1. Jan. 7 2005MDI WS SLAC Electron Detection in the Very Forward Region V. Drugakov, W. Lohmann Motivation Talk given by Philip Detection of Electrons and Photons at very low angle – extend hermiticity (Important for Searches, radiative events, calibrations)

2. Geometry Fast Beam Diagnostics Shielding of the inner Detector IP VTX LumiCal BeamCal FTD L* = 4m 300 cm LumiCal: 26 <  < 82 mrad BeamCal: 4 <  < 28 mrad So far for zero crossing angle

3. The Challenge e+e+ e-e- 15000 e + e - per BX 10 – 20 TeV 10 MGy per year Rad. hard sensors Technologies: Diamond-W Sandwich Scintillator Crystals e + e - Pairs from Beamstrahlung are deflected into the BeamCal GeV

4. Calorimeter Small Moli è re radius (1cm) High granularity (1/2 cm) Longitudinal segmentation (30 x 1 X 0 ) sensor Space for electronics Depositions from a high energy electron Signal (+background) event

5. Electron (Photon) Reconstruction – using beamstrahlung depositions of 10 (random) bunch crossings, the average background deposition and its rms in each pad is determined – Taking a ‘ signal ’ (electron + background) event, this average background deposition is subtracted in each pad – Remaining depositions larger than 5x the rms are kept. Chains of such pads in the region of the expected shower maximum are searched for – Adjacent chains are grouped to a shower and the energy and position is estimated.

6. √s = 500 GeV Single Electrons of 50, 100 and 250 GeV in the region of large background Comparison Sampling Heavy Crystal Comparison 500 GeV - 1TeV Reconstruction efficiencies

7. Efficiency less then 90% Minsk-Desy ‘ blind ’ regions √s = 500 GeV √s = 1000 GeV

8. Includes seismic motions, Delay of Beam Feedback System, Lumi Optimisation etc. (G. White) Efficiency to identify energetic electrons and photons (E > 200 GeV) Fake rate √s = 500 GeV Realistic beam simulation (Input from G. White)

9. Electron Fake Rate Beamstrahlung tails (> 50 GeV): ~ 1% Background Fluctuations (> 50 GeV): ~ 1% Radiative Bhabha Events Not yet studied: Incompletely reconstructed Bhabha’s – potentially a large fraction (Study done by A. Elagin)

10. Summary Using a Compact Fine Segmented Calorimeter electrons and photons can be detected to palar angles of about 5 mrad with reasonable Efficincy up to 1 TeV cm energy Electrons with energies near the beam energy can be detected with very high efficiency in regions with low depositions from beamstrahlung and still with high efficiency in regions largely affected by beamstrahlung (Similar results also obtained by T. Maruyama) The fake rate due to Beamstrahlung is at % level (even for realistic beam simulation) The Bhabha process needs more studies Future – development of a more realistic design of the calorimeter

11. 200 GeV Electrons Efficiency less then 90% Pile up effects

12. 250 GeV e- BG Si Layers Pair Background 250 GeV Electron E bg + E electron - Deposited Energy (arb. Units) SLAC ECFA - Durham2004 Electron detection with crossing angle Collaboration High precision design