Single and Multi-Photon Events with Missing Energy in e+e- Collisions at \sqrt{s} = 189 GeV

TL;DR

This paper analyzes single and multi-photon events with missing energy at 189 GeV to measure neutrino counts, set limits on supersymmetric particles, and test models with extra dimensions, providing new constraints on these theories.

Contribution

It provides the first measurement of the number of light neutrino flavors at 189 GeV and sets new limits on supersymmetric particles and extra-dimensional gravity models.

Findings

Number of neutrino flavors N_ν = 3.011 ± 0.077

Limits on neutralino and gravitino masses improved

Constraints on extra-dimensional gravity energy scale > 1 TeV

Abstract

Single and multi-photon events with missing energy are analysed using data collected with the L3 detector at LEP at a centre-of-mass energy of 189 GeV, for a total of 176 pb^{-1} of integrated luminosity. The cross section of the process e+e- -> nu nu gamma (gamma) is measured and the number of light neutrino flavours is determined to be N_\nu = 3.011 +/- 0.077 including lower energy data. Upper limits on cross sections of supersymmetric processes are set and interpretations in supersymmetric models provide improved limits on the masses of the lightest neutralino and the gravitino. Graviton-photon production in low scale gravity models with extra dimensions is searched for and limits on the energy scale of the model are set exceeding 1 TeV for two extra dimensions.