Search for narrow high-mass resonances in radiative decays of the Z⁰

Abstract

We search for new resonances, Y, with mass M_Y, in the range from 30 to 89 GeV, produced via the reaction e+e− → Z⁰ →γY, where Y subsequently decays into e+e−, μ+μ− or hadrons. We use 5.5.pb⁻¹ of data collected in the energy range 88.2 ≤ √s ≤ 94.2 GeV, near the Z⁰ peak. We obtain the following upper limits, at the 95% confidence level, on the product of the branching ratios: BR(Z⁰ → γY) × BR(Y → e+e−) < 2.8 × 10⁻⁴ for 30 < M_Y < 89, BR(Z⁰ →γY × BR(Y → μ+μ−) < 2.3 × 10⁻⁴ for 30 < M_Y < 89, BR(Z⁰→ γY) × BR(Y → hadrons) < 4.7 × 10⁻⁴ for 30 < M_Y < 86. These limits are valid for resonances with widths smaller than our mass resolution.