Basics of particle physics

Question 1

What are the natural units?

Answer 1

ℏ=c=1

Mass = 1GeV

Question 2

What are leptons?

Answer 2

Leptons are spin-1/2
fermions 
- They do not interact via the strong force
the electron (e) :0.511 MeV
neutrino (ν‎e) : <2 eV
The other generations :
the muon (μ‎): 	
105.7 MeV
muon-neutrino (νμ‎) :<0.19 MeV
the tau (τ‎) 1776.82 ± 0.16 MeV
 tau-neutrino (ντ‎)	
<18.2 MeV

Question 3

What are hadrons?

Answer 3

Strongly interacting particles re composed of quarks and antiquarks

Question 4

What are fermions?

Answer 4

They are spin 1/2

Question 5

What are the three generations of matter?

Answer 5

Generation 1 being the lightest
Generation 2 being the middle
Generation 3 most heavy generation there with the heaviest particle being the top quark.

Question 6

What are the force carriers?

Answer 6

EW - W & Z (beta decay): relative strength that is
much weaker than the EM or the strong force. It falls off with 1/r as well but
has another modifier which is contains the mass of the week bosons and it’s range is
thus smaller than that of the strong force.

Strong - g (quarks & nucleons): It’s relative strength
with respect to gravity is 1036 . It falls off with 1/r and has an infinite range
EM - γ: 0GeV (EM): It’s relative strength
with respect to gravity is 10^36 . It falls off with 1/r and has an infinite range

Question 7

How are particle interactions represented?

Answer 7

Feynman diagrams
give a visualisation of the calculation of transition probabilities from the initial to the final state

Particles are always depicted as going forwards in time
They meet or they couple to each other and to an interaction
particle at a so-called vertex.

Question 8

What is a annihilation diagram?

Answer 8

intermediate particles
hen you have the
outgoing final state where you have another vertex coupling the interaction to the outgoing particles

Question 9

What is a scatter diagram?

Answer 9

where you also have initial state and a final state – in this case the force carrier particle
cannot be produced as resonance because it exists for a too short amount of time so to
speak

Question 10

How can you split up particles consisting of quarks?

Answer 10

Two types of hadrons: – Baryons that are consisting of three quarks e.g the proton
and neutron and exotic particles like for example the lambda.

-Mesons consist of quark antiquark pairs. Examples are pions and kaons.

Question 11

What are the decay rules?

Answer 11

Heavier particles decay into lighter particles

selection rules due to quantum numbers related to forces as well as to symmetry principle

Quarks cannot exist freely due to their strengths

Question 12

Why is special relativity important?

Answer 12

The KE of particles approach or exceed their masses, resulting in time dilation, length contraction and loss of simultaneously and Lorentz transformation

Question 13

What is the 4-momentum?

Answer 13

Relativistic particles are described by 4-momentum
p = (p0,p1,p2,p3)
● Multiplication of scalar with 4-vector:
● Subtraction/Addition of 4-vectors: add linearly all entries (-1 can be +1)
● Multiplication of two 4-vectors gives a scalar → a “invariant” quantity
→ it is the same in all inertial systems

E^2−|p|^2=m^2
where m is the invariant or rest mass

Energy is conserved
● 3-Momentum is conserved
● 4-Momentum is conserved