Detecting Particles Martin Gallacher – University of Birmingham.
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Transcript of Detecting Particles Martin Gallacher – University of Birmingham.
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
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
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
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
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.
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
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: 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!