Triangle Universities Nuclear Laboratory

1. 2νββ 0νββ Prompt Region True Coincidences Background Region Gammas Random Coincidences n beam d+ beam 2H(d,n)3He Beam pick-off 4 atm 214Bi 0νββ? Triangle Universities Nuclear Laboratory Precision cross section measurement of Cu at 8 and 12 MeV for background reduction in the next generation of 0νßß decay experiments* M.A. Antonacci1, A. Chyzh2, J. Esterline3, S. Elliott4, B. Fallin3, A. Hime4, C.R. Howell3, A Hutcheson3, H.J. Karwowski5, J.H. Kelley2, M. Kidd3, D. Mei4, B. Spaun6, A.P. Tonchev3, W. Tornow3 1 Saint Vincent College, 2 North Carolina State University and TUNL, 3 Duke University and TUNL, 4 Los Alamos National Laboratory, 5 University of North Carolina at Chapel Hill, 6 Whitworth College Abstract Analysis and Results A Proposed Majorana Setup Renewed interest in observing 0nbb decay reactions has sparked efforts to experimentally verify the existence of such decays, and observe new physics beyond the Standard Model. These reactions, with half-lives around 1027 years, require an extensive understanding of background sources. The potential for neutron induced excitation of the shielding and detector materials is important for understanding and designing future 0nbbdecay experiments. Gamma transitions at 2041, 2615, and 3062 keV directly obscure 0nbbdecay detection of 76Ge at 2040 keV. Due to lack of experimental information in the nuclear database, high-resolution g-ray spectra from the interaction of mono-energetic and pulsed neutrons were measured at TUNL. The emitted g-rays were detected with 3 HPGe segmented clover detectors at 62°, 90°, and 135°. From these data, partial cross-sections for prominent g transitions in 63,65Cu were derived at En = 8 and 12 MeV. This experimental information will also help to understand the existing 0nbbdata and serve as a benchmark for statistical model calculations. • Neutron Time of Flight (TOF) • Take advantage of 400 ns beam pulsing to cut out unwanted background coincidence events • Keep only events that happen in time with beam neutrons, exclude g’s from beam stop, subtract random coincidences • Results in significantly better peak to Compton edge ratio • Clusters of segmented HPGe detectors • Setup located deep underground to shield from muon-induced neutron production • Requires thorough understanding of background sources, especially at 2041 keV and 3062 keV Segmented Enriched Germanium Assembly • Region of Interest • 2041 keV peak from 65Cu not evident • Suggests cross-section for this transition very low at 8 and 12 MeV • Good news for Majorana! Less obscuring of 76Ge 0nbb peak than originally expected Motivation: The Majorana Project In Search of 0νββ (A,Z)  (A,Z+2) + 2e- + 2ν (A,Z)  (A,Z+2) + 2e- Experimental Setup • 2nbb half life ~1020 yrs, 0νββ half life ~1027 yrs • Electrons and neutrinos share energy in 2nbb • Spike result of n annihilation, electrons carry away all decay energy in 0nbb • Demonstrates lepton number violation – physics beyond the Standard Model! 10MV FN Tandem Accelerator Shielded Neutron Source Area Observed Partial Cross-sections DENIS II negative ion source • Pulsed beam for precision coincidence timing • Tunable energy range (1-20MeV) • Easily collimated *only 20% of the TUNL complex is shown here • Answer standing questions about neutrinos: • Is the neutrino a Majorana particle? • What is the neutrino mass hierarchy? • What is the absolute neutrino mass scale? Beam Stop • 8 MeV and 12 MeV Neutrons produced at target area • 3 HPGe Segmented Clover detectors at 62°, 90°, 135° • Efficiency and energy calibrations with 60Co, 22Na, and 226Ra sources • Target runs with Pb and Cu wrapped in Fe foil for cross-section normalization • Blank run to aid in background subtraction 0νββ Observed? • Heidelberg-Moscow experiment1 • Claimed to have observed 0nββ peak around 2040 keV in 76Ge • Other Possibilities: • Cosmic muons can produce underground neutron flux inducing reactions in Pb shielding • 206Pb has (n,n′g) transition at 2041 keV • 65Cu has (n,n′γ) transition at 2041 keV • 207Pb has (n,n′γ) transition at 3062 keV, which can produce a double escape peak at 2040 keV Neutron Beam References • MaryKidd. Majorana and SEGA. • Dr. Henning Back (SEGA information) • Dongming Mei. Backgrounds in the Next Generation Double-Beta Decay Experiments. Los Alamos National lab. • J. Edward Ellis. PNNL Majorana Information Resource Page. <http://majorana.pnl.gov/>. 7 July 2006. Target Area HPGe detector *Supported in part by DOE grant DE-FG02-97ER41033 (Duke) and NSF grant NSF-05-52723. 1H.V. Klapdor-Kleingrothaus et al., Phys. Lett. B 586 (2004) 198