Download introduction to the standard model of particle physics

INTRODUCTION TO THE
STANDARD MODEL OF PARTICLE
PHYSICS
Class Mechanics
My office (for now): Dantziger B Room 121
My Phone: x85200
Office hours: Call ahead, or better yet, email....
Even better than office hours: Use the forum for the class on
Moodle. I’ll be reading it and answering questions so that
everyone can have access to the questions/answers.
Assignments: will be given posted on the website every week.
Solutions will be posted after 2 weeks. There is no requirement
to hand them in or even try to solve them, but.... if you do not
try to do them yourself you WILL fail.
TA: There is none.
Exams/quizzes: The final is on 24/5/2011, Moed B is on
18/7/2011. There will also be a midterm on 23/3/2011 which
will be worth up to 25% of the final grade.
Current Syllabus
(wishful thinking)
1
Introduction
Review of relativistic kinematics
Intro to scaering
2
Equations: Schroedinger, KleinGordon, and Dirac
Intro to Feynman Diagrams
Basic QED Processes
3
More QED
Quarks. the Eightfold Way, and
Isospin
4
Hadrons: Baryons, and Mesons
Quark Families
The Particle Zoo
5
Experimental Methods I:
Accelerators
Targets
Particle Detectors I
6
Experimental Methods II:
More Particle Detectors
Experiment Design
Data Analysis
7
Nucleon Form Factors: Elastic and
Inelastic
DIS and the Feynman's Partons
Bjorken Scaling
8
QCD and Scaling Violation
Intro to Weak Interactions:
Chirality, Maximal Parity Violation,
and Beta Decay
9
Weak Interactions II:
Charged and Neutral Weak Currents
The Conserved Vector Current
Hypothesis
Some more Isospin
10
Spontaneous Symmetry Breaking
and the Higgs Mechanism
11
Review of Modern Experiments I:
Nucleon Structure and Spin
EMC and Medium Modifications
LHC and Heavy Ion Experiments
12
Standard Model Failures
Beyond SM? Some possibilities
13
Beyond SM Modern Experiments:
EDM, Extra Symmetries, Direct
Searches
14
Intro to Quantum Field Theory:
Why Relativistic QM is not enough
QFT Formalism
Some Second Quantization
Hierarchy of Particles
Stuff you see around you is made up of
molecules.
Molecules are made up of Atoms.
Atoms are made up of Nuclei and Electrons.
Nuclei are made up of protons and neutrons
(collectively nucleons).
Nucleons are made from Quarks.
Quarks and Electrons are (as far as we know)
elementary particles.
So what are “Elementary” Particles
Elementary Particles are ‘point like’ (no internal structure) fermions (obey Fermi-Dirac)
with spin 1/2. They have no size we can measure (nothing to do with the ‘classical’
electron radius).
We know of 2 types of elementary particles: Quarks and Leptons.
(all) Quarks - have electric charge, either -1/3 or +2/3 the charge of an electron.
Quarks come in 6 different ‘flavors’:
up (u), down (d), strange (s), charmed (c), bottom (b), and top (t).
They also come in three different ‘colors’ (nothing to do with real color of course).
Usually we label them Red, Green, Blue.
Leptons - have charge 0 or -e.
They also come in six flavor:
electron, muon, tau
electron neutrino, muon neutrino, tau neutrino
Leptons have no color.
Antiparticles
All particles have a corresponding “antiparticle” which has the exact opposite value for
all quantum numbers (charge, color, magnetic moment, ....) and the same mass.
For notation we put either a + or - for the charges leptons (e-/e+) etc., or we use a bar
over the symbol for quarks and uncharged leptons.
When a particle and an anti-particle meet they annihilate and to a state with zero
quantum numbers (which can then recreate particles with quantum numbers, provided
these some up to zero).
Particle Families
Quarks and Leptons can be arranged in 3 ‘families’ or ‘generations’ (but we don’t know
why!)
Generation
1st
2nd
3rd
u
(up)
d
(down)
c
(charm)
s
(strange)
t
(top)
b
(bottom)
-1
e-
µ-
τ-
0
ve
vµ
vτ
+2/3
Quarks
-1/3
Leptons
Hadrons
Leptons show up as free particles (electrons mostly). Quarks are always bound into
‘white’ (colorless) states called Hadrons.
Red+Green+Blue=White, also Red+(anti)Red=Blue+(anti)Blue=Green+(anti)
Green=White.
Two type of Hadrons are found in nature:
Baryons, which are states of three bound quarks or anti-quarks (for anti-baryons):
Mesons (and anti-mesons) which are a bound state of a quark and anti quarks.
A few examples are:
particle
composition
charge
proton
uud
1
neutron
udd
0
antiproton
u̅u̅d̅
-1
antineutron
u̅d̅d̅
0
π+
ud̅
+1
π-
uu̅ or dd̅
0
π0
du̅
-1
No ‘exotics’ (like
qqqqq̅) have been
found yet
Interactions
The particles interact among themselves through 4 types of forces which we understand
to happen through the exchange of ‘field quanta’, which are boson particles, also known
as ‘gauge bosons’ for technical reasons which you will understand later.
Boson
Electromagnetism (QED)
photon
∞
0
1
Strong Interaction
gluon
10-15
0
1
Weak Interaction
W+, W-, Z0
10-18
~80 GeV
1
Gravity
Graviton
∞
0
2
Range Boson Mass Boson Spin
St
a
nd
ar
d
Mo
d
el
Force
The standard model also has at least one Higgs boson (but maybe more) which
explains the masses of the other particles (without the Higgs mechanism they
would be massless).
Range of the Forces
The range of the interactions is related to the mass of the exchanges gauge boson (M).
According to the uncertainty principle, it’s possible to ‘create’ a particle with energy
Δ∆E = Mc2, for a short time Δ∆t such that Δ∆E Δ∆t ~ h̄ (these are called ‘virtual particles’).
Such a particle particle can move a maximum distance of:
∆x = c∆t = c�/∆E = �c/M c2
Since the photon has zero mass, the range of the EM force is infinite.
The W boson has a mass of ~80 GeV/c2 the range of the weak force is:
−3
∆x = 0.197 (GeV f m)/80(GeV ) ∼ 2 · 10
useful to
remember
�c ∼ 0.197 GeV · f m
f m ∼ 10−18 m
What works where?
Weak
EM
Strong
Quarks
√
√
√
Charged
Leptons
√
√
×
Neutral
Leptons
√
×
×
Units
In this class we will try to use the so called ‘natural’ units, where we set
�=c=1
Using these units energy, mass, and momentum all have the same units (of energy).
1 eV ∼ 1.602 · 10
−19
J
�c ∼ 197 M eV f m
e2
1
α=
∼
�c
137
−36
1 eV ∼ 1.78 · 10
Kg
1 eV
−1
∼ 6.58 · 10
−16
1 eV ∼ 1.14 · 104 ◦ K
sec
Example: proton mass
938.272 MeV
938.272 · 106 eV = 1.5 · 10−10 J
1.5 · 10−10 /(3 · 108 )2 = 1.67 · 10−27 Kg
Example: ionization of H
atoms at ~13.6 eV
13.6 · eV ∼ 155 · 10 K
3