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?
create new short-lived particles and antiparticles, and photons
What did most physicists think about cosmic rays?
they were formed from terrestrial radioactive substances
How was the theory of cosmic rays being formed from terrestrial radioactive substances disproved?
when physicist + amateur balloonist Victor Hess, found ionising effects of the rays was significantly greater at 5000m than at ground level
What did further investigations into cosmic rays show?
cosmic rays were fast-moving protons or small nuclei
What do the fast-moving protons/ small nuclei in cosmic rays do?
collide with gas atoms in atmosphere, creating showers of particles and antiparticles that can be detected at ground level
What was used to discover new types of short-lived particles and antiparticles?
using cloud chambers and other detectors
What particles were discovered using the cloud chambers and other detectors?
the muon, pion and kaon
What is a muon?
a muon, or heavy electron is a negatively charged particle
What is the symbol for muon?
μ
What is the rest mass of a muon in comparison to an electron?
rest mass over 200 times the rest mass of the electron
What is the symbol of the pion?
π
What charge can a pion have?
positive, negative or neutral
What is the rest mass of a pion like?
rest mass greater then a muon but less than a proton
What is the kaon also known as?
K meson
What charge can a kaon have?
positive, negative or neutral
What is the rest mass of a kaon like?
rest mass greater than a pion but still less than a proton
How were kaons discovered?
when photographs from cloud chambers revealed existence of short-lived particles
In what numbers a kaon produced?
kaons are produced in twos
Through what interaction are kaons produced?
strong interaction
How are kaons produced?
When protons moving at high speed crash into nuclei and they each travel far beyond nucleus in which they originate before they decay
How long did kaons take to decay?
decay of kaons took longer than expected
What is one of the products of kaon decay?
pions
As kaons took longer than expected to decay + one product is pions, what does this mean?
kaons must decay via the weak interaction
What did the properties of kaons lead them to being called?
strange particles
How can these particles be produced?
using accelerators in which protons collide head-on with other protons at high speed
What is the kinetic energy of protons converted into?
mass in the creation of these new particles
What does a kaon decay into?
into pions, or a muon and an antineutrino, or an antimuon and a neutrino
What can a charged pion decay into?
into a muon and an antineutrino, or an antimuon and a neutrino
What does a π^0 decay into?
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 of energy, momentum and charge
