Fast Beam Diagnostics at the ILC Using the Beam Calorimeter Christian Grah, Desy FCAL Workshop February Cracow

FCAL Workshop Cracow, Feb 2006 C.Grah: Beamdiagnostics 2 Contents  Very forward region and BeamCal  Beam parameter reconstruction Principle Results on 20mrad geometry with the nominal ILC parameter set.  Summary and outlook

FCAL Workshop Cracow, Feb 2006 C.Grah: Beamdiagnostics 3 Very Forward Region LumiCal: 26 < θ < 82 mrad BeamCal: 4 < θ < 28 mrad PhotoCal: 100 < θ < 400 μrad

FCAL Workshop Cracow, Feb 2006 C.Grah: Beamdiagnostics 4 BeamCal  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) W:diamond sandwich calorimeter

FCAL Workshop Cracow, Feb 2006 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.

FCAL Workshop Cracow, Feb 2006 C.Grah: Beamdiagnostics 6 ILC B-Field Configurations 20mrad DID (R i (LumiCal) = 13.5cm) (R o (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

FCAL Workshop Cracow, Feb 2006 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 Luminosity development during first 600 bunches of a bunch-train. L total = L(1-600) + L(550600)*( )/50 G.White QMUL/SLAC RHUL & Snowmass presentation position and angle scan Improves L by more than 12% (500GeV)!

FCAL Workshop Cracow, Feb 2006 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 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)

FCAL Workshop Cracow, Feb 2006 C.Grah: Beamdiagnostics 9 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) and/orGEANT4 1 st order Taylor- Exp. Solve by matrix inversion (Moore-Penrose Inverse)

FCAL Workshop Cracow, Feb 2006 C.Grah: Beamdiagnostics 10 Coefficients of the Taylor-Matrix beam parameter i [au] observable j [au] parametrization (polynomial) 1 point = 1 bunch crossing by guinea-pig slope at nom. value  taylor coefficient i,j

FCAL Workshop Cracow, Feb 2006 C.Grah: Beamdiagnostics 11 Analysis for nominal ILC Parameters ILCNOM, 20mrad DID Quantity Nominal Value Precision oldnew xx 553 nm xx yy 5.0 nm yy zz 300  m 8.5 zz yy single parameter analysis

FCAL Workshop Cracow, Feb 2006 C.Grah: Beamdiagnostics 12 2mrad and 20mrad Analysis Quantity Nominal Value Precision 2mrad20mrad20mrad (2par) xx 553 nm xx yy 5.0 nm yy zz 300  m zz εyεy 40x10 -9 mrad εyεy xx yy N2x NN

FCAL Workshop Cracow, Feb 2006 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).

FCAL Workshop Cracow, Feb 2006 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.