Constraints on dark axion portal: Missing energy and fermion EDMs

We study a model in which a new interactions between the Standard Model (SM) photon and both the dark photon ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>γ</a:mi> <a:mi>D</a:mi> </a:msub> </a:math> ) and an axionlike particles (ALP or <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi>a</c:mi> </c:math> ) are described by the dark axion portal operator. The implications of this dark axion portal scenario for electron fixed-target experiments are presented. In particular, we investigate the missing energy signatures associated with production of dark photons and their subsequent invisible decays into stable dark sector fermions, <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:msub> <e:mi>γ</e:mi> <e:mi>D</e:mi> </e:msub> <e:mo stretchy="false">→</e:mo> <e:mi>χ</e:mi> <e:mover accent="true"> <e:mi>χ</e:mi> <e:mo stretchy="false">¯</e:mo> </e:mover> </e:math> . We discuss the discovery potential for such a scenario and derive projected sensitivity curves for the <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:mrow> <j:mi>NA</j:mi> <j:mrow> <j:mn>64</j:mn> <j:mi>e</j:mi> </j:mrow> </j:mrow> </j:math> and LDMX experiments. Furthermore, novel constraints of the <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"> <l:mrow> <l:mi>NA</l:mi> <l:mrow> <l:mn>64</l:mn> <l:mi>e</l:mi> </l:mrow> </l:mrow> </l:math> for <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"> <n:mn>9.37</n:mn> <n:mo>×</n:mo> <n:msup> <n:mn>10</n:mn> <n:mn>11</n:mn> </n:msup> </n:math> electrons on target are derived by considering two production mechanisms for invisible states: (i) the bremsstrahlung-like emission of an <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"> <p:mi>a</p:mi> <p:msub> <p:mi>γ</p:mi> <p:mi>D</p:mi> </p:msub> </p:math> pair, <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"> <r:mi>e</r:mi> <r:mi>N</r:mi> <r:mo stretchy="false">→</r:mo> <r:mi>e</r:mi> <r:mi>N</r:mi> <r:msup> <r:mi>γ</r:mi> <r:mo>*</r:mo> </r:msup> <r:mo stretchy="false">(</r:mo> <r:mo stretchy="false">→</r:mo> <r:mi>a</r:mi> <r:msub> <r:mi>γ</r:mi> <r:mi>D</r:mi> </r:msub> <r:mo stretchy="false">)</r:mo> </r:math> , and (ii) the exclusive vector meson photoproduction, <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"> <x:msup> <x:mi>γ</x:mi> <x:mo>*</x:mo> </x:msup> <x:mi>N</x:mi> <x:mo stretchy="false">→</x:mo> <x:mi>N</x:mi> <x:mi>V</x:mi> </x:math> , followed by the invisible decays of vector mesons, <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"> <ab:mi>V</ab:mi> <ab:mo stretchy="false">→</ab:mo> <ab:mi>a</ab:mi> <ab:msub> <ab:mi>γ</ab:mi> <ab:mi>D</ab:mi> </ab:msub> </ab:math> . Additionally, the constraints on the parameter space of <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"> <db:mi>C</db:mi> <db:mi>P</db:mi> </db:math> -violating, fermion-specific ALP and dark photon couplings are established. These constraints are derived from current experimental bounds on the electric dipole moments (EDMs) of SM fermions, incorporating loop-induced contributions to the EDMs of the electron, muon, and neutron.