1. Particle Physics Flashcards
1
Q
Relative mass of a proton?
A
1
2
Q
Relative mass of an electron?
A
0.0005
3
Q
Relative mass of a neutron?
A
1
4
Q
Relative charge on a proton?
A
1
5
Q
Relative charge on a neutron?
A
0
6
Q
Relative charge on an electron?
A
-1
7
Q
What is the nucleon number?
A
Number of protons + number of neutrons
8
Q
What letter can be used to represent the nucleon number?
A
A
9
Q
What are isotopes?
A
Atoms with a different number of neutrons, but the same number of protons
10
Q
What is a radioisotope?
A
An isotope that is radioactive
11
Q
What is carbon 14 used in?
A
Carbon dating
12
Q
What is the specific charge of a nucleus or ion?
A
Its charge per unit mass
13
Q
What is specific charge used in?
A
Mass spectrometry to identify nuclei
14
Q
How to calculate specific charge?
A
specific charger= Charge / mass
15
Q
Units for specific charge?
A
Ckg⁻¹
16
Q
What is each type of nucleus called?
A
A nuclide
17
Q
What is the range of the strong force?
A
3 fm (small)
18
Q
What is 1 fm in m?
A
10⁻¹⁵ m
19
Q
What does the strong force act between?
A
Nucleons (e.g. protons and neutrons)
20
Q
Is the strong force attractive or repulsive?
A
Both
21
Q
Why is the strong force both attractive and repulsive?
A
Otherwise the nucleus would collapse or explode
22
Q
When is the strong force attractive?
A
> 0.5 fm
23
Q
When is the strong force repulsive?
A
< 0.5 fm
24
Q
For light nuclei, what is the ratio of neutrons to protons?
A
Proton number = neutron number → the two particles must exist together
25
For heavy nuclei, what is the ratio of neutrons to protons?
More neutrons than protons (and very large nuclei and radioactive)
26
What is equilibrium separation?
A point when the resultant force is zero and the attractive and repulsive forces balance
27
What is the decay of americium-241 used for?
Smoke alarms
28
What is the decay of polonium-210 used for?
Ionisers
29
What force is responsible for beta decay?
The weak force
30
How strong is the weak force?
1 millionth the value of the strong force
31
How does the range of the weak force compare to that of the strong force?
It has a smaller range
32
What does the weak force act on?
Leptons and hadrons
33
What are the types of beta decay?
β+ and β-
34
When does beta decay occur?
When the nucleus emits an electron or a positron
35
What does a free neutron decay into in beta decay?
A proton, an electron and an anti-neutrino
36
What does a free proton decay into in beta decay?
A neutron, a positron and a neutrino
37
What type of beta decay is it when a free neutron decays into a proton?
β-
38
What type of beta decay is it when a free proton decays into a neutron?
β+
39
Why it called β- decay when a neutron decays into a proton?
An electron is produced
40
Why is it called β+ decay when a proton decays into a neutron?
A positron is produced
41
What are the energies of the particles emitted in beta and alpha decay?
* beta decay - beta particles emitted have a range of energies
* alpha decay - monoenergetic
42
What happens to the unaccounted-for energy in beta decay?
It is carried away by the neutrinos
43
What happens if the nucleus is still unstable after emitting alpha or beta radiation?
It is in an excited state, and gives off gamma radiation
44
What type of wave is gamma?
Electromagnetic
45
What is the mass and charge of gamma?
Has no mass or charge
46
What does the strong force overcome?
The electrostatic forces of repulsion between protons in the nucleus
47
Why was the existence of the neutrino hypothesised?
To account for conservation of energy in beta decay
48
What type of particle are neutrinos?
Leptons
49
What does an electromagnetic wave consist of?
An electric wave and a magnetic wave which travel together in phase
50
When are electromagnetic waves emitted?
When a charged particle loses energy
51
When can a charged particle lose energy (and an electromagnetic wave emitted as a result)?
* when a fast moving electron is stopped, slows down or changes direction
* when electrons move to a lower energy shell
52
In what form is electromagnetic radiation emitted?
Photons - bursts or packets of energy
53
How do photons travel?
