Category: Particle physics

July 4th, 2012 will go down in history as one of the most significant days in science history, and certainly of the last few decades. A new particle consistent with the long-sought Higgs Boson has been discovered at the Large Hadron Collider. Leading up to this discovery, I had been keeping up with various particle physics blogs, and the rumors I were reading pointed to a major announcement. Excited, I stayed up late on the 3rd just to watch the live webcast from CERN. I have to say, watching the excitement in the eyes and voices of the physicists giving the announcement of a 5-sigma detection of this new particle sent shivers down my spine.

Almost 50 years ago, a theoretical physicist by the name of Peter Higgs (who is still alive and kicking and was present in person for the announcement!) wrote a paper (initially rejected, no less!) describing a mechanism that would allow fundamental particles to acquire mass by virtue of interacting with the “Higgs field”, a field analogous to the gravitational and electromagnetic field, that permeates all space. (This field was only later called the Higgs field; Peter Higgs was far too modest to name the field after himself!). In this landmark 1964 paper, he pointed out, almost as an afterthought, that this field would have its own particle, which came to be called the Higgs Boson (again, he didn’t name it such himself!). As an aside, Higgs was not the only player in this game, there were several other scientists who contributed to our theoretical understanding of the Higgs mechanism and Higgs Boson. Rather than going into that here, I recommend you peruse the relevant Wikipedia articles, which discuss these issues in depth.

To drastically oversimplify matters, this mechanism was incorporated into the so-called Standard Model of particle physics and quickly became an essential feature of it. Up until now, it was the last puzzle piece of the Standard Model that had not been put into place. Just like the electromagnetic field has its corresponding “quantum”, or particle, namely, the familiar photon, so the Higgs field has its corresponding particle, the Higgs Boson. Unlike the photon, however, which each of us detects everyday with one’s retinas (assuming one is not blind, of course!), the Higgs Boson has been devilishly difficult to pin down. For, while the Standard Model predicts that it should exist, it inconveniently doesn’t tell us what its mass is. And, the details of how it behaves and how easy it is to detect depend crucially on its mass. That’s one of the reasons it has been so hard to find. Another is the fact that, whatever mass it has, it’s unstable, and once formed, immediately (within an incredibly small fraction of a second) decays into other particles. Thus, it cannot be observed directly, but only by observing the products of its decay and working backwards to infer its existence, sort of like inferring the existence of a long-extinct dinosaur by digging up its fossilized footprints.

Why is this important? Up to now, particle physicists strongly suspected that something like a Higgs field exists in nature, because otherwise, it is very difficult to account for the fact that many observed particles (such as quarks, and the W and Z bosons that mediate the weak force) have a non-zero mass. Theoretical calculations of the behavior of these particles work best when such particles are massless. The fact that they aren’t (we wouldn’t be here if they were!) obviously required an explanation, which was the motivation for a series of papers introducing the Higgs field. As stated before, the Higgs Boson is a byproduct of this additional field (you can think of it as an “excitation” of the field, sort of like a breaking wave of water on the beach is an “excitation” of the ocean it comes from). And particle physicists have been searching for it ever since, because the only way they know of confirming the existence of the Higgs field is to detect the particle associated with it.

Now, it appears they’ve finally found it. The fact that such a particle was predicted almost 50 years ago, and experimentally confirmed just this past year is as much a testament to the power of scientific theory as one will ever come across. I for one am excited, and I’m not even a particle physicist! On the other hand, many theories that have been posited in the interim to attempt to explain the mass of fundamental particles apart from the Higgs field and the Higgs boson have now fallen flat on their face with this new discovery. Such is the nature of science: you never know when a theory is going to be dramatically upheld, or completely ruled out, by a new discovery. And we scientists wouldn’t (or shouldn’t!) have it any other way!

So, what’s next? Now that this new particle has been discovered, there are several things that particle physicists are going to follow up on. The first thing is to continue collecting more data. The particle was originally discovered by sifting through the debris of trillions of proton collisions to look for the unique signature it would produce above the noisy background of all the other particles produced; the problem is orders of magnitude worse than looking for a needle in a haystack. More collisions that produce the particle are needed to determine its properties. The Standard Model predicts that the particle should have very specific decay modes into other particles. For example, it should most often decay into a pair of bottom quarks, and much less often into a pair of gamma ray photons. If the decay rates of the Higgs Boson differ from the Standard Model, even a little bit, then it would be a signpost pointing to new physics (what particle physicists refer to as anything beyond what the Standard Model already accounts for) just around the corner.

