- Perlmutter, S;
- Aldering, G;
- Goldhaber, G;
- Knop, RA;
- Nugent, P;
- Castro, PG;
- Deustua, S;
- Fabbro, S;
- Goobar, A;
- Groom, DE;
- Hook, IM;
- Kim, AG;
- Kim, MY;
- Lee, JC;
- Nunes, NJ;
- Pain, R;
- Pennypacker, CR;
- Quimby, R;
- Lidman, C;
- Ellis, RS;
- Irwin, M;
- McMahon, RG;
- Ruiz-Lapuente, P;
- Walton, N;
- Schaefer, B;
- Boyle, BJ;
- Filippenko, AV;
- Matheson, T;
- Fruchter, AS;
- Panagia, N;
- Newberg, HJM;
- Couch, WJ;
- Project, The Supernova Cosmology

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 SNe, at redshifts between 0.18
and 0.83, are fit jointly with a set of SNe from the Calan/Tololo Supernova
Survey, at redshifts below 0.1, to yield values for the cosmological
parameters. All SN peak magnitudes are standardized using a SN Ia lightcurve
width-luminosity relation. The measurement yields a joint probability
distribution of the cosmological parameters that is approximated by the
relation 0.8 Omega_M - 0.6 Omega_Lambda ~= -0.2 +/- 0.1 in the region of
interest (Omega_M <~ 1.5). For a flat (Omega_M + Omega_Lambda = 1) cosmology we
find Omega_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 open, Lambda = 0
cosmology also does not fit the data well: the data indicate that the
cosmological constant is non-zero and positive, with a confidence of P(Lambda >
0) = 99%, including the identified systematic uncertainties. The best-fit age
of the universe relative to the Hubble time is t_0 = 14.9{+1.4,-1.1} (0.63/h)
Gyr for a flat cosmology. The size of our sample allows us to perform a variety
of statistical tests to check for possible systematic errors and biases. We
find no significant differences in either the host reddening distribution or
Malmquist bias between the low-redshift Calan/Tololo sample and our
high-redshift sample. The conclusions are robust whether or not a
width-luminosity relation is used to standardize the SN peak magnitudes.