On July 4, the director of CERN, Europe’s particle physics laboratory near Geneva, announced to the scientific community: “We have a discovery.”
The finding is described as the final piece of the subatomic puzzle called the Higgs boson responsible for transferring mass to other subatomic particles. Determining how particles acquire mass is essential for understanding how they interact to form atoms, which in turn interact to become ourselves and the complex world we see around us.
About a hundred journalists also were on hand for the announcement so the discovery received wide coverage in the popular press. But the coverage that I read conveyed little about how the Higgs was found, why it took so long to find, how confident CERN is that it is the Higgs or what the next research steps might be. I will fill in some of that information for readers who are interested but do not read scientific journals.
Experimental verification of the Higgs was obtained from data generated by the Large Hadron Collider at CERN – the European Organization for Nuclear Research, (the acronym is from the name in French). The LHC allows beams of subatomic particles, in this case protons, to collide at high speeds creating a shower of both known and new particles, including a class of particles called bosons.
Out of this spray of tracks, two independent detectors at the LHC found convincing evidence for a boson of the right type to be the Higgs. The next step will be to ascertain if it is exactly like the one described in theory, or possibly something more exotic. But before discussing future research possibilities, a little background is needed.
The leading theory of how the subatomic world works, called the Standard Model, contains 12 elementary particles (depending on how you count), and four gauge bosons that transfer forces to the particles allowing them to interact. All the particles and bosons in the current model have been experimentally verified, but two major unknowns have remained: how particles acquire their mass, and how gravity interacts with the other forces? I will leave gravity aside for this discussion because the CERN discovery refers only to the first unknown.
In 1964, Peter Higgs a Scottish physicist, addressed the first mystery by hypothesizing that a field that permeates all space endows particles with their mass. Fields are a fundamental part of modern physics and can be thought of similar to a magnetic field that causes iron filings to line up. In the quantum world, a field also can be expressed mathematically as points or particles in the field. The Higgs hypothesis holds that the mass of each particle in the Standard Model is a measure of how strongly it is coupled to the Higgs field. The 83-year-old professor Higgs was on hand for the announced finding.
The Higgs is classified as a boson, but it is not like a gauge boson that transfers a force. The fact that it transfers mass makes it a unique type of element in the Standard Model, and partly explains why it took almost half a century to detect and why it is hard to verify once detected.
First, the boson was projected to be very heavy (it turned out to be 130 time as heavy as a proton). Experimentally detecting a particle that size requires protons to collide with each other close to the speed of light. The LHC, which was brought on line in 2010, was the first accelerator capable of creating those speeds. The LHC is enormous, and is housed in an underground doughnut-shaped tunnel 17 miles in circumference straddling the French/Swiss boarder. Protons travel in opposite directions around the circle and then collide.
Further complicating the search is that Higgs bosons are unstable and will almost instantly decay into different combinations of other particles when the protons collide. So the search was not to observe the boson directly, but to analyze the array of particles resulting from the collision to determine if any are the telltale track of the short-lived Higgs. That involved sifting through thousands of trillions of collisions.
Finally, the statistical requirement imposed for concluding that the detected array was not a statistical fluke was 1 in 3 million. Such a high level of confidence was demanded because the search is about establishing an essential link in our understanding of the universe.
While the new boson seemed to waddle and quack like the sought-after Higgs, it remains to be seen if it is exactly like the one predicted by the Standard Model. The evidence so far is equivocal. There are several theoretical alternatives, and many physicists would welcome an exotic new Higgs. It would open up the search for other unknowns not now addressed by the Standard Model such as why the universe is composed predominantly of matter and not antimatter, or what is dark matter whose presence now can only be deduced from its gravitational pull. The history of science tells us that those hoping for a new Higgs will most likely get their wish.
Reach Garth Buchanan at firstname.lastname@example.org.