University testing
The new Liverpool Semiconductor Detector Centre was recently opened by Sir David King, the Chief Government Scientist. Cleanroom Technology finds out more about the facility
The Liverpool Semiconductor Detector Centre (LSDC) was created through funds secured by the Department of Physics and the Astrophysics Institute of Liverpool John Moores University from the UK government's Joint Infrastructure Fund initiative. Since 1998, the investment of £3.1m has enabled the establishment of 450m2 of cleanroom equipped with state-of-the-art wire-bonding, wafer-probing and metrology equipment, and the complete refurbishment of the Oliver Lodge Laboratory workshops. This investment has been administered by PPARC and carried out by the Buildings & Estates and Physics Departments of the University, using mostly local contractors, and the Centre is now in operation. The LSDC gives Liverpool a unique, well equipped facility for a Physics Department. It makes possible the assembly and testing of large integrated detector systems based on sensors with spatial resolution of typically a few microns. It includes facilities for the construction of very large arrays of such detectors to allow areas of many square metres to be instrumented to detect the presence and spatial distribution of ionising radiation with micron precision. Work in the LSDC currently underpins activities in the High Energy and Nuclear Physics Groups at the University of Liverpool and the Astrophysics Research Institute of the Liverpool John Moores University. Two large projects (ATLAS End-Cap construction and the LHC-b Vertex Locator), supported through substantial PPARC funding, are already underway. They are concerned with the construction of large arrays of sensors for charged particle detection in two experiments at the 14 TeV Large Hadron Collider (LHC) 27km superconducting accelerator, which is presently under construction at CERN, Geneva.
ATLAS project At the LHC, ATLAS will be the largest experiment, measuring 46m long by 22m high and designed (along with its sister experiment CMS) to identify the new fundamental particles produced at the unprecedented collision energies. These measurements are expected to give answers to many leading theoretical questions, such as the origin of mass and the deep connections between all the different forces, matter and space-time. Within the ATLAS project, the UK's largest contribution is to the 60m2 silicon micro-strip based semi-conductor tracker (SCT), composed of a four-layer barrel section and two nine-layer end-cap sections. The tracker is composed of 4,000 modules, each of 1,536 channels with spatial resolution of around 10µm and is being built by an international collaboration of 30 institutes, with 11 UK groups contributing. The end-cap, which is being assembled at Liverpool with particular help from colleagues based in the northern Universities and CLRC, represents roughly half the UK's deliverables to the tracker. The high spatial resolution of the silicon detectors will be required to identify and accurately measure the hundreds of charged particle tracks produced every 25ns by the ultra-high energy head-on collisions of protons at the LHC. From this information, evidence for the Higgs and/or Supersymmetric particles etc will be extracted from the Pbytes of data to be recorded by the experiment.
LHC experiment The LHC-b experiment takes advantage of the 40 million per second high energy interactions at the LHC, not to look for the rare production of super-heavy new particles, but to study the properties of the short lived b-mesons that will be copiously produced. Experiments have now shown these particles reveal the subtle differences between matter and anti-matter which could lie at the heart of explaining why our universe seems now to contain no anti-matter (although presumably equal quantities of matter and anti-matter were initially created at the big bang). LHC-b will study these particles using unprecedented statistics to test the current theoretical understanding of how a universe of only matter came into being. On the LHC-b project, the vertex locator, which is being built at Liverpool and represents 20% of the total UK contribution, is LHC-b's most vital sub-detector. This is the detector that finds those particles produced containing the picosecond lifetime b-quark by accurately tracking the decay products back to the primary interaction point. The detectors have to sit as close as 1cm from the proton beam of the LHC, exposing them to 10s of Mrads of radiation. Production of detectors able to survive these extreme doses required extensive research and development with UK industry. LHC-b will use the vertex locator to sort out and record in real time a million events per hour containing b-quarks from the millions of interactions per second at the LHC.
A winning streak Winning such major roles on both projects relied crucially on the facilities of the LSDC. Roughly 70% of the PPARC supported activity at Liverpool University is for science programmes that now rely solely, or in large part, on the LSDC. Consisting of a cleanroom complex and workshop facilities, the Centre will first be used to build sensitive detector components for the LHC, under construction at CERN (the European Organisation for Nuclear Research) in Geneva. The goal of the LHC is to explore the fundamental nature of matter and the basic forces that shape our universe. UK research groups are widely involved and are contributing in particular to the semiconductor detectors on the ATLAS and LHC-b projects. Sir David said: "I am very pleased to be opening this new Semiconductor Detector Centre in Liverpool. This centre, and the detector systems it creates, will play a crucial role in the success of one of Europe's great scientific projects, the Large Hadron Collider being built at CERN, involving the study of fundamental particles – nature's ultimate building blocks. "These Government-funded facilities are great news for particle physics research, the scientific community in Liverpool and the wider academic community of the region." For the ATLAS experiment, the Liverpool group will be wire-bonding, testing and assembling into discs, 300 forward detector modules – a total of about two million wire bonds. During his visit, Sir David started the final bonding on the first of these critical components, marking the start of full production for this UK contribution to ATLAS.
