000004386 001__ 4386
000004386 005__ 20240617084052.0
000004386 037__ $$aBELLE2-PTHESIS-2024-014
000004386 041__ $$aeng
000004386 100__ $$aPaul Feichtinger
000004386 245__ $$aTest of light-lepton universality in tau decays with data from the Belle II experiment
000004386 260__ $$aVienna$$bAtominstitut TU Wien / HEPHY$$c2024
000004386 300__ $$a239
000004386 500__ $$aPresented on 14 06 2024
000004386 502__ $$aPhD$$bVienna, Technische Universität Wien$$c2024
000004386 520__ $$aThis thesis investigates light-lepton universality with electron-positron collision data from the Belle~II experiment at the SuperKEKB accelerator in Tsukuba, Japan. The data were recorded at a centre-of-mass energy of 10.58 GeV and are equivalent to an integrated luminosity of 362 fb$^{-1}$. Lepton universality is a property of the Standard Model of particle physics that implies that all leptons have equal couplings to the electroweak gauge bosons. This thesis aims to test the universality of electrons and muons in charged current interactions by measuring the gauge coupling ratio $g_{\mu}/g_{e}$. This ratio can be obtained from the branching fractions of the decays $\tau^{\pm} \to \mu^{\pm} \nu \bar{\nu}$ and $\tau^{\pm} \to e^{\pm} \nu \bar{\nu}$. The approach for this work will be to measure these branching fractions using $\tau$ leptons produced in the process $e^+e^- \to \tau^+\tau^-$, with both decaying to only one charged particle. Any deviation of $g_{\mu}/g_{e}$ from unity would indicate that lepton universality is violated, for example, through interactions with new gauge bosons. The result of this measurement is $g_{\mu}/g_{e} = 0.9974 \pm 0.0019$, which is consistent with the Standard Model expectation. Its precision is limited by systematic uncertainties related to lepton identification. At the moment, this measurement is the most precise test of lepton universality using tau decays obtained from a single experiment.
000004386 700__ $$aGianluca Inguglia$$edir.
000004386 700__ $$aChristoph Schwanda$$edir.
000004386 8560_ $$fpaul.feichtinger@oeaw.ac.at
000004386 8564_ $$uhttps://docs.belle2.org/record/4386/files/BELLE2-PTHESIS-2024-014.pdf
000004386 980__ $$aTHESIS