FUNDAMENTAL PARTICLES Year 14 Physics Erin Hannigan

1 Key Word List

■ Natural Philosophy – the science of matter and energy and their interactions. ■ Hadron – any elementary particle that interacts strongly with other particles. ■ Lepton – an elementary particle that participates in weak interactions. ■ Subatomic Particle – a body having finite mass and internal structure but negligible dimensions. ■ Quark – any of a number f subatomic particles carrying a fractional electric charge, postulated as building blocks of the hadrons. Quarks have not been directly observed but theoretical predictions based on their existence have been confirmed experimentally. ■ Atom – the smallest component of an element having the chemical properties of the element.

2 Fundamental Particles

■ Fundamental particles (also called elementary particles) are the smallest building blocks of the universe. The key characteristic of fundamental particles is that they have no internal structure. ■ There are two type of fundamental particles: – Particles that make up all matter, called fermions – Particles that carry force, called bosons ■ The four fundamental forces include: – Gravity – The weak force – Electromagnetism – The strong force

3 The Four Fundamental Forces

■ The four fundamental forces of nature govern everything that happens in the universe. ■ Gravity – The attraction between two objects that have mass or energy ■ The weak force – Responsible for particle decay – Physicists describe this interaction through the exchange of force-carrying particles called bosons. ■ Electromagnetism – Acts between charged particles, like negatively charged electrons and positively charged protons. – The greater the charge the greater the force ■ The strong force – Strongest of the four fundamental forces of nature.

4 Gauge bosons, leptons and hadrons (mesons and Baryons)

■ Gauge bosons – carrier particles for three of the four fundamental forces – W and Z bosons, which carry the weak force – Gluons, which carry the strong force – Photons, which carry the electromagnetic force ■ The only remaining fundamental force that has no known gauge boson is gravity. The theoretical gauge boson for gravity is called a graviton. ■ Leptons are a family of particles that are different from the other known family of fermions, the quarks. Electrons are a well-known example that are found in ordinary matter. ■ A hadron is a subatomic composite particle made of two or more quarks held together by the strong force in a similar way as molecules are held together by the electromagnetic force.

5 Quarks

■ A quark is a tiny particle which makes up protons and neutrons. Atoms are made of neutrons, protons and electrons. ■ A proton is composed of two up quarks, one down quark, and the gluons that mediate the forces "binding" them together. The color assignment of individual quarks is arbitrary, but all three colors must be present. ■ There are six types of quarks. These are called flavours: – Up – Down – Strange – Charm – Top – Bottom ■ Each quark has a matching antiquark. Antiquarks have a charge opposite to that of their quarks. ■ Only up and down quarks are found inside atoms of normal matter. Two up quarks and one down make a proton while two down quarks and one up make a neutron. The other four flavours are not seen naturally on Earth, but they can be made in particle accelerators. Some of them may also exist inside of stars.

6 Quarks continued…

■ Up – Subatomic particle that helps make up many larger particles, like protons. (charge of +2), and are the lightest of the six types. 3 ■ Down – Very small particle that helps make up many larger particles, like protons and neutrons. (charge of - 1), second lightest quark. 3 – Fermions, which means that no two of them can exist in the same space at the same time.

■ Strange – Subatomic particles that are so small, they are believed to not be able to be divided. (charge of -1), third lightest of the quarks. 3 – Also fermions ■ Charm – (charge of +2), third most massive of the six quarts. 3 – Also fermions

■ Top – Most massive of all the elementary particles. – Charge of +2, also a fermion. 3 ■ Bottom 1 – Fermionic with a charge of − . 3

7 Hadrons

■ A hadron is a subatomic composite particle made of two or more quarks held together by the strong force in a similar way as molecules are held together by the electromagnetic force. ■ Most of the mass of ordinary matter comes from two hadrons: the proton and the neutron. ■ Hadrons are categorized into two families: – baryons, made of an odd number of quarks – usually three quarks e.g. protons and neutrons. – mesons, made of an even number of quarks—usually one quark and one antiquark e.g. pions.

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