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Fast and Precise Luminosity Measurement at the ILC

Fast and Precise Luminosity Measurement at the ILC. Ch.Grah LCWS 2006 Bangalore. Overview. The forward region Luminosity measurement using LumiCal Requirements Systematics Physics background Fast luminosity monitor – BeamCal Using the pair background signal

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Fast and Precise Luminosity Measurement at the ILC

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  1. Fast and Precise Luminosity Measurement at the ILC Ch.Grah LCWS 2006 Bangalore

  2. Overview • The forward region • Luminosity measurement using LumiCal • Requirements • Systematics • Physics background • Fast luminosity monitor – BeamCal • Using the pair background signal • Beam parameter reconstruction • Summary and outlook Ch.Grah: Luminosity Measurement

  3. Forward Region – New Geometry 20mrad geometry (LDC) Ch.Grah: Luminosity Measurement

  4. Forward Region - Tasks 2mrad • LumiCal (26 (43)mrad < θ < 153 mrad) • Detection of low pT em interacting particles • Measure bhahba particles with high precision • BeamCal (5.6 mrad < θ < 28 (46) mrad) • Detection of low pT em interacting particles • Measure and analyse the deposition from pairs originating from beamstrahlung. • LHCal (new idea) • Low angle hadron calorimeter • PhotoCal (not drawn on this picture) • Analyse beamstrahlung photons in the range of ~100μrad • Minimize background from backscattering from pairs. 20mrad Ch.Grah: Luminosity Measurement

  5. Backgrounds (Old 20mrad Geometry) • 20mrad DID • backscattering from pairs hitting the LumiCal edge (K.Büsser) Sketch of old BeamCal geometry. Projection of LumiCal‘s inner radius. Energy deposited in LumiCal from pairs. Ch.Grah: Luminosity Measurement

  6. LumiCal Events Energy (GeV) θ (rad) • Requirements: Events BHWIDE generated events precision by: Bhabha scattering Ch.Grah: Luminosity Measurement

  7. Detector Performance Detector performance can be included into MC. How well we have to know? R.Ingbir Ch.Grah: Luminosity Measurement

  8. Systematic Effects Headon, 14,20 mrad X-angle outgoing beam 14 mrad X-angle detector axis 20 mrad X-angle detector axis without Including bias & resolution • Changing the detector position Ch.Grah: Luminosity Measurement

  9. Compensating Systematic Effects by MC Before correction after correction 20mrad X-angle Detector axis Y (cm) ΔL/L~10-2 X (cm) This is assuming knowing in perfect precision many parameters! So far these effects are all considered individually, so be careful! ΔL/L~10-3 Ch.Grah: Luminosity Measurement

  10. Physics Background  [deg] Energy [Gev] M.Pandurović/I. Božović-Jelisavčić • Four-lepton processes are the main source of physics background for luminosity measurement • Simulation of e+e- -> e+e-l+l- (l=e, μ, τ) background with WHIZARD • and Bhabha signal with BHLUMI • detector simulation BARBIE for track hitting detector frontface (generated track information was used) LUMICAL BEAMCAL LUMICAL BEAMCAL ≈10-3 tracks/BX Energy and polar angle of background Ch.Grah: Luminosity Measurement

  11. Background Suppression y [cm] y [cm] x [cm] x [cm] x [cm] x [cm] • background can be effectively surpressed signal/background before (top) and after applying the selection cuts (bottom) Ch.Grah: Luminosity Measurement

  12. BeamCal e+ e- e+e-pairs from beamstrahlung are deflected into the BeamCal BeamCal: 4 < θ < 28 mrad (headon) • 15000 e+e- per BX => 10 – 20 TeV • ~ 10 MGy per year • “fast” => O(μs) • Direct photons for θ< 400 μrad (PhotoCal) Deposited energy from pairs at z = +365 (no B-field) Ch.Grah: Luminosity Measurement

  13. New Geometry 20mrad DID (Ri(LumiCal) = 10.0cm at z=2270mm) (Ro(BeamCal) = 16.5cm) 20mrad AntiDID (14mrad seems necessary for AntiDID) An AntiDID configuration is close to the headon/2mrad design. BUT better be prepared for both possibilities. Ch.Grah: Luminosity Measurement

