Smashing the Standard Model: Physics at the CERN LHC Kenneth Johns University of Arizona
Jan 15, 2016
Smashing the Standard Model:
Physics at the CERN LHC
Kenneth JohnsUniversity of Arizona
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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
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First Beam in the LHCSept 10, 2008 in the ATLAS control
room
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First Beam in the LHCNo black hole or stranglet production
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First Beam in the LHCNo black hole or stranglet production
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First Malfunction at the LHCSept 19, 2008 in the LHC tunnel
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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
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Fundamental Forces
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Fundamental Particles
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Fundamental Particles
Or just another pattern to unravel?
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Standard ModelThe 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 ModelLocal gauge invariance
We first ask is the theory (L) invariant under global gauge transformations?
We next ask is the theory (L) invariant under local gauge transformations?
ψψmψγψiL μμ
by given is n Lagrangia Diracparticle free The
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Standard ModelWe can make the theory locally gauge
invariant by introducing a gauge covariant derivative that includes a gauge field
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!
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where
AeψψmψγψiL μ
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 ModelSpontaneous Symmetry Breaking (SSB)
occurs when a Lagrangian is invariant under some symmetry but the ground state (vacuum) is not Pencil falling
Heisenberg ferromagnet
2008 Nobel Prize to Nambu for discovering SSB
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Standard ModelHiggs 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 ModelConsider a charged self-interacting
complex scalar field (the Higgs field) Require the Lagrangian to be locally gauge
invariant
For 2 > 0 we have QED of charged scalars For 2 < 0 we have SSB and a continuum of
degenerate vacuum states
2*222
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Standard ModelThe Lagrangian for small perturbations
about the ground state
.interact2
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ation transformgauge specifica usingafter And
2/For
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A massive scalar (Higgs) with
A massive gauge boson with
And no massless Goldstone boson
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Standard Model
SummaryHiggs
Mechanism
MassiveGaugeBosons
LocalGauge
Invariance
MassiveHiggs Boson
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Standard ModelAn often used
analogy for mass generation
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Standard Model SuccessesTested from 10-17 to 1022 cmNo significant deviations (including
quantum corrections) at the 10-3 levelPredicted weak neutral currents –
discoveredRequired the existence of W, Z –
discoveredNecessitated charm and top –
discoveredPredicts only 3 neutrino families
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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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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.
Seeking the underlying patterns of matter
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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?
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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