Have we found the Higgs?

Physicist Peter Higgs stands in front of the CMS detector in 2008. This is generally conceded by all to be the only definitive observation of a Higgs in CMS. Photo: CERN

The Higgs boson has been found, right? You know this because you’ve heard it about it on the radio. If only it were that simple. Fermilab Today readers know to be more cautious.

The CMS experiment has long been feverishly working to find the Higgs boson. It is only due to editorial oversight that I restrain myself from using a long range of extreme superlatives to describe the performance of the LHC, the CMS detector and the analyzers working on the Higgs boson analyses. (Although words like unreal, amazing, and crazy-awesome all fit very well.) Using the 2012 data set (already larger than all the data recorded in 2011), combined with the 2011 data set (taken at a different energy), all analyzed almost the instant it was recorded, the CMS collaboration employed a breathtaking set of complex algorithms, all aimed to find the Higgs boson. To ensure that the measurement wasn’t tainted by the analyzers’ expectations, it was done “blind,” which means that the analyzers were forbidden to look at the data until the analysis techniques were developed and finalized. This was done by optimizing the procedures on data in regions in which the Higgs boson was ruled out. This approach meant the techniques were developed using data – and not just calculations – but data that didn’t color the final result. It was especially important given that the 2011 data gave hints of a discovery, and it would have been easy to let that information guide our thinking.

After intense scrutiny from the most skeptical members of the CMS community of some 3,000 scientists, the results were announced to the world in the early morning hours of July 4. This date was chosen to be able to both make the announcement at CERN and open the ICHEP conference, held in Melbourne, Australia. ICHEP is one of the most widely anticipated conferences of 2012 and one in which the first LHC results at 8-TeV collision energy was to be announced. These requirements explained the bleary-eyed reporters, physicists and science enthusiasts sitting in Fermilab’s One West.

Both CMS and ATLAS announced their results. CMS announced that we discovered a new boson with a mass of 125 GeV (133 times heavier than a proton). ATLAS then announced that they saw a new boson with mass about 126 GeV. Some context is in order. First, the significance of the CMS result is high (as is the ATLAS result). If our estimates of our uncertainty are correct, there is only 1 chance in 3.5 million of seeing this result if there were no new physics. The fact that there are two independent experiments is crucial as it greatly reduces the chances of a mistake that would be misinterpreted as a discovery. If both experiments see the same thing, you can be more confident that it is real.

However…and this is important…we don’t know if what we’ve seen is the Higgs boson. The Higgs boson is predicted to have specific properties, like a certain charge, a certain spin and a certain set of specific decay patterns (with specific ratios). The data thus far is NOT enough to definitively state that what has been observed is the Higgs boson predicted in 1964. It looks like a Higgs boson, but the final page in this saga has yet to be written.

—Don Lincoln

Joe Incandela of the University of California, Santa Barbara, has led CMS since January 2012. He represents the approximately 3,000 physicists who worked together to accomplish this exciting measurement. Photo: CERN
CERN Director General Rolf Dieter Heuer has presided over one of the most exciting times in CERN history. (And, given CERN’s very successful half-a-century scientific program, that’s saying something.) Photo: CERN