In one direction only in a straight line
54
What happens to an atom's energy when it emits a photon?
Its energy changes by an amount equal to the photon energy
55
What is the amount of energy contained in each quantum proportional to?
The frequency of the radiation
56
the equation for energy of a photon is found on the data sheet what do the symbols stand for?
E=hf=hc/λ
E=hf=hc/λ
E= energy in joules
h= planc constant (found on data sheet)
f= frequency (hz)
c=speed of light (3x10^8)
λ= wavelength (m)
57
What is the Planck constant measured in?
joule-seconds, Js
58
What is photon energy usually given in?
Electron-volts (eV)
59
What is one electron volt defined as?
The energy transferred when an electron is moved through a p.d. of 1V
60
What is the value of 1 eV?
1.6 x 10⁻¹⁹ J
61
What was Dirac's theory about particles and antiparticles?
For every type of particle, there is a corresponding antiparticle that:
* annihilates the particle and itself if they meet, converting total mass to photons
* has same rest mass and opposite charge
62
When does annihilation occur?
When a particle and its corresponding antiparticle meet and their mass is converted into radiation energy
63
What can the rest energy of an antiparticle be calculated from?
By using the rest mass of the colliding particles and E=mc²
E= energy (joules)
m= mass (kg)
c= speed of light (ms)
64
What is pair production?
When a photon (**γ**) with enough energy can change into a particle antiparticle pair
65
What is minimum energy required by the photon in pair production?
The rest energy of the particle pair
66
What are the four fundamental interactions?
* strong
* electromagnetic
* weak
* graviational
67
What is the exchange particle for strong interaction? what particles does the strong interaction affect?
* gluon (for quarks)
* pion (for nucleons)
hadrons feel the strong force only
68
what's the mass of a w gauge boson?
the mass of a w boson is around 100 times that of a proton and hence it has a tiny range.
69
What is the exchange particle for electromagnetic interaction? what particles are affected?
* A virtual Photon **γ. has zero rest mass + infinite range**
* **only charged particles are affected**
70
What is the exchange particle for weak interaction? what does it affect?
The weak interaction exchange particle is the W boson.
The weak force affects all particle types.
71
What is the exchange particle for gravitational interaction?
Graviton
72
Generally, what happens when two particles interact?
They exert equal and opposite forces on each other
73
What happens if two protons approach each other?
They repel and move away
74
Why do protons repel when they approach each other?
Due to the electromagnetic interaction and the exchange of a virtual photon
75
What would happen if we tried to intercept virtual photons?
We would stop the exchange from happening
76
What is the interaction model of repulsive forces?
Two people on skateboards facing each other - throwing a ball between them causes them to move away from each other
77
What is the interaction model of attractive forces?
Two people on skateboards - throw a boomerang and momentum causes them to move towards each other
78
In interaction diagrams, what do the straight and wavy lines represent?
* the lines do NOT represent the paths of the particles
* the wavy line shows the exchange particle and w bosons carry charge from one side of the diagram to the other.
79
What must be conserved in interaction diagrams?
Charge, lepton and baryon number
80
Describe the interaction diagram between two protons.
* lines show protons approaching
* wavy line shows virtual photon as the exchange particle
* then shows that protons move away
81
Describe the interaction diagram between a neutron and a neutrino.
* lines show neutron and neutrino approaching
* wavy line shows W⁻ boson as the exchange particle
* then shows that a proton and an electron move away
82
Describe the interaction diagram between a proton and an anti-neutrino.
* lines show proton approaching an anti-neutrino
* wavy line shows W⁺ boson as the exchange particle
* then shows that a neutron and a positron move away
83
Describe the interaction diagram for electron capture.
* lines show a proton and electron approaching each other
* wavy line shows W⁺ boson as the exchange particle
* then shows that a neutron and a neutrino move away
84
Describe the interaction diagram for β- decay.
* line shows neutron
* wavy line shows W⁻ boson as the exchange particle
* then shows that a proton, electron and anti-neutrino move away
85
Describe the interaction diagram for β+ decay.
* line shows proton
* wavy line shows W⁺ boson as the exchange particle
* then shows that a neutron, positron and neutrino move away
86
What is the process of electron capture?
