CCD-based vertex detectors

Over the past 20 years, CCD-based vertex detectors have been used to construct some of the most precise 'tracking microscopes' in particle physics. They were initially used by the ACCMOR collaboration for fixed target experiments in CERN, where they enabled the lifetimes of some of the shortest-lived charm particles to be measured precisely. The migration to collider experiments was accomplished in the SLD experiment, where the original 120 Mpixel detector was later upgraded to one with 307 Mpixels. This detector was used in a range of physics studies which exceeded the capability of the LEP detectors, including the most precise limit to date on the Bs mixing parameter. This success, and the high background hit densities that will inevitably be encountered at the future TeV-scale linear collider, have established the need for a silicon pixel-based vertex detector at this machine. The technical options have now been broadened to include a wide range of possible silicon imaging technologies as well as CCDs (monolithic and hybrid silicon pixel devices, DEPFET-based and SOI-based devices). However, there is a good chance that CCD-based detectors, or an architecture derived from CCDs, will still prove to be superior for this application. Groups in Europe, Asia and the USA are working semi-independently on various aspects of this development, with the goal of evaluating prototype detector elements within the next 5 years. If the CCD option is selected for one of the LC detector systems, it is hoped that these groups will join forces to construct the new detector. If the design goals can be achieved, this vertex detector will provide a tool not only for b and c tagging, but also for the measurement of 'vertex charge', allowing discrimination between b and b¯ jets, and between c and c¯ jets. Given the complex topological nature of much of the potential new physics in the TeV regime (multiple hadronic jets), such a tool could provide the key to unravel novel processes which may be unintelligible at the LHC.