What’s the matter?

Posted on January 13, 2012


Large Hadron Collider bAs mentioned in our brief look at the news, there are signs at the Large Hadron Collider in Geneva that the Higgs boson may have been found and that it may be unexpectedly light, at around just 125 GeV.This is not the only news from the LHC thoughand it seems also that they may have spotted that “special something” that means we have more matter today than we have anti-matter drifting about the universe. While the Higgs may have turned up in the two main detectors at the LHC, in the ATLAS and the CMS detectors which keep some 5,000 researchers happily employed this new result is from the much smaller group of 600 or so working on the LHCb device.

LHCb ExperimentFrom their studies, there seems to be a surprising and highly relevant difference in the decay rates of the short-lived particles known as mesons – made up of pairs of quarks. To be specific, they measured the decay rates of D0 mesons and their anti-matter equivalents known as anti-D0 mesons.

These can both decay into a couple of lighter mesons each, making a pion and an anti-pionor a kaon and an anti-kaon. According to the standard model of subatomic particles, it should not matter if the starting particle is a D0 or an anti-D0 meson – the chance of getting a pion / anti-pion pair should be pretty much the same in both cases, as should the chance of getting a kaon / anti-kaon pair. That makes it pretty easy to check by subtracting one from the other for both D0 and anti-D0 mesons – which is what the team did.

Interactions

Standard Model Interactions

If the decay rates were the same what you should get is, of course, a fat zero – nice and easy to spot. But it isn’t. There appears to be a difference of about 0.8% says Mat Charles of the University of Oxford. While it may seem tiny, that is about eight times bigger than could be expected from the standard model (see Physical Review for details).

Like the Higgs detection results, this work also has a stastical significance that puts it firmly in the realm of just-maybe: in this case a significance of 3.5 sigma or about one chance in 2,000 of being a fluke. So, like the Higgs work, this is also being checked to see if the results vanish into a mathematical fog.

Most interestingly, like the Higgs announcement, this work also puts a new and positive light on the possiblility of confirming certain aspects of super-symmetry which is fast becoming a serious contender to replace the standard model. Whatever these results mean, if true, the LHC has certainly lived up to its early expectations and is producing some fascinating results.

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