Chamber Tests

Background Particle Dead Time

One of the crucial performance parameters is the average deadtime for background signals. Since we expect rates of up to 1MHz per channel and since the LHCb muon system uses five fold coincidence for triggering (this is not very clever), the average deadtime i.e. the average discriminator output pulsewidth for a backgorund signal at the working point, should not exceed 50-60ns. The typical working point of a 2mm wire pitch quad gap chamber (working at >95% efficiency per double gap) is 2500V.

One board was connected to the cathode pads of the CERN M2R2 Prototype which contains single cathode pad (100pF) and double cathode pad (200pF) readout. In order to investigate the expected average dead time an Am241 source was used, which represents some kind of worst case background signals.

The threshold was set to a value where the noise count rate is <20Hz. This was 11fC for the 200pF pads and 8.57fC for the 100pF pads. The following plot shows the average deadtime of the positive amplifier.

You can also have a look at the individual dead time spectra for 100pF and 200pF cathode pad capacitance.

===============================================================

The following plot shows the average dead time for the negative amplifier. This 'kink' is due to some selection effect -- things will be cleaned up later .... it's not yet the final plot.

You can also have a look at the individual dead time spectra for 50pF and 270pF cathode pad capacitance.