Searching for SUSY

The CMS collaboration has so far seen no evidence of sparticles. (Courtesy: CERN/Michael Hoch)

By Matin Durrani

The first full year of data-taking at CERN’s Large Hadron Collider (LHC), which is now drawing to a close, has been a wake-up call for supersymmetry (SUSY) – a theory that has captivated physicists (or at least some of them) for the last 40 years.

SUSY’s central prediction – that for each of the Standard Model particles there exists a heavier “sparticle” sibling – remains firmly in the realm of imagination.

Quite simply, no firm evidence for SUSY has yet emerged, despite its aficionados claiming it’s been round the corner for the last 20 years.

But SUSY’s supporters remain undeterred.

In article in the December issue of Physics World magazine by science writer Matthew Chalmers, Savas Dimopolous of Stanford University insists “it’s very early to draw conclusions”, with Nobel laureate David Gross of the Kavli Institute for Theoretical Physics in Santa Barbara saying supersymmetry’s “alive and well”.

Whether evidence for SUSY emerges at the LHC partly depends on if – and where – the Higgs boson shows. If the Higgs weighs in at about 120 GeV, then “it really smells like SUSY”, according to Oliver Buchmuller of the CMS experiment at the LHC. A Higgs heavier than about 135 GeV could see SUSY running into trouble.

As Chalmers points out, for most physicists, the discovery of SUSY would be more remarkable than that of the Higgs. After all, the Standard Model of particle physics has withstood 35 years of tests at six or more decimal places, suggesting that the Higgs or something like it pretty much has to turn up at the LHC. “SUSY, by contrast, is more a well-founded hope”, writes Chalmers, and “the non-discovery of SUSY or something like it would just leave thousands of physicists felling gutted…and weaken the case for another multi-billion dollar collider”.

All eyes are now on an upcoming meeting at CERN on 12 and 13 December, at which results from the full 2011 dataset are due to be presented and discussed. The key sessions on the Higgs searches are set to take place at 2 p.m. local time on 13 December, featuring talks by Fabiola Gianotti of ATLAS and Guido Tonelli of CMS.

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