When a proton in a proton-rich nucleus turns into a neutron, as a result of interacting with an inner shell electron from outside the nucleus
87
Why can't strong or electromagnetic interaction be responsible for beta decay?
* strong force holds neutrons and protons in a nucleus together, but doesn't cause neutron to change into proton
* electromagnetic force only when a charged particle loses energy → neutron not charged
88
What do leptons exist as?
Particles on their own
89
What do quarks exist as?
Only exist bound together
90
Examples of leptons?
* electron
* electron neutrino
* muon
* tau
91
Which leptons are constituents of ordinary matter (1st family)?
* electons
* electron neutrinos
92
Which leptons are only found in cosmic rays and particle accelerators?
* muon
* muon neutrino
* tau
* tau neutrino
93
Charge on an electron neutrino?
0
94
Which quarks are part of the 1st family?
* up
* down
95
Which quarks are part of the 2nd family?
* charm
* strange
96
Which quarks are part of the 3rd family?
* top
* bottom
97
Which quarks are protons made up of?
Two up quarks and one down quark
98
Which quarks are neutrons made up of?
One up quark and two down quarks
99
Which quarks are antiprotons made up of?
Two antiup quarks and one antidown quark
100
What is the charge on an up quark?
+ 2/3
101
What is the charge on a down quark?
- 1/3
102
What is the charge on an antiup quark?
- 2/3
103
What is the charge on an antidown quark?
+ 1/3
104
What is a muon?
A heavier relative of the electron
105
What is the charge on a muon?
-1
106
What is a tau?
A heavier relative of the electron and muon
107
What is the charge on a tau?
-1
108
What is a strange particle?
A heavier relative of the down quark
109
What are hadrons?
Particles that feel the strong force
110
How do hadrons decay?
Weak interaction
111
What groups are hadrons split into?
* baryons - 3 quarks
* mesons - 2 quarks
112
Are protons and neutrons fundamental? Why is this?
No, they are made up of quarks
113
Are protons and neutrons mesons or baryons? Why is this?
Baryons - they are made up of three quarks
114
What is the only stable baryon?
Protons
115
What is the pion?
The exchange particle of the strong nuclear force
116
What do strange particles contain?
A strange quark
117
How are strange particles produced?
Strong interaction
118
How do strange particles decay?
Weak interaction
119
When is strangeness conserved?
Only in strong interactions
120
What do Kaons decay into?
Pions
121
Do leptons feel the strong force?
No
122
What force are leptons affected by?
Weak interaction
123
What do muons decay into?
Electrons
124
What can leptons and antileptons interact to produce?
Hadrons
125
How fast do neutrinos travel?
Almost as fast as light
126
How can leptons change into other leptons?
Weak interaction
127
Baryon number on up quarks?
1/3
128
Baryon number on down quarks?
1/3
129
Baryon number on strange quarks?
1/3
130
Baryon number on anti-up quarks?
-1/3
131
Baryon number on anti-down quarks?
-1/3
132
Baryon number on anti-strange quarks?
-1/3
133
Strangeness of an up quark?
0
134
Strangeness of a down quark?
0
135
Strangeness of a strange quark?
-1
136
Strangeness of an anti-strange quark?
1
137
What do mesons consist of?
A quark and an antiquark
138
What do pions consist of?
Up and down quarks
139
What do kaons consist of?
A strange quark and either an up or down quark
140
What charge can pions have?
Zero charge, or positively/negatively charged
141
What are the kaon combinations?
* strange-antiup (-1)
* strange-antidown (0)
* antistrange-up (1)
* antistrange-down (0)
142
When does beta decay occur?
When the nucleus emits an electron or a positron
143
What is conserved in beta decay?
Charge, spin, baryon number and lepton number
144
What else needs to be conserved (along with charge, spin, baryon and lepton no.) in particle reactions?
Energy and momentum
145
what are the two types of hadrons?
hadrons are made of baryons and mesons
146
what are the mesons quark compositions?
147
Describe the nuclear model of an atom.
• Central nucleus containing protons and neutrons • Electrons orbit the nucleus
148
What are nucleons?
