Particles Part 2 Flashcards
Space invaders
Cosmic rays are high-energy particles that travel through space from the stars,. When cosmic rays enter the Earth’s atmosphere, they create new short-lived particles and antiparticles, as well as photons. Further investigations showed that most cosmic rays were fast-moving protons or small nuclei. They collide with gas atoms in the atmosphere, creating showers of particles and antiparticles that can be detected at ground level. By using cloud chambers and other detectors, new types of short-lived particles and antiparticles were discovered
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New particles introduced
the muon or heavy electron (, a negatively charged particle with a rest mass over 200 times the rest mass of the electron
• the pion or a meson, a particle which can be positively charged,negatively charged, or neutral, and has a rest mass greater than a muon but less than a proton
• the kaon or K meson, which also can be positively charged, negatively charged, or neutral, and has a rest mass greater than a pion but still less than a proton.
Strange particles
, further cloud chamber photographs revealed the existence of short-lived particles we now refer to as kaons. Like pions, kaons are produced in twos through the strong interaction However, the decay of kaons took longer than expected and included pions as the product. This means that kaons must decay via the weak interaction. These and other properties of kaons led to them being called strange particles.
Particle decay
• A kaon can decay into pions, or a muon and an antineutrino, or an antimuon and a neutrino.
• A charged pion can decay into a muon and an antineutrino, or an antimuon and a neutrino. A °pion decays into high-energy photons.
• A muon decays into an electron and an antineutrino. An antimuon decays into a positron and a neutrino.
• Decays always obey the conservation rules for energy, momentum, and charge
How particles interact
Leptons interact through the weak interaction, the gravitational interaction, and through the electromagnetic interaction (if charged).protons neutrons ,pions and kaons
Hadrons can interact through all four fundamental interactions. They interact through the strong interaction and through the electromagnetic interaction if charged. Electrons muons neutrinos
Energy equation,
The total energy of the particles and antiparticles before and after the collision = their rest energy + their kinetic energy.
The rest energy of the products = total energy before -the kinetic energy of the products
Baryas and mesons
Baryons are protons and all other hadrons (including neutrons) that decay into protons, either directly or indirectly.
Mesons are hadrons that do not include protons in their decay products. In other words, kaons and pions are not baryons.
Baryons and mesons are composed of smaller particles called quarks and antiquarks.
Lepton collisions
, leptons and antileptons can interact to produce hadrons. two jets of hadrons are produced from an annihilation event. This event produces a quark and a corresponding antiquark, which move away in opposite directions, producing a shower of hadrons in each direction.
Neutrino types
They are produced in much smaller numbers when particles in accelerators collide.
Further rescarch on neutrinos showed that the neutrinos and
antineutrinos produced in beta decays were different from those produced by muon decays. In effect, neutrinos and antineutrinos from muon and antimuon decays create only muons and no electrons when they interact with protons and neutrons. If there were only one type of neutrino and antineutrino, equal numbers of electrons and muons would be produced.
Lepton rules
1 In an interaction between a lepton and a hadron, a neutrino or antineutrino can change into or from a corresponding charged lepton. An electron neutrino can interact with a neutron to produce a proton and an electron:
However, even though charge is conserved, an electron neutrino and a neutron could not change into an antiproton and a positron:
In muon decay, the muon changes into a muon neutrino.
In addition, an electron is created to conserve charge and a
corresponding antineutrino is created to conserve lepton number.
However, a muon cannot decay into a muon antineutrino, an electron, and an electron antineutrino even though charge is conserved.
