Terry Chan, promovendus aan het Nikhef, verdedigt zijn proefschrift maandag 22 maart 2021 online aan de Radboud Universiteit te Nijmegen.
“Beyond Vanilla – a search for lepton-flavour-violating Z → ℓτ decays with the ATLAS detector”
Leptons with essentially the same properties apart from their mass are grouped into three families or flavours. The number of leptons of each flavour is conserved in interactions, but this is not imposed by fundamental principles. Since the formulation of the Standard Model of particle physics, the observation of flavour oscillations among neutrinos has shown that lepton flavour is not conserved in neutrino weak interactions. To date, there is no experimental evidence that this also occurs in interactions between charged leptons – such an observation would be a sign for undiscovered particles or a yet unknown type of interaction.
In this thesis, a constraint on lepton-flavour-violating effects is set by searching for Z-boson decays into a τ-lepton and another lepton of different flavour with opposite electric charge. The branching fractions for these decays are measured to be less than 8.1 × 10−6 (eτ) and 9.5 × 10−6 (µτ) at 95% confidence level, using 139 fb−1 of proton–proton collision data at centre-of-mass energy √s = 13 TeV and 20.3 fb−1 at √s = 8 TeV. These results supersede the otherwise most stringent limits set by the Large Electron–Positron Collider experiments more than two decades ago.
“Beyond Vanilla – a search for lepton-flavour-violating Z → ℓτ decays with the ATLAS detector” (pdf)
De promotie zal online te volgen zijn op het youtubekanaal van de Radboud Universiteit:
http://www.ru.nl/aula/livestream
Promotoren: prof. dr. Prof. dr. N. de Groot en Prof. dr. S. Xella (Københavns Universitet, Denemarken)
contact: Terry Chan