First Search for Dark-Trident Processes Using the MicroBooNE Detector

We present a first search for dark-trident scattering in a neutrino beam using a dataset corresponding to <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mn>7.2</a:mn><a:mo>×</a:mo><a:msup><a:mrow><a:mn>10</a:mn></a:mrow><a:mrow><a:mn>20</a:mn></a:mrow></a:msup></a:mrow></a:math> protons on target taken with the MicroBooNE detector at Fermilab. Proton interactions in the neutrino target at the main injector produce <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:msup><c:mi>π</c:mi><c:mn>0</c:mn></c:msup></c:math> and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>η</e:mi></e:math> mesons, which could decay into dark-matter (DM) particles mediated via a dark photon <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:msup><g:mi>A</g:mi><g:mo>′</g:mo></g:msup></g:math>. A convolutional neural network is trained to identify interactions of the DM particles in the liquid-argon time projection chamber (LArTPC) exploiting its imagelike reconstruction capability. In the absence of a DM signal, we provide limits at the 90% confidence level on the squared kinematic mixing parameter <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msup><i:mi>ϵ</i:mi><i:mn>2</i:mn></i:msup></i:math> as a function of the dark-photon mass in the range <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mrow><k:mn>10</k:mn><k:mo>≤</k:mo><k:msub><k:mrow><k:mi>M</k:mi></k:mrow><k:mrow><k:msup><k:mrow><k:mi>A</k:mi></k:mrow><k:mrow><k:mo>′</k:mo></k:mrow></k:msup></k:mrow></k:msub><k:mo>≤</k:mo><k:mn>400</k:mn><k:mtext> </k:mtext><k:mtext> </k:mtext><k:mi>MeV</k:mi></k:mrow></k:math>. The limits cover previously unconstrained parameter space for the production of fermion or scalar DM particles <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mi>χ</m:mi></m:math> for two benchmark models with mass ratios <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mrow><o:msub><o:mrow><o:mi>M</o:mi></o:mrow><o:mrow><o:mi>χ</o:mi></o:mrow></o:msub><o:mo>/</o:mo><o:msub><o:mrow><o:mi>M</o:mi></o:mrow><o:mrow><o:msup><o:mrow><o:mi>A</o:mi></o:mrow><o:mrow><o:mo>′</o:mo></o:mrow></o:msup></o:mrow></o:msub><o:mo>=</o:mo><o:mn>0.6</o:mn></o:mrow></o:math> and 2 and for dark fine-structure constants <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mn>0.1</q:mn><q:mo>≤</q:mo><q:msub><q:mi>α</q:mi><q:mi>D</q:mi></q:msub><q:mo>≤</q:mo><q:mn>1</q:mn></q:math>. Published by the American Physical Society 2024