Comment »Posted on Friday 8 August 2008 at 12:12 pm by Jacob Aron
In Physics

It turns out that the Large Hadron Collider is not actually being switched on today – although that depends on you definition of “switched on”. It was my understanding that when the LHC had been cooled to nearly absolute zero,a very chilly 1.9 Kelvin (that’s -269.1 degrees Celsius), it would be put into operation. What this actually means is the scientists at CERN can begin firing proton beams through a small part of the LHC, in preparation for the first full circuit which is due to take place on September 10th – the official start-up date. They are testing the synchronisation of the LHC with the Proton Synchrotron (PS) and Super Proton Synchrotron (SPS), which get the proton beams up to the high energies required before injecting them into the LHC. Essentially, they’ve pushed the power button but it hasn’t finished booting up yet.

With that clarification out of the way I’ll get on to the real point of this post: what exactly is the LHC, and what does it do? Those of you who watched the LHC rap I put up yesterday may have some idea, so I’m sorry if my explanation is slightly less entertaining.

An ariel view of CERN, on the Swiss-French border. The biggest ring is the LHC itself, whilst the smaller rings are the Proton Synchrotron and Super Proton Synchrotron. Click for a larger image.

The LHC is the latest (and largest) particle accelerator to be built. A particle accelerator is exactly what it sounds like – it accelerates electrically-charged particles (such as the positively charged proton) to near the speed of light, and then the “Collider” part of the LHC steps in. Two beams are sent whizzing around the ring in opposite directions as they build up to speed, held on course by powerful superconducting magnets. Superconductivity allows the flow of particles with very little electrical resistance, but can only take place at extremely low temperatures – hence the cooling of the LHC.

A simulated collision in the LHC

When the two proton beams collide they explode into a mass of exotic particles. The particle the scientists are interested in finding is the Higgs boson. First theorised in 1964 by Peter Higgs (amongst other), the Higgs boson is basically a particle associated with the Higgs field, which tells other particles what their mass should be. The Higgs field covers the entire universe, and it’s as if heavier particles such as the top quark (one of the basic building blocks of matter) struggle to “swim” through the field, where as massless particles such as the photon don’t interact with it at all.

The trouble is, we can’t see this field. However, all fields have a particle associated with them (for example, the photon is responsible for electromagnetism) which means that if the Higgs boson is detected, this will prove the existence of the Higgs field and validate the Standard Model of particle physics. If the Higgs boson cannot be found, then something is wrong with the Standard Model, and a lot of physicists will be left scratching their heads. Hopefully once the LHC is in action it will be the former, and not the latter.


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