"Spin Doctors" Are Working on the Higgs Boson Question
Physicists announced today, speaking at the ongoing Moriond conference in La Thuile, Italy, that the new particle discovered at CERN last year that is most likely the Higgs boson is looking more and more like the real thing. However, more analysis is still required before a definitive statement can be made. One of the most important properties that it should have is spin-zero, as opposed to "spin-two". A positive identification of the particle is also possible through a detailed analysis of the way that it interacts with other particles.
"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."
The newest data is convergent toward the conclusion that the long-sought particle does exist and with the expected properties, and more results will be presented over the upcoming weeks. In time, particle physicists hope that it will once and for all close an important chapter in physics called the Standard Model (SM).
The announcements were made by more than 15 scientists from CERN on March 6 via a live webcast from an annual particle physics forum that has been held in La Thuile, Italy, since 1966.
If the particle turns out to not have spin-zero, it would have to be 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.
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.
A way to do this is to predict the strength with which the Higgs couples to other elementary particles, in the process giving them mass. This is done by analysing the data to infer the rates at which the Higgs-like particle decays into known lighter particles: W and Z bosons, photons, bottom quarks, tau leptons, electrons, and muons. These particles' signatures are then picked up by detectors to infer that a Higgs-like boson decayed into them.