Fast and Precise Luminosity Measurement at the ILC

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

Overview Ø The forward region Ø Luminosity measurement using Lumi. Cal § Requirements § Systematics § Physics background Ø Fast luminosity monitor – Beam. Cal § Using the pair background signal § Beam parameter reconstruction Ø Summary and outlook LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 2

Forward Region – New Geometry 20 mrad geometry (LDC) LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 3

Forward Region - Tasks Ø Lumi. Cal (26 (43) mrad < θ < 153 mrad) 2 mrad § Detection of low p. T em interacting particles § Measure bhahba particles with high precision Ø Beam. Cal (5. 6 mrad < θ < 28 (46) mrad) § Detection of low p. T em interacting particles § Measure and analyse the deposition from pairs originating from beamstrahlung. Ø LHCal (new idea) § Low angle hadron calorimeter 20 mrad Ø Photo. Cal (not drawn on this picture) § Analyse beamstrahlung photons in the range of ~100μrad Ø Minimize background from backscattering from pairs. LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 4

Backgrounds (Old 20 mrad Geometry) Sketch of old Beam. Cal geometry. Projection of Lumi. Cal‘s inner radius. Energy deposited in Lumi. Cal from pairs. 20 mrad DID Þ backscattering from pairs hitting the Lumi. Cal edge (K. Büsser) LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 5

Lumi. Cal Events Ø Requirements: BHWIDE generated events precision by: θ (rad) Bhabha scattering LCWS 2006, Bangalore Energy (Ge. V) Ch. Grah: Luminosity Measurement 6

Detector Performance Detector performance can be included into MC. How well we have to know? R. Ingbir LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 7

Systematic Effects Ø Changing the detector position Headon, 14, 20 mrad X-angle outgoing beam 14 mrad X-angle detector axis 20 mrad X-angle detector axis without Including bias & resolution LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 8

Compensating Systematic Effects by MC Y (cm) 20 mrad X-angle Detector axis Before correction after correction ΔL/L~10 -2 X (cm) This is assuming knowing in perfect precision many parameters! ΔL/L~10 -3 So far these effects are all considered individually, so be careful! LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 9

Physics Background M. Pandurović/I. Božović-Jelisavčić Ø Four-lepton processes are the main source of physics background for luminosity measurement Ø Simulation of e+e- -> e+e-l+l- (l=e, μ, τ) background with WHIZARD Ø and Bhabha signal with BHLUMI Ø detector simulation BARBIE for track hitting detector frontface (generated track information was used) LUMICAL BEAMCAL ≈10 -3 tracks/BX Energy [Gev] [deg] Energy and polar angle of background LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 10

y [cm] Background Suppression x [cm] signal/background before (top) and after applying the selection cuts (bottom) Ø background can be effectively surpressed LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 11

Beam. Cal e+ e- e+e- pairs from beamstrahlung are deflected into the Beam. Cal Ø 15000 e+e- per BX => Beam. Cal: 4 < θ < 28 mrad (headon) 10 – 20 Te. V Ø ~ 10 MGy per year Ø “fast” => O(μs) Ø Direct photons for θ < 400 μrad (Photo. Cal) LCWS 2006, Bangalore Deposited energy from pairs at z = +365 (no B-field) Ch. Grah: Luminosity Measurement 12

New Geometry 20 mrad DID (Ri(Lumi. Cal) = 10. 0 cm at z=2270 mm) (Ro(Beam. Cal) = 16. 5 cm) 20 mrad Anti. DID (14 mrad seems necessary for Anti. DID) An Anti. DID configuration is close to the headon/2 mrad design. BUT better be prepared for both possibilities. LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 13

Fast Luminosity Monitoring Ø Why we need a fast signal from the Beam. Cal? Ø We can significantly improve L! Ø e. g. include number of pairs hitting Beam. Cal in the feedback system Improves L by more than 12% (500 Ge. V)! 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 LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 14

Beamstrahlung Pair Analysis Ø A lot of information is stored in the energy distribution of beamstrahlung pairs hitting Beam. Cal. Ø Observables (examples): § § § § total energy first radial moment thrust value angular spread E(ring ≥ 4) / Etot E/N l/r, u/d, f/b asymmetries Ø 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) LCWS 2006, Bangalore detector: realistic segmentation, ideal resolution, bunch by bunch resolution Ch. Grah: Luminosity Measurement 15

