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 more than 28 supernovae discovered to date in the high-redshift supernova search of the Supernova Cosmology Project. We Ðnd an observational dispersion in peak magnitudes of this disperp MB \ 0.27 ; sion narrows to after "" correcting ÏÏ the magnitudes using the light-curve "" widthp MB,corr \ 0.19 luminosity ÏÏ relation found for nearby (z ¹ 0.1) Type Ia supernovae from the Cala n/Tololo survey (Hamuy et al.). Comparing light-curve widthÈcorrected magnitudes as a function of redshift of our distant (z \ 0.35È0.46) supernovae to those of nearby Type Ia supernovae yields a global measurement of the mass density, for a " \ 0 cosmology. For a spatially Ñat universe (i.e., not correspond to a unique value of the deceleration parameterWe present analyses and checks q 0 . for statistical and systematic errors and also show that our results do not depend on the speciÐcs of the width-luminosity correction. The results for are inconsistent with "-dominated, low-) " -versus-) M density, Ñat cosmologies that have been proposed to reconcile the ages of globular cluster stars with higher Hubble constant values.

No abstract

Abstract. This work is based on the rst results from a systematic search for high redshift Type Ia supernovae. Using lters in the R-band we discovered seven such SNe, with redshift z = 0 :3 , 0:5, before or at maximum light. Type Ia SNe are known to be a homogeneous group of SNe, to rst order, with very similar light curves, spectra and peak luminosities. In this talk we report that the light curves we observe are all broadened time dilated as expected from the expanding universe hypothesis. Small variations from the expected 1 + z broadening of the light curve widths can be attributed to a width-brightness correlation that has been observed for nearby SNe z 0:1. We show in this talk the rst clear observation of the cosmological time dilation for macroscopic objects.