Rare particle decay is bad news for exotic physics

Click on image to enlarge it (Image: CERN)

The two red lines seen emerging from the smoosh of particles above may look like the highly sensitive antenna of a strange organism, but they are actually the distinctive calling card of an incredibly rare particle transformation.

Physicists who work on the Large Hadron Collider at CERN, near Geneva, Switzerland, today confirmed that they had seen a particle called a B_s meson decaying into two muons. The latter are represented by the red lines above.

A signal that looked like this rare decay was glimpsed for the first time last year. On that occasion there were hints that around 1 in every 300 million B_s mesons decays this way, matching the predictions laid out in the standard model of particle physics, our leading theory of particles and forces.

Now the LHCb and CMS detectors at CERN have seen more decays and are able to confirm that this is the rate of decay of a B_s meson. That is good news for CERN's high-precision instruments, but bad news for those looking for signs of supersymmetry, an extension of the standard model which says all particles have a heavier partner.

That is because many supersymmetric models predict a higher rate of B_s meson to muon pair decay than suggested by the standard model, so these new observations count against those theories.

As scientists are finding with the Higgs boson, discovered at CERN last year, new physics can be hard to come by at the LHC.

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