The link between ordinary Standard Model (SM) photons and both dark photons and axion-like particles (ALPs) can be introduced through the dark axion portal coupling. Given the dark axion portal setup, in the present paper we refer to the dark photon as the mediator between SM and dark matter (DM) particles, implying that it decays predominantly into a pair of DM fermions. Furthermore, we discuss in detail the implication of the dark axion portal scenario for the lepton (electron and muon) fixed-target experiments. In particular, for the specific fixed-target facility we study the missing-energy signatures of the dark photon production followed by its invisible decay into stable DM particles. We investigate the potential to probe dark axion portal vertices with regarding signatures and derive the expected sensitivities of $\mathrm{NA}64e$, $\mathrm{NA}64\mu$, LDMX and ${\mathrm{M}}^3$. Moreover, we estimate the expected reach of $\mathrm{NA}64e$ from the projected statistics of the $J/\psi$ vector meson invisible decays. We also recast the BABAR monophoton bounds for the specific dark axion portal scenario. In addition, we modify the dark axion portal setup by including in the model both the hadron- and lepton-specific ALP couplings. As a result, we obtain the bounds on the combination of fermion-specific couplings of ALP from the fixed-target experiments. We discuss the implication of the modified dark axion portal scenario for the electric dipole moments (EDMs) of SM fermions. In addition, we derive novel constraints on the combination of the $CP$-violating neutron-specific ALP couplings from the existing bounds on neutron EDMs by taking into account the neutron anomalous magnetic moment.

中文翻译：

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使用 NA64e、NA64μ、LDMX、M3 和 BaBar 探测费米子和暗物质的暗轴子入口的意义

普通标准模型 (SM) 光子与暗光子和类轴子粒子 (ALP) 之间的联系可以通过暗轴子入口耦合引入。鉴于暗轴子入口设置，在本文中，我们将暗光子称为 SM 和暗物质 (DM) 粒子之间的介质，这意味着它主要衰变为一对 DM 费米子。此外，我们详细讨论了暗轴子入口场景对轻子（电子和μ子）固定目标实验的影响。特别是，对于特定的固定目标设施，我们研究了暗光子产生的缺失能量特征，然后是其不可见的衰变成稳定的 DM 粒子。我们研究了用相关特征探测暗轴子入口顶点的可能性，并得出预期的敏感性$\mathrm{不适用}64e$,$\mathrm{不适用}64\mu$, LDMX 和${\mathrm{米}}^3$. 此外，我们估计了$\mathrm{不适用}64e$从预计的统计数据$Ĵ/\psi$矢量介子隐形衰变。我们还为特定的暗轴子入口场景重铸了BABAR单光子边界。此外，我们通过在模型中包含强子和轻子特定的 ALP 耦合来修改暗轴子入口设置。结果，我们从固定目标实验中获得了 ALP 的费米子特异性耦合组合的界限。我们讨论了修改后的暗轴子入口场景对 SM 费米子的电偶极矩 (EDM) 的影响。此外，我们得出了对组合的新约束$C磷$-通过考虑中子反常磁矩，从中子 EDM 的现有界限中违反中子特异性 ALP 耦合。