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

Publication date: Available online 31 October 2019Source: Physics Letters BAuthor(s): Georgios Voutsinas, Emmanuel Perez, Mogens Dam, Patrick JanotAbstractIn 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−→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.

Source: Physics Letters B - November 13, 2019 Category: Physics Source Type: research