Quarks And Leptons BROWN

Question 1

What are cosmic rays?

Answer 1

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

Question 2

What did further investigation into cosmic rays show?

Answer 2

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

Question 3

By using cloud chambers and other detectors new short lived particles and anti particles were discovered including:

Answer 3

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

Question 4

How can muons, pions and kaons be created using an accelerator?

Answer 4

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

Question 5

What can a kaon decay into?

Answer 5

Pions
OR
A muon and an antineutrino 
OR
An antimuon and a neutrino

Question 6

What can a charged and uncharged pion decay into?

Answer 6

CHARGED
A muon and an antineutrino
OR
Antimuon and a neutrino

NEUTRAL
High energy photons

Question 7

What can a muon decay in to?

Answer 7

Electron and antineutrino

An antimuon decays into a positron and a neutrino

Question 8

What rules does decay always obey?

Answer 8

The conservation rules for energy, momentum and charge

Question 9

How do all these new particles and antiparticles fit in with each other and with protons, neutrons and electrons?

Answer 9

They are created through high energy interactions and apart from the neutrino they decay into other particles and antiparticles

Question 10

How can you classify the particles?

Answer 10

Into hadrons and leptons according to whether or not they interact through the strong interaction

Question 11

What are hadrons and what force do they interact through?

Answer 11

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

Question 12

What are leptons and what force do they interact through?

Answer 12

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

Question 13

How do you calculate the total energy of the particles and antiparticles BEFORE the collision?

Answer 13

the total energy of the particles and antiparticles before the collision = their rest energy + their kinetic energy

Question 14

How do you calculate the total energy of the particles and antiparticles AFTER the collision?

Answer 14

The total energy of the new particles and antiparticles after the collision = their rest energy + their kinetic energy

Question 15

Using the conservation of energy….

CALCULATION

Answer 15

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

Question 16

When kaons are created what else may also be produced?

Answer 16

Short lived particles with greater rest masses than protons, created through the strong interaction - HADRONS

Question 17

Which two groups can be hadrons be split into?

Answer 17

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

Question 18

What are baryons and mesons composed of ?

Answer 18

Composed of smaller particles called quarks and antiquarks

Question 19

If leptons and antileptons interact what do they produce?

Answer 19

Hadrons

Question 20

What would be shown if two jets of hadrons are produced from a single electron-positron annihilation event?

Answer 20

This event produces a quark and a corresponding anti quark which move away in opposite directions producing a shower of hadrons in each direction

Question 21

Give some information about neutrinos

Answer 21

They interact very little

Travel almost as fast as light

Produced in much smaller numbers when particles in accelerators collide

Question 22

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?

Answer 22

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

Question 23

What symbols are used for the muon neutrino and the electron neutrino?

Answer 23

Muon neutrino
Vu

Electron neutrino
Ve
And similarly for the two types of antineutrinos

Question 24

What happens to leptons in experiments and what does this show about them?

Answer 24

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

Question 25

There are 2 lepton rules, what is the rule for interactions between a LEPTON and a HADRON?

Answer 25

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

Question 26

There are 2 lepton rules, what is the rule for muon decay?

Answer 26

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

Question 27

What happens with the lepton number during change?

Answer 27

Is conserved

Question 28

What are the lepton numbers for leptons, anti leptons and non leptons?

Answer 28

Leptons +1 Anti leptons -1 Non leptons 0

Question 29

What did investigations show that led to kaons being classed as strange? What were they originally?

Answer 29

Originally called V particles - left v shaped tracks Called strange particles bc the v tracks decayed into pion only or into pions and protons

Question 30

Although these strange particles all decay through the weak interaction: Including points about kaons, strange particles and other particles such as sigmas

Answer 30

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

Question 31

When can strangeness change and when can it be conserved?

Answer 31

Strangeness is always conserved in a strong interaction whereas strangeness can change by -1, 0 or +1 in weak interactions

Question 32

Which 3 types should I know?

Answer 32

Up Down Strange

Question 33

What is the rule/quark composition for mesons?

Answer 33

Mesons are hadrons Each consisting of a quark and an antiquark

Question 34

What is the rule/quark composition for baryons and anti baryons?

Answer 34

Baryons and anti baryons are hadrons Consist of 3 quarks for a baryon Consist of 3 antiquarks for an anti baryon

Question 35

What quark composition does a proton have?

Answer 35

uud Only stable baryon

Question 36

What quark composition does a neutron have?

Answer 36

udd

Question 37

What quark composition does an anti proton have?

Answer 37

_ _ _ | u u d

Question 38

What is a sigma particle and what does it contain?

Answer 38

Baryon Strange quark

Question 39

How does a free neutron decay?

Answer 39

Deals into a proton, releasing an electron and an electron anti neutrino as in B- decay

Question 40

What happens to a neutron rich nucleus during B- decay? In terms of quarks, what happens?

Answer 40

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

Question 41

What happens to a proton rich nucleus during B+ decay? In terms of quarks, what happens?

Answer 41

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

Question 42

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?

Answer 42

Conservation of energy and conservation of charge Conservation of lepton numbers Conservation of strangeness

Question 43

Which conservation rule/s for interactions apply to all changes/interactions?

Answer 43

Conservation of energy and conservation of charge

Question 44

Which two conservation rules for interactions only apply to particle and antiparticle interactions and decays?

Answer 44

Conservation of lepton numbers Conservation of strangeness

Question 45

What is the conservation of energy and conservation of charge rule?

Answer 45

Apply to all changes in science The conservation of energy includes the rest energy of particles

Question 46

What is the conservation of lepton numbers rule?

Answer 46

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

Question 47

What is the conservation of strangeness rule?

Answer 47

Used only for particle and anti particle interactions and decays In any strong interaction strangeness is always conserved

Question 48

In any reaction what is conserved?

Answer 48

The baryon number