The Standard Model

Question 1

what is the standard model?

Answer 1

model that explains what the Universe is made from and what holds it together

Question 2

what does the standard model consist of?

Answer 2

6 quarks, 6 leptons and 4 force carrier particles

Question 3

what is meant by a ‘fundamental’ particle

Answer 3

a particle which cannot be subdivided

Question 4

what are fermions?

Answer 4

leptons and quarks (matter particles)

Question 5

what are hadrons?

Answer 5

particles made up of quarks

Question 6

what is a baryon?

Answer 6

particle made up of 3 quarks

Question 7

examples of baryons

Answer 7

proton (u,u,d)

neutron (u,d,d)

Question 8

what is a meson?

Answer 8

particle made up of one quark and one antiquark

Question 9

example of a meson

Answer 9

pion (π+)

Question 10

antimatter

Answer 10

for every type of particle, there is a corresponding antiparticle that looks and behaves the same but has the opposite charge

annihilate into pure energy when they meet

Question 11

evidence for the neutrino

Answer 11

beta decay

Question 12

what are the four interactions?

Answer 12

1. strong force
2. weak force
3. gravitational force
4. electromagnetic force

Question 13

name the 6 quarks

Answer 13

1. up
2. down
3. charm
4. strange
5. top
6. bottom

Question 14

quarks only exist…

Answer 14

bound together

Question 15

combinations of quarks only exist when…

Answer 15

the overall charge is a whole number

Question 16

why are quarks difficult to detect?

Answer 16

they have very short lifetimes

Question 17

charge of up, charm and top quarks

Answer 17

+2/3

Question 18

charge of down, strange and bottom quarks

Answer 18

-1/3

Question 19

how to matter particles interact?

Answer 19

by exchanging force carrier particles

Question 20

is the standard model a good theory?

Answer 20

yes - experiments have verified its predictions and all particles predicted by theory have been found
no - it does not explain everything, eg: gravity

Question 21

name the 6 leptons

Answer 21

1. electron
2. muon
3. tau
4. electron neutrino
5. muon neutrino
6. tau neutrino

Question 22

neutrinos

Answer 22

• have no electrical charge
• mostly pass through Earth without interacting with any atoms
• produced in great abundance in the early Universe
• have tiny mass
• huge numbers contribute to the total mass of the Universe

Question 23

leptons exist…

Answer 23

on their own

Question 24

charge of electron, muon and tau

Answer 24

-1

Question 25

charge of neutrinos

Answer 25

0

Question 26

how to denote antimatter

Answer 26

adding a bar above the symbol or changing sign

Question 27

anti particle of electron

Answer 27

positron

Question 28

PET Scanners

Answer 28

Positron Emission Tomography use antimatter particles (positrons) produced by radioactive tracers, to produce three dimensional images of the inside of the patient's body

Question 29

gravity and antimatter

Answer 29

gravity affects matter and antimatter in the same way as gravity is not a charged property and a matter particle has the same mass as its antiparticle

Question 30

discovery of the neutrino

Answer 30

- in the 1930s, the beta decay of the nucleus was studied closely - it was discovered that the total energy before and after did not match expectations leading Enrico Fermi to propose that another particle was involved - the particle would have very small mass and no charge **neutrino**

Question 31

beta decay of nucleus steps

Answer 31

1. neutron is made of one up quark and two down quarks 2. one the the down quarks is transformed into an up quark. the difference in charge is conserved by the emission of a W- boson 3. the neutron has become a proton 4. the W- boson is very short lived and decays into an electron and an electron anti-neutrino 5. the proton, electron and anti-neutrino move away from each other, emitting the electron as a beta particle.

Question 32

electromagnetic force

Answer 32

- causes like-charged things to repel and oppositely-charged things to attract - many everyday forces such as friction are caused by the electromagnetic force - acts of infinite distances - greater charge=greater force / greater distance=smaller force

Question 33

electromagnetic force charge carrier

Answer 33

photon | has zero mass and travels at speed of light

Question 34

gravitational force

Answer 34

- standard model cannot explain gravity - it is the force of attraction between all massive objects in the Universe - it is by far the weakest of the forces but infinite in range

Question 35

gravitational force charge carrier

Answer 35

has never been detected but has been given the name the graviton

Question 36

weak force

Answer 36

- responsible for the decay of massive quarks into lighter quarks and leptons - has very short range and is only effective within the radius of the nucleus - around 25 orders of magnitude greater than the gravitational force.

Question 37

weak force charge carrier

Answer 37

W+, W- and Z bosons | z bosons have no charge

Question 38

strong force

Answer 38

- reason why positively charged particles inside the atom don't repel and blow apart the nucleus - holds quarks together to form hadrons - strong only over short distances

Question 39

strong force charge carrier

Answer 39

gluon (GLUES quarks together) | has no mass or charge

Question 40

what are bosons?

Answer 40

the particles which give rise to forces