Colliding

The size and complexity of this great machine I have written about, the LHC, still boggles my mind. Most of the world was unaware of this machine before it went live in 2008, and then only because the only "news" broadcast about it had to do with the prediction of a few misguided freaks that it would destroy the world when they started it up. Seriously, I kid you not.

Well, we're all still here (and incidentally, we'll all be here in 2013 as well, pay no attention to that Mayan calendar myth), and the LHC has made great progress in its mission. It's working, and it's making discoveries.

To hear about the LHC and its discoveries is interesting, but I think many people don't yet know just how incredibly complicated this machine is, and how much human ingenuity it required to design and build. After all, it's looking for the most elusive creatures in the universe...

So what the heck is this thing, and why can't Dave stop writing about it?

The Large Hadron Collider is, at its most basic, a huge ring tunnel, some 17 miles in circumference, buried 500 feet underground on the French-Swiss border near Geneva. It was designed and built, and is run by the European Organization for Nuclear Research (CERN) based in Geneva. The primary purpose of the LHC is to discover particles supporting the Standard Model of physics, and in that way it was made to answer the most fundamental questions about the building blocks of our universe.

 

I've said that the LHC was really designed to find one particle and that is the Higgs Boson. That's not entirely true. The Higgs is the big prize, but there are other particles to be found after that, outside the Standard Model. There are inconsistencies in the Standard Model (that neither you nor I could ever understand, trust me) that nonetheless hint that it may need to be slightly revised and that revision may come in the form of a complimentary theory called Supersymmetry. This new theory could patch up the holes in the Standard Model but in order to confirm it, the new particles IT predicts must be found. Put that up on the shelf for later, for now it's all about the Higgs.

The Standard Model of physics predicts the existence of the Higgs, but it has never been seen. As I blogged earlier, the LHC may be on the verge of finding it. According to most high-energy physicists, the Higgs should be visible at well below the energies the LHC can generate.

What is this strange Higgs Boson anyhow? Well, firstly know that subatomic particles are mind-boggling in the extreme, they behave by rules that seem alien to us up here in the "big world", rules described by something called Quantum Mechanics. Elementary particles, the building blocks of atoms, behave in odd ways, and  they have equally odd names. Here's a chart of the particles of the standard model. All but the Higgs have been found in previous colliders.

Ok, I warned you: this is going to sound weird:

The particles come in different "flavors" based on their quantum numbers: Isospin, Charm, Strangeness, Topness, and Bottomness. There are four basic types of subatomic particle: Quarks, Leptons, Fermions (named after Enrico Fermi), and Bosons (named after physicist Satyendra Nath Bose). They are differentiated by their mass, charge, and spin. A Boson is a particle with integer spin (ie, 1). The Standard Model predicts that the emission and absorption of Bosons causes the "weak nuclear force", one of the four known forces of nature (the others being gravity, electromagnetic, and the strong nuclear).

The Higgs Boson is the missing link here, its interaction with the other Bosons is thought to explain how electroweak symmetry breaks down (the Higgs Mechanism) which leads (assuming you have a brain the size of a medicine ball) to an explanation of why other elementary particles have mass. The secret of mass and gravity lies somewhere tangled up in these Bosons.

The interactions of matter on this level are crazy in the extreme. For instance, the Pauli Exclusion Principle states that no two Fermions may occupy the same Quantum State simultaneously. And to make things really difficult, Quantum Mechanics states that the act of observing something at this level changes the reality of the interactions. Yeah, I didn't make that up...go read about it. Quantum Mechanics will blow your mind like nothing else you will ever read about. The math is solid, but finding confirmation is extremely difficult and requires scientists to go to extreme lengths...like building colliders that use the power of a city and cost billions of dollars. Nevertheless, we know Quantum Mechanics works, because its principles are exploited in products such as flash memory (as the circuits in computer chips become smaller, they begin to bump into the quantum world where the rules change and electrons start behaving very differently - at that level you may as well throw common sense out the window).

I'm not going to bother writing more about these particles because A) I'm in way over my head despite 25+ years of trying to understand it (and I've read entire books on it) and B) I want to have at least one or two of you stay till the end of this crazy post (I'm sure my sister has already bailed...I fully expect a "TOO LONG" comment to be left).

Suffice it to say, the Higgs Boson is very tricky and shy, and whatever it is, it requires enormous amounts of energy to agree to show itself in public.

That's where the LHC comes in. It is, by far, the largest science experiment ever constructed. It's a huge superconducting tunnel designed to accelerate proton beams around the main ring up to near the speed of light, while simultaneously accelerating another beam in the opposite direction. Once the beams are at full kinetic energy, they are channeled into a special chamber and collided together. The resulting collision breaks apart the protons and reveals their building blocks - these subatomic particles mentioned above. So, how do you capture this data? It isn't easy.

There are two main particle detectors in the LHC. Both of them are awe-inspiring. It is not a stretch to say that the detectors in the LHC are the most complicated electronic machines ever designed and built by humans. More than three thousand scientists and engineers from 165 scientific institutes in 38 countries designed and operate them. The instruments defy ordinary comprehension. These detectors are responsible for capturing the proton collisions and resulting particle trails and so they have to be incredibly sensitive. And that means complicated and expensive.

The first detector is called the Compact Muon Solenoid (CMS), although compact is definitely the wrong choice of wording here. Its two end caps (which look like flying saucers) are as big as five story buildings, and each weigh more than 3,000 tons. They contain millions of hair-like sensing wires and the CMS has more than 300,000 channels of superfast electronic sensors to capture the collision events. The CMS is actually located in France, as the LHC is spread across the border with Switzerland.

The other main detector is called ATLAS, a toroidal tube about 120 feet long that weighs in at 7,000 tons and is designed to capture new particle types across a wide range of energies. Its eight superconducting magnets (seen below) are powerful enough to crush a bus.

 

The decision on which detector to use (there are also four other smaller ones) is up to the scientists performing a given experiment and depends on what type of particle they're expecting to see.

Even with all this technology, capturing a collision is a rare thing. One physicist said getting a successful collision in a collider is like shooting two guns towards each other from opposite sides of Texas and hoping the bullets collide in the middle. So the LHC throws very large numbers of protons together to increase the odds.

Well, the LHC seems to be accumulating collisions at a much higher rate than previous colliders and I can't wait to see what it finds. Just yesterday in fact (and still unconfirmed) the ATLAS detector found a particle called Chi-b 3P, which is comprised of a "Beauty" quark and a "Beauty" anti-quark, bound together with the strong nuclear force...this particle was believed to exist in nature but never seen until now. In case you actually looked at that chart above and are wondering, a "Beauty" quark is another name for a "Bottom" quark...because it wasn't complicated enough already, we have to add some nicknames into the mix.

I'm really sorry this turned out so complicated. I hope I got it mostly right. This is just scratching the surface, the great people who discovered and continue to discover these elementary particles are true pioneers in a world both strange and wonderful.

Here's an image from the LHC taken this year that depicts a perfect collision captured by the CMS. Unlike past instruments, the CMS and ATLAS images are three-dimensional and color coded. In this image the red lines are the paths of the colliding proton beams. The yellow lines are the trails of all the particles as they broke apart from the colliding protons. The blue volume is the crystal barrel of the CMS, where the collisions take place. If this image isn't beautiful, I don't know what is.