Measurements of the Cosmological Parameters and from the First 7 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 high-redshift supernova search of the Supernova Cosmology Project. We nd an observational dispersion in peak magnitudes of M B = 0:27; this dispersion narrows to M B ;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 Call an/Tololo survey (Hamuy et al. 1996). Comparing lightcurve-width-corrected { 2 { 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, M = 0:88 +0:69 ?0:60 for a = 0 cosmology. For a spatially at universe (i.e., M + = 1), we nd M = 0:94 +0:34 ?0:28 or, equivalently, a measurement of the cosmological constant, = 0:06 +0:28 ?0:34 (<0.51 at the 95% conndence level). For the more general Friedmann-Lema^ tre cosmologies with independent M and , the results are presented as a conndence region on the M {{ plane. This region does not correspond to a unique value of the deceleration parameter q 0. We present analyses and checks for statistical and systematic errors, and also show that our results do not depend on the speciics of the width-luminosity correction. The results for-versus-M are inconsistent with-dominated, low density, at cosmologies that have been proposed to reconcile the ages of globular cluster stars with higher Hubble constant values.