Physics in perspective lecture 2012

Physics update course February 2012

Every year during the February half-term the Institute of Physics puts on a number of physics lecture aimed at 6th formers. I am going to write a little about each lecture.

The first lecture was given by Prof. Jonathon Butterworth and was entitled The Large Hadron Collider: Latest news from the energy frontier.

The professor started off by explaining that the LHC has to be 27km in order to produce the high energies required. It is full of superconducting magnets to make sure the particles move in a circle and collide head on. The magnets provide the centripetal force. The relevant formulas are F = mv2/r and F = Bqv and in the case of the LHC the two forces are equal to each other.

The professor then went on to review the standard model of elementary particles (quarks, leptons and bosons) and focussed on the origin of mass. Three generations of matter are required to explain antimatter. At the moment gravity doesn’t fit the standard model and we need to know how particles have mass.

Professor Butterworth’s research involves ATLAS, which detects the results of proton proton collisions (every 50ns bunches of protons collide). Silicon semiconductors are used in the tracking detectors. The detectors allow us to know the momentum and energy of the resultant particles. The path in the magnetic field tells us the momentum of charged particles. Liquid argons calorimeters are used for neutral particles. Muons are rare and ATLAS detects them. Neutrinos are also detected. Photon, gluon and quark collisions are also investigated. As particles fly apart potential energy increases and new particles/quarks are produced which is what the tracks show.

E = mc2 = hc/λ, high energy means small wavelengths and this is required if the Higgs particle is to be found.

As well as looking for the Higgs the LHC allows us to investigate the stages that the universe has gone through since the Big Bang. Higher and higher energy collisions are required to replicate the big bang. In the past the universe had a very high energy density. The professor went through the stages the universe had gone through.

The professor diverged slightly to talk about Feynman diagrams.

Feynman diagram of electron-positron annihilation.                                                                                The diagram is odd as photons have no mass. Feynman got round this problem by saying that forces are carried by “virtual” particles which have a transient existence. Don’t have to have “correct” mass (uncertainty principle).

The diagram above shows how the bosons diverged as the universe got older. At higher energies the weak forces and electromagnetic photons look the same. They diverged because W and Z bosons have mass and photons don’t. The Higgs boson may explain this.

The Higgs field is believed to fill the universe and the W, Z bosons go one way and photons go elsewhere. Higgs boson is described as exciting a wave like sound in air. The Higgs boson is believed to decay to two photons or two Z bosons or to two Z bosons.

Not discovering the Higgs particle is as exciting as finding it.

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