The fourth lecture was given by Dr Emily Nurse from UCL. She has worked on experiments at the two largest particle accelerators in the world – ATLAS (part of the LHC) and the CDF experiment at the Tevatron at Fermilab.
How do these experiments unlock the secrets of particles? Dr Nurse began her lecture by giving a brief history of our knowledge about the atom. In the 1800s we knew there were 92 atoms but we knew nothing about their structure. In the early 1900s we knew that the atom consisted of a nucleus plus electrons and that the nucleus consisted of protons and neutrons. We now know that protons and neutrons are made up of quarks. The standard model is a successful mathematical theory describing the fundamental building blocks and the interactions between them. The Higgs Boson is needed to help complete the standard model. The LHC has been investigating the Higgs, super symmetry and extra dimensions. The LHC can be described as a proton-proton collider (although lead ions are also being collided). Why is it so big? To produce the large energies required to allow us to probe deeper into the particle and to produce massive particles. If you are/have studied A level physics you will have come across the formula F = Bqv (where F is the force on a charged particle in a magnetic field, B is the magnetic field strength, q is the charge on the proton and v is the velocity of the proton). The momentum, P, of the particle is proportional to the radius of curvature (of the LHC) and B. ATLAS detects the results of colliding particles. Hopefully the particles live long enough to pass through ATLAS. If not they can be inferred by their products. Collecting the data is a very large job. Only one in 10 million interactions could produce the Higgs. In each run 2808 bunches of protons are used (a bunch consists of billions of protons). There are 31 million bunch-crossings (300 per second). The biggest challenge is saving the right events. Trigger systems are potentially interesting. Muons are quite penetrating.