Measuring velocity with the {open_quotes}optic boom{close_quotes}: The contribution of the Ring Imaging Cerenkov, Detector to the search for charmless beauty decay at fermilab

A charged particle traveling in a medium with a speed exceeding the speed of light in that medium produces Cerenkov radiation (light). This effect is, in a very loose sense, the optical analogue of a sonic boom. The light is emitted at a specific angle, {theta}, determined by the velocity, {beta}, of the particle according to the equation {beta}=1/(ncos{theta}) where n is the index of refraction of the medium. In the Ring Imaging Cerenkov Detector (RICH), light emitted at an angle {theta} is focused as a ring of radius r=f tan {theta} (f=local length) onto a detector. The velocity of the particle is calculated from the radius of the circular ring of light striking the detector, allowing the mass of the particle to be determined. E789 makes use of the well-known E605 RICH detector to study D- and B-meson decays. The physics explored by E789 and the operation of the RICH will be described, and images produced by analysis of data from the RICH will be presented.