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Transition-Radiation-Detectors (TRD)

Transition-Radiation-Detectors (TRD). Transition-Radiation-Detectors (TRD). How it works Transition radiation is emitted whenever charged particles cross an interface between two media with different dielectric functions. Predicted by Ginzburg & Franck (1946)

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Transition-Radiation-Detectors (TRD)

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  1. Transition-Radiation-Detectors (TRD)

  2. Transition-Radiation-Detectors (TRD) • How it works • Transition radiation is emitted whenever charged particles cross an interface between two media with different dielectric functions. • Predicted by Ginzburg & Franck (1946) • Experimentally observed by Goldsmith & Jelley (1959)

  3. The TRD working principle Relativistic charged particle Radiator Detector

  4. Yield per interface proportional to  =1/137 • About 100 foils to get on average a single photon • Many interfaces give interference pattern

  5. Depends on Lorentz factor  • For large  the yield saturates and the spectrum becomes harder

  6. Lorentz factors for some typical situations Particle p (GeV/c)  electron 0.1 196 0.5 978 1.0 1956 5.0 9784 pion 1 7.5 10 74 100 740 500 3703

  7. The yield saturates rapidly with the thickness of the foil d1 • Average TR energy proportional to d1

  8. The yield saturates slowly with the gap thickness d2

  9. TRD’s are especially useful to identify electrons against heavier particles (e.g. pions)

  10. To detect the TR photons a multiwire proportional chamber filled with a heavy gas is used

  11. Xe-based mixtures usually used • 10-20 mm gas depth is a good choice

  12. dE/dx in a TPC • TRD’s are really needed because other techniques may be not suited to the need of discriminating electrons from other particles

  13. TRD are able to “see” all dE/dx charged particles • However, for electrons, there is an extra boost

  14. Extra energy for electrons in a TRD

  15. Transition-Radiation-Detectors (TRD) • Basically, the structure of a TRD is made of • a set of N radiators (foils or fibers) • a set of N detectors (MWPC with Xe mixture) • combined into N layers of (Radiator+Detector) • To identify electrons: • Measure charge Q in one layer • Combine information from N layers to build probability

  16. From single layer...

  17. To the combined Likelihood information from N layers

  18. Typical results for a 5-6 layers TRD

  19. Summary of experiments employing Transition-Radiation-Detectors

  20. ALICE TRD

  21. CAD view • ALICE simulated Pb+Pb event at 5.5 A TeV

  22. TRD in ALICE TRD Electron ID

  23. TRD ALICE prototypes

  24. Improvement of tracking/momentum resolution

  25. Dielectron reconstruction in ALICE • Pb+Pb events at 5.5 A TeV

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