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The High-Z Supernova Search is an international collaboration to discover and monitor type Ia supernovae (SN Ia) at z > 0. 2 with the aim of measuring cosmic deceleration and global curvature. Our collaboration has pursued a basic understanding of supernovae in the nearby Universe, discovering and observing a large sample of objects, and developing methods to measure accurate distances with SN Ia. This paper describes the extension of this program to z \ 0. 2, outlining our search techniques and follow-up program. We have devised high-throughput filters which provide accurate two-color restframe B and V light curves of SN Ia, enabling us to produce precise, extinction-corrected luminosity distances in the range 0. 25 < z < 0. 55. Sources of systematic error from K-corrections, extinction, selection effects, and evolution are investigated, and their effects estimated. We present photometric and spectral observations of SN 1995K, our program's first supernova, and use the data to obtain a precise measurement of the luminosity distance to the z=0. 479 host galaxy. This object, when combined with a nearby sample of SN, yields an estimate for the matter density of the Universe of \M = -0. 2^+1. 0-₀. ₈ if \_\ = 0. For a spatially flat universe composed of normal matter and a cosmological constant, we find \M = 0. 4^+0. 5-₀. ₄, \_\ = 0. 6^+0. 4-₀. ₅. We demonstrate that with a sample of \ 30 objects, we should be able to determine relative luminosity distances over the range 0 < z< 0. 5 with sufficient precision to measure \M with an uncertainty of \ 0. 2.
Schmidt et al. (Sun,) studied this question.