Fundamental particles

In particle physics, matter is made up of fundamental particles that cannot be broken down into smaller parts. There are two main families of fundamental particles: quarks and leptons.

Quarks

Quarks are fundamental particles that combine to form hadrons (such as protons and neutrons). There are six types (called "flavours") of quarks:

• Up ($u$)
• Down ($d$)
• Strange ($s$)
• Charm ($c$)
• Top ($t$)
• Bottom ($b$)

Each quark has a specific electric charge:

Each quark has a corresponding antiquark with the opposite charge.

Hadrons: Baryons and Mesons

Hadrons are particles made from quarks. There are two types:

• Baryons: made of three quarks (e.g., protons and neutrons)
• Mesons: made of one quark and one antiquark

Protons and Neutrons

Protons and neutrons are not fundamental particles; they are baryons made from quarks:

• Proton ($p$): $uud$ (two up quarks, one down quark)
  • Charge: $2 \times (+\frac{2}{3}) + 1 \times (-\frac{1}{3}) = +1$
• Neutron ($n$): $udd$ (one up quark, two down quarks)
  • Charge: $1 \times (+\frac{2}{3}) + 2 \times (-\frac{1}{3}) = 0$

Quark Changes in Beta Decay

Beta decay involves changes in the quark composition of nucleons:

• Beta-minus ($\beta^-$) decay: A neutron changes into a proton.
  • Quark change: $d \rightarrow u$ (in the neutron: $udd \rightarrow uud$)
• Beta-plus ($\beta^+$) decay: A proton changes into a neutron.
  • Quark change: $u \rightarrow d$ (in the proton: $uud \rightarrow udd$)

Leptons

Leptons are another family of fundamental particles. The most familiar leptons are:

• Electron ($e^-$)
• Neutrino ($\nu$)

Leptons do not contain quarks and are not affected by the strong nuclear force.

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Summary Table