### Citation:

### Date Published:

jun### Abstract:

{We report measurements of the mass density, Omega\_M, and cosmological-constant energy density, Omega\_Lambda, of the universe based on the analysis of 42 type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these supernovae, at redshifts between 0.18 and 0.83, are fitted jointly with a set of supernovae from the Calán/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All supernova peak magnitudes are standardized using a SN Ia light-curve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8Omega\_M-0.6Omega\_Lambda\~{}-0.2+/-0.1 in the region of interest (Omega\_Młt}\~{}1.5). For a flat (Omega\_M+Omega\_Lambda=1) cosmology we find Omega\^{}flat\_M=0.28\^{}+0.09\_-0.08 (1 sigma statistical) \^{}+0.05\_-0.04 (identified systematics). The data are strongly inconsistent with a Lambda=0 flat cosmology, the simplest inflationary universe model. An ope