UK particle physicists have completed the first critical element of what will be the largest semi-conductor tracker ever built, the SCT which, when completed, will form the inner most core - the very heart - of the giant ATLAS detector. ATLAS is one of the four huge experiments on the Large Hadron Collider [LHC] particle accelerator currently being built at CERN on the Swiss/French border which is due to start operations in 2007.
The LHC will accelerate two beams of protons traveling in opposite directions at energy levels seven times higher than ever achieved before in an accelerator, and then collide the particles head on, creating yet more particles and replicating the conditions that existed just moments after the Big Bang at the birth of the universe. ATLAS will observe these dramatic collisions and the SCT will track and measure the momentum and directions of charged particles as they explode from the collision point. The resulting data and that obtained from the other three experiments on the LHC, will shed light on the fundamental properties of matter and help scientists understand why the universe looks the way it does today.
The entire SCT detector consists of 60 square metres of silicon detectors in the form of four concentric barrels and two end-caps. The first completed barrel has been populated with 384 silicon modules and each of the three outer barrels will carry progressively more modules with the fourth and final barrel having 672 silicon modules. The SCT overall is divided into 6 million channels and every channel has its own amplifier and data buffer. All four barrels of the SCT will be assembled in the UK using components from a world-wide collaboration of 37 Institutes.
Dr Tony Weidberg from the University of Oxford explains "The SCT will track charged particles as they move through silicon wafers to an accuracy of better than 20 microns - that's less than the diameter of a human hair - over the diameter of 1 metre. This will allow us to calculate their momentum, providing part of the picture of what happens when protons are collided at high energy. Other parts of the detector will pick up different particle properties, allowing us to reconstruct what happened in the collisions"
ATLAS brings experimental physics into a new territory and could reveal new processes and particles that would change our understanding of energy and the basic forces that have shaped our universe since the beginning of time.
Dr. Weidberg added "The new energy regime opened up by the LHC will allow ATLAS to search for the Higgs Boson and understand the mystery of why particles have mass. There are very strong indications that the exploration of this completely new energy regime will lead to the discovery of new physics, such as Supersymmetry which would imply the existence of exotic partners to all the previously discovered particles. The new physics might be even more exotic and involve extra spatial dimensions and the production of mini black holes".
The ATLAS experiment is the world's largest collaboration in physical sciences, involving more than 1800 scientists from around the world. The detector is a leviathan, measuring 46m long and 25m high, as large as a five-story building, and weighing 7000 tons. Yet at its heart, where the SCT will operate, narrow beams of particles will be focussed to collide in an area much less than 1 square mm. Out of nearly 1000 million collisions a second, only a few will have the special characteristics that might lead to new discoveries.
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