Photon Events with Missing Energy in e+e- Collisions at sqrt{s} = 130 to 209 GeV

Abstract

The production of single- and multi-photon events has been studied in the reaction e+e- -> gamma (gamma) + invisible particles. The data collected with the DELPHI detector during the years 1999 and 2000 at centre-of-mass energies between 191 GeV and 209 GeV was combined with earlier data to search for phenomena beyond the Standard Model. The measured number of light neutrino families was consistent with three and the absence of an excess of events beyond that predicted by the Standard Model processes was used to set limits on new physics. Both model-independent searches and searches for new processes predicted by supersymmetric and extra-dimensional models have been made. Limits on new non-standard model interactions between neutrinos and electrons were also determined.

Figures (12)

• Figure 1: $x_{\gamma}$ of selected single photons for three $\sqrt{s}$-bins. The light shaded area is the expected distribution from $e^+e^- \rightarrow \nu \bar{\nu}\gamma$ and the dark shaded area is the total background from other sources. Indicated in the plot is also the signal expected from $e^+e^-\rightarrow\tilde{G}\tilde{G}\gamma$ under the assumption that $m_{\tilde{{G}}}= 7 \cdot 10^{-6} ~ \rm{eV/c^2}$.
• Figure 2: Missing mass (or recoil mass) distributions of all single-photon events in DELPHI (from data recorded at $\sqrt{s}$ = 180-209 GeV). The figure shows the missing mass distribution from each calorimeter separately and the bottom plot shows the combined spectrum. The light shaded area is the expected distribution from $e^+e^- \rightarrow \nu \bar{\nu}\gamma$ and the dark shaded area is the total background from other sources. The signal expected from $e^+e^-\rightarrow\gamma G$ production is indicated (two extra dimensions and $M_{D}=0.75$ TeV/c$^2$ were assumed in this calculation).
• Figure 3: The single-photon cross-section measured by the STIC, FEMC and HPC detectors compared to the cross-section predicted by Koralz.
• Figure 4: Missing mass distribution observed after multi-photon preselection in the 190-209 GeV sample (a) and the combined 130-209 GeV sample (b).
• Figure 5: The remaining allowed regions. a) In the $\epsilon_{e L} - \epsilon_{e R}$ plane. b) In the $\epsilon_{\tau L} - \epsilon_{\tau R}$ plane. c) In the $\epsilon_{\alpha\beta L} - \epsilon_{\alpha\beta R}$ ($\alpha \neq \beta$) plane.