In “Celebrations as Higgs boson is finally discovered” (New Scientist, 04 July 2012), Celeste Biever enthuses,
There’s a 5-in-10 million chance that this is a fluke. That was enough for physicists to declare that the Higgs boson – the world’s most-wanted particle – has been discovered. Rapturous applause, whistles and cheers filled the auditorium at CERN, near Geneva, Switzerland.
True, but that’s not the highest level of certainty they were aiming for, and the announcement said “Higgs boson-like particle.”
Cause for celebration, certainly, but we might wish to find out what exactly we are celebrating. Right now it feels like celebrating someone’s birthday without knowing how old they are, exactly.
In “Gotcha! Higgs find will kick off new era of knowledge” (New Scientist, July 2012), Lisa Grossman offers a clearer picture:
Last December, the twin Higgs-hunting experiments at the LHC – CMS and ATLAS – reported shards suggesting a Higgs with a mass of around 125 gigaelectronvolts, but they were not statistically significant enough to claim a discovery. The convention is to declare victory when the statistical significance of a particle’s signal is 5 sigma, meaning the chance of something else producing it is less than one in a million. December’s signals were each about 2 sigma.
They did not find 5 sigma certainty, but they can work, in principle, with what they have found.
Perhaps it’s a bit like the detective who hopes to place the principal suspect at the scene of the murder – and has got as far as placing him in the back yard just before the murder. Does the detective want more certainty? Yes, because he can be sure that the court will. Can he work with what he has got? Yes, certainly.
In “Physicists declare victory in Higgs hunt” (Nature, 04 July 2012), Geoff Brumfiel clarifies, “Researchers must now pin down the precise identity of their new particle”:
The ways in which the new particle interacts with other particles is consistent with what was expected for a Higgs boson, although further measurements will need to be made to pin down its identity. In particular, physicists will want to determine whether the new boson has zero spin as predicted, according to Incandela.
The way in which the new particle decays into other particles will also be key to verifying its precise nature. Already, the new boson seems to be decaying slightly more often into pairs of gamma rays than was predicted by theories, says Bill Murray, a physicist on ATLAS, the other experiment involved in making the discovery. But, he is quick to add, the data are still very preliminary.
And there is work to be done.