Scientists and technicians at the European Laboratory for Particle Physics have completed the installation of one of the most fragile detectors forming part of the Large Hadron Collider beauty (LHCb) experiment.
The laboratory is commonly known by its French acronym CERN (Centre Europ'een pour la Recherche Nucl'eaire).
The LHCb is one of four large experiments running off CERN`s Large Hadron Collider (LHC), expected to start up in 2008.
Installing the sensor, the Vertex Locator (VELO) detector, in its final location in an underground experimental cavern, required precision work, says LHCb-VELO project leader Paula Collins.
"It was a very delicate operation," says Collins. "With its successful completion, the VELO is now in place and ready for physics."
A number of South African scientists are involved in the project - mostly in the field of grid computing. Once operational, the LHC is expected to generate data in the petabyte range. The LHC also uses services-oriented middleware to facilitate computing and data transfer.
The VELO is a precise particle-tracking detector that surrounds the proton-proton collision point inside the LHCb experiment. At its heart are 84 half-moon-shaped silicon sensors, each one connected to its electronics via a delicate system of more than 5 000 bond wires.
These sensors will be located close to the collision point, where they will play a crucial role in detecting "b quarks", to help in understanding tiny, but crucial differences in the behaviour of matter and antimatter.
The sensors are grouped in pairs to make a total of 42 modules, arranged in two halves around the beam line in the VELO vacuum tank. An aluminium sheet, only 0.3mm thick, provides a shield between the silicon modules and the primary beam vacuum, with no more than 1mm of leeway to the silicon modules.
Custom-made bellows enable the VELO to retract from its normal position of just 5mm from the beam line, to a distance of 35mm. This flexibility is crucial during the commissioning of the beam as it travels round the 27km ring of the LHC.
"The installation was very tricky, because we were sliding the VELO blindly in the detector," says Eddy Jans, VELO installation coordinator. "As these modules are so fragile, we could have damaged them all and not realised it straight away." However, the verification procedures carried out on the silicon modules after installation indicated that no damage had occurred.
The VELO project has been ongoing for the past 10 years, involving several institutes of the LHCb collaboration, including Nikhef, EPFL Lausanne, Liverpool University, Glasgow University, CERN, Syracuse University and MPI Heidelberg.
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