Eli5: It was posted in the science page that experiments at the Large Hadron Collider (LHC) have yielded the simultaneous appearance of three force-carrying elementary particles that had never been seen together before.

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Can anyone help me understand what this means and how important this discovery is?

In: Physics

5 Answers

Anonymous 0 Comments


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Anonymous 0 Comments

[This](https://www.independent.co.uk/independentpremium/world/cern-large-hadron-collider-new-particles-b2119168.html) is the only story I can find about the LHC finding three new particles (or other articles covering that story). If you’re looking at something else, please share your link.

These particles are not force carrying particles, at least not directly. They might help carry the strong force between nucleons the way that mesons do, but I don’t think so. Let’s break down what’s going on, though.

Quarks are the fundamental particle that make up protons and neutrons – these are *nucleons* because they live in the nucleus of atoms. Anything made of quarks is a *hadron*, which normally come as *baryons* (three quarks) or *mesons* (two quarks).

Quarks are not made of smaller things, they just *are*. Quarks come in six varieties: up, down, top, bottom, strange, and charm. The only stable combinations are two Ups and a Down (a proton), or two Downs and an Up (neutron). Why? There are a few rules, one of which is that the electric charge has to add up to a whole number, no fractions allowed. Quarks have fractional charge, so they can only be combined in ways to make a whole number (or zero).

Of course, the other rule is that the quarks themselves have to be stable and stick around long enough to make something bigger. Strange and charm quarks are massive and barely last for fractions of a second, so anything made of them also only last for fractions of seconds.

The other big rule is color charge. First, color charge has nothing to do with light or visible color, it’s just an analogy.

Think about electric charge. It comes in positive and negative, and they attract each other. Charged particles are more stable when they stick together to be neutral. The color force has six charges: red, green, blue; and, antired, antigreen, antiblue. Neutral is “white”. Again, I want to stress that this is nothing to do with visible color, it’s just an analogy that scientists use to make sense of it. Quarks can change color, and do, a lot, but the total has to stay neutral or “white”.

Baryons are made using three charges, either three normal colors or three anti-colors. Mesons are made of any normal color and its anti-color. Mesons are not very stable, but they *kind of* last for a little while. The strong nuclear force that holds nucleons together is really the color force “leaking” between nucleons because of mesons carrying color charge with them. The actual force carrier, though, is the gluon which transfers color charge between quarks, like photons do for electric charge.

What the LHC found was more exotic and extremely heavy hadrons made of five quarks or four quarks. The pentaquarks are made with three colors or anti-colors, *plus* an additional color/anti-color pair, like sticking a baryon and meson together. The fourquarks are made with two color/anti-color pairs, like two mesons together.

This isn’t groundbreaking in the sense that no new crazy weird forces were discovered. Scientists predicted that these particles could exist, they’re just hard to find because you need enormous energy to create them and they don’t last very long. Finding them just helped confirm those predictions and gives scientists more data to work with to refine the theories about how the color force works and the strong force and quantum mechanics in general. That’s not to say finding them wasn’t an accomplishment! They definitely wanted to find these and it definitely gives them more science to learn and do. But it’s not “holy shit scientists just proved that gravity isn’t real” or anything like that.

Anonymous 0 Comments

They smashed 2 protons together and that produced an electron, a muon, and a photon. None of these particles are new, it’s just that a proton-proton collision has never been seen to produce that specific combination of 3 particles before, which was predicted to be possible according to quantum chromodynamics. It’s really not possible to eli5 this any more than that. You’re much better off asking a physics sub like r/AskPhysics

Anonymous 0 Comments

The LHC collides protons with a very high energy with each other. The collisions produce many new particles, including very short-living particles that you can’t study elsewhere. What happens in each collision is random and some processes are very rare so we need many collisions to study them.

Based on known physics, we can predict how often the different outcomes should happen. But maybe there are new interactions that we don’t know about yet. The best place to search for them are reactions that are predicted to be very rare: Finding a needle in a haystack is easier if that haystack is smaller. Producing two specific short-living heavy particles plus an extra photon is one of these extremely rare events – expected to happen only once per 20 trillion collisions. One of the LHC experiments found collisions with that outcome, and the measured rate agrees with predictions.

It’s the expected outcome, so it’s not that significant on its own. It’s another place where we now know there is no new physics happening.