Smashing the Standard Model: Physics at the CERN LHC

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

First Beam in the LHC • Sept 10, 2008 in the ATLAS control room

First Beam in the LHC • No black hole or stranglet production

First Malfunction at the LHC • Sept 19, 2008 in the LHC tunnel

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

Fundamental Forces 8

Fundamental Particles

Fundamental Particles • Or just another pattern to unravel?

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)

Standard Model • Local 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?

Standard Model • We 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!

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

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 • 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

Standard Model • Consider a charged self-interacting complex scalar field (the Higgs field) • Require the Lagrangian to be locally gauge invariant • For m2 > 0 we have QED of charged scalars • For m2 < 0 we have SSB and a continuum of degenerate vacuum states

Standard Model • The Lagrangian for small perturbations about the ground state A massive scalar (Higgs) with A massive gauge boson with And no massless Goldstone boson

Standard Model Massive Higgs Boson • Summary Higgs Mechanism Local Gauge Invariance Massive Gauge Bosons

Standard Model • An often used analogy for mass generation

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

Standard Model Successes • There are no experimental discrepancies with Standard Model predictions • But no Higgs boson observation either

Standard Model Parameters • On the other hand, the Standard Model does contain a lot of parameters

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.

Fundamental Forces Interactions arise from Fields (classical field theory) Exchanged quanta (quantum field theory) 25

Fundamental Fermions There are three families of leptons and quarks 26

R R R L L L L L L R R R Higgs Graviton g Fundamental Particles • Or just another pattern to unravel?

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

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

Smashing the Standard Model: Physics at the CERN LHC