Beam scintillators $\mu$SC, $\mu$SCA

Two beam scintillators, $\mu$SC, a 0.2 mm thin muon trigger counter, and $\mu$SCA, a 2 mm thick veto counter with a 36 mm entrance hole, define the muons in front of the $\mu$PC1 chambers and the entrance window of the pressure tank (open diameter 40 mm). Scintillator $\mu$SC provides the fast muon timing signal for the lifetime measurement and discriminates against the much smaller signals from beam electrons which constitute for tuning conditions of the $\mu$E4 beam about 10% of the muon flux. The beam windows and the thickness of $\mu$SC will be chosen as thin as feasible to keep the useful muon momentum below 35 MeV/c. In our test runs, we have shown that with such a momentum more than 90% of the muons range out in the sensitive TPC volume (cf. Fig. 12 in section 4.1).