Search for anomalous photonic events with missing energy in ${\rm e}^+{\rm e}^-$ collisions at $\sqrt{s}$ = 130, 136 and 183 $\mathrm{GeV}$

The OPAL Collaboration:     G. Abbiendi - et al.

doi:doi:10.1007/s100520050442

2022 Impact factor 4.4

Particles and Fields

Eur. Phys. J. C 8, 23-40
DOI 10.1007/s100529901083

Search for anomalous photonic events with missing energy
in ${\rm e}^+{\rm e}^-$ collisions at $\sqrt{s}$ = 130, 136 and 183 $\mathrm{GeV}$

The OPAL Collaboration

G.Abbiendi² - et al.

² Dipartimento di Fisica dell' Università di Bologna and INFN, I-40126 Bologna, Italy

Received: 9 September 1998 / Published online: 1 March 1999

Abstract
Photonic events with large missing energy have been observed in $\mathrm e^+e^-$ collisions at centre-of-mass energies of 130, 136 and 183 GeV collected in 1997 using the OPAL detector at LEP. Results are presented for event topologies with a single photon and missing transverse energy or with an acoplanar photon pair. Cross-section measurements are performed within the kinematic acceptance of each selection. These results are compared with the expectations from the Standard Model process ${\rm e}^+{\rm e}^-\to\nu\overline{\nu}$ + photon(s). No evidence is observed for new physics contributions to these final states. Using the data at $\sqrt{s}$ = 183 GeV, upper limits on ${\sigma({\rm e}^+{\rm e}^-\to {\rm XY})\cdot{\rm BR}(\rm X \to Y \gamma)}$ and ${\sigma({\rm e}^+{\rm e}^-\to {\rm XX})\cdot{\rm BR}^2(\rm X \to Y \gamma)}$ are derived for the case of stable and invisible Y. These limits apply to single and pair production of excited neutrinos ( $\rm X = \nu^*, Y = \nu$ ), to neutralino production ( $\rm X={{\tilde{\chi}}^{0}}_{2}, Y={{\tilde{\chi}}^{0}}_{1}$ )and to supersymmetric models in which $\rm X = {{\tilde{\chi}}^{0}}_{1}$ and $\rm Y=\tilde{\mathrm{G}}$ is a light gravitino.