Protons and neutrons
149
What is the collective name for protons and neutrons?
Nucleons
150
How the charge and mass of protons, neutrons and electrons usually given?
• It can be given and coulombs and kilograms, but the numbers are very small (e.g. +1.60 x 10^-19 coulombs) • Therefore, the RELATIVE charges and masses are used instead sometimes (e.g. +1)
151
Do you need to learn the charges and masses of protons, electrons and neutrons?
No, they are given to you in the exam. However, you need to know the RELATIVE charges and masses.
152
What is the unit for charge of particles?
Coulombs (C)
153
What is the unit for the mass of a particle?
Kilograms (kg)
154
What is the charge of protons, neutrons and electrons?
• Protons = + 1.60 x 10^-19 C • Neutrons = 0 C • Electrons = - 1.60 x 10^-19 C
155
What is the mass of protons, neutrons and electrons?
• Protons = 1.67 x 10^-27 kg • Neutrons = 1.67 x 10^-27 kg • Electrons = 9.11 x 10^-31 kg
156
What is the relative charge of protons, neutrons and electrons?
• Protons = +1 • Neutrons = 0 • Electrons = -1
157
What is the relative mass of protons, neutrons and electrons?
• Protons = 1 • Neutrons = 1 • Electrons = 0.0005
158
What is the symbol for proton number?
Z
159
What is the symbol Z?
The proton number
160
What does the proton number determine?
Which element the atom is of.
161
What does the electron number determine?
The chemical behaviour and reactions.
162
What is another name for the mass number?
The nucleon number.
163
What is the nucleon number?
The number of protons and neutrons.
164
What is the symbol for nucleon number?
A
165
What is the symbol A?
The nucleon number.
166
What is an atom's relative atomic mass equal to?
The nucleon number (the number of protons and neutrons).
167
What are isotopes?
Atoms with the same number of protons but different number of neutrons.
168
What are the 3 isotopes of hydrogen and what is their composition?
• Hydrogen - 1 proton, 0 neutrons • Deuterium - 1 proton, 1 neutron • Tritium - 1 proton, 2 neutrons
169
How does changing the number of neutrons in atom affect it?
• Doesn't affect the chemical properties • Affects the stability of the nucleus -\> May cause decay
170
How can isotopes be used to find out how old a sample is?
The amount of radioactive carbon-14 left in a sample can be used to calculate the approximate age (if the object is made of organic matter).
171
Why can carbon-14 be used to find out how old stuff is?
• All living things contain the same percentage of carbon-14 taken in from the atmosphere • After they die, the amount of carbon-14 decreases with time as it decays • Looking at a sample, the amount of carbon-14 tells you how old it is
172
What is specific charge?
The ratio of the charge of a particle to its mass.
173
What is the unit for specific charge?
Coulombs per kilogram (C/kg)
174
What is the equation for specific charge?
Specific charge = Charge / Mass
175
What would happen in the nucleus if the strong attraction didn't exist?
Electrostatic repulsion would overcome gravity and the particles would fly apart.
176
What does the strong nuclear force do?
Binds nucleons together in the nucleus.
177
What are the properties of the strong nuclear force?
• Stronger than the electrostatic force • Very short range - only a few femtometres (the size of a nucleus) • Works equally between all nucleons (i.e. The force is the same between proton-proton, neutron-neutron, neutron-proton) • At very short separations, it is repulsive. At larger separations, it is attractive.
178
Describe how the strong nuclear force changes with separation.
• At very small separations (below 0.5fm), it is repulsive • At the "equilibrium distance" (about 0.5fm), no force is exerted • At larger separations (over 0.5fm), it is attractive. It reaches a maximum attractive value and then falls rapidly. It is almost zero past 3fm.
179
Why must the strong nuclear force be repulsive at very small separations?
Otherwise it would crush the nucleus to a point.
180
In what nuclei does alpha emission happen and why?
• Very big nuclei, like uranium and radium. • The nuclei are too massive for the strong nuclear force to keep them stable.
181
What happens to proton number and nucleon number when alpha decay happens?
• Proton number decreases by 2 • Nucleon number decreases by 4
182
Compare when alpha and beta emission happen.
