The Standard Model Flashcards
what is the standard model?
model that explains what the Universe is made from and what holds it together
what does the standard model consist of?
6 quarks, 6 leptons and 4 force carrier particles
what is meant by a ‘fundamental’ particle
a particle which cannot be subdivided
what are fermions?
leptons and quarks (matter particles)
what are hadrons?
particles made up of quarks
what is a baryon?
particle made up of 3 quarks
examples of baryons
proton (u,u,d)
neutron (u,d,d)
what is a meson?
particle made up of one quark and one antiquark
example of a meson
pion (π+)
antimatter
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
evidence for the neutrino
beta decay
what are the four interactions?
- strong force
- weak force
- gravitational force
- electromagnetic force
name the 6 quarks
- up
- down
- charm
- strange
- top
- bottom
quarks only exist…
bound together
combinations of quarks only exist when…
the overall charge is a whole number
why are quarks difficult to detect?
they have very short lifetimes
charge of up, charm and top quarks
+2/3
charge of down, strange and bottom quarks
-1/3
how to matter particles interact?
by exchanging force carrier particles
is the standard model a good theory?
yes - experiments have verified its predictions and all particles predicted by theory have been found
no - it does not explain everything, eg: gravity
name the 6 leptons
- electron
- muon
- tau
- electron neutrino
- muon neutrino
- tau neutrino
neutrinos
- 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
leptons exist…
on their own
charge of electron, muon and tau
-1
charge of neutrinos
0
how to denote antimatter
adding a bar above the symbol or changing sign
anti particle of electron
positron
PET Scanners
Positron Emission Tomography
use antimatter particles (positrons) produced by radioactive tracers, to produce three dimensional images of the inside of the patient’s body
gravity and antimatter
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
discovery of the neutrino
- 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
beta decay of nucleus steps
- neutron is made of one up quark and two down quarks
- one the the down quarks is transformed into an up quark. the difference in charge is conserved by the emission of a W- boson
- the neutron has become a proton
- the W- boson is very short lived and decays into an electron and an electron anti-neutrino
- the proton, electron and anti-neutrino move away from each other, emitting the electron as a beta particle.
electromagnetic force
- 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
electromagnetic force charge carrier
photon
has zero mass and travels at speed of light
gravitational force
- 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
gravitational force charge carrier
has never been detected but has been given the name the graviton
weak force
- 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.
weak force charge carrier
W+, W- and Z bosons
z bosons have no charge
strong force
- 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
strong force charge carrier
gluon (GLUES quarks together)
has no mass or charge
what are bosons?
the particles which give rise to forces
