000002966 001__ 2966
000002966 005__ 20220407002745.0
000002966 037__ $$aBELLE2-PTHESIS-2022-004
000002966 041__ $$aeng
000002966 100__ $$aMichael De Nuccio
000002966 245__ $$aSearch for Axion-Like Particles produced in e+e− collisions and photon energy resolution studies at Belle II
000002966 260__ $$aHamburg$$bDESY$$c2021
000002966 300__ $$a179
000002966 500__ $$aPresented on 19 10 2021
000002966 502__ $$aPhD$$bHamburg, University of Hamburg$$c2021
000002966 520__ $$aDespite the great successes achieved by the Standard Model (SM) in explaining and predicting the behavior and existence of particles, multiple phenomena are yet to be given a satisfying explanation. Amongst these is Dark Matter (DM), a kind of matter that would permeate the whole Universe and that so far has been observed only via its gravitational interactions. One possible extension of the SM, which may contribute to solve the mystery of DM and/or explain some astrophysical anomalies, are Axion-Like Particles (ALPs). The model taken into consideration in this thesis is of an ALP interacting with SM photons with a coupling strength gaγγ and having mass ma. This thesis describes a search for the direct production of such ALP via the process e+e− → γa(a → γγ), in the mass range 0.2 < ma < 9.7 GeV/c2. This search is performed using 0.445 fb−1 of data collected in 2018 by the Belle II detector. No evidence for ALPs is found, and a 95%-confidence-level upper limit is set on the coupling constant gaγγ at the level of 10−3 GeV−1. These limits are the strongest to date for 0.2 < ma < 1 GeV/c2. Given that the final state of the e+e− → γa(a → γγ) process is fully neutral, being made up by three photons, a proper kinematic fit with neutral particles may be a powerful tool to improve signal resolution. To achieve such a kinematic fit, a precise knowledge of the photon covariance matrix is needed. Such matrix is obtained from the results of photon resolution studies, whose status and results are presented in this thesis.
000002966 700__ $$aTorben Ferber$$edir.
000002966 8560_ $$fdenuccio@mail.desy.de
000002966 8564_ $$uhttps://docs.belle2.org/record/2966/files/BELLE2-PTHESIS-2022-004.pdf
000002966 980__ $$aTHESIS