The 'Sharpest Picture Yet' of the Higgs Boson
Two experiments at the Large Hadron Collider combine forces to give new precision to the elusive particle's properties.
CMS, one of the detectors used for this work. Image: CERN/Wikimedia
Over three years ago, researchers announced the discovery of the Higgs boson (or a "particle consistent with the Higgs boson," depending on how careful you're being). It was a long-sought key part of the Standard Model—the overarching theory of how fundamental particles interact—that had until then proved elusive.
But the Higgs didn't just pop out of the Large Hadron Collider and reveal all its secrets at first glance. On Tuesday, CERN (the European Organisation for Nuclear Research, best known for being the home of the LHC) reported the latest measurements of the particle, which it says give the "sharpest picture yet of this novel boson."
The new results shed greater light on how the Higgs is produced, decays, and interacts with other particles, and were presented at this year's Large Hadron Collider Physics Conference in St. Petersburg. They come from two of the major experiments around the collider, ATLAS and CMS. It's the first time the two groups have combined their analyses of many of the particle's properties, following their work earlier this year to give the best measurement yet of the Higgs's mass.
The Large Hadron Collider restarted at higher energies than ever in summer 2015, but this work uses data from its first run (it takes a lot of time to crunch the massive amounts of data from the world's largest particle collider).
So what do the new results tell us? Well, for a start, they're consistent with predictions from the Standard Model, so we don't have to figure out some "new physics"—physics beyond the scope of the Standard Model—just yet. CERN explains, however, that measuring the particle's properties in such detail means they can be used as a reference in the future.
The new results specifically look at the rates of how the Higgs boson decays into other particles. CERN writes that, "By combining their results, ATLAS and CMS determined with the best precision to date the rates of the most common decays."
It adds that this is essential to understanding the nature of the Higgs, as "Any deviation in the measured rates compared to those predicted by the Standard Model would bring into question the Brout-Englert-Higgs mechanism and possibly open the door to new physics beyond the Standard Model." The Brout-Englert-Higgs mechanism essentially explains how other fundamental particles have mass, so it's pretty important for our broader understanding of particle physics.
In a statement, CERN Director General Rolf Heuer said that combining the ATLAS and CMS experiments was necessary to reach this level of precision and would have taken two more years for a single experiment.
On the ATLAS site, spokesperson Robert McPherson said that, "With every new analysis, our understanding of the Higgs boson and the Standard Model continues to grow."
"As a result, these precise new measurements will be great tools in the search for 'New Physics,' helping ATLAS look for possible deviations from SM [Standard Model] predictions."