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Smashing the Standard Model:
Physics at the CERN LHC
Kenneth Johns
University of Arizona
Outline
 Opening remarks – 5 min

Destroyed magnets, black hole video
 Standard model and Higgs – 12 min
 CERN and LHC accelerator – 8 min
 ATLAS detector – 5 min
 October disaster – 5 min
 Higgs – 12 min



Production
Decay
Discovery potential
 Other LHC physics and conclusions – 5 min
 Total
 UA contributions
2
First Beam in the LHC
 Sept 10, 2008 in the ATLAS control room
3
First Beam in the LHC
 No black hole or stranglet production
4
First Beam in the LHC
 No black hole or stranglet production
5
First Malfunction at the LHC
 Sept 19, 2008 in the LHC tunnel
6
Physics at the LHC
“There are known knowns. These are
things we know that we know. There
are known unknowns. That is to say,
there are things that we know we don't
know. But there are also unknown
unknowns. There are things we don't
know we don't know.”
Donald Rumsfeld
7
Fundamental Forces
8
Fundamental Particles
9
Fundamental Particles
Or just another pattern to unravel?
10
Standard Model
 The Standard Model unifies the strong, weak,
and electromagnetic interactions in the sense
that they all arise from a local symmetry
principle


Local gauge invariance
A minor problem is that the symmetries of the
Standard Model do not allow for massive gauge
bosons
 There are no experimental contradictions to
the predictions of the Standard Model, which
is complete in that its mathematical structure
allows calculations to be carried out

Tested to a high precision (1 part in 1000)
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Standard Model
 Local gauge invariance
The free particle Dirac Lagrangia n is given by
L  iψ γ μ μψ  mψ ψ
 We first ask is the theory (L) invariant under
global gauge transformations?
 x    x   ei x 
 We next ask is the theory (L) invariant under
local gauge transformations?
 x    x   ei  x  x 
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Standard Model
 We can make the theory locally gauge invariant
by introducing a gauge covariant derivative
that includes a gauge field
   D      ieA
1 



where A  A  A    x 
e
 Now our Lagrangian does remain invariant
under local gauge transformations


Using this derivative leads directly to QED!
And tells us that the photon is massless!

L  iψ γμ ψ  mψ ψ  e  A
μ
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Standard Model
We could apply the same idea to the
weak interaction Lagrangian (SU(2))


We’d find the need for three gauge
covariant derivatives containing three
gauge bosons
We’d like to identify them as the W+, W-,
and Z except they too are massless
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Standard Model
 Spontaneous Symmetry Breaking (SSB) occurs
when a Lagrangian is invariant under some
symmetry but the ground state (vacuum) is not

Pencil falling

Heisenberg ferromagnet
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 2008 Nobel Prize to Nambu for discovering SSB
Standard Model
Higgs mechanism



We have SSB when a Lagrangian is
invariant under some symmetry but the
ground state (vacuum) is not
If the broken symmetry is a continuous
symmetry, then there necessarily exists
one or more massless spin 0 particles
(Goldstone bosons)
If the broken symmetry is a local gauge
symmetry, then the Goldstone bosons get
absorbed (eaten) by the massless gauge
bosons thereby acquiring mass
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Standard Model
 Consider a charged self-interacting complex
scalar field (the Higgs field)

Require the Lagrangian to be locally gauge invariant
1  2
2
2
* 2
L  D         
2


For 2 > 0 we have QED of charged scalars
For 2 < 0 we have SSB and a continuum of
degenerate vacuum states

2
0
 2 v2


2
2
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Standard Model
 The Lagrangian for small perturbations about
the ground state
For   v    i  / 2
And after using a specific gauge transform ation


1
qv

2 2
L        2   
A A  interact .
2
2
A massive scalar (Higgs)
with m2  2 2
2 2
A massive gauge boson
2
2 2
with mA  q v
And no massless Goldstone boson
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Standard Model
Summary
Massive
Higgs
Boson
Higgs
Mechanism
Local
Gauge
Invariance
Massive
Gauge
Bosons
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Standard Model
 An often used
analogy for mass
generation
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Standard Model Successes
Tested from 10-17 to 1022 cm
No significant deviations (including
quantum corrections) at the 10-3 level
Predicted weak neutral currents –
discovered
Required the existence of W, Z –
discovered
Necessitated charm and top –
discovered
Predicts only 3 neutrino families
21
Standard Model Successes
 There are no
experimental
discrepancies with
Standard Model
predictions
 But no Higgs boson
observation either
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Standard Model Parameters
On the other hand, the Standard Model
does contain a lot of parameters
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Seeking the underlying patterns of matter
The basic constituents of matter are
the 6 quarks and the 6 leptons, and
the 4 carriers of the fundamental
forces. The three quark and lepton
generations have very similar
properties.
All the particles we know of (protons,
neutrons, nuclei, atoms are made
from these simple building blocks.
As far as we know, there are no
smaller units than quarks and leptons.
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Fundamental Forces
Interactions arise from


Fields (classical field theory)
Exchanged quanta (quantum field theory)
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Fundamental Fermions
There are three families of leptons
and quarks
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Fundamental Particles
Or just another pattern to unravel?
e
 e 
e 
  e
u u u
d d d
u u u
  
 
  L
d d d
Z
0
W


  
 
 
  L


c c c
s s s
c c c
t t t
b b b
t t t
s s s
t t t

W

g
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So what is this thing called the
Standard Model we are trying to smash
– and why
Let’s start with the fundamental
particles and their interactions
You’ve seen this many times so I won’t
linger here
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One of the goals of physics is to
understand the common elements of
these forces and particles
Perhaps they can be unified in the
sense that electricity and magnetism
are unified as electromagnetism
And in fact, in the 1960’s it was shown
that the electromagnetic force and
weak force had a common origin
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