Fig. 3: Transverse impact parameter distributions of probe muons in the signal region.
From: Test of the universality of τ and μ lepton couplings in W-boson decays with the ATLAS detector
The signal region used to extract R(τ/μ) is enriched in di-lepton \(t\overline{t}\) events. The \(| {d}_{0}^{\mu }|\) distributions for each signal region (left, e–μ channel; right, μ–μ channel) and probe muon \({p}_{{\rm{T}}}^{\mu }\) bin (top, \(5<{p}_{{\rm{T}}}^{\mu }<10\,{\rm{GeV}}\); middle, \(10<{p}_{{\rm{T}}}^{\mu }<20\,{\rm{GeV}}\); bottom, \(20<{p}_{{\rm{T}}}^{\mu }<250\,{\rm{GeV}}\)) used in the analysis are shown. The data are represented by black markers and the different components contributing to this region, taken from simulation, are shown by stacked histograms. The different contributions are the two primary processes of interest used to extract R(τ/μ), μprompt from top quark decays (Prompt μ (top)) and μτ(→μ) from top decays (τ → μ(top)). The main backgrounds are also shown: events with a μhad (μ (hadron decay)), events with a Z boson decaying to a di-muon pair (Z → μμ), events with a Z boson decaying to a di-τ pair (Z → ττ) and the grouping of all remaining SM processes (Other SM processes). Distributions are shown after the fit has been performed. The y-axis label includes the value that defines the scaling of the variable bin width histogram. The bottom panels show the ratio of the data to the predicted expectation after the fit. The uncertainties on the data are the Poisson errors due to the limited size of the data sample. Blue bands indicate the ±1σ systematic uncertainties on the prediction with the constraints from the analysis fit applied. The contribution from ‘Other SM processes’ is dominated by di-boson and \(t\overline{t}+V\) production. The chi-squared statistic values range from 3.5 to 10.2 for eight degrees of freedom for the distributions.
