CERN muon detector gets major upgrade for better particle hunting

Weighing in at 14,000 tonnes, the CMS experiment at the Large Hadron Collider can now detect more of the subatomic particles created when protons are collided

By Gege Li

Noemi Caraban Gonzalez /CERN

Photographer
Noemi Caraban Gonzalez/CERN

THIS amazing instrument may be the world’s heaviest camera-like device. But instead of photons of light, it records something far more exotic: muons, produced by the collisions of billions of particles.

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Weighing in at 14,000 tonnes, the Compact Muon Solenoid (CMS) detector is one of four big experiments at the Large Hadron Collider, based at the CERN particle physics laboratory near Geneva, Switzerland. The LHC is the most powerful particle accelerator in existence and can push protons close to the speed of light.

The CMS sits at one of the LHC’s collision points, and it builds a picture of the particles produced when protons collide. It specialises in muons, negatively charged particles similar to electrons but more than 200 times heavier.

The solenoid magnet at its core bends charged particles, helping the CMS detect their charge and momentum. Muons are very shy of interacting with matter, so they pass undetected through most of the CMS. They are caught by components around the detector’s edge, providing extra information that allows the complex particle interactions occurring as protons collide to be reconstructed.

One of the particles that these collisions produce is the Higgs boson, the particle that gives all other fundamental particles mass and which has a characteristic decay into four muons.

In September, CERN finished installing the CMS’s outermost layer of muon detectors, letting it pick up muons that scatter at an angle of 10 degrees. CERN plans to add hundreds of new detectors to expand the range of muons it can detect.