• Alpha emission -\> In very large nuclei • Beta emission -\> In neutron-rich nuclei
183
What is the range of alpha particles and how can this be observed?
• Very short • By looking at tracks left by alpha particles in a cloud chamber or by using a Geiger counter to observe how count rate drops with distance
184
What is beta-minus decay?
The changing of a neutron into a proton, while emitting an electron and antineutrino from the nucleus.
185
In what nuclei does beta-minus decay happen and why?
• Neutron-rich nuclei • Having many more neutrons than protons in the nucleus makes it unstable
186
What happens to proton number and nucleon number when beta-minus decay happens?
• Proton number increases by 1 • Nucleon number stays the same
187
What is the range of beta particles?
Much greater than alpha particles.
188
What does the antineutrino in beta decay do?
Carries away some energy and momentum.
189
Describe how the first hypothesis about neutrinos was created.
• Scientists at first thought only electrons were emitted during beta decay. • However, it was observed that the energy after beta decay was less than before beta decay. • This led to the idea that another particle was emitted too, which carried the missing energy. • It would have to have no charge and almost zero mass. • This was later found to be the neutrino.
190
Remember to revise the graph of the strong nuclear force.
Pg 4 of the revision guide.
191
What is the order of the EM spectrum by increasing frequency?
• Radio waves • Microwaves • Infrared • Visible light • UV • X-rays • Gamma rays
192
What equation links frequency and wavelength of EM waves?
Frequency = Speed of Light in Vacuum / Wavelength f = c / lambda (NOTE: This is a variation of the "v = f x lambda" equation)
193
What is the speed of light in a vacuum?
3.00 x 10^8 m/s
194
What are photons?
Packets of electromagnetic radiation.
195
When are EM waves emitted?
When a charged particle loses energy. This can be when: • A fast-moving electron is stopped • An electron in a shell moves to a shell of lower energy
196
Describe the structure of an EM wave.
A magnetic wave and an electric wave at 90\* to each other and to the direction of travel. They are in phase. (See diagram pg 8 of textbook)
197
What is the equation for the energy of a photon?
Energy (J) = Planck's constant (Js) x Frequency (Hz) E = h x f
198
What is the wavelength of visible light?
400-700nm
199
What is Planck's constant?
6.63 x 10^-34 Js
200
What is the equation for the power of a laser?
Power = No. of photons passing a point per second x Photon energy P = n x E = n x h x f
201
What units may be used to give the energy of a photon?
Joules (J) or Mega electronvolts (MeV)
202
How many joules is one MeV?
1.60 x 10^-13 J
203
What equation can be used to calculate the rest energy of a particle?
E = m x c^2
204
What is an electronvolt?
The energy that one electron would gain when accelerated through a potential difference of 1 volt.
205
How do you convert from joules to MeV?
Divide by 1.6 x 10^-13.
206
What is an antiparticle?
A corresponding particle to a particle with the same mass and rest energy, but opposite charge.
207
What is the general unit for rest energy?
MeV
208
Describe simply the idea of energy and mass equivalence.
Energy can turn into mass and mass can turn into energy.
209
What is the rest energy of a particle?
The "energy equivalent" of the particle's mass.
210
What happens in terms of mass production when energy is converted into mass?
Equal amounts of matter and antimatter are produced.
211
What is the antiparticle of the proton?
Antiproton
212
What is the antiparticle of the neutron?
Antineutron
213
What is the antiparticle of the electron?
Positron
214
What is the antiparticle of the neutrino?
Antineutrino
215
What is beta-plus decay?
• When a proton turns into a neutron, and a positron and neutrino are emitted. • It is not a natural form of decay and it only happens in experiments.
216
What is pair production?
When a photon turns into a particle and antiparticle.
217
When can pair production happen?
When the photon has enough energy to produce the mass of the particle and antiparticle.
218
Which photons have enough energy to produce mass through pair production?
Gamma ray photons.
219
Where does pair production usually happen and why?
Near the nucleus, which helps conserve momentum.
220
What are the most common particles produced by pair production and why?
Electron-positron pairs because they have low mass.
