000003215 001__ 3215
000003215 005__ 20220915090425.0
000003215 037__ $$aBELLE2-MTHESIS-2022-013
000003215 041__ $$aeng
000003215 100__ $$aAlexander Heidelbach
000003215 245__ $$aSensitivity Study in the Search for $B^{\pm}\to K^{\pm}a$ (displaced $a\to\gamma\gamma$) Decays at Belle II
000003215 260__ $$aKarlsruhe$$bInstitute of Experimental Particle Physics$$c2022
000003215 300__ $$a105
000003215 500__ $$aPresented on 28 04 2022
000003215 502__ $$aMSc$$bKarlsruhe, Karlsruhe Institute of Technology$$c2022
000003215 520__ $$aIn a set of simple extensions of the Standard Model, Axion Like Particles (ALPs) arise as pseudo Nambu-Goldstone bosons of theories with a spontaneously broken Peccei-Quinn symmetry that is anomalous under the Standard Model gauge symmetry. Due to constraints in flavour-changing current  (FCNC) processes, involving the coupling of ALPs directly to Standard Model fermions and gluons, direct couplings of ALPs to the electroweak gauge bosons are particularly interesting. As a result of a coupling to $W$ bosons, ALPs can emerge in FCNC $b\to s$ transitions. Depending on the ALP mass and the coupling strength to photons a possible experimental signature is $B^{\pm}\to K^{\pm}a, a\to\gamma\gamma$ with long lived ALP decays. This thesis performs a sensitivity study in the search for the $B^{\pm}\to K^{\pm}a, a\to\gamma\gamma$ signature based on Belle II simulation samples corresponding to an integrated luminosity of 100\,fb$^{-1}$. The sensitivity study includes an optimised candidate selection and signal yield scans of the invariant di-photon mass distribution in the range of $0.175\,\text{GeV/c}^2$ to $4.600\,\text{GeV/c}^2$ for eight different ALP lifetimes between $0\,\text{cm}$ and $50\,\text{cm}$. Resulting expected limits are comparable to a similar search for $B^{\pm}\to K^{\pm}a, a\to\gamma\gamma$ on data collected by the BABAR experiment.
000003215 700__ $$aProf. Dr. Torben Ferber$$edir.
000003215 700__ $$aProf. Dr. Günter Quast$$edir.
000003215 8560_ $$falexander.heidelbach@kit.edu
000003215 8564_ $$uhttps://docs.belle2.org/record/3215/files/BELLE2-MTHESIS-2022-013.pdf
000003215 980__ $$aTHESIS