Particle Physics: The Search for the Essence of Matter

Ronan McNulty (University College Dublin)

Particle Physics has been around for a long time…

It is in our natureas humans to be

inquisitive and to ask“Why?”

• Thales: “Of what is the universe made?”

• Anaximander: “Worlds appear and disappear as a bubble in the apeiron”

• Democritus:

Atom = ‘indivisible’

• Morning Ireland:

“What is the stuff in stuff?”

• Particle Physics

– searches for the building blocks of matter

– explains how they behave

Mendeleev 1869"fearful symmetry independent of any

conception as to the nature of the elements

The Periodic Table

The New Periodic Table

Exploring the very small requires high energy

E=hυ=hc/λ λ=(1x10-6)/E metres

Exploring the very small requires high energy

E=hυ=hc/λ λ=(1x10-6)/E metres

To see down to 10-19m requires 10 TeV of energy

Cockroft & Walton 1932

Linear Accelerator

Circular Accelerator

A low energy particle accelerator...

The LHC

The LHC

Tracking chambers measure Momentum of charged particles

Calorimeters measure energy of neutral particles

LHC recreates conditions of early universe

• Investigate matter-

antimatter assymetry

of universe

• Understand the origin

of mass

• Might find dark matter

Particle Physics|

Astrophysics

Where is all the Antimatter gone?

Matter and Antimatter

created equal and opposite

Today only Matter remains

Where is all the Antimatter gone?

Matter and Antimatter

created equal and opposite

Today only Matter remains

Sakharov Conditions

�Baryon Number Violation

�CP Asymmetry

�Universe not in Thermal

Equilibrium during expansion

Our Matter World

Our Matter World

An Antimatter World

C

Our Matter World Our World reflected in a mirror

P

C

P

CP

C

P

CP

Inexact CP symmetry

explains inexact

matter/antimatter symmetry

LHCb experiment

Matter

Antimatter

Do the

decays

mirror

each

other?

C P

UCD helped build and test the VELO: Reconstruct particle trajectories to 1/100 mm

LHCb see the first LHC collisions!

So have we reached the end?Do we “know everything” ?

• We have our ‘periodic table’ of fundamental particles.

• It is complete.

• We understand how the particles interact via four forces.

• Why are particles massive?

• Why is the universe dominated by matter and not anti-matter?

• What is the ‘dark matter’ in the universe?

• Are quarks/leptons fundamental?

• Why are there exactly three families?

The more we knowthe more we knowwe do not know.