Search for inelastic boosted dark matter with the ICARUS detector at the Gran Sasso Underground National Laboratory

We present the result of a search for inelastic boosted dark matter using the data corresponding to an exposure of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mn>0.13</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mi>kton</a:mi><a:mo>·</a:mo><a:mi>year</a:mi></a:mrow></a:math>, collected by the ICARUS T-600 detector during its 2012–2013 operational period at the INFN Gran Sasso Underground National Laboratory. The benchmark boosted dark matter model features a multiparticle dark sector with a <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:msup><c:mrow><c:mi mathvariant="normal">U</c:mi><c:mo stretchy="false">(</c:mo><c:mn>1</c:mn><c:mo stretchy="false">)</c:mo></c:mrow><c:mrow><c:mo>′</c:mo></c:mrow></c:msup></c:mrow></c:math> gauge boson, the dark photon. The kinetic mixing of the dark photon with the Standard Model photon allows for a portal between the dark sector and the visible sector. The inelastic boosted dark matter interaction occurs when a dark matter particle inelastically scatters with an electron in the ICARUS detector, producing an outgoing, heavier dark sector state which subsequently decays back down to the dark matter particle, emitting a dark photon. The dark photon subsequently couples to a Standard Model photon through kinetic mixing. The Standard Model photon then converts to an electron-positron pair in the detector. This interaction process provides a distinct experimental signature that consists of a recoil electron from the primary interaction and an associated electron-positron pair from the secondary vertex. After analyzing 4,134 triggered events, the search results in zero observed events. Exclusion limits are set in the dark photon mass and coupling (<h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:msub><h:mi>m</h:mi><h:mi>X</h:mi></h:msub><h:mo>,</h:mo><h:mi>ε</h:mi></h:math>) parameter space for several selected optimal boosted dark matter mass sets and cover previously unexplored parameter space.