Josh McFayden: A new measurement of lepton-flavour universality with the ATLAS experiment
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Europe/London
Description
A remarkable feature of the Standard Model (SM) is that each lepton flavour (electron, muon, tau) is equally likely to interact with a W boson. This is known as Lepton Flavour Universality.
In a recent ATLAS measurement, a novel technique using events with top-quark pairs has been exploited to test the ratio of the probabilities for tau leptons and muons to be produced in W boson decays, R(τ/μ).
In the SM, R(τ/μ) is expected to be unity, but a longstanding tension with this prediction has existed since the LEP era, where, from a combination of experiments, R(τ/μ) was measured to be 2.7σ higher than the SM expectation.
If the LEP result were confirmed to O(1%) precision it would correspond to an unambiguous discovery of beyond the SM physics. This latest ATLAS measurement obtains this level a precision - please join the seminar to discover whether or not it agrees with LEP!