A miniature cradle of CCDs

26 August 1998

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This image shows one half of the innermost layer of the SLAC Large Detector (SLD), at the Stanford Linear Accelerator Center (SLAC) in California. While the overall detector weighs 4000 tonnes and is 12 m tall, the central "vertex detector" is only 15 cm across (see the rulers in the foreground). Its task is to make the most precise measurements possible of the tracks of particles created when electrons and their antiparticles (positrons) annihilate at the centre of the SLD in SLAC Linear Collider (SLC). The vertex detector - unique in particle physics was installed in January 1996 and has since allowed the SLD team to make several "world's best" measurements in particle physics.

The vertex detector is innovative in that it uses charge coupled devices (CCDs) to track the particles. It consists of three layers constructed of 48 "ladders", each ladder fitted with two CCDs of active length 8 cm, one each side of a thin motherboard. The 6 ladders on the inner half-layer of the detector are easiest to see here, and the inward-facing CCDs are visible as dark rectangles at the far end of each ladder. Each CCD comprises 3.2 million pixels, each 20 micron square, giving a total of 307 million pixels in the detector as a whole. The CCDs (which were made in the UK) measure points on particle tracks to a precision of about 4 microns, and together permit very precise extrapolation of tracks right back to the interaction region within the beam pipe. This allows the physicists to identify in particular "jets" of particles originating from bottom quarks produced in the annihilations.

Credit: SLAC / SLD

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