Transcript The Large Hadron Collider and Beyond Steve King, University of Southampton, 1

The Large Hadron Collider and Beyond
Steve King, University of Southampton,
Masterclass, 24th March, 2010
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Why “High Energy”?
There are three reasons:
1. The resolving power of a microscope is
limited by the wavelength L of the light.
L
L
e.g. bats use high frequency
sonar with wavelength less
than or about same the size
of an insect.
So, like bats, to see small things we need light with small wavelength
and high frequency – hence high energy photons since E  hf2
2. Einstein taught us that
E  mc
2
So high energy is
equivalent to large mass.
With high energies we
are able to produce very
heavy particles.
The basic unit of energy is the
“electron Volt” which is the energy that
a single electron receives when it passes
from the negative terminal to the
positive terminal of a 1 Volt battery.
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3. Boltzmann taught us that E kT so high energy E
means high temperature T where k is Boltzmann’s
constant. In the early Universe, just after the big bang, the
universe was very small and very hot.
So high energy physics teaches us about the early Universe.
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What have we learned from High Energy Physics?
- Matter is made of particles (“particle physics”)
To understand this, take an apple and a knife, and cut the apple in
half once. Then cut one half in half again. Then continue the process.
After some number of cuts you will arrive at a single atom.
Question: how many cuts are required?
Answer: only 84 times!
A single atom
A nucleus
with orbiting
electrons
nanometre
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




The electrical
attraction is
caused by
photon
exchange
-


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The nucleus of the atom is positively charged
It is made of protons (p) and neutrons (n)
The protons and neutrons are made of charged quarks
The quarks also carry a new “colour charge”
The quarks
are stuck
together by
gluons
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I think I finally
understand atoms
8
Nothing lasts for ever
The (free) neutron is radioactive and beta decays after 15 minutes
into proton, electron and “neutrino” (electron-like neutral particle)
This decay process is very weak (15 minutes is an eternity!)
Without such weak interactions the Sun would shut down!
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Neutrinos from the Sun
Question: How many neutrinos from the Sun are passing
through your fingernail in one second?
Answer: 40 billion! – day and night since neutrinos
can pass right through the Earth without interacting
Photo of Sun taken
underground using
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neutrinos
The four forces of Nature
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Quarks and Leptons
12
The mystery of spin
All observed elementary particles have spin i.e. spinning
angular momentum like a spinning top
In quantum mechanics the basic unit of angular momentum
is Planck’s constant h divided by 2
Photons and gluons have one unit of spin
e.g. polarization of light is due to the photon spin
Quarks and leptons have half a unit of spin
e.g. In chemistry each s-orbital can only be occupied by at
most two electrons, spin-up and spin-down.
N.B. Without spin any number of electrons could pile into
the lowest energy s-orbital and Chemistry AS level would
not exist – unfortunately you not exist either!
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What is the origin of the particle masses?
Mass
t
e
e

u
d


c
s

b
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The Higgs Boson
In the “Standard Model” the origin of mass is
addressed using a mechanism named after the
British physicist Peter Higgs.
This predicts a spinless particle: Higgs boson
According to
Higgs, space is
filled with a new
type of field
analagous to
magnetic or
electric fields…
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The CERN Large Hadron Collider (LHC)
Atlas
particle_event
_full_ns.mov
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Pictorial History of the LHC
10th September 2008 - LHC switched on
– BBC devote a whole day of coverage to “Big Bang day”
-Soothsayers predict the end of the World
- Scientists at CERN celebrate
Too many
late
nights?
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Pictorial History of the LHC
19th September 2008 – LHC explosion due to bad
soldering joint between two magnets – repairs took 14
months
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Pictorial History of the LHC
20th November 2009 – LHC switched on again
23rd November 2009 – first LHC proton- proton collisions
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Pictorial History of the LHC
16th December 2009 – LHC routine shut down for Christmas
28th February 2010 – LHC switched on again
19th March 2010 (last Friday) – LHC proton beams at 3.5 TeV
E=3.5 TeV
E 
mc2=0.938 GeV
mc 2
v2
1 2
c
v
 0.999999964
c
World land
speed record
for protons
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The CERN Large Hadron Collider (LHC) will
next Tuesday collide protons on protons at energy
of 3.5 TeV +3.5 TeV = 7 TeV
p
LHC plans to run at 7 TeV
for 18-24 months to
acquire as many collision
events as possible
1 TeV
p
H
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Supersymmetry ?
All particles in nature are either fermions or bosons.
Fermions have half units of spin, and tend to shy
away from each other, like people who always
stay in single rooms at the fermion motel.
Bosons have zero or integer units of spin, and
like to be with each other, like people who stay
in shared dormitories at the boson inn.
Supersymmetry says that for
every fermion in Nature there
must be a boson and vice-versa.
Supersymmetric particles have
not been observed (yet) so they
must be heavier - SUSY must be
broken by some mechanism
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u c t
d
s b
 e   
e  
The Generations of Matter
SPIN 0
BOSONS
Sleptons Squarks
Leptons
Quarks
SPIN ½
FERMIONS
u c t
d s b
 e   
e  
The Generations of Smatter
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BOSONS
FERMIONS
Gravitino
W  W  Z0
Photino
Gluino
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Could dark matter observed in the collisions of galaxy
clusters be the photino? – LHC will “see” it
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SUSY permits a unification of forces
Strong
Weak
Electromagnetic
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string1.avi
Strings live in
11 dimensions
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What if no Higgs or SUSY
is discovered?
My personal best bet for the first discovery at the LHC is
a heavier version of the Z boson called a Z-primed
Other possibilities include a fourth family, composite
quarks and leptons, extra dimensions, technicolour, black
holes (environmentally friendly), extra exotic particles
with weird charges and colours, etc..
Nightmare scenario: one Higgs boson and nothing else!
I DON’T BELIEVE THIS WILL HAPPEN
More likely LHC will discover something no-one has
thought of – let us hope that whatever is found will be of
great benefit humanity – I think there is every chance
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What has the LHC done for us?
Many technological and medical spin-offs:
-Medical imaging chips developed at CERN
-Software developed at CERN used in medical physics
-World Wide Web developed at CERN
Many top engineers and scientists trained at CERN
- Oxford positron systems founded by CERN physicst
- Young people attracted into science by CERN physics
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