Sunday, December 18, 2011

Searching for the Higgs boson

The Standard Model of particle physics describes the interaction of subatomic particles. You probably know all about atoms. An atom has a protons, neutrons, and electrons. Subatomic particles are the even smaller pieces of matter that make up what was once thought as the smallest piece of matter.

The Standard Model describes 16 different particles:
QuarkDS9.jpg
No, no, no...not THAT Quark


We have experimental evidence of all of these particles. The Higgs boson is a yet to be seen particle proposed in 1964 by British physicist Peter Higgs. Under the Standard Model, the Higgs boson would have to exist to explain why certain types of bosons (called W and Z) have mass but photons - which are also bosons - do not have mass1.

Fast forward from Peter Higgs to present day. You may have heard of the Large Hadron Collider (LHC). The LHC is arguably the most expensive, impressive, and...well, most awesome experiment ever. It has a 17 mile circumference, cost 6.4 billion dollars, and caused a big panic that the world was going to end (it didn't).

The LHC was built, in part, to look for the Higgs boson. Physicists have been looking since 2009, but this week a major announcement was made. I'd like to say, as this overconfident blogger, that the Higgs boson has been found, but I don't think it's quite the time for that celebration.  However, some really compelling evidence has surfaced in favor of the elusive Higgs. The two following quotes came this week from researchers at CERN:
"We have restricted the most likely mass region for the Higgs boson to 116-130 GeV, and over the last few weeks we have started to see an intriguing excess of events in the mass range around 125 GeV. This excess may be due to a fluctuation, but it could also be something more interesting."  - ATLAS experiment spokesperson Fabiola Gianotti 
"We cannot exclude the presence of the Standard Model Higgs between 115 and 127 GeV because of a modest excess of events in this mass region that appears, quite consistently, in five independent channels. The excess is most compatible with a Standard Model Higgs in the vicinity of 124 GeV and below but the statistical significance is not large enough to say anything conclusive. As of today what we see is consistent either with a background fluctuation or with the presence of the boson." - CMS experiment Spokesperson, Guido Tonelli
That may not sound like a very big deal. Each group found evidence of what may be the Higgs boson, but it is a very small signal that could just be noise. What makes this interesting is that two independent groups saw the same signal. It's not enough to say we've found it yet, but it's some very exciting news (at least for nerds like me).
Notes
[1] It is a really weird thing to think that photons (light) do not have mass but they do have momentum - which is usually described in physics as mass times velocity.

Further reading
 A BBC News articles: Here
CERN Press releases: Here and Here
A Nature article: Here