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Supersymmetry takes an arrow to the knee

Hiding places get narrower

Particle collision in the Large Hadron Collider

Supersymmetry isn’t quite dead yet, but the latest results out of the Large Hadron Collider are giving it some trouble.

A theory that’s been around since the 1960s, supersymmetry proposes that all fermions (the fundamental particles of matter) have corresponding bosons (the carriers of basic forces). At the moment, including the Higgs, there are five boson types, which doesn’t match the 12 fermion types that exist.

As this BBC piece notes, one attraction of supersymmetry is that as-yet-undiscovered and very massive particles would account for some of the universe’s dark matter. For example, a galaxy spinning faster than it should given what we know about its mass might contain particles from the “supersymmetry zoo”, giving it the right mass.

The problem is that the LHC outputs are increasingly eliminating the mass levels at which supersymmetry may exist. In the latest work, detailed at the Large Hadron Collider conference taking place in Kyoto, a new BS Meson decay rules out one of the proposed energies for supersymmetry.

New Scientist explains the importance of the BS interaction here.

Put simply: the frequency of a particular decay, from BS into a pair of muons provides what the LHCb people call an important “bench test” of supersymmetry. The Standard Model predicts one rate at which the decay will be observed; supersymmetry predicts that the decay would be observed more often.

The reason that the test hasn’t been applied before is that you need an awful lot of data to test something that only occurs a handful of times in a billion.

In the Kyoto presentation, Johannes Albrecht of LHCb said the collider had set the decay rate to once for every 300 billion BS mesons, in close agreement with the Standard Model.

New Scientist quotes Albrecht as saying “This measurement certainly further shrinks the allowed parameter space for SUSY, but unfortunately, one cannot fully rule out SUSY,” says Albrecht.

However, since some supersymmetry models permit the one-in-three hundred billion decay rate, the LHC boffins will have to keep chipping away at the problem. ®

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