# Particle Physics

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• Created by: claire
• Created on: 01-12-13 13:32

## Particles and Antiparticles

Pair Production

Photon with sufficient energy can change into a particle-anitparticle pair

hf=2E

Annihilation

Particle and corresponding antiparticle meet and mass is converted into radiation energy. 2 photons produced as a single photon would take away momentum which isn't allowed as no outside forces act.

hf=E

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## Particle Interaction

Electromagnetic Force

Electromagnetic force between 2 charged objects is due to exchange of virtual photons

Weak Nuclear Force

Causes neutron to change into proton or vice verca (beta plus and minus decay)

Causes neutrino to interact with neutron and make it change into a proton and emit an electron

Causes antineutrino to interact with proton and make it change into a proton and emit a positron

Causes proton in proton rich nucleus to interact with inner-shell electron and change into a neutron. Electron changes into a neutrino

Interactions due to exchange particles - W bosons

Strong Nuclear Force

Overcomes electrostatic force of repulsion between protons and keeps protons and neutrons together

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## Particles

Muon - negative charge, greater rest mass than electron                                                                      - decay into electrons and antineutrinos, positrons and neutrinos

Pion - negative, positive, neutral charge, greater rest mass than muon, less than proton                      - produced and decay through strong interaction                                                                         - charged decay into muons and antineutrinos, antimuons and neutrinos. Neutral decays                into high energy photons

Kaon - negative, positive, neutral charge, greater rest mass than pion, less than proton                        - produced through strong interaction, decay through weak interaction                                        - decay into pions, muons and antineutrons, antimuons and neutrinos

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## Particles

Hadrons - interact through strong interaction and electromagnetic if charged                                            - decay through weak interaction                                                                                              - protons, neutrons, pions, kaons

Baryons - protons and neutrons                                                                                                            - decay into protons

Mesons - pions and kaons

Leptons - interact through weak interaction and through electromagnetic if charged                                  - electrons, muons, neutrinos

rest energy of products=total energy before-kinetic energy of products

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## Leptons

Leptons and antileptons can interact to produce hadrons

Neutrinos and antineutrinos produced in beta decays are different from those produced in muon decays. Muon decay creates neutrino, antineutrino and muon when they interact with protons and neutrons. If only one type of neutrino and antineutrino, equal numbers of electrons and muons would be produced. Muon neutrino and electron neutrino (antineutrinos)

In an interaction between a lepton and hadron, a neutrino or antineutrino can change into a corresponding charged lepton

In muon decay, the muon changes into a muon antineutrino, an electron and electron antineutrino

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## Quarks and Antiquarks

Strangeness

Kaons decay into pions or pions and protons. They decay through weak interaction.

• Kaons that decay into pions are K mesons
• Other kaons have different rest masses greater than protons and decay either in sequence or directly into protons and pions

Strangeness is always sconserved in strong interaction but not weak interaction

Quarks

Mesons consist of a quark and antiquark.

• Neutral pion can be any quark-corresponding antiquark
• Each pair of charged mesons is a particle-antiparticle pair
• The antiparticle of any meosn is a quark-antiquark pair, another meson

Baryons consist of 3 quarks or 3 antiquarks for an antibaryon

• Proton - uud
• Neutron - udd
• Antiproton - udd (antiquarks)
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