Particle Sorting
Particle Physics Lesson 7
Name the quantities
Quantity
Unit
N
eV
ms-2
Hz
C
Name the quantities
Quantity
Unit
Force
N
Energy
eV
Acceleration ms-2
Frequency
Hz
Charge
C
Which equation?
Known Values
Value
E
λ=?
EK, f
φ=?
λ
f=?
v, u, a
s=?
λ, m
v=?
Equation
Rearranged
Which equation?
Known Values
Value
Equation
Rearranged
E
λ=?
E=hc/λ
λ=hc/E
EK, f
φ=?
hf=φ+EK
φ=hf-EK
λ
f=?
c=fλ
f=c/λ
v, u, a
s=?
v2=u2+2as s=(v2-u2)/2a
λ, m
v=?
λ=h/mv
v=h/mλ
Homework

Still no homework  will give to you
tomorrow.
Today’s Objectives

Explain what is meant by the terms hadron,
lepton, baryon and meson.

Recall the lepton numbers and baryon numbers
for a variety of particles.
Hadrons vs. Leptons




Hadrons are particles and anti-particles that can
interact through the strong interaction.
Examples are protons, neutrons, pions, kaons
Leptons are particles and anti-particles that do
not interact through the strong interaction.
Examples are electrons, muons, neutrinos.
Can you feel the force?

Both hadrons and leptons can interact through the
electromagnetic interaction if they are charged.

Hadrons can also interact through the strong
interaction and leptons can also interact through the
weak interaction.

Except when hadrons decay – that’s through the weak
interaction (remember β-decay involves W boson).
Some quick questions...





1. List these particles in the order of highest
mass:Electron, muon, neutron, K meson, pions,
protons.
2. What is a hadron?
3. What is a lepton?
4. Which quantities are conserved when a
particle decays?
Particle Cards

Sort the cards by mass (two column <1000
MeV/c2 on the left >1000 MeV/c2 ).

Why are there pairs of particles with the same
mass?
What do you notice about relative position of
leptons?
What do you notice about position of baryons?
What do you notice about position of mesons?



Now smash them together...





Total energy of particles before collision:Rest energy + kinetic energy  original particles
Total energy of particles after collision:Rest energy + kinetic  of the products
Conservation of energy means that Total energy
of particles before collision = Total energy of
particles after collision
Conservation of Energy

Rest energy of the products = total energy
before – the kinetic energy of the products.

E.g if two protons (rest energy about 1 GeV)
each have kinetic energy of 2 GeV and are made
to collide then total energy before = 6 GeV

If the kinetic energy of the products = 1.5 GeV
then that leaves 4.5 GeV left as rest energy of
the products.
Baryons

Hadrons come in two types:-

Those which eventually contain protons in their
decay products  Baryons

Those which do not include protons in their
decay products  Mesons
Particle Classification
Matter & Antimatter
Hadrons
Baryons
Leptons
Mesons
What question should be asked at each branch to classify the particles?
Some more quick questions...

What is a baryon?

What is a meson?
What are the baryon and lepton numbers for the
following?
Proton, kaon, neutrino, pi meson, antimuon,
neutron, anti proton, electron, antineutron.

Lepton & Baryon Numbers





If a particle is a lepton we assigned a lepton
number of L=1.
If a particle is an anti-lepton we assigned a
lepton number of L=-1.
If a particle is not a lepton we assign a lepton
number of L=0.
The same holds true for baryon number, B.
Baryon: B=1,anti-baryon:B=-1,not baryon: B=0
Baryon & Lepton Numbers
Particle
Type
Baryon Lepton Examples
No.
No.
Baryon
1
0
p, n, , , , , 
Anti-Baryon
-1
0
p, n , , , , , 
Meson
0
0
 , K , ,  ,  , J /
Lepton
0
1
e , e ,  , 
Anti-Lepton
0
-1
e , e ,   , 


Some Examples






Proton
Anti-Neutron
Electron
Neutrino
Plus Pion
Q=1, B=1, L=0
Q=0, B=-1, L=0
Q=-1, B=0, L=1
Q=0, B=0, L=1
Q=1,B=0, L=0
Note that isn’t a meson number. We can
identify mesons because they are neither baryons
nor leptons ie, B = 0 and L = 0
Summary

Hadrons “feel” the strong force, leptons do not.
Baryons include protons in their decay products,
mesons do not.

Leptons are light, hadrons are heavy.

Baryon number and lepton number are also
conserved in all decays.

Alpha and beta decay
220
86
Rn 
C
14
6
Answers
220
86
Rn  Po He
216
84
4
2
C  N  e  e
14
6
14
7
0
1

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