Beam-beam effects on the luminosity measurement at LEP and the number of light neutrino species

Abstract

In $e^{+}{e}^{-}$ collisions, electromagnetic effects caused by large charge density bunches modify the effective acceptance of the luminometer system of the experiments. These effects consequently bias the luminosity measurement from the rate of low-angle Bhabha interactions $e^{+}{e}^{-}\to e^{+}{e}^{-}$. Surprisingly enough, the magnitude of this bias is found to yield an underestimation of the integrated luminosity measured by the LEP experiments by about 0.1%, significantly larger than the reported experimental uncertainties. When accounted for, this effect modifies the number of light neutrino species determined at LEP from the measurement of the hadronic cross section at the Z peak.

arXiv commentVersion 4: Fix a typo in the conclusions: ${\sigma }_{had}=41.500\pm 0.037$ nb, and update Ref [9] (now published)

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• Measurements of Cross Sections and Forward-Backward Asymmetries at the Z Resonance and Determination of Electroweak Parameters
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• Precision measurement of the Z boson to electron neutrino coupling at the future circular colliders
• Challenging luminosity measurements at the Electron-Ion Collider
• New Physics contamination to precision luminosity measurements at future $e^{+}{e}^{-}$ colliders
• Challenges for FCC-ee Luminosity Monitor Design
• Circular and Linear ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ Colliders: Another Story of Complementarity
• Standard and Non-Standard Aspects of Neutrino Physics
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• Search for sterile neutrino with light gauge interactions: recasting collider, beam-dump, and neutrino telescope searches