January 23, 2026 Master Thesis Open Access

Schmitt, Frederik

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{
  "abstract": "<p>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.<br>\nDue 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.<br>\nWhile the ALP can decay into multiple signatures, this work focuses on a model where it decays predominantly into two resolved photons.<br>\nExperimentally, this allows the search for a peak in the invariant diphoton mass $M_{\\gamma\\gamma}$ from an ALP decay signal over the SM background.<br>\nBelle~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.<br>\nIn 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.</p>", 
  "author": [
    {
      "family": "Schmitt, Frederik"
    }
  ], 
  "id": "22389", 
  "issued": {
    "date-parts": [
      [
        2026, 
        1, 
        23
      ]
    ]
  }, 
  "language": "eng", 
  "title": "Search for Axion-Like Particles in $e^+ e^- \\to e^+ e^- \\gamma \\gamma$ Events at Belle~II", 
  "type": "thesis"
}