April 28, 2022 Master Thesis Open Access

Heidelbach, Alexander

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{
  "abstract": "<p>In a set of simple extensions of the Standard Model, Axion Like Particles (ALPs) arise as pseudo Nambu-Goldstone bosons of theories with a spontaneously broken Peccei-Quinn symmetry that is anomalous under the Standard Model gauge symmetry. Due to constraints in flavour-changing current &nbsp;(FCNC) processes, involving the coupling of ALPs directly to Standard Model fermions and gluons, direct couplings of ALPs to the electroweak gauge bosons are particularly interesting. As a result of a coupling to $W$ bosons, ALPs can emerge in FCNC $b\\to s$ transitions. Depending on the ALP mass and the coupling strength to photons a possible experimental signature is $B^{\\pm}\\to K^{\\pm}a, a\\to\\gamma\\gamma$ with long lived ALP decays. This thesis performs a sensitivity study in the search for the $B^{\\pm}\\to K^{\\pm}a, a\\to\\gamma\\gamma$ signature based on Belle II simulation samples corresponding to an integrated luminosity of 100\\,fb$^{-1}$. The sensitivity study includes an optimised candidate selection and signal yield scans of the invariant di-photon mass distribution in the range of $0.175\\,\\text{GeV/c}^2$ to $4.600\\,\\text{GeV/c}^2$ for eight different ALP lifetimes between $0\\,\\text{cm}$ and $50\\,\\text{cm}$. Resulting expected limits are comparable to a similar search for $B^{\\pm}\\to K^{\\pm}a, a\\to\\gamma\\gamma$ on data collected by the BABAR experiment.&nbsp;</p>", 
  "author": [
    {
      "family": "Heidelbach, Alexander"
    }
  ], 
  "id": "22123", 
  "issued": {
    "date-parts": [
      [
        2022, 
        4, 
        28
      ]
    ]
  }, 
  "language": "eng", 
  "title": "Sensitivity Study in the Search for $B^{\\pm}\\to K^{\\pm}a$ (displaced $a\\to\\gamma\\gamma$) Decays at Belle II", 
  "type": "thesis"
}