Double Beta Decay Studies for 150 Nd at Neutrino Ettore Majorana Observatory (NEMO)

1. Double Beta Decay Studies for 150Nd at Neutrino Ettore Majorana Observatory(NEMO) S.Söldner-Rembold, I.Nasteva, N.Fatemi-Ghomi The NEMO3 experiment investigates neutrinoless double beta decay (0vßß): a process when one of the neutrinos of the 2vßß is absorbed by the other vertex. The observation of this process would prove that neutrinos are Majorana particles, and lower limits on the experimentally measured half-life ( T1/20vßß)give an upper limit on Majorana neutrino mass. Internal and External Backgrounds for 2vßß decay: Internal backgrounds come from radioactive contaminants inside the source foil. They can mimic ßß events by three mechanisms: • ß decay accompanied by an electron conversion process. • Möller scattering of ß decay electrons in the source foil. • ß decay emission as two electron events if the γ-ray is not detected. Study of 2vßßdecay: Accurate measurement of the 2vßß half-life, energy, and angular distributions of the electrons of beta decays is very important, as this forms the only irreducible background to 0vßß. It is possible to reduce these backgrounds by the help of Monte Carlos (MCs). In order to do that, accurate measurement of the radioactive contaminants activities isvital. External background is defined as events produced by γ-ray sources located outside the source foils and interacting with them. 150Nd is one of the nine isotopes in the NEMO3 detector, and has one of the highest values of nuclear transition energy (Qßß= 3367 KeV). Therefore it has less background and a higher value of 2vßß half-life. 37 gr 150Nd 207Bi is one of the major sources of internal background to 150Nd →2vßß. One way to measure its activity is to look at 207Bi → eγchannel. 207Bi → eγEvent selection: • Only one electron with energy between 800 KeV and 1100 KeV. • Only one photon with energy between 270 KeV and 600 KeV. 150Nd → 2vßßEvent Selection: • Two common-vertex electrons with energy > 200 KeV • No delayed alpha decay in the event. We look at energy region with minimum background to 207Bi. Activity (A) = Number of decays per second A = 272 ± 5 (statistical) ± 25 (systematic) mBq/kg Energy sum of the two electrons before and after background reduction. The background is normalized to radioactive contaminants activities. cosine of the angle between the two electrons A preliminary result of half-life of 150Nd → 2vßß: T1/2= (8.55 ± 0.37 (statistical) ± 0.45(systematic))* 1018 years. Designed by: Nasim Fatemi-Ghomi