Subatomic Physics:
Particle Physics Lectures
“Physics of the Large Hadron Collider”
(plus something about neutrino physics)
1
Particle Physics Lectures Outline
1 - Introduction
The Standard Model of particle physics
The fundamental particles and forces
2 - Practical Particle Physics
6 - Protons, Quarks and Strong Interactions
Evidence for quarks and colour
4 - The LHC and colliders
Particle acceleration
Colliders
5 - Detecting particles
Interactions of particles in matter
The ATLAS Detector
The Higgs mechanism
9 - Neutrinos
and maybe some B-physics
10 - Beyond the Standard Model
Supersymmetry
Extra dimensions ...
Gluons, hadronisation
Quark Confinement
Measuring particle physics
Running coupling constant
Units, decays, scattering
7 - Weak Interactions
Quantum numbers
Muon and tau decay
3 - Quantum Electrodynamics (QED)
Weak quark decays
Anti-particles
Quantum description of electromagnetism 8 - Electroweak and the Higgs boson
W and Z bosons
Feynman diagrams
2
Particle Physics and Me
Dr Victoria Martin
JCMB room 5419 victoria.martin@ed.ac.uk
My research deals with Particle Physics at Colliders.
I’m currently involved with two projects:
1. The ATLAS experiment at
the Large Hadron Collider.
The LHC collides protons
on protons at 14 TeV.
2. The international linear collider (ILC).
Design is to collide electrons and
positrons at 0.5 - 1 TeV (or more?)
3
Books etc
• In conjunction with attending the lectures you will need to read around the
subject to fully understand the material.
Most up to date:
•
Level of this course: Particle Physics, by B.R. Martin &
G. Shaw, 3rd edition (Wiley 2008)
- 10 copies in JCM Library
•
More advanced: Introduction to Elementary Particles by
D. Griffiths, 2nd edition (Wiley 2008)
- 4 copies in JCM Library
Oldies (but goodies):
•
Introduction to High Energy Physics - D.H. Perkins, 4th edition
(CUP 2000)
•
Quarks and Leptons –F. Halzen & A.D. Martin (Wiley 1984)
Further Resources:
•
For more information that you could ever need on every
particle ever: http://durpdg.dur.ac.uk/lbl/
•
Information about LHC and LHC physics: www.cern.ch
www.atlas.ch
4
Subatomic Physics:
Particle Physics Lecture 1
Our current understanding:
“The Standard Model of Particle Physics”
5
From the Atom to Subatomic
from introductory
Subatomic slides
atom
nucleus
protons &
neutrons
quarks &
electrons
}
}
Nuclear
Physics
Particle
Physics
6
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7
The Standard Model
The current understanding of the fundamental
particles and the interactions between them is called
the “Standard Model of Particle Physics”.
Boson-mediated
FORCES
Gravity
?
Electro!
magnetism photon
W±
Weak
Z0
Strong
gluons
8
Basic Particles (1st Generation)
The particles that you know already, e.g. from beta decay: n ! p e! "#e
Basic Constituents of Matter
Four spin-" fermions
Leptons
Electron and neutrino
Quarks
Nucleons are bounds
states of up-quarks
and down-quarks
Particle
Symbol
Electric
Charge
Type
electron
e!
-1
lepton
neutrino
"e
0
lepton
up-quark
u
+2/3
quark
down-quark
d
!1/3
quark
• Nuclear physics description of beta decay: n ! p e! "#e
• Particle physics description of beta decay: d ! u e! "#e
9
Higher Generations
Nature replicates itself: there are three generations of quarks and leptons
1st Generation 2nd Generation 3rd Generation charge,e
electron
e!
muon
electron
neutrino
"e
muon
neutrino
down quark
d
strange
quark
up quark
$!
-1
"# tau neutrino "$
0
bottom
quark
b
!⅓
top quark
t
+⅔
#!
s
u charm quark c
tau
Ordinary Matter: built from the 1st generation
Higher Generations:
• copies of ("e, e#, u, d)
• undergo identical interactions
• only difference is mass of particles
• generations are successively heavier
Why 3 generations?
symmetry/structure not
understood!
