Video Transcript
Order the following particles
according to their mass from least to greatest: up quark, charm quark, top quark,
Higgs boson, electron.
On this list of particles, we have
three quarks, one boson, and one lepton. So let’s start by comparing similar
particles, that is, quarks to quarks, and then figure out where the Higgs boson and
electron fit in. Recall that in the standard model
quarks come in three pairs, often called generations. The up and down quark are the first
generation. The charm and strange quark are the
second generation. And the top and bottom quark are
the third generation.
Ordered this way, each of the
quarks in a particular generation have greater mass than the quarks in the preceding
generations. So the charm and strange quarks of
the second generation each have a greater mass than either the up or the down quark
of the first generation. And the top and bottom quarks of
the third generation each have a greater mass than the charm and strange quarks of
the second generation and, in turn, also a greater mass than the up and down quarks
of the first generation. So of up, charm, and top, we can
clearly see that top has a greater mass than charm, which has a greater mass than
up.
Now we just need to figure out
where the Higgs boson and the electron fall on this list. Recall that the Higgs boson is
actually the second most massive particle in the standard model, second only to the
top quark. So on our list, the Higgs boson
should go between the charm and the top quark. As for the electron, recall that
the electron has about one two thousandths of the mass of a proton, which is a
hadron, a composite particle made up of up and down quarks.
Even though only about one percent
of the mass of the proton is due to the mass of its constituent quarks, the proton
is so much more massive than the electron that it is still clear that the electron
is lighter than any of the quarks that make up the proton. Since the proton is made up of
quarks from the least massive generation, it’s clear then that the electron is less
massive than all of the quarks and actually belongs at the beginning of our
list. So our final list is electron with
the least mass, then up quark, charm quark, Higgs boson, and finally top quark with
the greatest mass.
