The Higgs Boson: without the maths and jargon

The Higgs Boson:without the maths and jargonDavid Hall

Graduate Seminar SeriesSt Catherines College MCR

11th May 2011

Questions to be answeredWhat is the Higgs boson?Why is it so important?Why do we think it exists?How is the LHC going to find it?+ any you might haveThe Higgs Boson 11/05/11David Hall1IntroductionEverything in the universe is made of atomsThese are made of 3 things:protonsneutronselectrons

Particle physics:Electron is fundamentalProtons and neutrons arentThe Higgs Boson 11/05/11David Hall2

The Standard ModelDecades of experiments have lead to the Standard Model

Protons and neutrons are made of up and down quarks

Ordinary matter is made of just 3 particles

Other leptons and quarks are harder to find

The Higgs Boson 11/05/11David Hall3The Standard ModelFour fundamental forcesElectromagnetism (electricity, magnetism and light)Strong (holds the nucleus together)Weak (radioactive decay)Gravity (motion of planets, galaxies)

Each has associated particles

The Higgs Boson 11/05/11David Hall4Symmetries in natureThis all seems great, so why do we need a Higgs boson?

Fundamental forces come from symmetries of nature

Problem:These same symmetries prevent particles from having massBut we know they doThe Higgs Boson 11/05/11David Hall5

The Higgs mechanismTo give particles mass, we need to break a symmetry

In the SM, this is done through the Higgs mechanism

Spontaneous symmetry breaking(pencil analogy)The Higgs Boson 11/05/11David Hall6

The Higgs mechanismTo give particles mass, we need to break a symmetry

In the SM, this is done through the Higgs mechanism

Spontaneous symmetry breaking(pencil analogy)The Higgs Boson 11/05/11David Hall6

Mexican hatThe Higgs bosonThe Higgs mechanism requires a Higgs fieldWhen a particle interacts with this field, it acquires mass(honey demonstration)The Higgs boson is an excitation of this fieldSo if we find the Higgs boson, then the Higgs mechanism is correctThe Higgs Boson 11/05/11David Hall7The Higgs bosonThe Higgs mechanism requires a Higgs fieldWhen a particle interacts with this field, it acquires mass(honey demonstration)The Higgs boson is an excitation of this fieldSo if we find the Higgs boson, then the Higgs mechanism is correctThe Higgs Boson 11/05/11David Hall7

Here I am!Peter Higgs

The Higgs Boson 11/05/11David Hall8Is the Higgs mechanism correct?SM describes perfectly everything ever seen

Higgs mechanism predicted mass of W and Z particlesExperimentally verified in 1983

The Higgs Boson 11/05/11David Hall9

Is the Higgs mechanism correct?SM describes perfectly everything ever seen

Higgs mechanism predicted mass of W and Z particlesExperimentally verified in 1983

There are alternativesBut we would also find them at the Large Hadron ColliderThe Higgs Boson 11/05/11David Hall9

Large Hadron Collider

Proton-proton accelerator27km circumferenceNearly 200m undergroundHighest energy ever!The Higgs Boson 11/05/11David Hall10Large Hadron ColliderProton-proton accelerator27km circumferenceNearly 200m undergroundHighest energy ever!

ATLAS:Detectors surrounding the collision pointMeasure particles energies and tracks

The Higgs Boson 11/05/11David Hall10

Large Hadron Collider

The Higgs Boson 11/05/11David Hall11How is the Higgs boson produced?When the protons collide, new particles can be producedDifferent particles have different probabilities

Very rarely, we will produce a Higgs bosonThe Higgs Boson 11/05/11David Hall12

Finding the Higgs bosonSo youve made your Higgs boson

But it decays immediately

What to depends on the mass of the Higgs boson

This means we exclude a range of masses

The Higgs Boson 11/05/11David Hall13

Finding the Higgs boson

The Higgs Boson 11/05/11David Hall14The futureWere closing in on the Higgs bosonIf its there, well find it in the coming yearsThe Higgs Boson 11/05/11David Hall15