10
Antiparticles
More in PP Lec 2 (&
Combining relativity and quantum mechanics implies
Quantum Physics §14.5)
every particle has a corresponding antiparticle
Antiparticles of the SM particles are antimatter
Compared to its matter partner, an
antiparticle has:
• equal mass
• opposite electric charge
“Track”
left by a
positron
• opposite “additive” quantum numbers
(e.g. opposite colour charge)
Example: positron (e+) antiparticle of the electron (“anti-electron”)
Discovered in 1931 by Carl Anderson
Notation: bar over symbol or minus
e.g. for first generation:
u ↔ ū
plus
d ↔ d̄
e− ↔ e+
νe ↔ ν̄e
11
Schrödinger and Klein Gordon
• Quantum mechanics describes momentum and energy in terms of operators:
∂
�
Ê = i�
p�ˆ = −i�∇
∂t
∂
�2 2
• E=p2/2m gives time-dependent Schrödinger:
∇ Ψ(�r, t) = i� Ψ(�r, t)
−
2m
∂t
ΨE (�r, t) = ψE (�r) exp {−iEt/�}
• The solution with a definite energy, E:
• However for particles near the speed of light E2=p2c2+m2c4
2
2 ∂
Ψ(�r, t) = −�2 c2 ∇2 Ψ(�r, t) + m2 c4 Ψ(�r, t)
−�
2
∂t
• Solutions with a fixed energy, Ep=+(p2c2+m2c4)$, and three-momentum, p:
Ψ(�r, t) = N exp {i(�
p · �r − Ep t)/�}
• Also solutions with a negative energy, En=!Ep = !(p2c2+m2c4)$, and momentum, "p:
Ψ∗ (�r, t) = N ∗ exp {i(−�
p · �r + Ep t)/�}
• Negative energy solutions are a direct result of E2=p2c2+m2c4.
• We interpret these as anti-particles
12
Subatomic Forces
from introductory Subatomic slides
• At subatomic scales interactions between particles and nuclei are
caused by the three subatomic forces:
• The electromagnetic force
• The weak nuclear force
• The strong nuclear force
• The interactions due to these forces are evident in:
• Scattering: e.g. scattering of protons on protons at the LHC
• Particle Decay: e.g. decay of radioactive nuclei, decays of cosmicray muons
• Nuclear Fission and Fusion, e.g.: reactions in a nuclear reactor
235
92 U
+n→
236
92 U
→
144
56 Ba
+89
36 Kr + 3n
13
The Forces of Particle Physics
Strong
Electromagnetic
• Strongest force
• Acts on quarks only
• propagated by (8) gluons, g
• 2nd strongest force
• Acts on charged particles
• propagated by photon, %
Weak
Gravity
• 3rd strongest force
• Acts on all particles
• propagated by W± and Z0 bosons
• weakest force - negligible at
PP scale
• Acts on all particles
• Quantum mechanical description uses
“messenger particles” to propagate the
force between particles.
• Messenger particles are spin-1 bosons
• e.g. beta decay n!p e! "#e
by a
W!
boson
propagated
time
14
Colour Charge
• Every particle which feels the electromagnetic force carries an
electric charge: either positive or negative.
• The strong and weak forces also have charges associated with them.
Colour charge
• Only quarks (and gluons) experience the strong force.
• Every quarks carries a “colour charge” quantum number: either red,
blue or green. (This is in addition to their electric charge.)
• Every anti-quark also carries a “colour charge” quantum number:
either anti-red, anti-blue or anti-green.
Weak Hypercharge
Summary of Standard Model Vertices
force.
At this point
have discussed all fundamental fermions
• All quarks and all leptons experience the! weak
and their interactions with the force carrying bosons.
• “Weak hypercharge” is charge associated with the weak force. We
! Interactions
characterized by SM vertices
won’t use weak hypercharge much in these
lectures.
