Search for neutrinoless double beta decay with the NEMO-3 detector: first results

The NEMO-3 detector, which has been operating in the Frejus Underground Laboratory since February 2003, is devoted to searching for neutrinoless double beta decay (ββ0ν). The expected performance of the detector has been successfully achieved. Half-lives of the two neutrinos double beta decay (ββ2ν) have been measured for 100Mo, 82Se, 96Zr, 116Cd and 150Nd. After 265 days of data collection from February 2003 until March 2004, no evidence for neutrinoless double beta decay (ββ0ν) was found from ∼7 kg of 100Mo and ∼1 kg of 82Se. The corresponding lower limits for the half-lives are 3.5×1023 years at 90% C.L for 100Mo and 1.9×1023 years for 82Se. Limits for the effective Majorana neutrino mass are <0.7−1.2 eV for 100Mo and <1.3−3.2 eV for 82Se. Radon is the dominant background today and a Radon-free purification system will be in operation by the end of September 2004. The NEMO-3 expected sensitivity after 5 years of data is 0.2 eV.