Analysis Concept Beam Parameters • determine collision • creation of beamstr. • creation of e+e- pairs Observables 1 st order Taylor-Exp. • characterize energy distributions in detectors guinea-pig (D. Schulte) Taylor + nom LCWS 2006, Bangalore Matrix * Δ Beam. Par Observables = FORTRAN analysis program (A. Stahl) and/or GEANT 4 Solve by matrix inversion (Moore-Penrose Inverse) Ch. Grah: Luminosity Measurement 16

observable j [au] Coefficients of the Taylor-Matrix parametrization (polynomial) slope at nom. value taylor coefficient i, j 1 point = 1 bunch crossing by guinea-pig beam parameter i [au] LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 17

Analysis for nominal ILC Parameters single parameter analysis Quantity ILCNOM, 20 mrad DID LCWS 2006, Bangalore sx sx sy sy sz sz y Nominal Value Precision 553 nm old 4. 8 3. 9 new 2. 9 7. 4 5. 0 nm 0. 1 0. 2 0. 1 0. 4 8. 5 6. 7 6. 3 2. 0 0. 6 300 mm Ch. Grah: Luminosity Measurement 0 18

2 mrad and 20 mrad Analysis Quantity sx sx sy sy sz sz Nominal Value Precision 553 nm 2 mrad 3. 1 5. 2 20 mrad 2. 9 7. 4 20 mrad (2 par) 2. 8 7. 6 5. 0 nm 0. 3 0. 2 0. 3 0. 4 4. 8 8. 5 11. 1 3. 7 6. 3 7. 4 300 mm εy 40 x 10 -9 mrad 1. 7 2. 9 5. 2 εy 0 4. 2 4. 1 4. 7 17. 7 9. 3 10 x y 0 0. 5 0. 6 N 2 x 1010 0. 01 N 0 0. 01 0. 02 0. 03 LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement . . . 19

Beam. Cal Geant 4 Simulation Ø Need precise simulation for showering/realistic bfield map. Includes: § § § flexible geometry (beam crossing angle, layer thickness, variable segmentation, calorimeter tilt) simplified Di. D/anti. D magnetic field input – GP generated e+e- pairs output – root tree with energy distribution in segments 1 BX ~ 200 min @ 2. 4 GHz CPU Shower visualization LCWS 2006, Bangalore A. Sapronov Energy/Layer distribution Ch. Grah: Luminosity Measurement 20

G 4 Simulation with simplified B-field 20 mrad DID Deposited energy in sensor layer all layers layer 8 20 mrad Anti. DID σz, μm LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 21

Using Bfield Map Energy deposited in the sensors of the forward Beam. Cal. All layers LCWS 2006, Bangalore Layer 8 Ch. Grah: Luminosity Measurement 22

Summary Ø Redesign of the forward region has been done to cope with 20 mrad DID (worst case). Ø Lumi. Cal § Investigated physics and selection cuts to effectively reduce background. § Investigated systematic effects (displacement, resolution, bias. . ). . . and recommend Lumi. Cal to be centered around outgoing beam. § A luminosity measurement of ΔL/L ≈ 10 -4 is feasible so far. Ø Beam. Cal § Intratrain feedback of Beam. Cal has the potential to increase the luminosity significantly. § A fast beamdiagnostics has potential to access many beam parameters (intratrain). § This is also feasible for 20 mrad. § Have set up a G 4 simulation of Beam. Cal for realistic shower development and for realistic b-field map. LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 23

Outlook Ø Lumi. Cal: extend background study by detector simulation, crossing angle Ø Lumi. Cal Geant 4 simulation for both design, pad and strip version, are in work Ø Use the Beam. Cal G 4 simulation for the beamdiagnostics § Choose a subset of the detector information for the analysis Ø Detector & Readout R&D => talk by W. Wierba (DAQ session) Ø Find more details at: http: //www. ifh. de/ILC/fcal LCWS 2006, Bangalore Ch. Grah: Luminosity Measurement 24