The ATLAS ExperimentWhat infinetely small particles tell us about our infinitely

big Universe

October 3th

McGill University - ATLAS Group

Studying the smallest constituents of matter and how they interact with each other

What for?

● Find clues to understand our Universe○ What is it made of?○ Understand its past and birth

● Unify forces in an universal theory

What is particle Physics?

We are

here!

How to classify everything that we see?

Mendeleev Periodic Table

From atoms to quarksThomson, 1897

Discovery of electron

Rutherford, 1909-1911 Existence of a nucleus

Chadwick, 1932 Discovery of neutron Gell-Manm & Zweil, early 60s

Postulate existence of quarks

The Standard Model of particles

Pauli, 1930Postulate existence

of neutrino

neutrino(very very small

mass)

4 fundamental forces (interactions) in our Universe:

How is this holding together? FORCES!

Colour Charge

Electric Charge

Mass

Weak Charge

In the Standard Model, the forces are mediated by a force carrier particle: the Gauge Boson

● Electromagnetism: photon● Weak force: Z, W● Strong force: gluon● Gravity: graviton

How does it works? Gauge Bosons

The Standard Model of particles

Who’s that guy?

● The Higgs mechanism provides mass to the particles of the Standard Model.

● ATLAS and CMS announced discovery in July 2013

Rolling in the Higgs

Tiny little bump here!

Problem: Funny particles (like the Higgs) are rare. To increase the chance of seing them, create a tremendous amount of particles.

Solution: Take low mass particles, give them lots of energy and collide them to create heavy unstable particles. (E= mc2)

Challenge: looking for a needle in a haystack!

Particles factories

The LHC at CERN

ATLAS

CMSALICE

LHCb

● 100 m underground

● 27 km in circumference

● 40M collisions/s

The ATLAS detector

● 7000 tons● 45m long, 35m high● 170 universities and

institutes● 35 countries● 3000 people

beam pipe

proton bunch

The ATLAS collaboration

University of AlbertaUniversity of British ColumbiaCarleton UniversityMcGill UniversityUniversité de MontréalUniversity of ReginaSimon Fraser UniversityUniversity of TorontoTRIUMFUniversity of VictoriaYork University

Particles produced during the collision must be detected.

● Onion shape apparatus● Each layer detects one

type of particles● Possible to understand what type of collision happened

Detectors

The detection information is processed and stored by computers all over the world

● Sort through 40M collision/s● Record ~ 400 that we find promising

Data recording and storage

~ 10 TB/day

Atoms, electrons Electricity Transistors Computers

World Wide Web

Origin and composition of the

Universe

Scientific and technological headways

● Still a lot to discover!● Much phenomena remains unexplained

to date (Does dark matter do exist? What is it made from? What about gravity?)

Find more information on:www.atlas.ch

Conclusion