Good Morning to Beautiful Geneva and CERN!
Today was a very information heavy kind of day where we learned a lot about how particle accelerators work and how they don't work. Simon Albright gave us a talk about how each of the particle accelerators work in CERN and also about the processes in general. It shouldn't surprise you to learn that a particle accelerator's job is to add energy to a particle. This could be the 27km loop of the LHC that gradually speeds up already ridiculously fast particles, or it could be your microwave at home that accelerates the particles inside the cavity while making your food warm. The interesting thing we took away from this talk was that CERN's job is not to make measurements or detect particles really. CERN is in the particle accelerating business. Experimenters will ask for certain things to be accelerated and CERN will start accelerating!
Very briefly, a particle accelerator using a combination of electromagnetic forces to accelerate the particle in either velocity or direction. The Electric side referred to as RF energy, or radiofrequency energy is required to bring the particles to higher speeds. Meanwhile, if you are going to change the direction or focus a beam of particles you would need to use magnets. In the case of a linear collider, you are just speeding the particles up in a straight line, hence linear. In the case of a circular collider you would need to do both. There needs to be parts that turn the beam, parts that focus the beam and parts that push the beam. They can't be in the same point, so you need an area (called an RF cavity) where the particles are pushed (think pushing a kid every time the swing comes back to you, the kid goes higher each time).
The Synchrocyclotron we visited before is an example of a circular collider. What is interesting about this is that as you increase the speed of the particles, you are causing the particles to take bigger and bigger circles. Think of spinning around holding a ball on a string. As you spin faster, the ball flies farther away from you. However, what we see is that as the speed increases, eventually, you reach a point that the particle can't get any faster at that frequency, so you must increase the RF. This is because the faster you go, the more special relativity matters and you need more force to accelerate something. So you need to change the RF to keep the particle in synch with the changing field so it can keep getting pushed by the electric field. In a synchrocyclotron, that is exactly what happens, the RF and the Magnetic field are increasing together. This is what most but not all of the accelerators at CERN are.
Many are linear accelerators: line LINAC3 (Linear Accelerator 3), LINAC4, CLEAR (CERN Linear Accelerator for Research), and ISOLDE (Isotope Separator Online). While others are circular like LEIR (Low Energy Ion Ring), BOOSTER, SPS (Super Proton Synchrotron), and LHC.
After that, we learned about Particle detectors from a doctoral student at CERN, Veronika Kraus, studying how to make better silicon detectors in the center of the CMS machine to withstand the high radiation that is present while making 600 Million collisions/second give or take.
She told us about how we can measure different particles and really hit home the amount of different measuring devices needed to find all of the particles and work to find which collisions created which particles. Very briefly:
Particle identification based (almost always) on their distinct interactions with matter:
• Charged particles (z, B, e- , μ+ , p, π+ )
– Ionization & excitation, Bremsstrahlung, Cherenkov radiation, Transition radiation, Multiple scattering
• Photons (γ)
– Photoelectric effect, Compton scattering, Pair production, Rayleigh & Thomson scattering
• Hadrons (π, p, n)
– Hadronic interactions: Elastic/inelastic scattering with nuclei, Neutron capture, Spallation, Nuclear reactions
– Neutrons: interact only via the strong force
• Neutrinos (ν)
– Detected indirectly via “missing energy”
I won't go into all of this; it's very dense, but trust to say it is amazing the number of detectors needed to measure each or even some of these. 
Detectors are built like onions and each layer measures something new. The inner chambers trace the paths of particles using silicon chips, the green measures electromagnetic particles (photons, positrons, and electrons) the yellow measures hadrons (neutron, protons, antiprotons) and the kind of brownish is for measuring muons which are much harder to catch so you need more material. the grey bit in the midst of all of this is the solenoid that give the CMS its name, Compact Muon Solenoid. It provides the magnetic field that causes the charged particles to turn in the detector, similar to how the magnets in the accelerator do the same.
Lastly came Louis Roberto Flores Castillo who came and talked about the finding of the Higgs. It was an amazing talk. Louis had a way of breaking down incredibly difficult topics like why measurements are fundamental like charge and spin, but others like mass become break down the math. If particles had mass themselves, none of the math of particle physics would work. It turns out that mass must be a process of interaction with something else in order to keep the particles safe in these equations, so that was where the Higgs field came in and if there is a field, in physics, there must be a force carrier; in this case, the Higgs boson.
Dr. Castillo gave us so many more explanations ranging from why photons and gluons are both mass zero but only photons are long range carriers while gluons break away after only a ridiculously small space. He talked about how impossible it was to get funding for the LHC and how even though it was impossible, it was done. Phew....what a day.
Good night from Switzerland!
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