January 23, 2026 Master Thesis Open Access

Schmitt, Frederik

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    <subfield code="a">&lt;p&gt;Axion-like particles (ALPs), as analyzed in this thesis, present compelling beyond standard model scenarios with a yet mostly unexplored range in phase space, particularly the GeV ALP-mass range.&lt;br&gt;
Due to the high collision rate and the high precision detector, the Belle II experiment is an ideal environment to search for GeV ALPs at a particle collider experiment.&lt;br&gt;
While the ALP can decay into multiple signatures, this work focuses on a model where it decays predominantly into two resolved photons.&lt;br&gt;
Experimentally, this allows the search for a peak in the invariant diphoton mass $M_{\gamma\gamma}$ from an ALP decay signal over the SM background.&lt;br&gt;
Belle~II already published a search for the same ALP model; however, this is the first effort to perform an experimental sensitivity study for the $t$-channel $e^+ e^- \to e^+ e^- a, a \to \gamma \gamma $ process.&lt;br&gt;
In this work, I present an analysis strategy that demonstrates the feasibility of analyzing the fully reconstructed Photon fusion process at Belle II and yields comparable sensitivity to that obtained from analyzing ALP-Strahlung ($\e^+ e^- \to \gamma a, a \ to \gamma \gamma$ events.&lt;/p&gt;</subfield>
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    <subfield code="a">Search for Axion-Like Particles in $e^+ e^- \to e^+ e^- \gamma \gamma$ Events at Belle~II</subfield>
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