Quarks And Leptons BROWN Flashcards
What are cosmic rays?
High energy particles that travel through space from the stars, including the sun
When they enter the earths atmosphere they create new short lived particles, antiparticles and photons
The ionising effect of the rays was significantly greater at 5000m than at ground level
What did further investigation into cosmic rays show?
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 short lived particles and anti particles were discovered including:
Muon - heavy electron
- symbol u
- negatively charged
- rest mass over 200 times the rest mass of the electron
- decays through the weak interaction
Pion -pion meson
- can be positively charged, negatively charged or neutral
- has a rest mass greater than a muon but less than a proton
- produced in twos through the strong interaction
Kaon - kaon meson
- has a rest mass greater than a pion but still less than a proton
- produced in twos through the strong interaction
- decay via the weak interaction
- aka strange particle
How can muons, pions and kaons be created using an accelerator?
This is where protons collide head on with other protons at high speed
The kinetic energy of the protons is converted into mass in the creation of these new particles
So these new particles could be studied under controlled conditions by teams of physicists using accelerators to create them
What can a kaon decay into?
Pions OR A muon and an antineutrino OR An antimuon and a neutrino
What can a charged and uncharged pion decay into?
CHARGED
A muon and an antineutrino
OR
Antimuon and a neutrino
NEUTRAL
High energy photons
What can a muon decay in to?
Electron and antineutrino
An antimuon decays into a positron and a neutrino
What rules does decay always obey?
The conservation rules for energy, momentum and charge
How do all these new particles and antiparticles fit in with each other and with protons, neutrons and electrons?
They are created through high energy interactions and apart from the neutrino they decay into other particles and antiparticles
How can you classify the particles?
Into hadrons and leptons according to whether or not they interact through the strong interaction
What are hadrons and what force do they interact through?
Particles and antiparticles that can interact through the strong interaction and through the electromagnetic interaction if charged
Can interact through all four fundamental interactions
Apart from the proton which is stable hadrons tend to decay through the weak interaction
Eg/ protons neutrons pion mesons kaon mesons
What are leptons and what force do they interact through?
Particles and antiparticles that do NOT interact through the strong interaction
Interact through the weak interaction and through the electromagnetic interaction if charged
Eg/ electrons muons neutrinos
How do you calculate the total energy of the particles and antiparticles BEFORE the collision?
the total energy of the particles and antiparticles before the collision = their rest energy + their kinetic energy
How do you calculate the total energy of the particles and antiparticles AFTER the collision?
The total energy of the new particles and antiparticles after the collision = their rest energy + their kinetic energy
Using the conservation of energy….
CALCULATION
The rest energy of the products = total energy before - the kinetic energy of the products
When kaons are created what else may also be produced?
Short lived particles with greater rest masses than protons, created through the strong interaction - HADRONS
Which two groups can be hadrons be split into?
BARYONS
Protons and all other hadrons including neutrons that decay into protons either directly or indirectly
MESONS
Hadrons that do NOT include protons in their decay products
In other words kaons and pions are not Baryons
What are baryons and mesons composed of ?
Composed of smaller particles called quarks and antiquarks
If leptons and antileptons interact what do they produce?
Hadrons
What would be shown if two jets of hadrons are produced from a single electron-positron annihilation event?
This event produces a quark and a corresponding anti quark which move away in opposite directions producing a shower of hadrons in each direction
Give some information about neutrinos
They interact very little
Travel almost as fast as light
Produced in much smaller numbers when particles in accelerators collide
Research on neutrinos showed that the neutrinos and antineutrinos produced in beta decays were different to those produced by muon decays. What effect do neutrinos and antineutrinos from muon and anti muon decays have?
Those from muon decays create only muons and no electrons when they interact with protons and neutrons
If there were only one type of neutrino and anti neutrino, equal numbers of electrons and muons would be produced
What symbols are used for the muon neutrino and the electron neutrino?
Muon neutrino
Vu
Electron neutrino
Ve
And similarly for the two types of antineutrinos
What happens to leptons in experiments and what does this show about them?
Leptons can change into other leptons through the weak interaction and can be produced or annihilated in particle-antiparticle interactions
But all experiments on them indicate that they don’t break down into non-leptons they appear to be fundamental
There are 2 lepton rules, what is the rule for interactions between a LEPTON and a HADRON?
In an interaction between a LEPTON AND A HADRON a neutrino or anti neutrino can change into or from a corresponding charged lepton
An electron neutrino can interact with a neutron to produce a proton and an electron
There are 2 lepton rules, what is the rule for muon decay?
In MUON DECAY the muon changes into a muon neutrino
In addition an electron is created to conserve charge and a corresponding anti neutrino is created to conserve lepton number
However a muon can not decay into a muon anti neutrino, an electron antineutrino even though charge is conserved
What happens with the lepton number during change?
Is conserved
What are the lepton numbers for leptons, anti leptons and non leptons?
Leptons +1
Anti leptons -1
Non leptons 0
What did investigations show that led to kaons being classed as strange? What were they originally?
Originally called V particles - left v shaped tracks
Called strange particles bc the v tracks decayed into pion only or into pions and protons
Although these strange particles all decay through the weak interaction:
Including points about kaons, strange particles and other particles such as sigmas
Those that decay into pions only were referred to as kaons
Strange particles are created into twos
The others such as the sigma particle were found to:
- have different rest masses which were always greater than the protons rest mass
- decay either in sequence or directly into protons and pions
When can strangeness change and when can it be conserved?
Strangeness is always conserved in a strong interaction whereas strangeness can change by -1, 0 or +1 in weak interactions
Which 3 types should I know?
Up
Down
Strange
What is the rule/quark composition for mesons?
Mesons are hadrons
Each consisting of a quark and an antiquark
What is the rule/quark composition for baryons and anti baryons?
Baryons and anti baryons are hadrons
Consist of 3 quarks for a baryon
Consist of 3 antiquarks for an anti baryon
What quark composition does a proton have?
uud
Only stable baryon
What quark composition does a neutron have?
udd
What quark composition does an anti proton have?
u u d
What is a sigma particle and what does it contain?
Baryon
Strange quark
How does a free neutron decay?
Deals into a proton, releasing an electron and an electron anti neutrino as in B- decay
What happens to a neutron rich nucleus during B- decay? In terms of quarks, what happens?
A neutron in the neutron rich nucleus changes into a proton, releasing an electron and an electron neutrino
In quark terms a down quark changes to an up quark
What happens to a proton rich nucleus during B+ decay? In terms of quarks, what happens?
A proton in the proton rich nucleus changes into a neutron, releasing a positron and an electron neutrino
In terms of quarks, an up quark changes to a down quark
Particles and anti particles obey certain conservation rules when they interact. Some rules apply to all interactions and decays and some do not. What are the three rules?
Conservation of energy and conservation of charge
Conservation of lepton numbers
Conservation of strangeness
Which conservation rule/s for interactions apply to all changes/interactions?
Conservation of energy and conservation of charge
Which two conservation rules for interactions only apply to particle and antiparticle interactions and decays?
Conservation of lepton numbers
Conservation of strangeness
What is the conservation of energy and conservation of charge rule?
Apply to all changes in science
The conservation of energy includes the rest energy of particles
What is the conservation of lepton numbers rule?
Used only for particle and anti particle interactions and decays
In any change the total lepton number for each lepton branch before the change is is equal to the total lepton number for that branch after the change
What is the conservation of strangeness rule?
Used only for particle and anti particle interactions and decays
In any strong interaction strangeness is always conserved
In any reaction what is conserved?
The baryon number
