5 Conclusions

The Archeops experiment has observed a large portion of the sky. Maps from the two highest sensitivity detectors at 143 and 217 GHz show consistent, sky-stationary anisotropy signal that appears inconsistent with any known astrophysical source other than CMB anisotropy. The angular power spectrum of this signal at multipoles between $\ell=15$ and $\ell=350$ shows a clear peak at $\ell\simeq 200$. These results are consistent with predictions by inflationary-motivated cosmologies. Archeops provides the highest signal-to-noise ratio mapping of the first acoustic peak and its low-$\ell$ side of any experiment to date and covers the largest number of decades in $\ell$. It has been obtained with a limited integration time (half a day) using a technology similar to that of the Planck HFI experiment. An extensive set of tests limits the contribution of systematic errors to a small fraction of the statistical and overall calibration errors in the experiment. More data reduction is under way to increase the accuracy and $\ell$ range of the power spectrum. The determination of cosmological parameters are discussed in a companion paper (Benoît et al. 2003a).

Acknowledgements

The authors would like to thank the following institutes for funding and balloon launching capabilities: CNES (French space agency), PNC (French Cosmology Program), ASI (Italian Space Agency), PPARC, NASA, the University of Minnesota, the American Astronomical Society and a CMBNet Research Fellowship from the European Commission. Healpix package was used throughout the data analysis (1998).