Measurements of the Cosmological Parameters Ω and Λ from the First Seven Supernovae at z ≥ 0.35

We have developed a technique to systematically discover and study high-redshift supernovae that can be used to measure the cosmological parameters. We report here results based on the initial seven of >28 supernovae discovered to date in the highredshift supernova search of the Supernova Cosmology Project. We find a dispersion in peak magnitudes of σMB = 0.27; this dispersion narrows to σMB,corr = 0.19 after “correcting” the magnitudes using the light-curve “width-luminosity” relation found for nearby (z ≤ 0.1) type Ia supernovae from the Calán/Tololo survey (Hamuy et al. 1996). Comparing lightcurve-width-corrected magnitudes as a function of redshift of our distant (z = 0.35–0.46) supernovae to those of nearby type Ia supernovae yields a global measurement of the mass density, ΩM = 0.88 +0.69 −0.60 for a Λ = 0 cosmology. For a spatially flat universe (i.e., ΩM + ΩΛ = 1), we find ΩM = 0.94 +0.34 −0.28 or, equivalently, a measurement of the cosmological constant, ΩΛ = 0.06 +0.28 −0.34 (<0.51 at the 95% confidence level). For the more general Friedmann-Lemâıtre cosmologies with independent ΩM and ΩΛ, the results are presented as a confidence region on the E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720; saul@LBL.gov Center for Particle Astrophysics, U.C. Berkeley, California 94720 Space Sciences Laboratory, U.C. Berkeley, California 94720 University of Stockholm CNRS-IN2P3, University of Paris Institute of Astronomy, Cambridge, United Kingdom Royal Greenwich Observatory, Cambridge, United Kingdom Anglo-Australian Observatory, Sydney, Australia Fermilab, Batavia, Illinois 60510 University of California, Berkeley, California 94720 Mt. Stromlo and Siding Springs Observatory, Australia University of New South Wales, Sydney, Australia