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arXiv 2012.02142hep-phhep-ex
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轻介子衰变中暗扇区的新的多轻子特征

Novel multi-lepton signatures of dark sectors in light meson decays

Matheus Hostert, Maxim Pospelov

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16 pages, 6 figures, 1 table
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摘要：

指出K介子衰变为多重带电轻子是探测光暗粒子$X$的新途径。以前被忽略的通道，如$K^+\to π^+ \left(XX \to 2(e^+e^-)\right)$、$K_L\to π^0 \left( XX \to 2(e^+e^-)\right)$和$K_S\to \left(XX \to 2(e^+e^-)\right)$，可能有非常大的速率，不仅超过标准模型的预期，也可能超过背景，如中性π介子的达利兹衰变。我们将这个想法应用到暗扇区模型中，其中暗希格斯玻色子或重中性轻子的产生导致具有几个可见暗光子的最终状态。我们还研究了最近提出的一个MeV尺度的QCD轴子模型，其中由于轴子与轻介子的非线性相互作用，K介子衰变到多个轴子态的速率很大。此外，我们还指出了在π衰变中这个轴子的新的探测，如在$π^+ \to ν\left((e^+)^* \to e^+ a\to e^+e^+e^-\right)$中$a$的单产生，在π俘获$π^-+(p \text{ or D})\to aa + (n\text{ or }nn) \to 2(e^+e^-) + (n\text{ or }nn)$中的双产生，以及$π^0 \to aaa\to 3(e^+e^-)$。对于$17$ MeV的轴子，后者的衰变被固定在$\mathcal{B}(π^0\to a a a) = 1.0 \times 10^{-3}$。

英文摘要：

We point out kaon decays to multiple charged leptons as a novel probe of light dark particles $X$. Previously neglected channels, such as $K^+\to π^+ \left(XX \to 2(e^+e^-)\right)$, $K_L\to π^0 \left( XX \to 2(e^+e^-)\right)$, and $K_S\to \left(XX \to 2(e^+e^-)\right)$ may have very large rates, exceeding not only the Standard Model expectations but also possible backgrounds, such as Dalitz decays of neutral pions. We apply this idea to dark sector models where the production of dark Higgses or heavy neutral leptons leads to final states with several visible dark photons. We also investigate a recently proposed model of an MeV-scale QCD axion, where the rates for kaon decays to multiple axion states are large due to the non-linear interactions of the axion with the light mesons. In addition, we point out new probes of this axion in pion decays, such as the single production of $a$ in $π^+ \to ν\left((e^+)^* \to e^+ a\to e^+e^+e^-\right)$, double production in pion capture $π^-+(p \text{ or D})\to aa + (n\text{ or }nn) \to 2(e^+e^-) + (n\text{ or }nn)$, as well as $π^0 \to aaa\to 3(e^+e^-)$. The latter decay is fixed at $\mathcal{B}(π^0\to a a a) = 1.0 \times 10^{-3}$ for a $17$ MeV axion.

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