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Crikey Clarifier: what’s the Large Hadron Collider up to?

Since early April the Large Hadron Collider (LHC) has been back up and running at increased velocity in 27 kilometres of tunnels under Geneva, in the hope of discovering the answers to some of science’s most elusive questions.

The 2012 run broke records for particle collision, but after two weeks of experiments at record speeds, physicists are becoming confident the LHC is on track to reach even greater heights in 2012 — in particular, the discovery of the Higgs boson, or “God particle”.

Crikey picks the brains of Dr Paul Jackson, professor of particle physics at the University of Adelaide, about what exactly the LHC does, and what answers they’re looking for.

In layman’s terms, what is the Higgs boson particle, and how is the Large Hadron Collider attempting to find it?

Jackson said: “In layman’s terms, a particle is the smallest element of nature, so the smallest subset that makes up all of the matter and forces in the universe. What the Large Hadron Collider is doing is trying to accelerate protons to the highest speeds and energies we’ve ever done, and using Einstein’s of knowledge e=mc2 translate that energy into heavy, more massive particles that have never been created or observed on the Earth.”

What’s so significant about the Higgs boson?

Dr Jackson calls the Higgs boson the “missing piece in the standard model of particle physics”.

We have a very accurate and predictive model of all of the particles that we have so far measured. So we can go away and measure the properties of these particles, for example their mass, and we have a set of tables of how heavy these things are, but we have no idea why they have these different masses. The reason why the Higgs boson is so interesting is that it provides a mechanism to give mass to all these particles that we’ve measured,” he said.

The reason why we want to be able to be able to measure this is to see whether Higgs’ theory is true, as to whether this particle exists and is giving mass to all these other particles, and if it looks the way we think it should look.”

What happens if the Higgs boson is proven to exist — what then?

The puzzle of the standard model, Dr Jackson says, would be relatively complete.

But there are a number of outstanding issues in particle physics that can’t be answered by this standard model. For example, there’s the idea that there is a ‘dark matter’ component to the universe, a substance that doesn’t interact with these particles that make up the standard model, and we have no idea what it is. So particle physicists won’t be out of a job just yet,” he said.

And what would it mean if it doesn’t exist?

That’s where it gets interesting, according to Jackson: “If the particle is proven not to exist, it’s a blessing and a curse. From the scientist’s point of view it’s pretty cool, because it means we’re wrong and that we’ve been barking up the wrong tree for all these years, and that there’s some completely different mechanism that endows particles with their masses.

So from our experimentalist perspective it’s kind of interesting, because we have to go back to the drawing board and come up with a new theory that explains it.

From the standpoint of telling everyone that we built this big expensive machine to find the Higgs boson, and that it’s not there, we look a bit stupid. But there has to be something like the Higgs boson, whether its exactly like Higgs and the others predicted or if it’s some other particle that carries some other type of mechanism — there has to be something there in nature. So hopefully with the energies that we’re creating at the Large Hadron Collider there could be something else to find.”

What makes 2012 such an exciting year?

Well I agree that 2012 should be the year we know the answer to the Higgs boson question,” Jackson said

What’s been done differently this year is that the energy of the collisions at the LHC has been increased (in technical terms, from 7 teraelectronvolts [TeV] to 8TeV). This means that we have additional energy going into these collisions, so there is an extra kick for the statistics of Higgs bosons that we could be creating. And this should give us enough events to confirm or deny its existence.”

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  1. Lisa Randall wrote recently a very good book ‘Knocking on Heaven’s Door’, which contains large sections on the Large Hadron Collider, how it’s constructed, how it works, what they hope to find …

    Apparently, and it’s mind boggling, nucleons (neutrons and protons) don’t just consist of 3 quarks. They consist of 3 quarks in a sea of virtual particles - particle/antiparticle pairs, which flash into and out of existence in times too short to measure.

    And most of the mass of nucleons is in the virtual particles, not the ‘real’ quarks.

    And most of the nucleons consist of empty space.

    So when two protons traveling at almost light velocity in opposite directions collide, most of the time the quarks and virtual particles sail on past each other without interacting. Occasionally a quark or a virtual particle might collide, the rest of both nucleons continuing unimpeded.

    It’s collisions of the virtual particles that are of interest, because they have most of the mass, hence energy, and potentially generate the most interesting novel high energy particles, if they exist.

    by wayne robinson on Apr 26, 2012 at 1:36 pm

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