Many physicists strongly suspect that the Standard Model is not the whole story, for various reasons. One is its inability to explain why the various particles have the particular masses they do, which seem to follow no discernable pattern. Another is why there are so many different kinds of particles to begin with. Another big one is the fact that it doesn’t account for gravity at all. But, to date there have been only a handful of observations that have been at odds with its predictions, which have been confirmed to astounding precision time and time again. The LHC was built in part to probe new frontiers that might tell us more about how the Universe works at its most fundamental level and give us clues to how we might solve some of the Standard Model’s problems. Now that we’ve found the last missing piece of the Standard Model, what this piece tells us could be the bridge to a fundamental new understanding of the physical Universe, and that’s something to get excited about!

My area of expertise in science, namely the field of Meteorology, is a rather specialized field. It can be viewed as a subset of fluid mechanics, which itself is a subset of classical (or Newtonian) mechanics (or physics). In other words, a meteorologist is a specialized classical physicist, who barely rubs shoulders with that other realm of physics: quantum and particle physics. Indeed, to be perfectly honest, quantum physics is more general, but just because one is a quantum physicist doesn’t mean that one automatically understands all the vagaries of classical physics. What I mean is, classical physics is itself a subset of quantum physics, in that it is an approximation to quantum physics on macroscopic scales, that is the familiar scales of everyday life. But, it is far from obvious how the myriad interactions between particles and forces result in the overwhelming complexity of physical phenomena on macroscopic scales. (It is sometimes said that macroscopic physics “emerges” out of quantum physics). The scales are just so different that it is, at least at the present time, practically (if not theoretically) impossible to fully understand the deep connections between scales, even though we know they are there. It so happens that classical mechanics is an excellent approximation to quantum mechanics (and is rather easier to handle) at macroscopic scales, which is why the exploration of classical physics, without recourse to quantum effects, is still a fruitful scientific enterprise and is likely to be for the foreseeable future.

Nevertheless, I have always been interested in quantum and particle physics out of pure scientific curiosity, and have always meant to educate myself on it as a side pursuit. I just needed a catalyst. A colleague of mine sent me an email a few months ago regarding a potential discovery of a new particle at the Tevatron particle accelerator at Fermilab. I looked into it, and before I knew it, I was immersed in a Wikipedia link-fest, learning about the fascinating world of particle physics. I stumbled upon several blogs maintained by both experimental and theoretical particle physicists, and frustrated that I didn’t understand the jargon and the various graphical plots they were discussing, I decided to pick up an introductory book on particle physics.

I learned about the elegant beauty of the so-called “Standard Model” of particle physics (see here), how much of it is based on rather simple physical principles which collectively are called “symmetries” of nature, and how the different particles interact with each other through the four fundamental forces of the natural world that have so far been discovered: electromagnetism, gravity, and the strong and weak nuclear forces. I learned about unsolved puzzles, such as why the photon, the particle that “carries” the electromagnetic force, has no mass, but the W and Z bosons, the particles that “carry” the weak nuclear force, are quite massive.

Then I learned more about the Higgs boson, that one missing piece of the Standard Model, the one that would explain why all the other particles have the masses they do (or, in the case of the photon, why they do not). All other particles that are predicted by the Standard Model have been discovered just as it predicted they should be, except for the Higgs boson (see here). Without getting into too much detail, this particle interacts with it’s own corresponding “field”, the so-called Higgs field, and with all the other particles in the Standard Model, and in doing so, “endows” them with the masses they have. As we speak, there is an ongoing effort at the Large Hadron Collider in Europe to find the Higgs boson, for while the Standard Model predicts that it should exist, it doesn’t tell us what mass it has. So far, the search has been able to rule out the Higgs boson over a wide range of masses, and it is running out of places to hide, so to speak. If the Higgs boson is *not* found, or if it is found within a particular range of masses, it would mean that the Standard Model of particle physics is not the whole story, and that there is far more to discover about the inner workings of nature. Even if it is found just like the Standard Model says it should be, there is still much more work to do, and there are other areas of physics where we still have many mysteries to solve.

This particle has been dubbed the “God Particle” by the media, probably in no small part due to its elusive status, and yet its central importance to at least one unsolved question in physics, namely, why do the different particles have the masses they do? Why are some more massive than others? For example, the proton is much more massive than its oppositely charged counterpart, the electron. Why do some particles have no mass at all (like the photon)? Why do any of them have any mass at all? What *is* the nature of mass anyway? You get the idea. It’s an important particle. While the name “God Particle” sounds provocative and mysterious, I don’t think the motivation behind naming it that was anything but flippant.

As far as subatomic particles in general are concerned, I think they are all fascinating and display a profound beauty and elegance, and even simplicity (in a sense), in their interactions (as do the mathematical equations that describe them). To me, this underlying symmetry and order is suggestive of a deeper beauty, elegance, and even simplicity (again, in a sense) in the God behind them. So, I propose that they should all be called “God Particles”.