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L.Suszycki †‡

Instrumentation of the very forward region of the TESLA detector – summary of the Workshop on Forward Calorimetry and Luminosity Measurement, Zeuthen, 13-14 November 2002. L.Suszycki †‡ Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy,Cracow, Poland

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L.Suszycki †‡

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  1. Instrumentation of the very forward region of the TESLA detector – summary of the Workshop on Forward Calorimetry and Luminosity Measurement, Zeuthen, 13-14 November2002 L.Suszycki†‡ Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy,Cracow, Poland ECFA DESY Linear Collider Workshop Prague, 15th-18th November 2002 †For the LCAL group: K. Afanaciev, V. Drugakov, G. Klämke, E. Kousnetzova, W. Lohmann, A. Stahl, M. Ternick ‡For the LAT group:H. Abramowicz, A. Eskreys, S. Kananov, D. Kisielewska, A. Kowal, A. Levy, L. Suszycki, W.Wierba

  2. Very forward region of TESLA Two calorimeters: • LCAL – Luminosity CALorimeter covering angles 5 – 27.5 mrad, actually it is“Beam Calorimeter” • LAT – Low Angle Tagger covering angles 27.5 – 83.1 mrad, actually it is“Luminosity Calorimeter” L.Suszycki: Instrumentation...

  3. Tasks for the very forward region detectors • Precision luminosity measurement • Beam diagnostics • Detection and measurement of electrons and photons at small angles • Extension of the energy flow measurement down to small angles • Shielding of the tracking detectors against backscattered beamstrahlung L.Suszycki: Instrumentation...

  4. Beamstrahlung • Energy deposition via e+e- pairs ~20 TeV/bunch cr.One year of runs makes a dose ~10 Mgy/year in LCAL a need of radiation hard sensors • Radial distribution up to ~4 - 5cm  LAT should be save • Azimuthal anizotropy caused by magnetic field L.Suszycki: Instrumentation...

  5. LCAL design • Shape • Two technology options: • crystal PbWO4 – Moliere radius ~2 cmLSO crystals considered • diamond-tungsten sandwich - Moliere radius ~1 cmSegment size ~half of RM • Readout via optical fibres L.Suszycki: Instrumentation...

  6. LCAL segmentation R-z projection x-y projection 30 layers = 30 radiation lengths 12 rings L.Suszycki: Instrumentation...

  7. Half barrel of the diamond-tungsten sandwich calorimeter LCAL calorimeter L.Suszycki: Instrumentation...

  8. L.Suszycki: Instrumentation...

  9. Background in LCAL Example of a 250 GeV electron event1. Generated 2. Background added 3. Reconstructed L.Suszycki: Instrumentation...

  10. Detection of particles in LCAL Simple algorithm to find electron or gamma: • search for cells with signal > 3 sigma of background • require longitudinal chain of such cells Efficiency and energy resolution depend on number of ADC bits  10 bits sufficient L.Suszycki: Instrumentation...

  11. Energy measurement in LCAL Energy resolution as functions of : R Energy L.Suszycki: Instrumentation...

  12. Angular resolution of LCAL Energy dependence R dependence L.Suszycki: Instrumentation...

  13. Fake events in LCAL • High energetic particles in background • Beamstrahlung fluctuationsElectron energy spectrum generated (tail >20 GeV only is shown) ...and reconstructed L.Suszycki: Instrumentation...

  14. Beam diagnostics in LCAL Measurement of x and z ExerciseInput:x = 600 nm, z = 250 mResult:x = 597 nm, z = 241 mMore about: see A.Stahl talk at this workshop L.Suszycki: Instrumentation...

  15. 14 `cylinders` in R24 `sectors` in 40 `rings` in z13440 cells assumed for MC studies Conical setup R: 4 to 12 cmz: 140 to 200 cm Silicon-tungsten sandwich 40 X0 deep LAT geometry L.Suszycki: Instrumentation...

  16. Elastic e+e-  e+e- radiative e+e-  e+e-  Example of elastic Bhabha event  (scale ratio 8:1!) Born approximation d/d ~ -3 tot(27.5, 83.1mrad)5nb Bhabha scattering L.Suszycki: Instrumentation...

  17. Luminosity measurement • R = L ·obs , where obs =theor  acceptance • For L = 3.4 · 1034 cm-2s-1 rate R  170 Hz  `one minute` luminosity possible on-line • Systematic errors:1. from detector acceptance • Since tot(min, max) ~ min-2 - max-2  min-2 • then L/L = 2min/ min = 2rmin / rmin • With rmin  5 cm, L/L = 10-4 needs rmin = 2.5 m • Challenging for mechanics and thermal stability!Use of interferometry to monitor position and shape? • 2. from theoryAt LEP energy theor. error achieved 5. 10-4.At TESLA may be harder L.Suszycki: Instrumentation...

  18. L.Suszycki: Instrumentation...

  19. Luminosity measurement (cont`d) • Luminosity spectrum due to • ISR • Beamstrahlung • Beam energy spread • can be measured through acolinearity of Bhabha events - • - resolution better than 0.1 mrad necessary • Background and corrections • Beamstrahlung • Synchrotron radiation • Beam-gas bremsstrahlung • Thermal photons from the rest gas • Beam size effect • So far no estimations done... L.Suszycki: Instrumentation...

  20. LAT shower example Only photons (blue) and electrons (red) over 5 MeV are displayed L.Suszycki: Instrumentation...

  21. LAT calorimetryShowers well contained within ~ 30 radiation lengths: L.Suszycki: Instrumentation...

  22. LAT – showers...Two examples of hits generated by 250 GeV electrons:Upper plots show all hits, lower plots show the shower coresStrong scattering may affect energy measurement L.Suszycki: Instrumentation...

  23. LAT energy response and resolution L.Suszycki: Instrumentation...

  24. Much poorer performance in the first bin (first cylinder)  the effect increasing with energy LAT angular uniformityEnergy response Energy resolution L.Suszycki: Instrumentation...

  25. rec calculated using a simple energy weighting Accuracy not satisfactory Background not incorporated More sophisticated algorithm must be used for Bhabha measurement LAT angular resolution L.Suszycki: Instrumentation...

  26. LAT fiducial volume Remark: LAT size is 27.5 to 83.1 mrad L.Suszycki: Instrumentation...

  27. LAT fiducial volume (cont`d).Energy deposit as a function of polar angle All events cut Edep > 2.5 GeV L.Suszycki: Instrumentation...

  28. LAT performance improvedEnergy cut Edep > 2.5GeV applied Energy response and resolution Angular resolution L.Suszycki: Instrumentation...

  29. Summary and outlook LCAL • Advanced studies of the several technologies • Detection of hard electrons and gammas with high efficiency feasible • Fake events due to beamstrahlung fluctuations may be a problem • Beam diagnostics looks promising • R&D started LAT • First MC studies done • Problems with energy resolution and angular resolution • Shape and segmentation is still an open questionflat LAT “ l=5m” option is very recommended:1. Makes mechanical design more realistic2. Improves resolution • Single module for tests will be prepared soon The LCAL+LAT proposal will be recommended by the PRC, so let`s look forward in this adventure! L.Suszycki: Instrumentation...

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