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Higgs particle seems to exist


http://t3.gstatic.com/images?q=tbn:ANd9GcSLG3M0gZsrCfGEzxQkwVFIn2IDC4rfY2Tvn_I0rEQAuwAOg0BTVwIt looks like there will be a major announcement on Wednesday July 4th regarding the existence of the long postulated particle the Higgs boson of the Standard Model. Its existence had been conjectured in the mid 1960s. I’ve read several articles including some from prominent blogs maintained by top physicists in the area, and here is briefly what I gather from them:

1. The Higgs particle exists.

2. But some of its observed decay properties are at variance with those predicted by the Standard Model (the leading theory in Particle Physics) — and apparently significant. Particularly in the decay rates of the Higgs into two photons and into WW particles. The other decays seem to agree with theory.

3. The evidence for the Higgs particle is still indirect — in that they cannot see it directly, but they do see its ‘footprints’.

4. The evidence for its existence would appear to have risen to around a 4 sigma level of confidence (or maybe a little more?), which is about 99.99% certainty. In December 2011, the data back then allowed for a 3 sigma certainty, which is 99.7% confidence level. To be considered a discovery in Physics the criterion is to attain 5 sigma confidence — 99.9999%. (See the little table below for what these sigmas, or standard deviations, are.)

5. The Higgs mass is around 125 GeV. (Pretty heavy! About 133 times  the proton mass!)

6. Several independent experiments (at CERN and in the US) seem to be in general agreement.

So it looks like the Higgs exists but not quite exactly the one predicted. However, the experts will make the announcement on Wednesday. It is notable that they chose to announce on July 4th as well as having invited 5 key physicists, including Peter Higgs (shown in the photo here), to the event.

What do these sigma’s mean?  Basically, statistical degrees of certainty. Briefly,
1 sigma = 67% certainty;
2 sigma = 95% certainty;
3 sigma = 99.7% certainty (considered good evidence but not a discovery);
4 sigma = 99.99% certainty
5 sigma = 99.9999% certainty (considered ‘certain’ or a discovery).


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