We analyze the cosmological constraints that Archeops ( [ Benoît et al .
2002 ] ) places on adiabatic cold dark matter models with passive power-law initial fluctuations .
Because its angular power spectrum has small bins in \ell and large \ell coverage down to COBE scales , Archeops provides a precise determination of the first acoustic peak in terms of position at multipole l _ { peak } = 220 \pm 6 , height and width .
An analysis of Archeops data in combination with other CMB datasets constrains the baryon content of the Universe , \Omega _ { b } h ^ { 2 } = 0.022 ^ { +0.003 } _ { -0.004 } , compatible with Big-Bang nucleosynthesis and with a similar accuracy .
Using cosmological priors obtained from recent non–CMB data leads to yet tighter constraints on the total density , e.g . \Omega _ { tot } = 1.00 ^ { +0.03 } _ { -0.02 } using the HST determination of the Hubble constant .
An excellent absolute calibration consistency is found between Archeops and other CMB experiments , as well as with the previously quoted best fit model .
The spectral index n is measured to be 1.04 ^ { +0.10 } _ { -0.12 } when the optical depth to reionization , \tau , is allowed to vary as a free parameter , and 0.96 ^ { +0.03 } _ { -0.04 } when \tau is fixed to zero , both in good agreement with inflation .