A Study of single and multiphoton events in e+ e- collisions at center-of-mass energies of 161-GeV and 172-GeV

Events from electron-positron collisions where photons are the only particles detected in the final state are studied using the data collected by the ALEPH detector at LEP. The data consist of 11.1 pb $\sp{-1}$ at $\sqrt{s} = 161$ GeV, 1.1 pb$\sp{-1}$ at 170 GeV and 9.5 pb$\sp{-1}$ at 172 GeV. The $\rm e\sp+e\sp-\to\nu\bar\nu\gamma(\gamma) $ and $\rm e\sp+e\sp-\to\gamma\gamma(\gamma)$ cross sections are measured. The data are in good agreement with predictions based on the Standard Model, and are used to set upper limits on anomalous photon production. Searches for supersymmetric particles in channels with one or more photons and missing energy have been performed. Cross-section upper limits are derived for two different Supersymmetry models. A lower limit of 71 GeV/$c\sp2$ at 95ib/zoneinfo/MET.L. is set on the mass of the lightest neutralino $\rm\chi\sbsp{1}{0}\ (M\sb{\tilde e\sb{R}} = 1.5M\sb{\chi\sbsp{1}{0}}$ and $\tau\sb{\chi\sbsp{1}{0}}\le 3$ ns) for the Gauge-Mediated Supersymmetry Breaking model. Constraints on compositeness models and excited electrons are studied using the differential cross section for $\rm e\sp+e\sp-\to\gamma\gamma(\gamma)$ events.