Huge digital cameras record tiny particles

The ALICE detector, owned by the European Organization for Nuclear Research (CERN) - is located more than 90 meters underneath this colorful building in Geneva. ALICE is a huge digital camera capable of photographing even the smallest building blocks of the universe - the components of an atom's nucleus.

In addition to ALICE, three other detector cameras, named ATLAS, CMS, and LHCb, keep a record of particle collisions at the LHC. To see them you have to go deep below the rock of the French and Swiss Alps.

When protons or lead ions smash together at the speed of light the smallest elementary particles are released - and this is what it looks like to the CMS detector. Scientists believe our universe was created from such particles in the first billionth of a second after the Big Bang.

This is where lead ions and hydrogen protons are accelerated. They fly through a vacuum tube with the energy of a speeding train and are kept on track by massive electromagnets. The pipe has a circumference of 27 kilometers and can be accessed through the four large detectors where the particle collisions take place.

The electromagnets that keep the particle beam on track are made of superconducting inductors. The cables must be kept at a chilly minus 271.3 degrees Celsius (minus 456 Fahrenheit) so they no longer have any electrical resistance. To cool them down, the collider sends a whole lot of liquid helium through the pipes.

The LHC is not a perfect circle but instead consists of long straight stretches interrupted by curves, where magnets redirect the beam. The electromagnets are extremely precise. Just before a collision they focus the beam in exactly the angle so that the probability of two particles colliding is very high. The clash then happens right in the middle of the detector.

The detectors are as big as multi-level houses. But they all had to be brought into the mountain in smaller parts through narrow shafts like this one. Underneath it is a gigantic cavern where ALICE was put together.

This is the ALICE detector when it is opened for maintenance. When in operation, ion beams collide in its center. New particles are created, flying off in different directions through several layers of silicon chips, similar to the sensors of a digital camera. The chips and other detectors record the particles' routes. ALICE can capture 1.25 gigabytes of digital data each second.

This blue chunk is another huge electromagnet, an important part of the ALICE detector. It creates a field making it possible to identify particles that are created during the high-speed collisions. Scientists study the direction the new particles travel. For instance, they can determine whether particles were neutral or positively or negatively charged.

The ATLAS detector has a special gauge, the so-called muon spectrometer, which lies outside the detector’s heart, just like large wings. With these wings a heavy relative of the electrons - the muon - can be caught. Muons are difficult to find because they only exist for two millionths of a second.

All detectors have a control room, just like this one for ATLAS. Once the collider is in operation, no one is allowed to stay inside the underground facilities. An out of control proton beam can melt 500 kilograms of copper and escaped helium could cause frostbite and suffocation. The particle stream could even create radioactivity.

The detectors deliver data 40 million times per second. But because not all collisions are interesting for scientists, the data has to be filtered. In the end, no more than 100 interesting particle collisions per second remain. That’s still more than 700 megabytes of data per second - about what fits on a commercial CD. All data initially lands here in CERN’s data processing center.

CERN produces an amount of data per year that if it were stored on CD, the pile would be 20 kilometers high. Even though such a tape library can hold a lot of data, it is still not enough. So the data are distributed worldwide. More than 200 universities and research institutes have created a worldwide CERN computer network with their data processing centers.

Particle physicists from around the world have access to CERN data. The center sees itself as a service provider for universities and institutes conducting basic research. A common project for everyone's benefit.