Muon Bremsstrahlung Showers leaking into the CTD

Events where the muon bremsstrahlung occurs just before the muon traverses the CTD or inside the CTD volume usually cause many tracks to be seen in the CTD. Moreover, because of the solenoidal field in ZEUS, particles will be bent away from their initial trajectory and cause a wide area of cells to be hit near the region where the muon leaves the inner volume. Figure 6.8 shows such an event. MUFFIN tries to identify the cells which have been hit by such particles by using the trajectory of the muon and the direction of the magnetic field to calculate the plane in which the particles' trajectories are located. MUFFIN allows the vector pointing from the cell to the muon trajectory to deviate from the normal to the magnetic field.

Figure 6.8: Example of a cosmic muon traversing the ZEUS detector. The view shows the event seen from the FCAL, the beam pipe being in the center. This muon has had a bremsstrahlung near the beam pipe and charged particles have been bent by the magnetic field and hit the BCAL- EMC. The muon trajectory is known to high precision because two opposing muon chamber tracks were found.