1. Analysis of Beamstrahlung Pairs ECFA Workshop Vienna, November 14-17, 2005 Christian Grah

2. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs2 Outline  Very Forward Calorimetry  Fast luminosity monitoring  Analyzing pairs from beamstrahlung with BeamCal  Pair distributions in different geometries and magnetic field configurations  Summary & outlook

3. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs3 Very Forward Region LumiCal: 26 < θ < 82 mrad BeamCal: 4 < θ < 28 mrad PhotoCal: 100 < θ < 400 μrad

4. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs4 Very Forward Calorimeters  LumiCal:  Precise measurement of the luminosity by using Bhabha events (very high mechanical precision needed).  Extend coverage of the ILC detector.  Photocal  Beam diagnostics from beamstrahlung photons.  BeamCal:  Detection of electrons/photons at low angle.  Beam diagnostics from beamstrahlung electrons/positron pairs.  Shielding of Inner Detector.

5. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs5 BeamCal: Beam Diagnostics and Fast Luminosity Monitoring  15000 e + e - per BX => 10 – 20 TeV  ~ 10 MGy per year  “fast” => O(μs)  Direct photons for  < 400  rad (PhotoCal) e + e - pairs from beamstrahlung are deflected into the BeamCal e+e+ e-e- Deposited energy from pairs at z = +365 (no B-field, TESLA parameters)

6. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs6 BeamCal: W-Diamond Sandwich Length = 30 X 0 (3.5mm W +.5mm diamond sensor) ~ 15 000 channels ~1.5/2 cm < R < ~10(+2) cm Space for electronics

7. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs7 Fast Luminosity Monitoring  Pair signal included into the fast feedback system. Luminosity development during first 600 bunches of a bunch-train. L total = L(1-600) + L(550600)*(2820-600)/50 G.White QMUL/SLAC RHUL & Snowmass presentation position and angle scan L improvement for 500 GeV

8. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs8 Beamstrahlung Pairs  Observables (examples):  total energy  first radial moment  thrust value  angular spread  E(ring ≥ 4) / Etot  E / N  l/r, u/d, f/b asymmetries detector: realistic segmentation, ideal resolution, bunch by bunch resolution  Beam parameters  σ x, σ y, σ z and Δσ x, Δσ y, Δσ z  x offset  y offset  Δx offset  Δy offset  x-waist shift  y-waist shift  Bunch rotation  N particles/bunch  (Banana shape)

9. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs9 Analysis Concept Observables Δ BeamPar Taylor Matrix nom = + * Beam Parameters determine collision creation of beamstr. creation of e + e - pairsguinea-pig(D.Schulte) Observables characterize energy distributions in detectorsFORTRAN analysis program (A.Stahl) 1 st order Taylor- Exp. Solve by matrix inversion (Moore-Penrose Inverse)

10. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs10 beam parameter i [au] observable j [au] parametrization (polynomial) Slopes 1 point = 1 bunch crossing by guinea-pig slope at nom. value  taylor coefficient i,j

11. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs11 σxσx σyσy σzσz Δσ x Δσ y Δσ z 0.3 %0.4 %3.4 %9.5 %1.4 %0.8 % 0.3 % 0.4 %3.5 % 11 % 1.5 % 0.9 % 0.9 % 1.0 % 11 % 24 % 5.7 % 24 % 1.6 % 1.9 % 1.8 % 1.1 % 16 % 27 % 3.2 % 2.1 % Multi Parameter Analysis

12. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs12 Moving to 20mrad crossing angle with DID  Boost the generated pairs (GuineaPig) according to crossing angle.  Shift center of detector to the outgoing beam.  New segmentation of the detector and blind area for the incoming beam.  Use a simplified implementation of DID field. (B.Parker & A.Seryi) Coordinate system

13. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs13 Old Geometry for 20mrad QuantityNominal ValuePrecision xx 553 nm4.8nm xx 3.9nm yy 5.0 nm0.1 nm yy zz 300  m8.5  m zz 6.7  m yy 02.0nm PRELIMINARY! Multi Parameter Analysis has also been done. Applied the algorithm to the old 20mrad geometry, using TESLA parameters.

14. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs14 20mrad crossing angle – old geometry Here: ILC nom. beam parameters Sketch of BeamCal geometry. Projection of LumiCal‘s inner radius. Energy deposited in LumiCal from pairs.

15. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs15 Backgrounds 20mrad solenoid 20mrad DID  backscattering from pairs hitting the LumiCal edge Background simulations by Karsten Buesser.

16. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs16 First try to fix  Changed geometry:  increased aperture of LumiCal by 3 cm  increased outer radius of BeamCal by 3 cm  increased apertures in between accordingly Situation improved but still a factor of ~5 worse than in the 2mrad case. Larger increase of the aperture is necessary, which will increase the background from backscattering from the BeamCal... Study is ongoing. Hits in TPC

17. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs17 Options for 20mrad under investigation DID, small aperture DID, large aperture (R i (LumiCal) > 13cm) 20mrad AntiDID 14mrad AntiDID

18. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs18 Summary  A fast luminosity signal can significantly increase the luminosity.  Analyzing beamstrahlung grants access to many beam parameters.  Promising results also for 20mrad case.  Single and Multiparameter analysis is feasible.  The Very Forward region design for large crossing angles needs:  The AntiDID field configuration OR  A massively increased aperture (LumiCal’s inner radius).

19. 11/16/2005Ch.Grah: Analysis of Beamstrahlung Pairs19 Outlook  The beam diagnostics, which was based upon a FORTRAN/HBOOK code is now being ported to a GEANT4 based simulation, including:  Usage of b field map files.  Realistic detector response.  Fast shower parameterization.  Optimization of observables.  Studies on the new 20mrad geometry are ongoing.