NEPAL

Understanding the performances of the experiment is a key ingredient to obtain reliable physics results. We participate in the measurement of track reconstruction efficiencies using a tag-and-probe technique in tau events as illustrated on Fig. 1. The idea is to use events where one tau decays in a leptonic channel (\(\tau \to e\nu\nu\)) and the other in a three-prong hadronic channel (\(\tau \to 3\pi\nu\)), only reconstructing 3 tracks (called tag tracks). The fourth track is then the probe track and the tracking efficiency is given by the number of events where the four tracks are found divided by the number of events where 3 or 4 tracks are found.

We also adapted this idea to measure the rate of fake tracks, corresponding to tracks reconstructed by mistakenly associated hits from different tracks. The rate is in that case given by the number of events where 5 tracks are found divided by the number of events where 4 or 5 tracks are found.