Quarkery

Susan, aghast. “But I thought the Standard Model was supposed to be the Theory of Everything.”

Jim, abashed. “A lot of us wish that phrase had never been invented. Against the mass of the Universe it’s barely the theory of anything.”

Me, typecast. “That’s a heavy claim, Jim. Big Physics has put many dollars and fifty years of head time into filling out that elegant table of elementary particles. I remember the celebration when the LHC finally found the Higgs boson in 2012. I’ve read that the Higgs field is responsible for the mass of the Universe.”

“A little bit true, Sy, sort of. We think it’s responsible for about 1% of the mass of all the matter we understand. There’s another mechanism that accounts for the other 99%.”

Eddie, downcast. “I’m lost, guys. What Standard Module are you talking about?”

“Do you remember the Periodic Table of the chemical elements?”

“A little. Science class had big poster up on the wall. Had all kinds of atoms in it, right?”

“Yup. Scientists spent centuries breaking down minerals and compounds to find substances that chemical methods couldn’t break down any further. Those were the chemical elements, things like iron and carbon and oxygen. The Periodic Table arranges elements so as to highlight similarities in how they’ll interact. The Standard Model carries that idea down to the sub‑subatomic level.”

“Wait, sub‑subatomic level?”

“Mm-hm. Chemists would say that ‘subatomic‘ is about electrons, protons and neutrons. Count an atom’s electrons. That and some fairly simple rules can tell you what structure types it prefers to participate in and what it reacts with. Count the protons and neutrons in its nucleus. That gives you its atomic weight and starts you on the road to figuring reaction quantities. That’s all that the chemists need to know about atoms. All due respect, Susan, but physicists want to dig deeper. That’s what the Standard Model is all about.”

“So you’re saying that the protons and neutrons are made of these … quarks and things? Is that what comes out of those collider experiments?”

“No on both, Eddie. You ever whack a light pole with a baseball bat?”

“Sure, who hasn’t?”

“The sounds that came out, do you think the pole was made of them?”

“Course not, and I never bought the Brooklyn Bridge, neither.”

“Calm down, Eddie, just making a point. Suppose before you whacked that pole you’d attached a whole string of sensitive microphones all up and down it, and then when you whacked it you recorded all the vibrations your whack set off. Do you think with the recorded frequencies and a lot of math a good audio engineer could tell you what the pole is made of and how thick the casing is?”

“Maybe.”

“That’s what’s going on with the colliders. They whack particles with other particles, record everything that comes out and use math to work out what must have happened to make that event happen. Theory together with data from a huge number of whacks let people like Heisenberg, Gell‑Mann, Ne’eman and Nishijima to the seventeen boxes in that table.”

“‘Splain those particles to me.”

“Don’t think particles, think collections of properties. The Periodic Table’s ‘iron‘ box is about having 26 electrons and combining with 24 grams of oxygen to form 80 grams of Fe2O3. In the Standard Model table, the boxes are about energy, charge, lifetime, some technical properties, and rules for which can interact with what. We’ve never seen a free‑standing quark particle and there’s good reason to think we never will. We mostly see only two‑ or three‑quark mixtures. Some of the properties, like charge, simply add together. It takes a mixture to make a particle.”

“Then how did they figure what goes into a box?”

“Theoreticians worked to find the minimum set of independent properties that could still describe observations. Different mixtures of up and down quarks, for instance, account for protons, neutrons and many mesons.”

Vinnie, at last. “Hi, folks, sorry I’m late to the party. What are we arguing about and which side am I on?”

Higgs candidate LHC event trace
Electrons (green) and muons (red) exiting the event

~~ Rich Olcott