- More Information about the Silicon Vertex Tracker. Information about the work on the SVT 'AToM' readout chip can be found here.
Excellent particle identification for hadrons and leptons over a large range of solid angle and momentum is an essential requirement for meeting the physics objectives of BABAR. In particular, measurements of CP violation require particle identification (PID), both to reconstruct exclusive final states and to tag the quark content of the other B in the event. Information from the drift chamber, calorimeter, and the instrumented flux return can be used to identify most of the leptons and many of the hadrons. However, these systems are not sufficient to distinguish charged pions from kaons with momenta greater than about 0.7 GeV/c, or protons above 1.3 GeV/c, as is required to obtain efficient tagging and event reconstruction. To meet these requirements, a new type of PID system has been chosen for BABAR. This barrel region detector is called DIRC for "Detection of Internally Reflected Cherenkov light". It is a ring imaging Cherenkov detector based on total internal reflection and uses long, rectangular bars made from synthetic fused silica ("quartz") as both radiator and light guide. It is thin (both in radius and radiation length), fast, robust, and tolerant of background.