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Moenig, K.

Paper Title Page
FRPMN012 Bias on Absolute Luminosity Measurements at the ILC from Beam-Beam Space Charge Effects 3907
  • C. Rimbault, P. Bambade
    LAL, Orsay
  • K. Moenig
    DESY Zeuthen, Zeuthen
  • D. Schulte
    CERN, Geneva
  A way to determine luminosity at the International Linear Collider (ILC) is to measure the Bhabha event rate in a finely segmented calorimeter (LumiCal) at very low polar angles in the very forward region of the detector. An absolute precision between 10-4 and 10-3 is needed for a number of key physics measurements. Besides theoretical uncertainties on the Bhabha cross section and experimental errors when identifying Bhabha events in the LumiCal, the very strong beam-beam space charge effects which characterise the ILC e+e- collisions lead to a major bias in the counting rate, which drastically limits the luminosity measurement if uncorrected. In this paper, Bhabha event samples produced with the BHLUMI generator are used in the context of the GUINEA-PIG beam-beam simulation to study how beamstrahlung radiation and electromagnetic deflections affect the proposed experimental selections. A corrective method based on determining the luminosity spectrum within the LumiCal is suggested to minimise the resulting errors. The expected residual uncertainty after correction is estimated based on simulations with realistic beam conditions.