The CDF Cherenkov luminosity monitor

We have built a novel device for precision measurements of luminosity in the CDF experiment at the high pp-bar collision rates expected during Run II. The detector consists of long, conical, gaseous Cherenkov counters that point to the collision region and monitor the average number of inelastic pp-bar interactions by measuring the number of particles, and their arrival time, in each bunch crossing. For these primary particles, using isobutane at atmospheric pressure as a radiator, a large amount of Cherenkov light (∼100 photoelectrons) will be collected, with good amplitude and time resolutions, onto small and efficient PMTs. Suitable amplitude thresholds will be applied to discriminate from non-primary particles and other backgrounds which yield little light in the counters. This detector is expected to reliably perform bunch-by-bunch luminosity measurements at peak instantaneous luminosities of 2x1032 cm-2 s-1 with six interactions per bunch crossing, on average, and respond to a 132 ns bunch spacing