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# The Standard Model

## Practice

### practice problem 1

How many confirmed elementary particles are there in the standard model?

#### solution

There are 17 names that refer to known fundamental particles…

The 17 named fundamental particles of the Standard Model
12 fermions 5 bosons
up quark charm quark top quark gluon
down quark strange quark bottom quark photon
electron muon tau W boson
electron neutrino muon neutrino tau neutrino Z boson
higgs boson

…but the answer to this question isn't 17. Since some of these particles come in more than one type and some names correspond to more than one particle.

Start with the fermions. Quarks come in 6 flavors and 3 colors, which gives us 18 unique quarks.

18 quarks
red up quark red charm quark red top quark
green up quark green charm quark green top quark
blue up quark blue charm quark blue top quark
red down quark red strange quark red bottom quark
green down quark green strange quark green bottom quark
blue down quark blue strange quark blue bottom quark

The leptons come in 6 flavors, 3 of which are neutrinos, but none of which are colored. There is nothing to multiply here. Just add 6 leptons to the 18 quarks to get 24 matter fermions.

6 leptons
electron muon tau
electron neutrino muon neutrino tau neutrino

Fermions are matter particles. For every particle of matter there is a corresponding antiparticle of antimatter. This matter-antimatter symmetry means we have to double the number of fermions from 24 to 48.

* also known as the positron
18 antiquarks
antired antiup quark antired anticharm quark antired antitop quark
antigreen antiup quark antigreen anticharm quark antigreen antitop quark
antiblue antiup quark antiblue anticharm quark antiblue antitop quark
antired antidown quark antired antistrange quark antired antibottom quark
antigreen antidown quark antigreen antistrange quark antigreen antibottom quark
antiblue antidown quark antiblue antistrange quark antiblue antibottom quark
6 antileptons
antielectron* antimuon antitau
electron antineutrino muon antineutrino tau antineutrino

On to the bosons. Gluons come in 8 color combinations. Here's one way to write them out.

8 gluons
 rb + br √2
 −i (rb − br) √2
 rr − bb √2
 rg + gr √2
 −i (rg − gr) √2

 gb + bg √2
 −i (gb − bg) √2
 rr + gg − 2bb √6

There are two kinds of W boson, one kind of Z boson, and one kind of photon for a total of 4 electroweak bosons.

4 electroweak bosons
photon W+ boson W boson Z0 boson

There is only one kind of Higgs boson.

1 higgs bosons
higgs boson

Since bosons aren't matter particles, they have no antiparticle counterparts. There are no "antibosons". I think we're ready to wrap it up. 8 gluons, 4 electroweak, and 1Higgs gives us 13 bosons in total.

 + 48 total fermions + 13 total bosons = 61 known elementary particles

Behold!

All 61 confirmed elementary particles in the Standard Model
18 quarks
red up quark red charm quark red top quark
green up quark green charm quark green top quark
blue up quark blue charm quark blue top quark
red down quark red strange quark red bottom quark
green down quark green strange quark green bottom quark
blue down quark blue strange quark blue bottom quark
6 leptons
electron muon tau
electron neutrino muon neutrino tau neutrino
18 antiquarks
antired antiup quark antired anticharm quark antired antitop quark
antigreen antiup quark antigreen anticharm quark antigreen antitop quark
antiblue antiup quark antiblue anticharm quark antiblue antitop quark
antired antidown quark antired antistrange quark antired antibottom quark
antigreen antidown quark antigreen antistrange quark antigreen antibottom quark
antiblue antidown quark antiblue antistrange quark antiblue antibottom quark
6 antileptons
antielectron antimuon antitau
electron antineutrino muon antineutrino tau antineutrino
8 gluons
 rb + br √2
 −i (rb − br) √2
 rr − bb √2
 rg + gr √2
 −i (rg − gr) √2

 gb + bg √2
 −i (gb − bg) √2
 rr + bb − 2gg √6
4 electroweak bosons
photon
W+ boson
W boson
Z0 boson
1 higgs boson
higgs boson

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