Question Video: Arranging Subatomic Particles according to Their Masses Physics • 9th Grade

List the following particles in order from greatest mass to least mass: top quark, strange quark, photon, tau neutrino, electron, proton, up quark.

03:08

Video Transcript

List the following particles in order from greatest mass to least mass: top quark, strange quark, photon, tau neutrino, electron, proton, up quark.

Okay, so, of this list of seven particles, we want to put them in order from greatest to least mass. And as we look over these particles, we see we have three quarks, a top quark, a strange quark, and an up quark; a proton and an electron, those are particles that may be more familiar to us; and then a photon and something called a tau neutrino. When we think about a photon, we recall that this is a particle that has zero mass. So, whatever the order of the rest of our list, we know that photon will come last because nothing can have less mass than zero mass.

Now, this particle right below the photon, the tau neutrino, this is known as a particle that does have mass, but it has the least mass of all particles that do. In other words, its mass is not zero but just barely so. So, working backwards then, we know the last item on our list will be the photon, and the next to last will be the tau neutrino. At this point, our remaining choices are the three quarks and the proton and the electron. Protons we can recall are made up of quarks. Specifically, one proton is made from two up quarks and one down quark. And from this, we can reasonably guess that a proton is more massive than any quark, and indeed this is true. And going further than that, we know a proton is more massive than an electron, about 2000 times more massive. All this tells us that the particle at the beginning of our list, the most massive one, is the proton.

That leaves us with our three quarks and the electron. We want to find out how these particles rank in terms of mass. One way to help us with this is to recall, as we did earlier, that a proton is made of two up quarks and one down quark. It turns out that only about 10 percent of a proton’s mass actually comes from the mass of the quarks that make it up. But nonetheless, this suggests that the mass of a quark is greater than the mass of an electron, which, as we recalled, is about one 2000th that of a proton. And it turns out that our intuition is correct. An electron is indeed less massive than any type of quark, which means we can write it as the third to last item on our ranked list. So now, the only question that remains is of the top, strange, and up quarks, what is their mass ranking?

As we said, the up quark is part of what makes up a proton, and it’s part of the lightest set of the quark pair types. That is if we consider up, down; charm, strange; and top, bottom, then the mass of each one of these types decreases as we go from right to left. This shows us that an up or down quark is less massive than a charm or strange quark, which is less massive than a top or bottom quark.

And that shows us how we can write in the last three options on our list, the top, strange, and up quarks. Of the three, the top quark has the most mass, followed by the strange quark and then, lastly, the up quark. So now, we have our completed list. In order from greatest to least mass, we have the proton, the top quark, the strange quark, the up quark, the electron, the tau neutrino, and the photon.

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