The ATLAS detector is the world’s largest general-purpose particle detector, measuring 46m long, 25m high and 25m wide. It weighs 7,000t and consists of 100 million sensors that measure particles produced in proton-proton collisions in CERN’s Large Hadron Collider 3 (LHC).


The first piece of ATLAS was installed in 2003 and since then many detector elements have journeyed down the 100m shaft into the ATLAS underground cavern. This last piece completes this gigantic puzzle.

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

Known as the small wheel, this is the final element to complete the ATLAS muon spectrometer, and will be journeying 100m into its underground experimental cavern. There are two ATLAS small wheels; though small in comparison to the rest of the ATLAS detector, they are each 9.3m in diameter and weigh 100t including massive shielding elements.

They are covered with sensitive detectors to identify and measure the momentum of particles that will be created in the LHC collisions. The entire muon spectrometer system contains an area equal to three football fields, including 1.2 million independent electronic channels. As particles pass through a magnetic field produced by superconducting magnets, this detector has the ability to accurately track them to the width of a human hair.

“These fragile detectors comprise the largest measuring device ever constructed for high energy physics,” said George Mikenberg, ATLAS muon project leader.

Ariella Cattai, leader of the small wheel team, responded: “One of the major challenges is lowering the small wheel in a slow motion zigzag down the shaft and performing precision alignment of the detector within a millimetre of the other detectors already in the cavern.”