  14. Fast Luminosity Monitoring • Why we need a fast signal from the BeamCal? • We can significantly improve L! • e.g. include number of pairs hitting BeamCal in the feedback system Improves L by more than 12% (500GeV)! position and angle scan G.White QMUL/SLAC RHUL & Snowmass presentation Luminosity development during first 600 bunches of a bunch-train. Ltotal = L(1-600) + L(550600)*(2820-600)/50 Ch.Grah: Luminosity Measurement

  15. Beamstrahlung Pair Analysis • A lot of information is stored in the energy distribution of beamstrahlung pairs hitting BeamCal. • Observables (examples): • total energy • first radial moment • thrust value • angular spread • E(ring ≥ 4) / Etot • E / N • l/r, u/d, f/b asymmetries • Beam parameters • σx, σy, σz and Δσx, Δσy, Δσz • xoffset • yoffset • Δx offset • Δy offset • x-waist shift • y-waist shift • Bunch rotation • N particles/bunch • (Banana shape) detector: realistic segmentation, ideal resolution, bunch by bunch resolution Ch.Grah: Luminosity Measurement

  16. Analysis Concept • Beam Parameters • determine collision • creation of beamstr. • creation of e+e- pairs • guinea-pig • (D.Schulte) • Observables • characterize energy distributions in detectors • FORTRAN • analysis program (A.Stahl) • and/or • GEANT4 1st order Taylor-Exp. Taylor Matrix Observables Observables Δ BeamPar = + * Solve by matrix inversion (Moore-Penrose Inverse) nom Ch.Grah: Luminosity Measurement

  17. Coefficients of the Taylor-Matrix parametrization (polynomial) slope at nom. value  taylor coefficient i,j observable j [au] 1 point = 1 bunch crossing by guinea-pig beam parameter i [au] Ch.Grah: Luminosity Measurement

  18. Analysis for nominal ILC Parameters single parameter analysis ILCNOM, 20mrad DID Ch.Grah: Luminosity Measurement

  19. 2mrad and 20mrad Analysis ... Ch.Grah: Luminosity Measurement

  20. BeamCal Geant4 Simulation • Need precise simulation for showering/realistic bfield map. Includes: • flexible geometry (beam crossing angle, layer thickness, variable segmentation, calorimeter tilt) • simplified DiD/antiDiD magnetic field • input – GP generated e+e- pairs • output – root tree with energy distribution in segments • 1 BX ~ 200min @ 2.4 GHz CPU A.Sapronov Energy/Layer distribution Shower visualization Ch.Grah: Luminosity Measurement

  21. G4 Simulation with simplified B-field 20mrad DID Deposited energy in sensor layer all layers layer8 20mrad AntiDID σz, μm Ch.Grah: Luminosity Measurement

  22. Using Bfield Map Energy deposited in the sensors of the forward BeamCal. All layers Layer 8 Ch.Grah: Luminosity Measurement

  23. Summary • Redesign of the forward region has been done to cope with 20mrad DID (worst case). • LumiCal • Investigated physics and selection cuts to effectively reduce background. • Investigated systematic effects (displacement, resolution, bias ....)...and recommend LumiCal to be centered around outgoing beam. • A luminosity measurement ofΔL/L ≈ 10-4 is feasible so far. • BeamCal • Intratrain feedback of BeamCal has the potential to increase the luminosity significantly. • A fast beamdiagnostics has potential to access many beam parameters (intratrain). • This is also feasible for 20mrad. • Have set up a G4 simulation of BeamCal for realistic shower development and for realistic b-field map. Ch.Grah: Luminosity Measurement

  24. Outlook • LumiCal: extend background study by detector simulation, crossing angle • LumiCal Geant4 simulation for both design, pad and strip version, are in work • Use the BeamCal G4 simulation for the beamdiagnostics • Choose a subset of the detector information for the analysis • Detector & Readout R&D => talk by W.Wierba (DAQ session) • Find more details at: http://www.ifh.de/ILC/fcal Ch.Grah: Luminosity Measurement

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