Today my cousin's husband put me in contact with someone at CERN (he used to work at CERN). Josh, the CERN guy, arranged for me to do an underground tour of the site where he works. There are several experiments that run at CERN and his is in France, called the Compact Muon Solenoid (CMS). There are 2 others, ALICE & ATLAS, which both run in different parts of the Large Hadron Collider (LHC). Each experiment studies different things. ALICE, for example, looks at the particles when heavy ions such as lead are smashed together. CMS study the collisions between protons and it was this site they discovered the Higgs Boson particle in 2012. The track is 100m below the surface and 27km long. The original input the make the proton beam is hydrogen gas. That's it, simple hydrogen. It goes through 4 accelerators, each with their own track, before it is fast enough to enter the LHC. The particle beam chamber is only about 20cm round but the entire casing at the detectors is 5 storeys high! The beam is surrounded be superconductor magnets that are cooled to 1.9 kelvin (-271c). It takes 1 month to cool the magnets from room temperature to this temp! I learned that what we tell students is wrong. We tell them that the smallest particles are electrons, protons & neutrons. Well protons and neutrons are made up of even smaller particles called quarks! Protons are made from 2 up quarks and 1 down quark which give a proton the charge of +1. Neutrons are made from 2 down quarks and 1 up quark which gives it the 0 charge. Plus there are quarks called strange, charm, top and bottom. Funny names! So, when the proton beams collide the particles formed in the collisions fly out everywhere. The detectors are massive and have a variety of different types of detectors and layers for each one. Each detector is made for specific particles and there are also some calorimeters (measure energy) to catch particles. Computers then collect the data and can produce graphical displays. Each partical has a signature that the team can use to identify it. Photons make no track and just show up in the calorimeter while muons go through all layers to the outer layer. Nutrinos are buggers and rarely show up, identified by a gap in the data. Josh also showed me the data area where all the cables from the detectors go into and all the cables from there go up to the control room. I have never seen so many cables in my life. If any 1 cable is dislodged or completely pulled out, the entire data collecting system stops. The LHC has only been running 3 times since it began operating in 2008. Each time it runs is for 2-3yrs. Then they shut it down for upgrades. It will be shut down next year for 2yrs. Sitting this time the researchers work on analysing the data & do maintenance, repairs & upgrades. It was so incredibly interesting to learn about this amazing piece of machine. It is a true marvel! If you ever get the chance to visit, you really should.
Photo of the magnets in the tunnel. There are 1500 of these!
The inside of the beam tube. The proton beams run in opposite directions.
The inside of the detector model. The gold/brass bit in the middle is what Josh works on
One of the graphical displays that can be produced from the data showing the tracks of the particles. The red one going to the edge is a muon.
This interactive display is a large case of a liquid substance and you push a button to inject particles into it. The particles show up as they collide with the particles in the substance. You can actually SEE the particles in real life! They are no longer invisible things! I took this picture after we injected electrons.
This is a sample of the detector Josh works on. It is a ginormous chunk of brass basically which the particles collide with.
This is the inside of a linear accelerator which is the first stage of accelerating the proton beam.
A near life size model of the detector in the tunnel. This one is just for show and not made of the real stuff. It is still very impressive!
A map of the whole site. We were right at the very top of the track at CMS whereas the rest of the accelerators & detectors are concentrated in the lower half of the track.
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