Single- and Multi-Photon Events with Missing Energy in e+e- Collisions at LEP

TL;DR

This study measures single- and multi-photon events with missing energy at LEP, confirming Standard Model predictions and setting limits on theories with extra dimensions and supersymmetry.

Contribution

It provides precise measurements of photon events, confirms the number of light neutrino species, and sets new limits on models with large extra dimensions.

Findings

Number of neutrino species N_nu = 2.98 +/- 0.05 +/- 0.04

Cross sections agree with Standard Model

Lower limits on gravity scale between 0.65 and 1.5 TeV

Abstract

Single- and multi-photon events with missing energy are selected in 619/pb of data collected by the L3 detector at LEP at centre-of-mass energies between 189GeV and 209GeV. The cross sections of the process e^+e^- -> nu nu gamma (gamma) are found to be in agreement with the Standard Model expectations, and the number of light neutrino species is determined, including lower energy data, to be N_nu = 2.98 +/- 0.05 +/- 0.04. Selection results are also given in the form of tables which can be used to test future models involving single- and multi-photon signatures at LEP. These final states are also predicted by models with large extra dimensions and by several supersymmetric models. No evidence for such models is found. Among others, lower limits between 1.5TeV and 0.65TeV are set, at 95% confidence level, on the new scale of gravity for the number of extra dimensions between 2 and 6.