Science Interviews


Sun, 7th Sep 2008

Using the LHC in Research

Tara Shears from the University of Liverpool

Listen Now    Download as mp3 from the show The Large Hadron Collider

Chris - Dr Tara Shears is from the University of Liverpool and she works on the [LHC]b detector. Sheís looking for antimatter. Tara, thank you for joining us on the Naked Scientists. Tell us a bit about your work.

Tara - My experiment LHCb was designed to look into the question of why, when we think the universe started in equal mixture of matter and antimatter, why there only seems to be one type: matter, around today. We think this inequality arose some time very early in the Universeís history Ė sometime in the first minute even. We donít know why it should be. We donít know why that happened. We think itís due to some difference in the behaviour of matter and antimatter but weíre not quite sure what.

Chris - So what youíre saying is thereís basically two types of stuff. Thereís matter and antimatter. This will be like the North and South Pole of a magnet. What we see in the Universe at the moment is all the North Poles, begging the question of, ĎWhere have all the South Poles gone?í

Tara - Thatís exactly right. Antimatterís really, in a sense, like the mirror reflection of ordinary matter. We can find out whether itís present anywhere because one particular peculiarity that antimatter has is that whenever it meets normal matter it annihilates. Itís quite dramatic. If you have a gram of matter meeting a gram of antimatter you get an explosion equivalent to about 5 kilotons of TNT.

Chris - So you can actually make antimatter?

Tara - You can generate antimatter at CERN in very, very small amounts. What happens at the LHC is that when we have the beam collisions, the proton-proton collisions, as Ben [Allanach]ís already told you we convert the energy of those beams into new particles. Some of those new particles will be antimatter particles.

Chris - So theyíre made of the same building blocks as matter particles them?

Tara - Thatís right. To give you an example, for every quark we have an antimatter quark equivalent. For something like the electron thereís an antimatter equivalent that we call a positron. Every particle that we know about in the universe also has its antimatter equivalent.

Chris - How can we turn matter into antimatter, though?

Tara - What happens in the LHC is in the collision we either generate matter in the form of matter or antimatter, if that makes sense. It comes in one variety or the other. What we detect in our experiments is maybe the decay products of those particles (they donít live for very long) and what those particles decay to and identifying them we can infer whether we had a fundamental particle in the first place that was matter or antimatter.

Chris - Youíre starting with a beam of protons. These are matter protons though, arenít they? If you can make antimatter using those does that argue theyíre made of the same thing as antimatter?

Tara - Not at all because youíve got to think that when we have this beam collision we have a certain amount of energy. Whatever collides in those protons (and like Ben said itís like swishing two wet rags together or two squidgy oranges) only part of the proton collides with each other. That converts to pure energy and if we apply Einsteinís equation to mass, to particles, antimatter particles have the same mass as normal particles. In that respect these collisions - it doesnít really matter whatís colliding together. You have this annihilation of energy and then that energy can be distributed into different particles. It doesnít matter whether itís matter or antimatter.

Chris - And then presumably this will give us insights into the nature of antimatter so we can understand perhaps how they use it.

LHCb experiment

A view inside the LHCb cavern © CERN

Tara - Thatís what weíre hoping with the LHCb experiment. Weíre hoping to get a better handle on the behaviour of antimatter as opposed to ordinary matter. We think there must have been some difference to give rise to this asymmetry which has allowed our universe to exist in the one state today.

Chris - Where do you think all the antimatter has gone? Is it just all jostled somewhere or is it in some other dimension that we canít see?

Tara - Thatís the $100,000,000 question, isnít it? I wish I knew the answer to that. We donít know basically. Thatís why we built the experiment. Thatís why weíre doing our research. We donít know if thereís some peculiarity in the behaviour of antimatter which means that it decays more quickly than normal matter. Thatís why it all seems to die out more quickly in the known universe. There are theories around that I donít even pretend to understand which say we could have antimatter in alternative, parallel universes. Thatís where it all went and we just happen to be in a parallel universe where thereís only matter. There are many hypotheses but little experimental evidence to pin down the explanation.


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