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Fast Beam Diagnostics at the ILC Using the Beam Calorimeter

Fast Beam Diagnostics at the ILC Using the Beam Calorimeter. Christian Grah, Desy FCAL Workshop 12-13 February Cracow. Contents. Very forward region and BeamCal Beam parameter reconstruction Principle Results on 20mrad geometry with the nominal ILC parameter set. Summary and outlook.

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Fast Beam Diagnostics at the ILC Using the Beam Calorimeter

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  1. Fast Beam Diagnostics at the ILC Using the Beam Calorimeter Christian Grah, Desy FCAL Workshop 12-13 February Cracow

  2. Contents • Very forward region and BeamCal • Beam parameter reconstruction • Principle • Results on 20mrad geometry with the nominal ILC parameter set. • Summary and outlook C.Grah: Beamdiagnostics

  3. Very Forward Region LumiCal: 26 < θ < 82 mrad BeamCal: 4 < θ < 28 mrad PhotoCal: 100 < θ < 400 μrad C.Grah: Beamdiagnostics

  4. BeamCal e+ e- e+e-pairs from beamstrahlung are deflected into the BeamCal Deposited energy from pairs at z = +365 (no B-field) • 15000 e+e- per BX => 10 – 20 TeV • ~ 10 MGy per year • “fast” => O(μs) • Direct photons for q< 400 mrad (PhotoCal) W:diamond sandwich calorimeter C.Grah: Beamdiagnostics

  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. C.Grah: Beamdiagnostics

  6. ILC B-Field Configurations 20mrad DID (Ri(LumiCal) = 13.5cm) (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. DID: Detector integrated Dipole, B-field aligned with the incoming beam AntiDID: B-field aligned with the outgoing beam C.Grah: Beamdiagnostics

  7. 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 C.Grah: Beamdiagnostics

  8. 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 C.Grah: Beamdiagnostics

  9. Analysis Concept Taylor Matrix Observables Observables Δ BeamPar nom • 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. = + * Solve by matrix inversion (Moore-Penrose Inverse) C.Grah: Beamdiagnostics

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

  11. Analysis for nominal ILC Parameters single parameter analysis ILCNOM, 20mrad DID C.Grah: Beamdiagnostics

  12. 2mrad and 20mrad Analysis ... C.Grah: Beamdiagnostics

  13. Status of Analysis • GuineaPig files for ILCNOM ready (~400 pair files). • New geometry ready. • Single and multiparameter analysis started. Mostly done for • 2mrad • 20mrad DID • Good progress in the Geant4 implementation (A.Sapronov‘s talk). C.Grah: Beamdiagnostics

  14. Summary & Outlook • Including a fast signal of number of pairs or total energy into the feedback system can significantly increase luminosity of the accelerator. • Analyzing the spatial energy distribution of beamstrahlung pairs hitting the BeamCal grants access to many beam parameters. For highly correlated parameters measurements from other systems can be included (e.g. PhotoCal). • 20mrad geometry is implemented with DID field approximation. • ILCNOM investigation is in work. • Geant4 simulation is running, BC observable calculation and beam parameter reconstruction can be done with some limitations. Next: • Geant4 simulation with realistic b-field map and compare to simplified one. • Hopefully no fast shower simulation has to be included (cpu time dependent). Fast shower simulation is implemented in Geant4 for homogenous detector…. • Find most interesting regions (layers) in the BeamCal segments. • Need background calculation for our 20mrad geometry. C.Grah: Beamdiagnostics

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