{#sec:background}
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Staus as heavy metastable charged particles usually leave the detector. This leads to a signal in the tracker and muon chambers. Muons are the only background. Therefore, we first study this background in order to devise suitable cuts, which we can then take into account in the calculation of the signal in the next subsection.

The di-muon rate for the moderate and high ${p_\text{T}}$-range is much smaller than the single muon rate and the possible sources are considerably fewer in the case of di-muons. For a $p_{\rm T}$-cut smaller and around $15{\ensuremath{\,\textnormal{GeV}}}$, $b$- and $c$-decays are the dominant sources of di-mouns. Above $15{\ensuremath{\,\textnormal{GeV}}}$ the DY production begins to dominate [@Albajar:687291]. In addition to a high $p_{\rm T}$-cut, the $b$- and $c$-contributions can be further reduced by isolation cuts. This feature relies on the fact that $b$ and $c$ quarks are always produced close to jets while muons from heavy mother particles (like $Z$ or $t$) tend to be well-separated from the other decay products—they are isolated [@Amapane:687467].

As preselection cuts on the data, we require two opposite-sign muon-like particles each satisfying

-   $p_{\rm T}$-cut: $p_{\rm T}>50{\ensuremath{\,\textnormal{GeV}}}$

-   Barrel cut on the pseudorapidity: $|\eta|<2.5$

-   Isolation cut: $\Delta\mathcal{R}_{\mu, {\rm 