Silicon tracking detectors in high-energy physics

Abstract

Since the fifties, semiconductors have been used as energy spectrometers, mainly in unsegmented ways. With the planar technique of processing silicon sensors in unprecedented precession, strip-like segmentation has allowed precise tracking and even vertexing, culminating in the early eighties with NA11 in the tagging of heavy flavor quarks—here the c-quark. With the later miniaturization of electronics, dense detector application was made possible, and large-scale systems were established in the heart of all LEP detectors, permitting vertexing in barrel-like detectors. At the time of LEP and the TEVATRON, tasks were still bifurcated. Small silicon detectors (up to three layers) did the vertexing and further out, gaseous detectors (e.g., drift chambers or time-projection chambers) with larger lever arms did the tracking. In RUN II of the CDF detector, larger silicon tracking devices, still complemented by a huge drift chamber, began to use a stand-alone tracking. At the LHC, ATLAS and CMS bifurcate in a slightly different way. Silicon pixel detectors are responsible for the vertexing, and large volume silicon strip detectors (up to 14 layers) are the main tracking devices. Silicon tracking systems are a fundamental part of modern multipurpose high-energy physics experiments. Despite the vertexing and thus the heavy quark tagging, silicon tracking detectors in combination with a strong B-field deliver the most accurate momentum measurement, and for a large range, also the best energy measurement. In this paper, the functionality of pixel and strip sensors will be introduced, and historical examples will be given to highlight the different implementations of the past 30 years.