First Dark Matter Search Results from COUPP-4 at SNOLAB

New data are being reported by the COUPP (Chicagoland Observatory for Underground Particle Physics) from the operation of a 4.0 kg CF3I bubble chamber at SNOLAB. The effectiveness of ultrasound analysis in discriminating alpha decay background events from single nuclear recoils has been confirmed, with a lower bound of >99.3% rejection of alpha decay events. Twenty single nuclear recoil event candidates and three multiple bubble events were observed during a total exposure of 553 kg-days distributed over three different bubble nucleation thresholds. The effective exposure for single bubble recoil-like events was 437.4 kg-days. A neutron background internal to the apparatus, of known origin, is estimated to account for five single nuclear recoil events and is consistent with the observed rate of multiple bubble events. This observation provides world best direct detection constraints on WIMP-proton spin-dependent scattering for WIMP masses >20 GeV/c2 and demonstrates significant sensitivity for spin-independent interactions.

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