Section: 11 | Summary Tables of Particle Properties |

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SUMMARY TABLES OF PARTICLE PROPERTIES

Fundamental Particles

Modern physical theory postulates the existence of several fundamental (elementary) particles, that is, physical particles that have no substructure and are not made of other particles. Over the last few decades, experimental evidence has identified a number of these particles, which have been classified using a framework developed in the Standard Model (Ref. 1). The highest level of classification is fermions and bosons. Fermions are particles that have a spin value of 1/2, 3/2, etc., and follow Fermi-Dirac statistics as well as obey the Pauli Exclusion Principle. Bosons are particles that have an integer value of spin, including zero (0), and follow Bose-Einstein statistics. Fermions are the particles that make up matter, and bosons are the particles that carry forces.

Fermions

Fermions can be divided into two primary categories: leptons and quarks. Leptons do not undergo strong interactions, while quarks do. Leptons are further divided into two classes: charged (electron, muon, and tau, which differ by mass) and uncharged (neutrinos, also of three types, electron neutrino, muon neutrino, and tau neutrino).

Quarks are characterized by three properties (“flavors”): up/down; charm/strange; and top/bottom and carry a fractional charge. To date, quarks are experimentally seen only as composite particles, such as protons and neutrons.

Each lepton and quark (matter particles) has an equivalent “antimatter” version. In addition, fermions are divided into families, usually called generations, in which particles in higher generations (second and third) have greater mass than in a lower generation: Mass (electron)<<Mass (muon)<<Mass (tau).

Bosons
Bosons can be elementary or composite particles. Composite bosons are made up of other bosons (spin zero or integer, such as a meson, which is made up of one quark and one antiquark) or fermions, such that the net spin is zero or an integer. For example, the carbon-12 nucleus has six protons and six neutrons with zero spin and is therefore a boson.

Elementary quarks are all gauge bosons, that is carriers of force, except the Higgs boson, which is a scalar boson. Photons are force carriers of the electromagnetic field. W and Z bosons are force carriers that mediate the weak force. Gluons are force carriers for the strong force. Some theories of quantum gravity postulate a force carrier for gravity, graviton, a boson of spin plus or minus two, but that has not been either proven or disproven experimentally yet.

Properties

The table summarizes data for the known fundamental particles. The references contain considerable additional data for particles as well as reviews of topics in particle physics and cosmology. In particular, the reviews of particle physics (Refs. 2-5) summarize much of particle physics and cosmology. It lists, evaluates, and averages measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. Particle properties and search limits are listed in the Summary Tables (see Ref. 5). Complete information is published online on the Web site of the Particle Data Group <http://pdg.lbl.gov>.

Column definitions for the table are as follows.

Column heading	Definition
Name	Name of fundamental particle
Symbol	Symbol commonly used for the particle
F/B	Fermion (F) or Boson (B); see discussion above
Class	Whether the particle makes up matter (Matter) or carries force (Force)
Gen.	Particle family (also called generation; for fermions only
Spin	Spin quantum number
Charge	Electric charge
Mass	Particle mass
Mass units	Units for mass
Mass uncert.	Uncertainty in mass value
Mass uncert. units	Units for mass uncertainty
Note	Footnote applicable

References

Cottingham, W. N. and Greenwood, D. A., An Introduction to the Standard Model of Particle Physics, Second Edition, Cambridge University Press, 2008.
Zyla, P. A. et al. (Particle Physics Group), Prog. Theor. Exp. Physics 2020, 083C01, 2020.
pdgLive, 2020. <pdg.lbl.gov/Viewer.action>
Tanabashi, M. et al. (Particle Data Group), Phys. Rev. D 98, 030001, 2018.
Particle Physics Data Group, 2020 Particle Physics Booklet, Physics Division, Lawrence Berkeley National Laboratory, U.S. Department of Energy, Berkeley, CA, 2020.

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Properties of Fundamental Particles

Name	Symbol	F/B	Class	Gen.	Spin	Charge	Mass	Mass units	Mass uncert.	Mass uncert. units	Note
Continued on next page...
Electron	e	F	Matter	First	1/2	-1	5.485 799 090 70 × 10^-4	u	± 0.000 000 000 16 × 10^-4	u
	e						0.5109 989 461	MeV	± 0.000 000 0031	MeV	a
	e						9.109 383 7015 × 10^-31	kg	± 0.000 000 0028 × 10^-31	kg	a
Muon	μ	F	Matter	Second	1/2	-1	0.113 428 925 7	u	± 0.000 000 0025	u
	μ						105.6583 745	MeV	± 0.000 0024	MeV	a
	μ						1.883 531 627 × 10^-28	kg	± 0.000 000 042 × 10^-28	kg	a
Tau	τ	F	Matter	Third	1/2	-1	1.776.86	MeV	± 0.12	MeV
	τ						3.167 54 × 10^-27	kg	± 0.000 21 × 10^-27	kg	a
Electron neutrino	ν_e	F	Matter	First		< 4 × 10^-35	< 1.1	ev	90% confidence
Muon neutrino	ν_μ	F	Matter	Second		< 4 × 10^-35	< 0.19	MeV	90% confidence
Tau neutrino	ν_τ	F	Matter	Third		< 4 × 10^-37	< 18.2	MeV	90% confidence
Up quark	u	F	Matter	First		2/3	2.16	MeV	+0.49;-0.26	MeV
Down quark	d	F	Matter	First		-1/3	4.67	MeV	+0.48;-0.17	MeV
Charm quark	c	F	Matter	Second		2/3	1.27	GeV	± 0.02	GeV
Strange quark	s	F	Matter	Second		-1/3	93	MeV	+11;-5	MeV
Top quark	t	F	Matter	Third		2/3	172.76	GeV	± 0.30	GeV	b
Bottom quark	b	F	Matter	Third		-1/3	4.18	MeV	+0.3;-0.2	MeV
Photon	γ	B	Force			< 1 × 10^-46	< 1 × 10^-18	eV		eV
W boson	W	B	Force				80.379	GeV	± 0.012	GeV

^aConversion factor from u (atomic mass units) to MeV and kg is more uncertain than the mass of the electron in u (atomic mass units).
^bDirect measurement cross-section value is 162.5 +2.1; -1.5.
^cTheoretical value; a mass as large as a few MeV may not be precluded.

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