Particle Physics Experiments

1. Particle Physics Experiments HEP Detectors and their Technologies Silvia Schuh CERN

2. Overview • Introduction and Concepts • Properties of Particles • Which are measurable? How? • Particle Interactions • Particle Detectors in HEP • Tracking Detectors • Energy Measurement • Particle Identification • Infrastructure • Existing Particle Detectors Silvia SCHUH, CERN

3. For a HEP Experiment one needs… A theory a cafeteria Mary Gaillard Murray Gell-Mann a tunnel for the accelerator and magnets and stuff Clear and easy to understand drawings Courtesy O. Ullaland, SSL 2006 Silvia SCHUH, CERN

4. … and also … Data analysis An experiment BUT: We will just concentrate on the detectors Courtesy O. Ullaland, SSL 2006 Silvia SCHUH, CERN

5. Progress Cycle physics theories technologies & materials knowledge / progress experiments detectors Courtesy C. Joram, SSL 2003 Silvia SCHUH, CERN

6. Useful units & relations energy E: measured in eV momentum p: measured in eV/c mass m0: measured in eV/c2 1 eV is a small energy: 1 eV = 1.6·10-19 J mbee = 1g =5.8·1032 eV/c2 vbee = 1 m/s  Ebee = 10-3 J = 6.25 ·1015 eV ELHC = 14 · 1012 eV However, LHC has total stored beam energy 1014 protons  14 · 1012 eV  108 J or, one 100t truck at 100 km/h Courtesy O. Ullaland, SSL 2006 Silvia SCHUH, CERN

7. Elementary Particles Silvia SCHUH, CERN

8. Fundamental Forces p n n p n n p n n n p p n p p p p p p n q q Electromagnetic force Strong force Weak force rel strength = 1 range = 10-15 rel strength < 10-2 rel strength = 10-5 range = 10-17 rel strength = 10-38 range = 10-15 weakest ’force’: in microcosm insignificant Silvia SCHUH, CERN

9. Particle Detection Cloud Chamber + Magnet Observer Flux of particles • Particles cannot be seen/measured “directly” • Measurement occurs via interaction with matter  magnetic fields • Observation  Conversion into optical images or current/voltage signals Courtesy O. Ullaland, SSL 2006 Silvia SCHUH, CERN

10. Studying Interactions • via annihilation • via the production of new particles • via scattering • all interactions are produced in • Colliding Beam Experiments or • Fixed Target Experiments Silvia SCHUH, CERN

11. Colliding particles - an artists view - q q e+ Z e- time • Usually we can only ‘see’ the end products of the reaction, but not the reaction itself. • In order to reconstruct the reaction mechanism and the properties of the involved particles, we want the maximum information about the end products ! Courtesy C. Joram, SSL 2003 Silvia SCHUH, CERN

12. Ideal Detectors? • In an ideal detector, one could record 100% of any interaction, capture and measure perfectly all properties of all emerging particles, and by this reconstruct the complete event. • This would give us the power to compare the interaction directly to theoretical predictions without most uncertainties. • NB: (In)Efficiency • not all particles are detected, some leave the detector without any trace (neutrinos), some escape through not sensitive detector areas (holes, cracks for e.g. water cooling and gas pipes, cables, electronics, mechanics) Silvia SCHUH, CERN

13. Particle Properties • Which properties does a particle have? • energy • momentum • charge • mass • life time • spin • decay modes • And which of those are measurable? Silvia SCHUH, CERN

14. Particle Properties • Which properties can we derive? • Mass • Spin • A bit more abstract from angular distributions Silvia SCHUH, CERN

15. Particle Properties Interaction point Decay point Distance • charge • lifetime Silvia SCHUH, CERN

16. Measuring Particle Properties • momentum • velocity - time of flight - RICH • energy - calorimeter Silvia SCHUH, CERN

17. Which particles can be detected? • Charged Particles • Neutral Particles • Different particle types interact very differently with the detector material. Silvia SCHUH, CERN

18. Particle Interactions - charged particles • Ionization • Basic mechanism in tracking detectors e- • Excitation/Scintillation p p p g e- p • (Multiple) elastic scattering w/ atoms of detector material • Unwanted, changes initial direction • Photon radiation • Bremsstrahlung (accelerated charge radiates photons), Cherenkov light (faster than light in medium), Transition radiation Silvia SCHUH, CERN

19. Particle Interactions - photons  + atom  atom+ + e- • Photo effect • photo detectors: knock-out electrons on photo cathodes (vacuum and gas) or at semi conductors (surface) • Photo Multiplier Tubes (PMT), photo diodes • Compton scattering (e-g scattering) • not used for particle detection • used for polarization measurement of beams at e+e- machines  + e ' + e' • Pair production (ge+e-) • initiates electromagnetic shower in calorimeters, unwanted in tracking detectors  + nucleus  e+e- + nucleus  + e- e+e- + e- +  opening angle = 0o(!) Silvia SCHUH, CERN

20. Particle Interactions - other • Hadronic Particles • Strong Force – Inelastic nuclear interaction • Charged and uncharged hadrons (p, K, p, n ...) • Result: nuclear fragments (really measured are charged fragments) • Neutrinos • „No“ interaction in particle detectors at accelerators • Signature: Missing Energy Silvia SCHUH, CERN

21. A Typical Detector Concept Interaction point Magnetic spectrometer tracking detector Hadronic calorimeter Muon detectors Electromagnetic calorimeter Precision vertex detector Silvia SCHUH, CERN

22. Passage of Particles - Ingredients Electromagnetic Calorimeter Hadronic Calorimeter Muon System Tracker • Photons • Electrons • Hadrons • Muons Silvia SCHUH, CERN

23. Passage of particles - summary undetected neutrinos... electromagnetic hadronic shower muon detection with improved momentum measurement (long lever arm) energy measurement by creation and total absorption of showers momentum measurement by curvature in magnetic field Silvia SCHUH, CERN

24. … and in real life… ATLAS Silvia SCHUH, CERN

25. … and in real life… ATLAS Silvia SCHUH, CERN

26. … and in real life… ATLAS Magnified how real (single) particles look like in ATLAS Silvia SCHUH, CERN

27. End of Day 1