6 March 2013
A question of spin for the new boson
Physicists speaking today at the Moriond conference in La Thuile, Italy, have announced that the new particle discovered at CERN last year is looking more and more like a Higgs boson. However, more analysis is still required before a definitive statement can be made. The key to a positive identification of the particle is a detailed analysis of its properties and the way that it interacts with other particles. Since the announcement last July, much more data has been analysed, and these properties are becoming clearer.
The key property that will allow us to say whether or not it is a Higgs particle is called spin. If this particle has spin-zero, then it is a Higgs particle. If not, then it is something different, possibly linked to the way gravity works. All the analysis conducted so far strongly indicates spin-zero, but is not yet able to rule out entirely the possibility that the particle has spin-two.
"Until we can confidently tie down the particle's spin," said CERN Research Director Sergio Bertolucci, "the particle will remain Higgs-like. Only when we know that is has spin-zero will we be able to call it a Higgs."
Even then, the work will be far from over. If the new particle is a Higgs, it could be the Higgs as predicted in the 1960s, which would complete the Standard Model of particle physics, or it could be a more exotic particle that would lead us beyond the Standard Model. The stakes are high. The Standard Model accounts for all the visible matter in the Universe, including the stuff that we are made of, but it does not account for the 96% of the Universe that is invisible to us - the dark universe. Finding out what kind of Higgs it is will rely on carefully measuring the particle's interactions with other particles, and that may take several years to resolve.