Particle Physics

Particle Physics

Aim: To determine what matter is made of, particle physics searches for elementary particles, particles that can not be broken down any further.

Particle Colliders

To deduce the finer structure of matter, particles are smashed together.

Types of particle accelerators 1. Linear colliders2. Cyclotrons3. Synchrotrons

Linear Accelerators

Use electric fields to accelerate charged particles.

eg Crooke’s tube An early linac

Linear Accelerators

eg cathode ray tube televisions

(CRT TV)

Linear Accelerators

Electrons are heated at the cathode (-). They accelerate towards the anode (+)

Try the linac simulation

Particle Accelerators

Linear Accelerators

A progressive linac. The voltage switches from + to – progressively attracting and repelling the charged particle.

The chamber is evacuated.

Linear Accelerators

Stanford Linear Accelerator Center (SLAC) is the largest linac, 3.2 kilometers long and accelerates electrons to 25 GeV.

Cyclotron

A circular particle accelerator.

It uses magnetic fields to turn charged particles in a circular path.

How does this work?

The motion of charged particles in magnetic fields

Magnetic fields are drawn like an arrow

When the arrow travels away, it looks like this

X

When the arrow comes towards you it looks like a

point .

Magnetic field going into the page

x x x x x x x x

x x x x x x x x

x x x x x x x x

x x x x x x x x

Electron moving at right angles

x x x x x x x x

x x x x x x x x

x x x x x x x x

x x x x x x x x

v

Experiences a force at right angles to it direction of motion

x x x x x x x x

x x x x x x x x

x x x x x x x x

x x x x x x x x

F

The charged particle travels in a circlex x x x x x x x

x x x x x x x x

x x x x x x x x

x x x x x x x x

F

Cyclotron

The charged ions start in the centre.

As they accelerate their radius increases.

They eventually leave the dees

Cyclotron

Synchrotrons

Eg Fermilab circumference= 6.3km CERN c=27km• turn the charged particles with magnetic fields • vary the magnetic field to ensure the radius is

fixed. This way the charged particle goes round and

round the same “race track” and can be accelerated to VERY high speeds, 99.99% the speed of light!

Magnetic fields focus the particle beam as it travels around the track.

LHC

http://public.web.cern.ch/public/en/lhc/Facts-en.html

Cloud Chamber

Radioactive material & a cloud chamber

Formative Practical InvestigationParticle Collider Simulator

Aim: Determine what shape and size the object is inside the detector.

How fast will you make the incoming particle?Will you vary the speed?What will be the direction of your incoming particle?How will you be systematic in your approach?How will you record your results?

Particle Detectors

How can we see the unseeable?Cloud chambers – use super saturated vapour.

Charged particles cause the vapour to condsense into a liquid.

Bubble chambers – use super heated liquid.Charged particles cause the liquid to start

boiling.

Particle Detectors

Only charged particles leave tracks.

Magnetic fields turn particles according to their charge.

Scientist can work out the charge, mass and speed of the particles.

Discovery of the omega minus particlePredicted 1962, found 1964.

Modern particle physics uses solid state detectors and banks of computers.

Particle Physics >1950’s

So instead of finding elementary particles in particle detectors, a whole “zoo” of particles were discovered.

!

Baryons are subatomic particles. The Greek word 'barys' means 'heavy'.

This is a list of baryons known to date. Proton, Neutron, Delta, Lambda, Charmed lambda, Bottom lambda, Sigma, Xi, Charmed Xi, Omega, Charmed Omega

• Mesons (from the greek “middle”) such as pions, kaons, eta-mesons.

• Some particles existed for very very short periods of time.

• Scientist found it hard to make sense of the bewildering array of new particles.

In search of giants part 4

In search of giants part 5

Particle Physics >1950’s

So instead of finding elementary particles in particle detectors, a whole “zoo” of particles were discovered.

Murray Gell Mann

Gell Mann tried to make sense out of this array of particles in a similar way that Mendeleev made sense out of the elements. He realised there were patterns in their properties.

Murray Gell Mann

He proposed the existence of quarks, elementary particles that combine to form many different particles (1964)

There are six ‘flavours’ of quarks!

Quarks have fractional charge!

The up quark is the lightest.

Proton

u

ud

Two up quarks and one down quark

d

ud

2 down quarks and 1 up quark

Neutron

u

ud

There are force particles called gluons which glue protons (or neutrons) together.

Current theory of matter

Particles we call ordinary matter (has mass, occupies space) is composed of elementary fermions, namely quarks and leptons.

LeptonsMatter Fermions

Quarks

Neutrinos

• an elementary particle • travels close to the speed of light• electrically neutral• can pass through matter almost undisturbed. • extremely difficult to detect. • Neutrinos have a very small, but nonzero

mass.

Hadrons - matter made of quarks

Baryons are made of three quarksMesons are made of one quark and one antiquark

(don’t write)

Fermionic matter is made of these 12 particles.

(don’t write)

2nd generation are just heavier versions of the 1st generation particles.

(don’t write)

3rd generation even heavier still.Tau, tau neutrino – 1974~1977Bottom – 1977Top quark -1992

If there are so many types of hadrons, mesons and leptons why don’t we see them every day?? Why is most of the matter we experience only protons, neutrons and electrons?

Stability and Energy

This triangle can be in the following configurations –

Energy of A > Energy of B > Energy of C

AB

C

Stability and Energy

Triangle A would quickly “decay” into a lower energy state, C as it is completely unstable.

AC

Stability and Energy

Even B would eventually decay in C with a tiny input of energy. It is not very stable.

BC

Stability and Energy

As the object moves into a lower energy state some energy is released.

BC

Stability and Energy

It would require an input of energy to move the object into a higher energy state

B

C

Many things behave in a similar way.

Eg Electrons in energy levelsElectrons can jump up to higher energy levels with the input of energy.The electrons then fall back down to a lower, more stable energy configuration, releasing energy in the form of electromagnetic radiation (light)

• Unstable elements are said to be radioactive. They decay to more stable elements with the release of energy. The newly formed elements have less energy and are more stable.

• Unstable fermions decay into stable fermions.• Eg taumuonelectron

The most stable particles compose most matter you see – the electron (neutrino) has the lowest energy of any lepton

The proton (uud) is the lowest energy state of any hadron.

The neutron is less stable (ddu)and has a half life of 10 minutes when not in a nucleus!

SummaryFermions

Quarks Leptons

Hadrons Electrons Neutrinos

Baryons Mesons

Protons Neutrons