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HEP Experiments

HEP Experiments. Detectors and their Technologies Sascha Marc Schmeling CERN. Overview. Introduction and Concepts Properties of Particles Are they measurable? If yes, how? HEP Detectors @CERN Main Sub-Detectors Infrastructure. Studying Interactions. by scattering by annihilation

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HEP Experiments

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  1. HEP Experiments Detectors and their Technologies Sascha Marc Schmeling CERN

  2. Overview • Introduction and Concepts • Properties of Particles • Are they measurable? • If yes, how? • HEP Detectors @CERN • Main Sub-Detectors • Infrastructure

  3. Studying Interactions • by scattering • by annihilation • and the production of new particles • all interactions are produced in • Colliding Beam Experiments or • Fixed Target Experiments

  4. Ideal Detectors? • In an ideal detector, one could record the full interaction, capture and measure 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.

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

  6. Particle Properties • Which properties can we derive?

  7. Particle Properties • charge • lifetime

  8. Measuring Particle Properties • momentum • velocity time of flight • energy calorimeter

  9. e- p p p g e- p Measurement Principles • Measurement occurs via the interaction (again…) of a particle with the detector (material) • creation of a measureable signal • Ionisation • Excitation/Scintillation • Change of the particle trajectory • curving in a magnetic field, energy loss • scattering, change of direction, absorption

  10. Which particles can be detected? • Charged Particles • Neutral Particles • Different particle types interact very differently with the detector material.

  11. Interaction point Magnetic spectrometer tracking detector Hadronic calorimeter Muon detectors Electromagnetic calorimeter Precision vertex detector A Typical Detector Concept

  12. Ingredients Electromagnetic Calorimeter Hadronic Calorimeter Tracking Subsystem Muon System

  13. Passage of Particles • Electrons • Photons • Hadrons • Muons • Mesons

  14. Tracking Detectors • measure the tracks of emerging particles • determine • charge and • momentum in connection with a magnetic field • tracks are reconstructed from measured space-points do not use dense material!

  15. How do tracking detectors work? • two main flavors • ionization detectors • Geiger-Müller counter • MWPC • TPC • silicon detectors • scintillation detectors Multi-Wire Proportional Chamber Time Projection Chamber

  16. cathode - + - + signal - + - + Anode Wire - + t = 0 + Gas-filled tube + + HV + + - + - - - - t = t1 Ionization Counters

  17. Anode wires Cathode: pads or wires Realization: wire chamber (MWPC) Nobel prize: G.Charpak, 1992 y x Tracking

  18. ITC (ALEPH) Inner Tracking Chamber MWPC

  19. MWPC gives r,f E B - - + - - + - - + - - - - - + - Anode Wires - + + Gas-filled cylinder Time Projection Chamber z = vdrift t

  20. TPC ALICE TPC sector detail

  21. ALEPH TPC

  22. Uncertainties on track origin and momentum Limitations • Precision limited by wire distance Error on space point  d cannot be reduced arbitrarily! Uncertainties on space points

  23. 0.2 - 0.3 mm Now precision limited by strip distance 10 - 100 mm Silicon wafers, doped Creation of electron-hole pairs by ionising particle Same principle as gas counters Step forward:Silicon Microstrip Detectors

  24. OPAL VDET ALEPH VDET Future ATLAS tracking detector Silicon Microstrip detectors...

  25. Increase in precision =Beam crossing point 0 1cm x

  26. Mean Lifetime of tau t=290 x 10-15 sec !! --> ct = 87 mm !?

  27. Total reflection Photomultiplier: converts light into electronic signal PM Scintillating material Put many fibers close to each other --> make track visible Scintillation Detectors

  28. Calorimeters • Basic principle: • In the interaction of a particle with dense material all/most of its energy is converted into secondary particles and/or heat. • These secondary particles are recorded • eg. Number, energy, density of secondaries • this is proportional to the initial energy

  29. Electromagnetic Showers Lead atom Block of Matter, e.g. lead

  30. How to measure the secondary particles? • 1. With sampling calorimeters: Sandwich structure ! Total amount of signals registered is proportional to incident energy. But has to be calibrated with beams of known energy! Detectors, such as wire chambers, or scintillators Dense blocks, such as lead

  31. Sampling Calorimeters

  32. ALEPH ECAL pions electron

  33. photons muons

  34. signal Photo diode photons Crystal (BGO, PbWO4,…) How to measure the secondary particles? • 2. With homogenous calorimeters, such as crystal calorimeters:

  35. Sandwich structure ! Total amount of signals registered is proportional to incident energy. Same energy lost in nuclear excitations! Has to be calibrated with beams of known energy! Detectors, such as wire chambers, or scintillators Dense blocks, such as iron, uranium Hadronic calorimeters • Hadronic particles (protons, neutrons, pions) can traverse the electromagnetic calorimeters. They can also interact via nuclear reactions ! • Usually: Put again a sampling calorimeter after the ECAL

  36. iron ALEPH 

  37. Particle Identification • Basic principles: • via different interaction with matter (see previous transparencies) • by measuring the mass from the decay products • by measuring the velocity and independently (!) the momentum • Observables sensitive to velocity are • mean energy loss • Cherenkov radiation

  38.  Elost  / path length = func( particle-velocity v/c ) Bethe-Bloch formula Mean Energy Loss • Particles which traverse a gas loose energy, e.g. by ionization  Elost amount of ionization size of signals on wires Note : if plotted as a function of v and not p all the bands would lie on top of each other!

  39. Cherenkovlight wavefront c0 = speed of light in vacuum Cherenkov Radiation • Particles which in a given medium travel faster than the speed of light in that medium emit radiation: Cherenkov radiation

  40. HEP Experiments @CERN • All these concepts have been put together and realized in large detector systems • Examples at LEP • ALEPH , OPAL , L3 , DELPHI • Fixed Target • NA48 • Future experiments at LHC • ATLAS, CMS, LHCb, ALICE

  41. See http://pdg.lbl.gov/atlas/index.html ATLAS

  42. See http://cmsinfo.cern.ch/Welcome.html/

  43. Infrastructure • experiments are not only detectors • you need • possibilities to control the detectors • possibilities to take the data out and record it • possibilities to analyze the recorded data • …

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