KS − KL interference term from the timedependent rate would be sensitive to viable NP scenarios
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