221
The minimum energy of a photon in pair production is equal to...
...the total rest energy of the particles produced.
222
What is the symbol for rest energy?
E0
223
What is the equation for the minimum energy of a photon during pair production?
Minimum energy of photon = 2 x Rest energy of each particle produced Emin = 2E0 or h x fmin = 2E0
224
What happens when a particle and antiparticle meet?
• Annihilation • All of the mass of the particles is converted back to energy.
225
The total minimum energy of both photons produced in annihilation is equal to...
... the total of the minimum energies of the particle and antiparticle.
226
What is the energy for the minimum energy of a photon produced in annihilation?
Total minimum energy of both photons = Total minimum energy of particle and antiparticle 2Emin = 2E0 ...and so... Emin = E0
227
Is the interaction between two distant objects instantaneous?
No - this is explained by the need for exchange particles, which cause forces.
228
What is the collective name for exchange particles?
Gauge bosons
229
What are the four fundamental forces?
• Weak nuclear force • Strong nuclear force • Electromagnetic force • Gravity
230
What is the exchange particle of electromagnetic force?
Virtual photon (gamma symbol)
231
What particles are affected by the electromagnetic force?
Charged particles
232
What is the exchange particle of the weak nuclear force?
W+, W- and Z0 bosons
233
What particles are affected by the weak nuclear force?
All types
234
What is the exchange particle of the strong nuclear force?
• Gluons exchanged between quarks • Pions exchanged between nucleons
235
What particles are affected by the strong nuclear force?
Hadrons only
236
What is the exchange particle of gravity?
Graviton
237
What particles are affected by gravity?
All types
238
Is particle physics concerned with gravity?
Not really - it is usually ignored because it is very feeble unless large masses are involved.
239
What is the mass of a W boson?
About 100 times that of a proton.
240
Compare and explain the ranges of a W boson and a photon.
• W boson - Very short range because it has a large mass. This means it requires a lot of energy to create and can't travel very far. • Photon - Infinite range because it has zero mass.
241
What are the different types of line on a Feynman diagram used to represent?
• Gauge bosons (exchange particles) - wiggly lines • Other particles - straight lines
242
What are the rules for drawing Feynman diagrams?
• Incoming particles start at the bottom and move upwards • Baryons and leptons can't cross from one side to the other • Make sure charges on both sides balance • A W- particle going to the left has the same effect as a W+ parcial going to the right
243
What exchange particle is involved in two electrons repelling each other?
Virtual (gamma) photon
244
What are electron capture and electron-proton collisions?
• Electron capture is when a proton and electron are attracted by the electromagnetic interaction and a W+ boson goes from the proton to the electron, causing a neutron and neutrino to be formed. • Electron collision is when the proton and electron collide. The same products are formed but a W- boson travels from the electron to the proton instead.
245
What is the difference between electron capture and electron-proton collision?
• In electron capture, a W+ boson travels from the proton to the electron. • In electron-proton collisions, a W- travels from the electron to the proton.
246
What is the particle equation for beta-minus decay?
Neutron -\> Proton + Electron + Antineutrino
247
What is the particle equation for beta-plus decay?
Proton -\> Neutron + Positron + Neutrino
248
Why is an antineutrino produced in beta-minus decay, while a neutrino is produced in beta-plus decay?
To conserve lepton number.
249
What is a virtual particle?
Particles which exist for only a very short time and cannot be detected.
250
Remember to learn specific Feynman diagrams.
Pg 9
251
Practice drawing our a spider diagram of the different types of particles.
Do it!
252
What are hadrons?
Particles that feel the strong nuclear force. They are not fundamental.
253
What are hadrons made of?
Quarks
254
Are hadrons fundamental particles?
No, they are made of quarks.
255
What are the two types of hadrons?
• Baryons • Mesons
256
What is the difference between baryons and mesons?
• Baryons - Made of 3 quarks and decay into a proton directly or indirectly • Mesons - Made of a quark and antiquark and do not decay into a proton
257
Name some baryons.
• Protons • Neutrons • Other particles (e.g. Sigmas)
258
What is the only stable baryon?
