The last piece of the ATLAS detector, the world’s largest general-purpose particle detector, has been lowered down a 300 feet shaft at the European Organization for Nuclear Research's (CERN) underground facility along the Swiss-French border.

The ATLAS detector, measuring 46 metres long, 25 metres high and 25 metres wide, will detect and trace particles called muons expected to be produced in particle collisions in the CERN accelerator, known as the Large Hadron Collider (LHC).

"This is an exciting day for us," said Marzio Nessi, ATLAS technical coordinator, in a statement "The installation process is coming to its conclusion and we are gearing up to start a new programme of physics research."

The final piece lowered today was one of the two "small wheels" in the ATLAS muon spectrometer, and weighs in 100 tonnes including massive shielding elements. This concludes the construction of the high-tech device which started in 2003.

Experiments are slated to begin later this year. The project will look for signs of the Higgs particle, which is believed by some scientists to be responsible for giving other particles their mass. CERN said in its statement that its entire muon spectrometer system contains an area equal to three football fields, including 1.2 million independent electronic channels.

CERN, the Geneva-based European Organization for Nuclear Research, is the world's leading laboratory for particle physics. Its Member States are: Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. The United States is one of the Observers.