LONDON The last of the 4 barrels that make up the central part of the Semiconductor Tracker (SCT), the heart of the biggest physics collaboration in the world have left Oxford for its new home at the European Particle Physics Laboratory, CERN, near Geneva.
At CERN, physicists from around the world are assembling the Large Hadron Collider (LHC) which will send two counter-rotating beams of particles round an underground ring at 99.999999 per cent of the speed of light. When the beams are brought into collision, a shower of new particles will be produced reproducing conditions similar to those immediately after the Big Bang. These will be studied at four detectors around the ring. The largest of these detectors is called ATLAS and at its heart lies the SCT tracking the movements of the charged particles produced in the high-energy collision.
The SCT detector consists of a central region and two end caps. The central region is formed of four concentric barrels, covered with 2112 silicon modules (30 square metres worth!). The modules were produced by collaborators in different countries and sent to the University of Oxford for precision assembly. To be assembled, each of the fragile silicon modules had to be mounted on an ultra-lightweight carbon fibre cylinder using a specialised robot.
Each silicon module has 1536 channels, where each channel is a separate detector element which is connected by a wire bond to an individual channel of an ASIC which contains all the read out electronics.
Dr Richard Nickerson, who led assembly of the SCT at Oxford, said, “The assembly of the SCT barrels has proved to be a very challenging project and so we are all extremely pleased to see it reach a successful conclusion with 99.5% of the 3 million channels working – even more than we hoped for as we had built in an element of redundancy.”
The SCT will track the positions of charged particles passing through the detector with an accuracy of better than 20 microns (less than the diameter of a human hair) over one metre. A superconducting solenoid will provide a magnetic field of 2 Tesla so from these measurements it will be possible to calculate the momentum of the particles, an important clue in sorting through the debris of a high energy particle collision. This information forms a crucial part of the data gathered by the full ATLAS Detector system and will be essential in the task of unravelling the physics in these complex events.
The ATLAS experiment is the world's largest collaboration in physical sciences, involving more than 1800 scientists from around the world. The SCT is a collaborative international project with UK physicists coming from university research groups at: Birmingham, Cambridge, Glasgow, Lancaster, Liverpool, Manchester, Oxford, Queen Mary University of London, Rutherford Appleton Laboratory, Sheffield and University College London