Cherenkov ring segments obtained with PC84, PC85, PC86 and PC87 with an aerogel radiator setup. The display shows raw data from the 4 HPD silicon sensors. The geometrical position of the 4 sensor displays does not exactly correspond to their real position of the HPDs in the experimental set-up.  

All 4 HPDs were powered in parallel by the same set of 4 HV supplies (photocathode, bleeder, electrodes 2 and 3). The photocathodes were kept at a voltage of -15 kV.

No correction for the slightly different electron optical parameters (demagnification) of the tube is applied. As was discovered after the end of the beam period, the electronics readout card of the lower HPD was badly adjusted.

The random noise per pixel and trigger is below 1 permille.