Principle of operation of the cms silicon strip detector
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Principle of operation of a silicon strip detector is illustrated in . Typical + + + + configurations include p -n, n -p and n -n sensors. In a p -n configuration the generated holes + drift along the electrical field, created by the bias voltage, to the p doped strips while the + electrons drift to the n backplane. For LHC applications where radiation-damage is especially + + critical n -p or n+-n sensors that can be operated under-depleted are used. Furthermore in n - + p or n -n sensors electrons are collected which are less sensitive to trapping generated by radiation effected due to their higher mobility. The area of the detectors use in HEP are limited to the standard wafer sizes used in high-resistivity processing by industry, which has increased the wafer size from 4” to 6”. Investigation of production on larger wafers is ongoing. The use of silicon strip detectors in HEP particle started in fixed target experiments at CERN and FNAL to study particles containing the charm quark. The theoretical expectations in the 1970s for the lifetime ( τ ) of the lowest mass charm states were of the order of 0.1 ps (c τ 30 μ m) with a production cross section of a few microbarns. Therefore charm events should exhibit a primary vertex and at least a secondary vertex with a separation between primary and secondary vertices of the order of βγ c τ , βγ being the relativistic factor of the charm state and τ its lifetime. The detectors necessary to study charm were required to have spatial resolution 6 better than 10 μm, good particle separation, rate capability of about 10 Hz and low multiple scattering and photon conversion. As can be seen from Table 1, which summarizes the state of the art technologies available in 1979, there was no technology that could yield the good position resolution and low dead time necessary to study charm. The introduction of silicon detectors, which achieve excellent spatial resolution and can be operated at much higher interaction rates, was critical for studying not only charm but all heavy quarks. Silicon strip sensors processed with planar technology were adopted for the NA11 experiment at the SPS at CERN and the E706 experiment at FNAL to identify and measure charm mesons properties. NA11collectect π − Be data at 120, 175 and 200 GeV at the SPS. E706 was designed to perform a comprehensive study of direct photon production in .
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