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Transcript
New Frontiers in
Particle Physics
Jeff Forshaw
University of Manchester
1
What we know
• There are a few elementary
particles that interact with
each other.
• The interactions come in four
types:
Gravity Electromagnetism
Weak
Strong
2
Standard Model
• Crowning glory of 20th Century
physics.
• A single theoretical framework
that describes the weak, strong
and electromagnetic interactions
of (nearly) everything!
ne
W
d
eu
4
Foundations
Input
• Particle content of world
• Gauge symmetry of forces
Then impose the following
Rules
• Quantum mechanics
• Relativity
1979 Nobel Prize for
Glashow, Weinberg & Salam
5
What is Gauge
Symmetry?
Y
Ye
ij(x)
• Multiply quantum wavefunction
by a space-time dependent
complex phase.
• Insist that this is a symmetry.
• Photons and the electric charge
emerge as new physical concepts!
6
Beyond electric
charge
• Colour charge
• Weak charge
• Electric charge
QCD
Electroweak
The Standard Model is not a GUT!
But it does partially unify three of
Nature’s four forces.
7
The Higgs Boson
That’s almost the whole story….
But the gauge symmetries of the
Standard Model do not permit
particles to carry mass!
Q. How is mass generated?
A. By the non-trivial action of
the vacuum!
It grabs hold of things!
8
The Standard Model
Works!
• Experiments around the world,
especially at CERN, have
tested the Standard Model to
remarkable accuracy.
(1 part in a thousand)
1999 Nobel Prize to ‘t Hooft & Veltman
• A “light” Higgs is predicted.
We await the LHC (2005) for
a detailed study of the Higgs.
9
Mass of Higgs is less than 300 GeV
(95% confidence).
(from data collected at LEP, SLC and
the Tevatron.)
10
A simulated Higgs event at LHC
11
Beyond the Standard
Model
Despite all its successes the
Standard Model can never hope
to explain some things.
There must be NEW physics!
12
There are lots (more than 20)
free parameters whose values
are not explained.
What is the origin of gauge
symmetry?
Why are there 3 generations?
Are the particles fundamental?
How does confinement work?
13
A 5th force?
Is the Higgs particle there?
Maybe it’s not!
In any case, something must
show up when we start to
collide particles with energies
bigger than of order 1 TeV.
14
Do the neutrinos carry mass?
Why are they so light?
15
Neutrinos
In the Standard Model, the
neutrinos do not carry mass.
But data say otherwise!
Sub eV scale masses.
Could this be the first evidence
of a Grand Unified Theory?
Next decade will see extensive
study of the “neutrino sector”.
16
How we’ll study the neutrinos:
17
18
Why is the world nearly 100%
matter when the Big Bang would
have spewed out initially equal
amounts of matter and anti-matter?
19
CP Violation
Sakharov:
If Big Bang is to produce unequal
amounts of matter & anti-matter
CP must be violated.
“Physics is not the same when all
particles are replaced by their
corresponding anti-particles and
then everything is viewed in a
mirror.”
New frontier experiments:
SLAC (BaBar) in USA
KEK (Belle) in Japan (1999).
20
What is the “dark matter”?
21
Dark Matter
There is a lot more matter in the
Universe than is visible to us!
What is it?
UK physicists actively searching
for the dark matter at the Boulby
salt and potash mine in Yorkshire.
22
Candidates for Dark
Matter
23
The Boulby Mine
24
What about gravity!?
25
Beyond particles:
String Theory &
Quantum Gravity
Since Einstein, a dream of
particle physicists has been to
find a single theory that explains
all natural phenomena, including
gravity.
Over the years string theory has
emerged as the undisputed
leader in the pursuit for a
Theory of Everything.
26
Strings
Rather than particles, the basic
building blocks of all things are
postulated to be tiny pieces of
“string” that vibrate.
Typical distance: 10 -33 cm
So they look like point particles
when viewed in experiments.
The different modes of vibration
lead to the spectrum of particles
we see in experiment.
27
Gravity and gauge symmetry
emerge “for free”!
No evidence yet though.
Astonishingly, the theories also
only make sense if the Universe
has extra curled up dimensions!
Superstrings are 1-dimensional
objects vibrating in a space-time
of 10 dimensions.
28
Supersymmetry
For string theories to make
sense, the world must be
supersymmetric.
SUSY particles could well be
produced at the LHC.
29
30
Duality
Around 1995, string theorists
led by Ed Witten at Princeton
discovered that all their
seemingly different theories are
in fact different aspects of the
same theory!
To date, nobody has managed
to write down the underlying
theory. Although it has been
given a name: M-Theory.
31
11-dimensional
supergravity
Type
IIA
Type
IIB
M-Theory
E8xE8
heterotic
SO(32)
heterotic
Type I
32
The future
We are poised at the edge of
a new era of physics beyond
the Standard Model.
Supersymmetry & ToE
Higgs and the origin of mass
Neutrino physics
CP violation
Dark Matter
33
Experiment will lead the way
Today:
BaBar, HERA, LEP, Tevatron, Boulby
Near term:
MINOS
Large Hadron Collider
Long term:
New linear collider
Muon collider & neutrino beam
???????
34