Particle physicists wowed the globe a decade ago. The Higgs boson, a massive, transient particle essential to their enigmatic explanation of how other fundamental particles acquire their mass, was discovered on July 4, 2012, according to 6000 researchers working with the largest atom-smashing machine in the world, the Large Hadron Collider, at the European particle physics laboratory. The discovery propelled scientists into the public eye, finalized the standard model theory, and confirmed a 45-year-old forecast.
Then there was the extended hangover. Physicists were concerned that the 27-kilometer-long ring-shaped Large Hadron Collider (LHC), which began collecting data in 2010, would only create the Higgs and nothing else, giving no clue as to what lay beyond the standard model. So far, the worst-case scenario has come to pass. Barry Barish, a physicist at the California Institute of Technology, admits, “It’s a little disheartening.” “I thought we’d find supersymmetry,” says the standard model’s leading extension.
Many physicists believe it is too early to be depressed. After three years of modifications, the Large hadron collider is finally ready for the three of five scheduled runs, and among the billions of proton-proton collisions it will generate every second, a new particle could emerge. In reality, the Large hadron collider should be able to run for another sixteen years and collect 16 times as much data as it already does with subsequent upgrades. All of these data could point to the presence of new particles and phenomena.
However, some physicists believe that collider physics is doomed. “If they don’t find anything, this field will die,” Juan Collar, a physicist at the University of Chicago who searches for dark matter in smaller experiments, says. Expectations of an immediate breakthrough have given way to the prospect of a long, uncertain journey toward discovery, according to John Ellis, a theorist at King’s College London. “It’ll be like extracting teeth rather than teeth coming out.”
The standard model has been battling with physicists since the 1970s. Ordinary matter, according to this theory, is made up of lightweight particles called up quarks and down quarks, which connect in trios to form protons and neutrons, as well as electrons and featherweight particles known as electron neutrinos. In particle collisions, two sets of heavier particles linger in the vacuum, waiting to be shot into life. The photon carries the electromagnetic force, the strong force binds quarks via the gluon, and the weak force is carried by the hefty W and Z bosons.
Everything scientists have seen at particle colliders so far is described by the standard model. It cannot, however, be the final hypothesis of nature. It excludes the force of gravity, as well as unexplained, unseen dark matter, which appears to outnumber regular matter six to one in the cosmos.
That was supposed to be broken by the LHC. The LHC is able to create particles that are too large to be created anywhere else because the protons in its ring clash at an energy that are roughly seven times higher than at any previous collider. Many physicists imagined finding new force-carrying particles or perhaps mini–black holes in a matter of years a decade ago. “In supersymmetric particles, one would drown,” says Beate Heinemann, director of particle physics at DESY in Germany. Physicists thought that finding the Higgs boson would take longer.
Instead, the Higgs was discovered in just three years, thanks to the fact that it is less massive than many scientists thought, weighing roughly 133 times the mass of a proton, making it easier to make. No other new particle has been discovered in the ten years since that ground-breaking discovery.
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