Ask Ethan: Can Free Quarks Exist Outside Of A Bound-State Particle?
“In our low-energy, modern-day Universe, we only find quarks and antiquarks in bound, hadronic states: baryons, anti-baryons and mesons. But that’s only because the quarks that conventionally exist are long-lived, at low densities, and at low enough energies and temperatures. If we change any one of those three, the existence of free quarks is not only possible, but mandatory.
If the conditions for forming a bound state aren’t met, then confinement is impossible. The four ways we know how to get there are to create a top quark, to look to the early stages of the hot Big Bang, to collide heavy ions together at relativistic speeds, or to look inside the densest objects (like neutron stars or the hypothetical strange quark stars) to find the quark-gluon plasma inside. It’s not an easy feat to accomplish, but if you want to create matter in the most extreme states we know of, you have to go to extreme ends to get there.”
Have you ever wondered, if protons and neutrons are made of quarks, whether it’s possible to have a quark (or antiquark) exist outside of a bound-state system? There are lots of ways that we’ve tried to separate quarks out from their bound states that fail. Split a proton apart and it will split, but into other bound states. Take a meson and pull the quark and antiquark apart, and a new antiquark/quark pair will snap into existence to give you two new mesons instead. Even if you create a quark/antiquark pair in a collider that move in opposite directions, they hadronize and only produce the baryons and mesons we can detect: bound states.
But that’s not the end of the tricks up our (and the Universe’s) sleeve. We can create free quarks after all. If you’re curious, you can now find out how.
At Last, Physicists Understand Where Matter’s Mass Comes From
“The way quarks bind into protons is fundamentally different from all the other forces and interactions we know of. Instead of the force getting stronger when objects get closer — like the gravitational, electric or magnetic forces — the attractive force goes down to zero when quarks get arbitrarily close. And instead of the force getting weaker when objects get farther away, the force pulling quarks back together gets stronger the farther away they get.
This property of the strong nuclear force is known as asymptotic freedom, and the particles that mediate this force are known as gluons. Somehow, the energy binding the proton together, the other 99.8% of the proton’s mass, comes from these gluons.”
Matter seems pretty straightforward to understand. Take whatever system you want to understand, break it up into its constituents, and see how they bind together. You’d assume, for good reason, that the whole would equal the sum of its parts. Split apart a cell into its molecules, and the molecules add up to the same mass as the cell. Split up molecules into atoms, or atoms into nuclei and electrons, and the masses remain equal. But go inside an atomic nucleus, to the quarks and gluons, and suddenly you find that over 99% of the mass is missing. The discovery of QCD, our theory of the strong interactions, provided a solution to the puzzle, but for decades, calculating the masses in a predictive way was impossible. Thanks to supercomputer advances, though, and the technique of Lattice QCD, we’re finally beginning to truly understand where the mass of matter comes from.
Come get the scoop, and then tune in to a live-blog of a public lecture at 7 PM ET / 4 PM PT today to get the even deeper story!