THE ALL-SILICON STRIP CMS TRACKER: MICROTECHNOLOGY AT THE MACROSCALE

The CMS silicon strip tracker is the largest device of its kind ever built, and is the first instance of a large collider detector relying exclusively on this all-silicon technology for tracking. With an instrumented surface of over 200 m2, and over nine million readout channels, it is two orders of magnitude larger than the silicon vertex detectors of the LEP experiments, and 30–40 times larger than the silicon inner detectors of the CDF and D0 experiments at the Tevatron. It makes use of microelectronics technology, but deploys it at the macroscale. The photograph below shows the completed CMS silicon tracker, ready for installation in the experiment, side by side with the silicon strip vertex detector of the OPAL experiment at LEP. Approximately a decade and more than two orders of magnitude in scale separate these two silicon strip detectors. [Formula: see text] In the following we motivate the choice of an all-silicon tracker for the CMS experiment, and discuss the reasons for the major design choices that define the system.

Quarkonium Production at LEP with the OPAL Detector

Evidence for the production of ϒ mesons in hadronic Z0 decays has recently been reported by the OPAL experiment at LEP. ϒ mesons are identified from their decays into e+e- and μ+μ- pairs. These decays provide a clear signature, since the e+e- and μ+ μ- background with invariant mass around 10 GeV/c2 is found to be small. In the first part of this report, a summary of the ϒ analysis is presented and possible production mechanisms are discussed. In the second part, studies on charmonium production are presented. Charmonium studies are based on an inclusive sample of J/ψ candidates, used to derive inclusive J/ψ and ψ′ rates, and the prompt J/ψ rate as well. Finally, since prompt J/ψ mesons are expected to be produced at LEP by the same production mechanisms as for the ϒ, a more general discussion on quarkonium production via fragmentation processes is presented.