About a month ago I visited CERN, arguably the most famous research organization in Europe. It is the place where the World Wide Web has been invented, and the home of the Large Hadron Collider. I was very excited about the trip, much like Sheldon Cooper. Here are some facts which were new to me:
... about CERN:
- CERN was founded after the WWII by a bunch of European countries. They were exhausted by the war, and the only way to catch up with the USA and USSR in fundamental science was to join forces.
- The original name was Conseil Européen pour la Recherche Nucléaire (European Council for Nuclear Research), which abbreviated to CERN. Later the name has been officially changed to European laboratory for particle physics, which is both more relevant and less fearful for the locals, however the brand CERN is used now even in official documents.
- There are almost 3,000 full-time employees, but most of them are engineers and not scientists. There are a lot of visiting researchers though.
- There are 20 member states now (primarily EU states), and 6 observer states (such as Russia and the USA).
- CERN's annual budget is about € 1 billion, it is funded by the member states in proportion to their economical power, e.g. Germany gives 20% of the money.
- The budget money are spent to infrastructure and support, all the individual experiments are funded by research groups and their universities.
- In spite of the USA is not a member state, it leads on the number of researchers who work on CERN projects (more than thousand), second is Germany, third is Russia (yes, we still have a good shape in particle physics). It turned out that everybody at CERN spoke Russian, even the janitor. :)
... about the LHC:
- It is in fact a circular tunnel of 27 km in circumference lying 175 m beneath the ground.
- The tunnel was used before the LHC, it was build in 1983 for the Large Electron-Positron Collider. In 2008 it was upgraded to be able to accelerate heavy particles like protons to become the Large Hadron Collider (remind that proton and neutron are thousand times heavier than electron).
- The tunnel is about 4 meters in diameter, one can walk there or ride a bike.
- The tunnel encapsulates two small pipes for the particles that intersect at four points (to make the tracks' lengths equal, like in speed scating arenas). There are more then a thousand of electric magnet dipoles along the pipe. They are not that big as I imagined before.
- It is nearly vacuum and zero temperature inside the tubes.
- Proton beams are not generated inside the LHC. First, they are accelerated in the linear accelerator and almost reach the speed of light c. While the speed is rising, it becomes harder and harder to increase it since it cannot overcome the speed of light. Then they are accelerated in the small circular accelerator, and only after that they are injected into the LHC where during 40 minutes the beams are accelerated to speed as much close to c as possible.
- When accelerated, the beams are being observed during 10 hours. They suffer about 10,000 collisions per second, about 20 pairs of protons collide each time. Since the speed is large, the energy of that collisions is enormous.
- The collisions take place within special locations called detectors. We visited a control centre of one of them, ATLAS. A detector has multiple layers, each able to register certain kind of particles, like photons.
- Ten thousand collision per second would yield really big amount of data, so only few of them are selected to be logged. I don't know how they select those collisions, machine learning might be used. :)
- All the collected data are spread into servers all over the world. An authorized researcher may log in to the grid network and execute her script to analyse the data.
... about Higgs boson:
- Higgs boson is a hypothetical particle, existence of which would prove the standard model of particle physics.
- Higgs boson appears as a result of collision of two protons and large amount of energy. The protons in the LHC are accelerated enough to produce theoretically sufficient energy.
- Higgs boson is very heavy and thus unstable. In theory, it decays into either four muons or two photons. So, if there will be two counter-directed light beams registered by the detector, this will be an evidence of the boson. See the picture below for example of likely detector output in case of the boson shows up.
- Scientist say that if Higgs boson would not be detected, all the modern knowledge on particle physics will crush. They will be obliged to develop a new theory from scratch.
- There are no published results that report on Higgs boson detection so far...
Don't you want to be a theoretical physicist now? =)