ATLAS experiment at the ATLAS experiment at the CERN Large Hadron ColliderCERN Large Hadron Collider

Peter Watkins,Head of Particle Physics Group,University of Birmingham, UK

p.m.watkins@bham.ac.uk

Point 1 activities and Point 1 activities and perspectivesperspectives

Marzio NessiMarzio Nessi

ATLAS ATLAS plenary plenary

22ndnd October October 20042004

Large Hadron Collider (LHC)

Outline of talkOutline of talk

• Building blocks of the universe Building blocks of the universe • Why do experiments at the LHC ?Why do experiments at the LHC ?• LHC, ATLAS and collaborationLHC, ATLAS and collaboration• Searching for a new particle Searching for a new particle • Recent LHC newsRecent LHC news

Acknowledgements – Acknowledgements – Many slides from LHC colleaguesMany slides from LHC colleagues

4

10-10 m(thickness of humanhair ~ 10-5 m)

10-14 m 10-15 m < 10-18 m

The very small

electron

up quarkdown quark

nucleus protonneutron

Fundamental ForcesFundamental Forces

Gravity – solar system, galaxies …- extremely weak force

Electromagnetic – atoms, electricity ….. - carried by photons

Weak force

Strong – binds quarks inside proton carried by gluons

– beta decay and how stars generate energy

- carried by massive W and Z bosons

All forces are carried by particles !

Higgs boson?

The Higgs BosonThe Higgs BosonOne key objective of the LHC is to understand the origin of mass – is it due to a universal Higgs field? (A Higgs field everywhere with the Higgs boson as the force carrier?).

Massless particles are not impeded by the Higgs field and, thus, travel at the speed of light. Analogy: Downhill skier experiences no drag by the snow field.

Light particles interact weakly with the Higgs field and travel slower. Analogy: Snowshoes on the top of the snow field experience some drag.

Heavy particles interact strongly with the Higgs field and travel very slowly. Analogy: Wading through the snow field is a big drag! We call this drag “Mass”.

What else is out there?What else is out there?

• Various ideas considered…Various ideas considered… Dark matter Dark matter •

Extra Extra dimensionsdimensions of space of space•

Suggested by superstring theory

Microscopic Microscopic black holesblack holes

The LHC experiments can look for all of these.

Also sensitive to something “completely different”

The LHC experiments can look for all of these.

Also sensitive to something “completely different”

The Large Hadron Collider (LHC)The Large Hadron Collider (LHC)

The LHC is a 27km accelerator that collides counter-rotating beams of protons of up to 7 TeV.(Tev = million million eV)

Energy densities similar to billionths of a second after the big-bang will be recreated at collision points

CERN laboratory on Swiss – French border

Mont Blanc

Geneva

Airport

Building the LHCBuilding the LHCIn the main ring:

1746 superconducting magnets

… including 1232 15m SC dipoles

… weighing 27 tonnes each

… producing 8.36 Tesla

… and running at –270c

… needs 700,000 litres liquid He

… and 12 million litres liquid N2

The fastest racetrack on the The fastest racetrack on the planetplanet

The protons will

reach

99.9999991%

speed of light,

and go round the

27km ring 11,000

times per second

At four places the beams intersect

Collision pointsCollision points

Hot spots too !Hot spots too !

When the two beams of protons collide, they will generate temperatures

1000 million times hotter than the heart of the sun,

but in a minuscule space

7,000 tonnes 42m long22m wide22m high

2,800 Physicists169 Institutes37 Countries

ATLAS DetectorATLAS Detector

(About the height of a 5 storey building)

Electromagnetic CalorimeterElectromagnetic Calorimeter

A basic calorimeterA basic calorimeter

Total # of particles is proportional to energy of incoming particle

Active detector slices produce a signal proportional to the number of charged particles traversing

Basics

The past

Challenges

Where to start?

Detector Design Tracker Calorimetry Particle ID

LHC detectors

“Events”

Final thoughts

Muon DetectorsMuon Detectors

E2 = p2c2+ m2c4

• Proton bunches collide 40 million Proton bunches collide 40 million times a second times a second

• ~25 proton-proton collisions occur ~25 proton-proton collisions occur each time each time

• 1000000000 collisions per sec – 1000000000 collisions per sec –

200 per second limit for recording200 per second limit for recording• Select the most ‘interesting’ Select the most ‘interesting’

collisions in few microsecondscollisions in few microseconds

Discovering a new particleDiscovering a new particle

The collision rate challengeThe collision rate challenge

Searching for Rare PhenomenaSearching for Rare Phenomena

9 or

ders

of

mag

nitu

deThe HIGGS

All interactions

Number of collisions

Collision energy

50 magnets repaired 3 km of beam

pipe cleaned

LHC status and plansLHC status and plans

• Large Hadron ColliderLarge Hadron Collider restarted in Nov 2009 and restarted in Nov 2009 and is working well is working well

• World record was set for collision energy in World record was set for collision energy in December 2009December 2009

• On March 30On March 30thth 2010 the collision energy was 2010 the collision energy was increased to 7 TeVincreased to 7 TeV

• Some early measurements already publishedSome early measurements already published• Search for Higgs boson needs more collisions Search for Higgs boson needs more collisions

Z boson candidateZ boson candidate

SummarySummary

• Many people are interested in the LHC and Many people are interested in the LHC and the key ideas arethe key ideas are widely accessible widely accessible• The searches for new particles are only just The searches for new particles are only just

beginning and will last for a decadebeginning and will last for a decade

• We work on sharing the excitement of the We work on sharing the excitement of the project with the widest possible audienceproject with the widest possible audience

• We need your help to do this to an even wider We need your help to do this to an even wider audience!audience!

Thanks for listening