Should we worry about what the LHC is not finding?
By Richard Webb in Grenoble The Higgs boson is still missing – but perhaps we should be more worried about what else the Large Hadron Collider hasn’t found yet. That’s the main message to come out of a conference in Grenoble, France, this week, where physicists have gathered to chew over the first results from the world’s most muscular particle smasher, sited at CERN near Geneva, Switzerland. Finding the Higgs would complete the “standard model”, our best stab yet at explaining the fundamental particles and forces of nature. But we already know that some weighty questions, such as the relationship between the strengths of different forces in the cosmos, or the nature of the dark matter thought to make up about three-quarters of its mass, lie beyond the standard model’s scope. To answer these questions, physicists look to a grander construction known as supersymmetry. Supersymmetry proposes that every particle predicted by the standard model has a meatier cousin that turns up only at extremely high energies. But the LHC has not found any such super-particles. “Squarks” and “gluinos”, partners of the standard-model quarks and gluons, have been ruled out at energies up to 1 teraelectronvolts (TeV), according to an analysis of the LHC’s first year of collisions. That is just the range in which the simplest family of supersymmetric models predicts these particles should be found. More energies and more complex models remain to be explored, but “the air is getting thin for supersymmetry”, says Guido Tonelli of the LHC’s CMS collaboration. At the same time, there is no sign yet of gravitons – particles that transmit gravity and are essential for a quantum theory of the force – below an energy of 2 TeV. The missing particles leave some physicists wondering whether they have been asking the right questions up to now. But Rolf-Dieter Heuer, CERN’s director general, counsels against hasty conclusions. With the machine still ramping up to full power, the LHC has produced just one-thousandth of the data it eventually should deliver. “Something will come,” he says. “We just have to be patient.” In the case of the Higgs boson, at least, he’s confident that something will come sooner rather than later. The LHC has already found the first tantalising glimpses of what might turn out to be this elusive particle, but more findings are needed to confirm or deny its existence. “We will have answered the Higgs’s Shakespeare question – to be or not to be – by the end of next year,” Heuer predicts. More on these topics: