SMuK 2023 – wissenschaftliches Programm
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T: Fachverband Teilchenphysik
T 133: Top, EW II
T 133.2: Vortrag
Donnerstag, 23. März 2023, 17:45–18:00, HSZ/0103
A direct measurement of the invisible width of the Z-boson with the ATLAS detector — •Martin Klassen — Kirchhoff-Institut für Physik, Heidelberg
The invisible width of the Z-boson, ΓZ(inv), is a fundamental parameter of the Standard Model. It is related to the number of light neutrinos that couple to the Z-boson, and its precise measurement allows for tests of the Standard Model. ΓZ(inv) has been indirectly measured at LEP with a precision of 0.3% and was in addition also directly determined using events with a photon and missing transverse energy to a precision of 3.2%.
At the ATLAS experiment, ΓZ(inv) can be obtained by measuring the ratio of Z → νν+jets to Z → ll+jets events (Rmiss) as function of the Z boson’s transverse momentum pT. This approach is sufficient because the production cross section and the branching ratios can be decoupled leading to the relation Rmiss= ΓZ (inv)/ ΓZ(ll) and the leptonic widths of the Z are already precisely measured. The ratio measurement benefits form a large degree of cancelation of many of the experimental and theoretical uncertainties. For this to work the phase spaces of selected Z → νν and Z → ll events need to be as similar as possible, and residual differences are corrected for using simulations.
In this talk the analysis strategy will be presented and it will be shown that the experiments at the Large Hadron Collider can obtain competitive results 30 years after the first direct measurement of ΓZ(inv) at LEP.