ELECTROMAGNETIC (QED)
e
15
-
q Model
CouplesVertices
to CHARGE
Summary ofHigher
Standard
Orders
e
Qe
Does NOT change
! eAt this point have qdiscussed all fundamental
fermions
FLAVOUR
So far
lowest
order
term in t
2 considered
andonly
their
with the
force carrying
bosons.
e interactions
γ
α=
γ
4π series.
perturbation
Higher
order
terms also
! Interactions
characterized
by SM
vertices
STRONG (QCD)
contribute
ELECTROMAGNETIC (QED)
time
What do the particles do?
see: JH D&R lectures 2, 14, 15
q
e
+
q
Lowest Order: e
gs
q Qeγ
e
Particles interact via one of the forces: strong,
e
q
gs2
electromagnetic or weak.
αs = e2
g
γ α = 4π
γ
e
4π
Couples to COLOUR
+ to CHARGE
Couples
Does NOT change
Does NOT change
FLAVOUR
µ
FLAVOUR
µ
WEAK Charged Current
STRONG (QCD)
ν
-
d’u Changes FLAVOUR
e
Two main interactions:
gwVckm q Couples to COLOUR
gw
d
e Order:
For
coupling
u gs
• Particle scattering
"#eQUARKS:
Second
Does
NOT change
q
BETWEEN
generations
+
+
+
+
e α =ggw2 2 µ W- e W Wµ+ FLAVOUR
• can be elastic or inelastic
s
αsw= 4π
g
4π
• we’ll mainly consider inelastic scattering
WEAK Neutral
ChargedCurrent
Current
e!
-e.g.
scattering
of
electron
and
positron,
•
qµ Changes FLAVOUR
e
µe ν, eνe e
"d’
µ
producing a pair of muons e+e!&µ+µ!e-, νeg
! g V
+....
e
• Particle decay
• e.g. Beta decay: d ! u e! "#e
• e.g. Muon decay: µ!&e! "#e "µ
-
w
g 2
Third Order:
αw = w
µ qw
u
0
Z
W
4π
ckm
W
Does
NOT change
For
coupling
"#eQUARKS:
FLAVOUR
BETWEEN
generations
0+
Z
W
Dr M.A. Thomson
We’ll
learn
all about
WEAK
Neutral
Current
these type ofe diagrams
, νe
e-, νe the course
throughout
q
Z
0
q
+....
e!
Does NOT change
16
Z0
FLAVOUR
Hadrons: Mesons & Baryons
• Free quarks have never been observed - quarks are locked inside hadrons
• Hadrons are bound states of quarks: either (qqq) or (qq̅)
• Charge of hadron is always integer multiple of electric charge, e
• Colour charge of hadron is always neutral
• Two types of hadrons – mesons and baryons (also anti-baryons! q͞q͞q)
Baryons = qqq
Mesons = qq̅
Three quark bound states
Bound states of quark anti-quark pair
Fermions: spin 1/2 , 3/2 ...
Bosons: spin 0, 1 , 2
e.g. proton (uud), neutron (udd)
e.g. pions
q
anti-baryons e.g. anti-proton
+
π
π−
π
0
= (ud̄)
= (ūd)
1
= √ (uū − dd̄)
2
q̅
q
•
q
q
p
n
=
=
(uud)
(udd)
p̄
=
(ūūd̄)
17
Summary
The Standard Model of Particle Physics
An elegant theory that describes accurately (almost) all
measurements in particle physics
Matter
• fermions, spin-"
• 3 generations of quarks & leptons
Quarks and Leptons Charge, e
Interaction
Gauge
Bosons
Charge,
e
"e
e
"µ
µ
"'
'
0
!1
Strong
gluons, g
0
u
d
c
s
t
b
+2/3
!1/3
Electromagnetic
Photon, %
0
Weak
W, Z
0, ±1
Gravity
graviton?
0
• Antimatter partner for each
•
Forces
• mediated by the exchange of
spin-1 bosons
fermion
Quarks bind together to form
hadrons - mesons and baryons
18