Monday, November 12, 2012

Supersymmetry dealt a blow

The popular physics theory of supersymmetry was dealt a blow by the publishing of a crucial paper by CERN. Physicists who work at the Large Hadron Collider (LHC) look at specific particles, which are unstable. This just means that they split into smaller particles as they decay. Of course, there are many different kinds of smaller particles into which the larger particle can split. Some of the decays rarely happens.

According to the standard model, the decay in the question only happens in three out of 109 B-decays (A B-decay is a decay where a B-meson decays. A B-meson is a particle consisting of a anti-bottom quark and an up, down, strange, or charm quark). The fraction of all decays that lead to a particular final result is also called the branching ratio. So of all the possible decays that the B-meson can do, only 3 x 10-9 of the decays lead to the decay in the paper. Actually, they treat two different B-decays, but the branching ratio of both of them is in the order of magnitude ~10-9 - 10-10. According to Supersymmetry, the branching ratio of these decays is much higher.

What this all comes down to is if we have a billion of the large particles, only one of them splits into a certain combination of smaller particles. Thus, we say that the chance for that certain decay is one in one billion. The article is about one particular kind of decay.

Now, different theories have different chances for that particular decay of happenings. In the standard model, that is one in one billion. In super symmetry, it's maybe one in one million. That means it happens a thousand times more often.

Sometimes, scientists don't know whether a decay actually happens at all. But down at LHC, they've found the decay, so they know it happens. But they've only found it once out of maybe a billion other decays.

While this decay happens rarely, it happens many times in LHC. What's new with this publication is that they are now fairly certain that the amounts of decays they detect aren't some kind of freak accident or a problem with the test. The probability that background processes can produce the observed number of decay candidates is 5x10-4 and corresponds to a statistical significance of 3.5 sigma. That is that if they did the same experiment 5x104 times, one of them would be wrong.

This all comes down to that the standard model predicts that one in one billion decays is that particular decay, but super symmetry predicts maybe a thousand in one billion decays is that particular decay. So, according to SUSY, this decay should have happened many more times than this single one they've found. This means that right now, the standard model seems correct and super symmetry has something wrong.

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