1. Challenges in Lumi Measurement Some studies of sensitivity to systematic uncertainties Amsterdam 31. March ‚03 Achim Stahl DESY Zeuthen

2. Method BHLUMI (Ver. 4.04) No Detector Simulation Generate an event  calculate coordinates on calorimeter  apply systematic shifts  recalculate coordinates  apply selection cuts  count events  Lumi E+, E- > 0.8 Ebeam Acol < 11.5o 30 mrad < θ+ < 75 mrad 30 mrad < θ-< 75 mrad

3. Offset of Beams from Axis 2 107 events  stat = 2.2 10-4,  same events for each point

4. Offset of Beams from Axis Lin. Coeff. ≈ 0 Quadratic Coeff.: Δoffset < 200 μm 2 107 new events,  same picture

5. Inner Radius of Calorimeter ΔL/L ≈ 1.3 10-4/ μm

6. Longitudinal Distance of Calorimeters ΔL/L ≈ -0.0033 / mm z+ - z- < 60 μm

7. Center-of-Mass Energy ΔL/L ≈ -7 ΔE / E Not possible from spectrometer

8. Conclusions To achieve ΔL / L ≈ 10-4: Beam Offsets: < 200 μm Inner Radius of Cal < 0.75 μm Distance of Cals < 60 μm Center-of-Mass Energy: process dependent but that‘s not all yet