Relative Alignment System

The inner tracking system of CDF for Run-2 consists of silicon detectors to identify B mesons from their finite path length (~0.5 mm) before they decay. Identifying the bottom mesons is essential to following up CDF's discovery of the top quark and to CDF's upcoming discovery of CP violation with b quarks. These tracking detectors need to achieve a resolution on the order of 10-20 microns.

UCLA is building a relative alignment monitor called RASNIK ("Relative Alignment System of NIKhef") for the CDF tracking detectors. This is an inexpensive system that was invented by NIKHEF in Amsterdam. It is an optical device, but does not use lasers, only an infrared light-source, a mask, convex lens and CCD camera, as shown below,

Changes in alignment are seen as a movement of the image of the mask on the CCD camera. The fine detail on the mask allows movement of less than 1 micron to be detected. The system was originally used in the CHORUS neutrino oscillation experiment, and is described in a NIM article.

The system being built here will be used to monitor the relative alignments of the CDF tracking detectors: SVX, ISL and COT with sub-micron precision on a time-scale of seconds. We will also use it to monitor the exact positions of the end-plug calorimeters. We are considering other uses in the experiment and accelerator.

The projector, which contains the lens, coded mask, and LED, next to a penny and bus token.

Go find out about the Radiation Tests.

Download an actual coded mask. (500kB). You probably need to print it out to see the detail.

Go back to UCLA-CDF homepage.