Proton - this means all baryons will decay in sequence and eventually form a proton.
259
Are antibaryons found in ordinary matter?
No, because they annihilate with baryons.
260
What values are particles given in baryon number conservation?
• Baryons = +1 • Antibaryons = -1 • Other particles = 0
261
What are some examples of antibaryons?
• Antiprotons • Antineutrons
262
Why does beta decay happen?
Neutrons are not stable baryons, but protons are, so a neutron will decay into a proton.
263
Are mesons stable?
No
264
What are the different types of meson?
Pions and kaons
265
What is another name for a pion?
Pi-meson
266
What is another name for a kaon?
K-meson
267
What is the difference between pions and kaons?
• Pions - Lighter, less unstable, not strange • Kaons - Heavier, more unstable, strange
268
What happens to kaons?
They decay into pions.
269
How were pions and kaons discovered?
In cosmic rays.
270
How do mesons interact with baryons?
Through the strong force.
271
What are the general rules for determining the type of interaction in a reaction?
• If any leptons involved at all -\> Weak interaction • If strangeness isn't conserved -\> Weak interaction • All others -\> Strong interaction
272
What are leptons?
Particles that do not feel the strong interaction. They are fundamental.
273
What are the different leptons?
• Electrons • Muons • Neutrinos • Tau
274
What happens to muons?
The eventually decay into electrons. This is because muons are unstable.
275
What can muons be described as?
Heavy electrons.
276
What is the mass and charge of neutrinos?
• Mass - Almost zero • Charge - Zero
277
How does lepton conservation work?
• There are 3 generations of lepton number - electron, muon and tau • Each lepton number must be conserved separately • Each normal lepton and its respective neutrino is given a lepton number of +1 • Each anti-lepton and its respective antineutrino is given a lepton number of -1
278
What are the symbols for each lepton number?
• Electron lepton number = Le • Muon lepton number = Lmuon • Tau lepton number = Lt
279
What are antiparticles of hadrons made from?
Antiquarks
280
How do strange particles (e.g. kaons) interact?
• Created by the strong interaction • Decay via the weak interaction
281
Strange particles are always produced in pairs (e.g. K+ and K-). Why?
The strangeness cancels out to become 0, so that strangeness is conserved. Therefore, the reaction is a strong interaction.
282
What are the types of quark?
•Up • Down • Strange
283
What is the charge of an up quark?
+2/3
284
What is the charge of a down quark?
-1/3
285
What is the charge of a strange quark?
-1/3
286
What is the charge of an anti-up antiquark?
-2/3
287
What is the charge of an anti-down antiquark?
+1/3
288
What is the charge of an anti-strange antiquark?
+1/3
289
What is the strangeness of a strange quark?
-1
290
What is the strangeness of an anti-strange antiquark?
+1
291
What is unusual about strangeness?
• It is not ALWAYS conserved • Strange quarks are given a strangeness of -1 and anti-strange antiquarks are given a strangeness of +1
292
What quarks make up a proton?
uud
293
What quarks make up an antiproton?
anti-u, anti-u, anti-d
294
What quarks make up a neutron?
udd
295
What quarks make up an antineutron?
anti-u, anti-d, anti-d
296
What are baryons made of?
3 quarks
297
What are mesons made of?
A quark and an antiquark
298
What is the antiparticle of a pi-plus meson?
A pi-minus meson.
299
Remember to revise the diagram on mesons.
Pg 14 of the revision guide
300
What is a weak interaction in terms of quarks?
A weak interaction is something that changes the quark type (e.g. A neutron (udd) turning into a proton (uud))
301
What properties are conserved in an interaction?
• Charge • Baryon number • Strangeness (only in strong interactions) • Lepton number (all 3 generations separately)
302
Can a quark exist on its own?
No.
303
What is quark confinement?
The idea that quarks cannot exist not their own.
304
Through which interaction do hadrons tend to decay?
Weak
305
Describe the mass, range and charge of a W boson.
• Non-zero rest mass • 0.001fm range • Can be positively or negatively charged
306
What are the quarks in a K0 meson?
• Anti-s • d
307
What are the quarks in an anti-K0 meson?
• s • Anti-d
