An embedding technique to determine genuine $\tau \tau$ backgrounds from CMS data

The $\tau$-embedding technique is a data-driven method, where $\mu \mu$ events are selected from data, and the muons are replaced by simulated $\tau$ decays. In this way a hybrid event is created, which only relies on the simulation for the well understood $\tau$ decay. The remainder of the event, by construction, provides a better description of the data than full simulation, especially for challenging simulation tasks, such as the underlying event or multijet production. The $\tau$-embedding technique is actively used by CMS to estimate standard model backgrounds that contain genuine $\tau$ decays. The current status, recent developments and improvements of the technique are presented.