Early this morning, CERN held a press conference to announce the latest results from its quest to find the Higgs boson, the very last unobserved particle that makes up the Standard Model of physics. The announcement included "strong indications for the presence of a new particle," but is it the Higgs? We'll take you through it from start to finish.
What CERN Found
Here's how the CERN scientists describe the discovery:
"We observe in our data clear signs of a new particle, at the level of 5 sigma, in the mass region around 126 GeV." -ATLAS experiment spokesperson Fabiola Gianotti
"The results are preliminary but the 5 sigma signal at around 125 GeV we're seeing is dramatic. This is indeed a new particle. We know it must be a boson and it's the heaviest boson ever found." -CMS experiment spokesperson Joe Incandela
And here's what CERN is seeing:
The curve on this graph represents the number of decay events at specific energy levels that physicists expect to see when they smash protons together in the LHC. That little bump? That's where there CERN has seen a significant number of unusual events at about 125 GeV that means that something new is going on.
Now, the "5 sigma signal" referenced by CERN means that scientists are 99.9999% sure that the thing they're looking at is a new particle and not something else, and 5 sigma is the standard for declaring that a new particle exists. Technically, today's results are at a 4.9 sigma level, which is just under that. The particle itself was spotted at an energy level of 125.3 ± 0.6 GeV, which is "in agreement with the standard model [Higgs boson] at 95% confidence range."
Why So Cautious?
CERN pointedly stops just short of saying that it's found the Higgs boson, instead saying that there is "strong evidence" for the discovery of "a particle consistent with the Higgs boson."
What we know for sure is that CERN has almost definitely found a new particle. It's a boson. It's very heavy, and it's in the place where the Higgs boson should be. But proving that it's the Higgs is going to take more work, and being scientists, CERN doesn't want to make any assumptions. CERN heavily stressed that its announcement today consists of preliminary results, because it hasn't had time to completely analyze all of the data that the LHC has collected.
What Happens Next
Publication of the results announced today is expected around the end of the month, and CERN says that "a more complete picture of today's observations will emerge later this year after the LHC provides the experiments with more data."
If CERN publishes in late July that it's found the Higgs, why are they going to keep running the experiment? Well, it's one thing to find the Higgs, and it's another thing to figure out its properties. There are two ways that things could go from here: either further experiments will show that the Higgs has all of the properties that we expect it to have, or experiments will show that the Higgs has some weirdness going on that might help explain some of the things that the Standard Model can't. As CERN says:
"Standard Model describes the fundamental particles from which we, and every visible thing in the universe, are made, and the forces acting between them. All the matter that we can see, however, appears to be no more than about 4% of the total. A more exotic version of the Higgs particle could be a bridge to understanding the 96% of the universe that remains obscure."
The sense you get here is that particle physicists are not-so-secretly hoping that analysis of the Higgs will reveal some exotic secret sauce, opening the door to new physics and making up for some of the shortfalls of the Standard Model. And whatever happens with the Higgs analysis over the next few months, the LHC will keep on smashing protons together to see what more it can reveal about the universe.