Seminar Details

Recent Results in Two-Neutrino Double Beta Decay

Nicole Larson, NSCL
Thursday, January 26, 11:00 AM - Research Discussion
NSCL Lecture Hall

Double beta (2β) decay is an extremely rare form of decay that has only been observed in a handful of isotopes [1]. There are two possible mechanisms for double beta decay. The first is explained by known physics, and is identified as the two-neutrino mode, wherein a nucleus increases its proton number by two, and emits two electrons and antineutrinos. The second mode is neutrinoless double beta decay and is forbidden in the standard model [2]. Though the neutrinoless mode has never been observed, its observation would prove that neutrinos are Majorana leptons, i.e. that neutrinos are their own antiparticle [2]. Study of the two-neutrino mode remains the only observable measure of double beta decay and is important to investigate in its own right. Two neutrino decay can be used to study particle properties, investigate candidate 2β nuclei, and calculate theoretical parameters for the decay matrix elements for both modes [2,3]. Recent results from two experiments, NEMO-3 (Neutrino Ettore Majorana Observatory) and EXO-200 (Enriched Xenon Observatory) provide new results for Te-130 and Xe-136 [2,4]. In past geochemical measurements of Te-130, two conflicting values of the half-life were measured. NEMO-3 sought to reconcile this difference, and measured a half-life closer to the lower value, 7.00.9 x 1020 yr, which is also the most precise measurement to date [4]. EXO-200 is the prototype for the larger scale EXO experiment and was the first experiment to directly observe the decay of Xe-136. The measured half-life was 2.110.04(stat)0.21(syst) x 1021 yr, which is notable in that it is an order of magnitude lower than the previously set lower limits [2]. References: 1. A. S. Barabash, Phys. Atom. Nucl. 74, 603 (2011). 2. N. Ackerman et al., Phys. Rev. Lett. 107, 212501 (2011). 3. A. S. Barabash, Phys. Atom. Nucl. 73, 162 (2010). 4. R. Arnold et al., Phys. Rev. Lett. 107, 062504 (2011).