A silicon tracker for Christmas

The CMS experiment installed the world’s largest silicon tracker just before Christmas.

Marcello Mannelli: physicist and deputy CMS project leader, and Alan Honma, physicist, compare two generations of tracker: OPAL for the LEP (at the front) and CMS for the LHC (behind). There is quite a difference between 1m² and 205m²..

The CMS tracker team couldn’t have hoped for a better present. Carefully wrapped in shiny plastic, the world’s largest silicon tracker arrived at Cessy ready for installation inside the CMS magnet on 18 December. This rounded off the year for CMS with a major event, the crowning touch to ten years of work on the project by over five hundred scientists and engineers. "Building a scientific instrument of this size and complexity is a huge technical and scientific achievement", said Jim Virdee, CMS spokesman.

CMS received an early Christmas present on 18 December when the silicon tracker was installed in the heart of the CMS magnet.

Covering a total surface of 205 m², the equivalent of a singles tennis court, the CMS semiconductor silicon strip tracker is unique of its kind. Despite its colossal size compared with the previous generation of silicon trackers at LEP - like the "tiny" 1m² vertex detector of the OPAL experiment (see photo) - its performance potential is exceptional. "The tracks of each and every one of the charged particles that will be produced in the particle collisions inside the CMS detector at the LHC will be reconstructed with a precision of 20 microns", explains Peter Sharp, project leader with CMS.

The tracker, which could be regarded as the largest image sensor the world has ever seen, is made up of silicon sensors assembled into 15200 highly sensitive modules designed to withstand high levels of radiation over a ten-year period. There are a total of 10 million detector strips read by 80,000 microelectronic chips. "This achievement seemed almost unimaginable in the 1990s", acknowledges Marcello Mannelli, deputy project leader. ‘The team has clearly taken an enormous step forward. Now it’s time to commission the detector. The tracker is so powerful that we have yet to understand its full potential. It’s a bit like having just completed the construction of a Formula 1 car and having to learn how to drive it…"