Detecting Detecting ParticlesParticles

Detecting Particles

Martin Gallacher – University of Birmingham

ContentsContents

The Spark chamberThe Spark chamber Early particle detectorsEarly particle detectors The ATLAS detectorThe ATLAS detector The Atlantis Event DisplayThe Atlantis Event Display How to recognise particle events at How to recognise particle events at

ATLASATLAS

The Spark ChamberThe Spark Chamber

The spark chamber The spark chamber detects cosmic ray detects cosmic ray muonsmuons

The spark shows The spark shows the track of the the track of the muon through the muon through the chamberchamber

The Origin of Cosmic RaysThe Origin of Cosmic Rays

Stars Supernovae

Black Holes Other galaxies

Cosmic Cosmic ‘Rays’ ‘Rays’ reach reach EarthEarth

Muons and NeutrinosMuons and Neutrinos

MUON (MUON (µ) – has charge and mass (like a µ) – has charge and mass (like a heavy electron).heavy electron).

Easy to detect!Easy to detect!

Arrive at a rate of a few per cmArrive at a rate of a few per cm2 2 per min per min

NEUTRINO (ν) – no charge, negligible massNEUTRINO (ν) – no charge, negligible mass

Difficult to detect!Difficult to detect!

Arrive at a rate of hundreds of millions per Arrive at a rate of hundreds of millions per cmcm22 per min per min

How the Spark Chamber How the Spark Chamber WorksWorks

Early Particle DetectorsEarly Particle Detectors

Cloud Chamber Bubble Chamber

A discarded bubble chamber at Fermilab

The cloud chamber at the Cavendish museum

Identifying ParticlesIdentifying ParticlesCloud chamber photo

Evidence for the positron

Bubble chamber photo

Electron-positron production

Modern Particle Modern Particle DetectorsDetectors

The ATLAS DetectorThe ATLAS Detector7000 tonnes of detector sits 100m underground

The ATLAS DetectorThe ATLAS Detector44m in length and 22m In diameter (about the size of a 5 storey building – bigger than the Poynting building)

The ATLAS experiment is a collaboration of about 2100 scientists from 167 institutions in 37 different countries.

A Typical DetectorA Typical DetectorInner detector (Tracker)Measures charge and momentum of charged particles in magnetic field

Electro-magnetic calorimeterMeasures energy of electrons, positrons and photons

Hadronic calorimeterMeasures energy of hadrons (particles containing quarks), such as protons, neutrons, pions, etc.

Muon detectorMeasures charge and momentum of muons

Neutrinos are only detected indirectly via ‘missing energy’ not recorded in the calorimeters

Inner Detector (Tracker)Inner Detector (Tracker)

Comprises of pixel detectors in the centre than semiconductor tracker (SCT) and finally transition radiation tracker (TRT).

1.15m in radius and 7m long

Solenoid MagnetSolenoid Magnet

Surrounds the inner detector and is contained in a cryostat

Produces a 2T magnetic field

EM CalorimeterEM Calorimeter

Barrel in cryostat

Endcap

Hadronic Calorimeter Hadronic Calorimeter

The calorimeters fill the gap between the outside of the inner solenoid and the muon system

Toroid MagnetsToroid Magnets

The largest toroid magnet ever built !

Outer diameter 20.1m and 25.3m long

Muon DetectorMuon DetectorMuons are the only charged particles which can pass through the calorimeters. The muon system therefore acts like the inner tracker but outside the calorimeters to measure the muon properties alone.

Proton Collisions in ATLASProton Collisions in ATLAS

End-on view

Side view

Rolled out energy plot

Control Panel

Inner detector (Tracker)

Electromagnetic calorimeter

Hadronic Calorimeter

Muon detector

Example: WeSpotting an electron!

Look for a track in the tracker and a deposit of energy in the electromagnetic calorimeter

To find out more about an object in the event click on ‘Pick’

Then click on the object you want to look at eg the track of the electron.

The selected object then becomes grey

The transverse momentum (pT) then appears in the bottom left corner

Example: WeSo what about the neutrino?

Dashed red line means no track – something is missing

Neutrino is indicated by missing ET of more than 10GeV

Next event•Click on ‘Next’

Example: WSpotting a muon•Track in the tracker with high pT

•Track in the muon detector (orange)•Also have some other fragments not associated with the muon

Example: Zee

Characteristics:

2 electrons in the event

Example: ZCharacteristics:

2 muons in the event

Here:• one in central region

Example: Z

2 muons in the event

Here:• one in central region• one in forward region

•Particles in forward region are not seen in “end-on” projection! Only in “side” projection

Example: ZCharacteristics:

2 muons in the event

Example: background

Characteristics:• Does not contain We, W, Zee, Z

Example: background

Characteristics:• Does not contain We, W, Zee, Z• Typically bundles of particles (jets) are produced

NB: Jets have hits in both the Electromagnetic and Hadronic calorimeters

RecapRecap Analyse each event and classify into 1 Analyse each event and classify into 1

of 5 categories (Wof 5 categories (Wee, W, W, Z, Zee, ee, ZZ, background) by ticking the , background) by ticking the correct boxcorrect box

Click ‘Next’ to go to the next eventClick ‘Next’ to go to the next event WARNING: There is one event that WARNING: There is one event that

won’t fit into one of the above won’t fit into one of the above categories – the elusive Higgs boson categories – the elusive Higgs boson event (Hevent (H, H, Heeee or Heeee or Heeee) – ) – find this and win a prize!find this and win a prize!