Particles and Waves: 1 - The Standard Model

Question 1

What is the standard model?

Answer 1

The Standard Model is a model of fundamental particles and interactions.

Question 2

Where does the evidence for the existence of quarks come from?

Answer 2

The evidence for the existence of quarks comes from high-energy collisions between electrons and nucleons, carried out in particle accelerators.

Question 3

What is a nucleon?

Answer 3

A proton or a neutron.

Question 4

What are hadrons?

Answer 4

Composite particles that are made up of quarks.

Question 5

How many types of hadron are there and what are they called?

Answer 5

2. Baryons and Mesons.

Question 6

What are baryons?

Answer 6

Baryons are like protons and neutrons and are made up of 3 quarks.

Question 7

What are Mesons made up of?

Answer 7

Mesons are made up of quark - antiquark pairs so they are very unstable, e.g. a pion (π+) is made of an up quark and a down anti - quark.

Question 8

What are examples of Mesons?

Answer 8

A pion (π+).

Question 9

What are examples of Baryons?

Answer 9

Protons and Neutrons.

Question 10

Are Mesons unstable?

Answer 10

Yes they are very unstable.

Question 11

What are protons made of?

Answer 11

2 up and 1 down quarks.

Question 12

What are neutrons made of?

Answer 12

2 down and 1 up quarks.

Question 13

What is this (π+) pion made of?

Answer 13

1 up and 1 down anti - quark.

Question 14

What are leptons?

Answer 14

Leptons are the fundamental particles, i.e. they can’t be split into anything smaller.

Question 15

What are the 1st generation leptons?

Answer 15

The electron.

Question 16

What are the 2nd generation leptons?

Answer 16

The muon.

Question 17

What are the 3rd generation leptons?

Answer 17

The tau.

Question 18

What do all leptons have in common?

Answer 18

They are negatively charged.

Question 19

What is the charge of a neutrino and what does this mean for the neutrino?

Answer 19

Neutrinos have no charge,because of this they never interact with any other particles.

Question 20

How were neutrinos initially discovered?

Answer 20

Neutrinos were initially discovered in radioactive beta decay experiments.

Question 21

In beta decay what does a neutron decay into, why must another particle be admitted and what is the other particle that is admitted.

Answer 21

In beta decay, a neutron decays into a proton and an electron. In order for mass charge and energy to be conserved another particle must be admitted. This particle is the neutrino.

Question 22

What is the equation of the beta decay of a neutron?

Answer 22

A neutron

->

proton + electron + neutrino

Question 23

What are facts about the Strong (nuclear) Force?

Answer 23

• Electrostatic theory predicts that the protons in the nucleus should fly apart. This does not happen so there must be another force and holds the nucleons together.
• Extremely short range force that holds particle of the same charge together - holds quarks together to form hadrons. (HOLDS TOGETHER PARTICLES IN THE NUCLEUS)

Question 24

What is the exchange particle/force carrier for the strong (nuclear force)?

Answer 24

The gluon because they glue particles together.

Question 25

What are facts about the weak (Nuclear) force?

Answer 25

* Involved in radioactive beta decay. * Extremely short range force. * Is weaker than the strong nuclear force (hence its name). * Experienced in quark and lepton interactions. * ASSOCIATED WITH RADIOACTIVE BETA DECAY

Question 26

What is the exchange particle/force carrier of the weak (nuclear) force?

Answer 26

The W and Z bosons.

Question 27

What are facts about the electromagnetic force?

Answer 27

* Combination of electrostatic and magnetic forces. * Has infinite range * ACTS BETWEEN CHARGES

Question 28

What is the exchange particle/force carrier of the electromagnetic force?

Answer 28

The photon.

Question 29

What are facts about the gravitational force?

Answer 29

* Has infinite range * Weakest of the 4 fundamental forces * ACTS BETWEEN MASSES - requires large masses to produce significant forces.

Question 30

What is the exchange particle/force carrier for the gravitational force?

Answer 30

The graviton

Question 31

What do fermions consist of?

Answer 31

Fermions, the matter particles, consist of quarks (six types: up, down, strange, charm, top, bottom) and leptons (electron, muon and tau, together with their neutrinos).

Question 32

In the standard model what does each particle have and what is evidence for this?

Answer 32

In the Standard Model, every particle has an antiparticle and the production of energy in the annihilation of particles is evidence for the existence of antimatter.

Question 33

Why are protons and the neutrons not fundamental particles?

Answer 33

They are composed of other particles/quarks, (fundamental particles are not). (they are composite particles).

Question 34

All baryons are hadrons, but not all hadrons are baryons why is this statement correct?

Answer 34

``` Baryons are (hadrons as they are) composed of (three) quarks. Mesons/some hadrons are made from a quark - anti-quark pair so are not baryons. ```