PARTICLE PHYSICS AND THE LHC

(THE GIGANTIC SEARCH FOR THE MINUSCULE STUFF)

Andreas Papaefstathiou High Energy Physics Group (Theory)

Cavendish Laboratory

The Plan...

Particle Physics in a Nutshell!

The Large Hadron Collider.

My Research. (in just one slide!)

What is Particle Physics? (in a nutshell)

Are there fundamental, indivisible particles which make up matter? How do they behave?

Empedocles (5th century B.C.): Matter made up of Earth, Air, Fire, Water. Two forces: Love and Strife.

The Real “Atoms”Democritus: All matter made of fundamental particles that are indestructible, Atoms.

Not far from the truth...

However, atoms are not truly indivisible: made up of heavy nucleus, in turn containing protons and neutrons. Light electrons orbit around the nucleus.

Electrons are in fact indivisible (as far as we know!)

BUT: protons and neutrons are not fundamental! They have substructure.

Quarks and LeptonsProtons and neutrons are composite: they are made up of fundamental, indivisible, particles called quarks.

There are 6 “flavours” of quarks. Funny names: up, down, charm, strange, top, bottom.

In addition: Leptons: electron, muon, tau and three corresponding neutrinos.

Three quarks for Muster Mark! Sure he has not got much of a bark

And sure any he has it's all beside the mark.

—James Joyce, Finnegan’s Wake

Forces of NatureFour forces govern the interaction between the matter particles.

The act of sitting on a chair makes use of two: Gravity (keeps you from floating about!) and the electromagnetic force (keeps you from falling through the earth!).

Less familiar: Strong (keeps the nuclei from falling apart) and Weak forces (responsible for radioactivity).

More Particles?!For each force: “Force Carriers”. e.g. The photon carries the electromagnetic force.

One additional particle: The Higgs Boson. Responsible for giving mass to particles.

These are the basic ingredients of the Standard Model (SM) of Particle Physics.

The Higgs is the only particle not been detected experimentally!

Now What?The Standard Model doesn’t seem to be the end of the story...

It remains incomplete: Gravity is not included in the theory!

There are huge numbers in the theory: e.g. the “Planck mass” is 10000000000000000 (10^16) times the proton mass! Very “unnatural”.

No explanation for the number of particles or forces.

Strong indications towards a “Unified” theory of forces.

A Light in the DarkGuiding Principles: Symmetry, Naturalness, “Beauty”.

A very important guiding principle: Agreement with Experiment.

Current Experiment: The Tevatron at Fermilab, Chicago, USA.

Upcoming Particle Physics experiment: The Large Hadron Collider at CERN, Geneva, Switzerland.

What does the LHC do?The LHC accelerates and smashes protons together at energies we have never experimented directly with: a maximum energy of 14 Tera Electron Volts (TeV).

The quarks inside the protons interact with each other and combine to produce other particles.

Using sophisticated detectors we observe what comes out and look for unusual events: (hopefully) New Physics!

The process is like looking for needles in a haystack.

Looking for: e.g. The (elusive) Higgs Boson, “Supersymmetry”, Extra Dimensions + more!

CERN LHC

Black Holes at the LHC? CUPS 29/10/08

Large Hadron Collider

5

LEP/LHC …

27 km circumference

Busstepp, Cambridge, 2008 Christopher Lester / Cavendish / CERN 7

Circle Line …

22.5 km circumference

LHC Facts27 km Circumference. Built in a pre-existing tunnel (previously the LEP experiment).

Protons are accelerated by a series of superconducting magnets cooled down to -271° Celcius (colder than outer space).

The total energy of the LHC proton beam is equivalent to: The kinetic energy of 120 elephants running at 40 km/h or the kinetic energy of a fu$y loaded Airbus A320 at landing speed.

The proton beams are 0.03 mm in diameter at the point where they come together.

Toroid Magnets Solenoid Magnet SCT Tracker Pixel Detector TRT Tracker

Muon Detectors Tile Calorimeter Liquid Argon Calorimeters

22

m

46

m

A Toroidal LHC ApparatuS

Muon Detector

Man for scale

MAGNETIC FIELD

MAGNETIC FIELD

Muons bend away from us.

Anti-muons bend toward us.

Calorimeters and Central Solenoid

Man for scale

More facts...

September 10: First beam circulating around the ring.

Failure last month due to a tiny resistance appearing in the superconducting magnets causing them to heat up and the helium used for cooling to leak.

Unfortunately due to the repairs and the fact that electrical power is expensive in winter, normal startup is expected in spring 2009.

First Beam Data

Black Holes at the LHC? CUPS 29/10/08

First Beam Event Display

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My Research (in a slide)The W Boson is the particle which carries weak force: Mass ~ 80 Giga Electron Volts (GeV)

Hypothetical heavy particle, called W’ (prime) predicted by many theories. They have to be more massive than ~ 1000 GeV.

The LHC will look for the W’, and will be able to find it if it has a mass of less than 6000 GeV.

Finally,

Thanks to my Supervisor, Bryan Webber, the members of the Cambridge Supersymmetry Working Group for their comments and support and the STFC Research Council for funding me!

Thank you for your attention!

Any Questions?

Appendix: Is the LHC Safe?

Could the LHC create a Black Hole that would swallow up the planet?

The answer is NO: The kind of collisions which take place at the LHC happen all the time in cosmic ray collisions.

Black Holes evaporate by emitting Hawking radiation.

The fact that old planets and stars exist demonstrates that the LHC is in fact absolutely safe!