Characterizing the Peak in the Cosmic Microwave Background Angular Power Spectrum

A peak has been unambiguously detected in the cosmic microwave background angular spectrum. Here we characterize its properties with fits to phenomenological models. We find that the TOCO and BOOM/NA data determine the peak location to be in the range 175–243 and 151–259, respectively (at $95\%$ confidence) and determine the peak amplitude to be between $\approx 70$ and $90\mu \mathrm{K}$. The peak shape is consistent with inflation-inspired flat, cold dark matter plus cosmological constant models of structure formation with adiabatic, nearly scale invariant initial conditions. It is inconsistent with open models and presents a great challenge to defect models.