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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.

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
* Also known as the positron
6 anti­leptons
anti­electron* anti­muon anti­tau
electron anti­neutrino muon anti­neutrino tau anti­neutrino

This matter-antimatter symmetry means we have to double the number of fermions from 24 to 48. If neutrinos turn out to be their own antiparticles, which is yet to be determined, then this number would need to be modified.

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
 rg + gr √2
 −i(rg − gr) √2

 gb + bg √2
 −i(gb − bg) √2
 rr − bb √2
 rr + bb − 2gg √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 (that we know of).

1 Higgs boson
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 1 Higgs gives us 13 bosons in total.

 + 48 fermions + 13 bosons = 61 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
 rg + gr √2
 −i(rg − gr) √2

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

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