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The Gas Č erenkov Detector for the Crystal-Barrel Experiment at ELSA

Hemholtz-Institut für Strahlen- und Kernphysik der Uni Bonn. supported by SFB/TR 16. The Gas Č erenkov Detector for the Crystal-Barrel Experiment at ELSA. D. Kaiser. Nucleon Resonances. Breit-Wigner parametrisation. photoproduction reactions with nucleon resonances at the CB experiment:

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The Gas Č erenkov Detector for the Crystal-Barrel Experiment at ELSA

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  1. Hemholtz-Institut für Strahlen- und Kernphysik der Uni Bonn supported by SFB/TR 16 The Gas Čerenkov Detector for the Crystal-Barrel Experiment at ELSA D. Kaiser

  2. Nucleon Resonances Breit-Wigner parametrisation • photoproduction reactions with nucleon resonances at the CB experiment:  N  N*  ... • problem: overlapping resonances • partial wave analysis • polarisation observables D. Kaiser

  3. polarisation time [hours] Double Polarisation • polarised target • polarised photonbeam • Bonn Frozen Spin Target • longitudinally polarised protons • in a butanol target • @ 30-50 mK in frozen-spin mode • polarisation 70 – 90% • repolarisation every ~ 60 h • total relaxation time ~ 360 h • linear polarised photon beam by use of • unpolarised electron beam and diamond radiator •  50% @ 3.2 GeV • circular polarised photon beam by use of • longitudinally polarised electron beam and amorphous radiator •  55% @ 2.4 GeV D. Kaiser

  4. Electron Accelerator ELSA D. Kaiser

  5. Crystal-Barrel Experiment e- beam Gas Čerenkov detector goniometer tagger polarised target g camera Crystal-Barrel detector MiniTAPS e- beam dump GIM D. Kaiser

  6. Electromagnetic Background • due to: • pair production • Compton scattering for hydrogen target in full angular acceptance: ~1.000 e± 1 hadr. for butanol target under forward angles: ~100.000 e± 1 hadr.  need for supression already on trigger level D. Kaiser

  7. Čerenkov Effect • discovered 1934 by P.A. Čerenkov (and S.I. Vavilov) • Nobelprice 1958, together with I.E. Tamm and I.M. Frank • charged particles with high velocity generate electromagnetic radiation in dielectric media D. Kaiser

  8. Čerenkov Effect observable radiation for a particular angle c: with threshold for Čerenkov radiation: D. Kaiser

  9. Čerenkov Effect • threshold energy “adjustable“ by use of different Č media • useful for particle discrimination and determination • simple set-up with Č medium and photon detector  Čerenkov threshold detector • other set-ups possible (e.g. RICH) D. Kaiser

  10. Čerenkov Effect • approx.1700 photons/cm in water approx. 2 photons/cm in CO2 range of normal PM Used photomultiplier: Hamamatsu R1584-03SEL D. Kaiser

  11. Gas Čerenkov Detector - drawing and picture D. Kaiser

  12. Gas Čerenkov Detector -positioning andangular space coverage MiniTAPS Gas Čerenkov detector forward crystals D. Kaiser

  13. Gas Čerenkov Detector • periodic repolarisation of the target • easy in- and output of the detector is required D. Kaiser

  14. gas system partial pressure sensor scale Modifications D. Kaiser

  15. Simulation of the Efficiency • verification of the efficiency of the detector  maximum efficiency of 99.97 % D. Kaiser

  16. Determination of the Efficiency • done at the old CB area • e± from pair production / Compton scattering on a carbon target  efficiency of 99.72 % ± 0.45 % D. Kaiser

  17. Installation in the CB Set-up more adaptions needed: • electronic • trigger logic • DAQ • analysis software ExPlORA D. Kaiser

  18. Use as Veto Detector Start of readout if two tagged hits in the Crystal-Barrel-, Forward- or MiniTAPS detector were found Start of readout if two tagged hits in the Crystal-Barrel-, Forward- or MiniTAPS detector were found, with applied Čerenkov veto D. Kaiser

  19. Use as Veto Detector cut on events correlated in time  number of suppressed events in the subdetectors D. Kaiser

  20. Čerenkov Detector as Time Reference D. Kaiser

  21. Čerenkov Detector as Time Reference D. Kaiser

  22. Summary • Gas Čerenkov detector modified for use in the Crystal-Barrel experiment • tests and determination of the efficiency • detector integrated and in use • as veto detector • as time reference • data taking has already started D. Kaiser

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