So about a year ago, physicists at CERN announced the discovery of the Higgs boson (or more technically, a “Higgs-like particle” that has now been confirmed to be the Higgs) in the LHC. And you probably haven’t heard much about the collider since then. Part of that is because the the discovery (or non-discovery) of the Higgs at the energies the LHC was probing at was one of the biggest tests of the Standard Model of Particle Physics, which was one of the major selling points of building the LHC in the first place. And since February of this year, the LHC has been shut down to allow for technical improvements that will turn it into an even more energetic detector (and in particle physics, the more energetic you are, the more you can see). If you’re really tuned into CERN, you may know that in November of last year, researchers announced observations of a rare kind of meson decay into muons (which are like heavier electrons).
But part of the reason also seems to be that the results from before the shutdown don’t give physicists much new to theorize on. The Higgs boson was discovered to have the mass predicted by the Standard Model, and so served as a great test of that. But that also means it doesn’t really offer anything new for theorists. And though the muon decay hasn’t been verified yet to the statistical significance that particle physicists consider to mean a discovery, what has been found so far still fits into the Standard Model. Neither of these findings fit into most of the common models of supersymmetry, which is believed to be a necessary component of string theory, which is currently the dominant idea to go beyond the Standard Model to a “theory of everything”.
The stakes for various new physics that researchers hope to find at the LHC.
As a physics major, I feel contractually obligated to have a post about the Higgs boson since that has dominated science news for the last week. But I honestly feel a bit unprepared for this, because my concentration was applied physics, and I decided to take electrical engineering courses instead of particle physics. So while I know what things like bosons ARE, I can’t really work out all the math that goes into this stuff. But one thing I do understand is energy. And if you’re privy to Einstein, you may realize that means I can claim some understanding of mass.
If you’ve read some of the several thousand Higgs articles (if I had intentionally set myself for some pun based on “particle”, I would be so awesome right now) written this week, you’ve probably heard something about the Higgs boson and/or field being responsible for all mass, based on something like this analogy. If you’ve also checked physics blogs or sites, you may have noticed there’s a big asterisk to that statement. The Higgs field, if the Standard Model of Particle Physics is right, is responsible for the mass of all elementary particles, which is a much smaller set of things than all mass in a universe of composite particles.
For what you see in everyday matter, the Higgs only affects quarks and electrons. Quarks are the elementary particles that make up protons and neutrons, which you might remember from chemistry or physics. For those catching on to particle physics’ wonderful naming scheme, you might be wondering how a “composite” can have more mass than the elementary particles it is made of. This is where Einstein kicks in. Quarks are held together in protons and neutrons through an interaction called the strong force. This force (here’s that wonderful naming scheme again) is quite strong. Forces carry energy, and Einstein proved that energy E is equal to mass (m) times the speed of light (c) squared. The energy from the strong force holding a neutron or proton’s components together and energy from quarks moving around actually makes up about 90% of the mass we measure for protons and neutrons.
The strong force is actually kind of notorious for its high energy. It’s also weird because the strong force actually gets stronger as quarks move farther apart and weaker as they get closer. This leads to another interesting phenomena with quarks: it’s practically impossible to observe an individual one. If you try to pull quarks apart from each other, at a certain distance, quark and anitmatter quark pairs form from the energy of the strong force between the original quarks, because it can actually take less energy (in the form of mass) to have more quarks than to have the strong force between two or three highly separated quarks. The common analogy is that of a rubber band. If you stretch a rubber band past a certain point, you end up with two (albeit broken) rubber bands.