2.1 The Particle Zoo Flashcards
What are cosmic rays
High energy particles that travel through space from the stars including the Sun.
What happens when cosmic rays enter the Earth’s atmosphere
They create new short-lived particles and antiparticles as well as photons.
What did most physicists think when cosmic rays were first discovered
That they were from terrestrial radioactive substances
New types of short-lived particles and antiparticles were discovered:
Muon
Pion
Kaon
What is the muon
Symbol μ
Also known as a heavy electron
A negatively charged particle with a rest mass over 200 times the rest mass of the electron
What is a pion
Also known as π meson Can be positively charged π + Can be negatively charged π - Can be neutral π 0 Has rest mass greater than muon but less than proton
What is a kaon
Also known as K meson Can be positively charged K+ Can be negatively charged K- Can be neutral K0 Has rest mass greater than pion but still less than proton
Who predicted the existence of exchange particles for the strong nuclear force between nucleons
Hideki Yukawa
Called them mesons
What did the cloud chamber photograph obtained by Carl Anderson show
An unusual track that could’ve been produced by an exchange particle
Through further experiments, particle shown to be a heavy electron (muon)
Who discovered Yukawa’s meson
British physicist Cecil Powell
From tiny microscopic tracks found in photographic emulsion exposed to cosmic rays at high altitude
Called them π mesons or pions
Yukawa’s prediction was correct
What did further cloud chamber photographs (less than a year after Powell’s discovery) reveal
The existence of short-lived particles now known as kaons
How do kaons decay
Via the weak interaction
Therefore were led to being called ‘strange particles’
The kinetic energy of the protons is converted into mass in the creation of…
…the new particles (mesons)
What can a kaon decay into
Pions, or a muon and an antineutron, or an antimuon and a neutrino
What can a charged pion decay into
A muon and an antineutrino, or an antimuon and a neutrino.
What does a π 0 meson decay into
High-energy photons
What does a muon decay into
An electron and an antineutrino
What does an antimuon decay into
A positron and a neutrino
What do decays always obey
The conservation rules for energy, momentum and charge
Why is a TV tube in a traditional TV an accelerator
How did traditional TVs work
Because it accelerates electrons inside the tube through a potential difference of about 5000V
Electrons form beam that hits the inside of TV screen
Magnetic fields produced by electromagnets deflect beam so scans screen to create an image
What is the longest accelerator in the world
The Stanford linear accelerator in California
3km through p.d. of 50000 million volts
Electrons collide with target to form particle-antiparticle pairs
What is the biggest accelerator in the world
The large hadron collider at CERN near Geneva
Accelerate charged particles to energies of more than 7000 GeV
27km circumference ring constructed in circular tunnel
Where and when was the Higgs boson discovered
At CERN in 2012
What is the Higgs boson
An uncharged particle
Was predicted in 1964 as the cause of the rest mass of W bosons
