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Status of bb decay Ruben Saakyan UCL Outline Motivation bb decay basics Results so far Current experiments Future projects and sensitivity Motivation Neutrino Mixing Observed ! e Ue1 Ue2 Ue3 1 U1 U 2 U 3 2 U1 U 2 U 3 3 From KamLAND, solar and atmospheric 0.5 0.87 0 U 0.61 0.35 0.71 0.61 0.35 0.71 VERY approximately 2 mLMA 5 105 eV 2 (7 meV )2 2 matm 2.5 103 eV 2 (50 meV )2 Neutrino MASS What do we want to know? • Relative mass scale (-osc) • Mass hierarchy (-osc and bb) • Absolute mass scale (bb +3Hb+cosmology) mmin ~ 0 - 0.01 eV mmin ~ 0.03 - 0.06 eV Dirac or Majorana preferred by theorists (see-saw) or Only from bb e 1 2 3 Ue12 Ue22 Ue32 From -osc Mixing bb Decay Basics 276 As 0+ 76 Ge Qbb Endpoint Energy 0+ bb 2+ 0+ 76 Se In many even-even nuclei, b decay is energetically forbidden. This leaves bb as the allowed decay mode. bb Decay Basics 2bb and 0bb L = 2 e e p n n p e n p n e p • 2bb – Allowed in SM second order weak process. Observed for several isotopes • 0bb – Requires massive Majorana neutrinos (even in presence of alternative mechanisms) bb Decay Basics. Energy Spectrum 76Ge example Two Neutrino Spectrum Zero Neutrino Spectrum 1% resolution (2 ) = 100 * (0 ) 0.0 0.5 1.0 1.5 Sum Energy for the Two Electrons (MeV) 2.0 Qbb Endpoint Energy bb Decay Basics. Rates 2 1/ 2 1 2 T (0 0 ) G ( E0 , Z ) M 0 1/ 2 + + 1 0 T (0 0 ) G ( E0 , Z ) M + + 0 2 2 2 m 2 G – phase space, exactly calculable; G0 ~ Qbb5, G2 ~ Qbb11 M – nuclear matrix element. Hard to calculate. Uncertainties factor of 2-10 (depending on isotope) Must investigate several different isotopes! <m> is effective Majorana neutrino mass Isotopes of Interest 48Ca, 76Ge, 100Mo, 150Nd,136Xe, 116Cd, 96Zr, 82Se,130Te Effective Majorana Mass m 2 2 N U 2 ei mi i U 2 ei i <mee> Ue32 m3 min 2 N Ue12 m1 Ue22 m2 b i e mi Physics Reach Normal Hierarchy Inverted Hierarchy Degenerate m1 ~ 0 meV ~55 meV M ≥ 100 meV m2 ~ 7 meV ~55 meV M m3 ~ 55 meV ~0 meV M <mbb> ~ 5 meV 28 or 55 meV M/2 or M Solar + KamLAND + Atmospheric (Ue3~ 0) 2 2 mbb 0.5 m1 + 21 0.866 2 m12 + m21 The Experimental Problem ( Maximize Rate/Minimize Background) Natural Activity: (238U, 232Th) ~ 1010 years Target: (0bb) > 1025 years Detector Shielding Cryostat, or other experimental support Front End Electronics etc. + Cosmic ray induced activity An Ideal Experiment bE m Mtlive m 1 Mtlive 1 4 Large Mass (0.1t) BG 0 Good source radiopurity Demonstrated technology Natural isotope BG 0 Small volume, source = detector Tracking capabilities Good energy resolution or/and Particle All requirements can NOT be satisfied Red – must be satisfied ID Ease of operation Large Q value, fast bb(0) Slow bb(2) rate Identify daughter Event reconstruction Nuclear theory Results from previous experiments <m> < 0.35 – 1.0 eV mscale ~ 0.01 – 0.05 eV from oscillation experiments Hieldeberg-Moscow (Gran Sasso) (Spokesperson: E. Klapdor-Kleingrothaus, MPI) <m> = 0.4 eV ??? • 5 HPGe 11 kg, 86% 76Ge • E/E 0.2% • >10 yr of data taking <m> < 0.3 – 0.7 eV If combine HM and IGEX Current Experiments NEMO-3 (Tracking calorimeter) See Jenny’s talk CUORICINO (bolometer) CUORICINO Detector (Gran Sasso) (Milano LNGS, Firenze, Berkeley, S. Carolina) ~ 14 kg 130Te • High natural abundance of 130Te – 34% (no enrichment) • Good E/E ~0.3% at 2.529 MeV Spokesperson: E. Fiorini, Milano CUORICINO Status •2.26 kg×yr (since Feb’03) • BG 0.2 c/keV/kg/yr T1/2(0) > 5×1023 yr (90%) NEMO-3 <m> < 0.8 – 3.2 eV <m> < 0.9 – 2.1 eV (Preliminary - TAUP’03, September, Seattle ) A Great Number of Proposals (Some may start taking data in 2008-2010) COBRA Te-130,Cd-116 10 kg CdTe semiconductors DCBA Nd-150 20 kg Nd layers between tracking chambers SuperNEMO Se-82, Various 100 kg of Se-82(or other) foil CAMEO Cd-116 1 t CdWO4 crystals CANDLES Ca-48 Several tons CaF2 crystals in liquid scint. CUORE Te-130 750 kg TeO2 bolometers EXO Xe-136 1 ton Xe TPC (gas or liquid) GEM Ge-76 1 ton Ge diodes in liquid nitrogen GENIUS Ge-76 1 ton Ge diodes in liquid nitrogen GSO Gd-160 2 t Gd2SiO5:Ce crystal scint. in liquid scint. Majorana Ge-76 500 kg Ge diodes MOON Mo-100 Mo sheets between plastic scint., or liq. scint. Xe Xe-136 1.56 t of Xe in liq. Scint. XMASS Xe-136 10 t of liquid Xe COBRA, SuperNEMO See later talks by Kai Zuber, Ruben Saakyan Cryogenic Underground Observatory for Rare Events - CUORE Berkeley Firenze Gran Sasso Insubria (COMO) Leiden Milano Neuchatel U. of South Carolina Zaragoza Spokesperson Ettore Fiorini Milano CUORE CUORICINO×20 270 kg 130Te (~ 750 kg natTe) CUORICINO BG 0.001c / keV / y / kg 200 Compact: 70×70×70 cm3 5 yr in Gran Sasso: <m> ~ 0.04 eV The Majorana Project Duke U. North Carolina State U. TUNL Argonne Nat. Lab. JINR, Dubna ITEP, Moscow New Mexico State U. Pacific Northwest Nat. Lab. U. of Washington LANL LLNL U. of South Carolina Brown Univ. of Chicago RCNP, Osaka Univ. Univ. of Tenn. Co-Spokespersons Frank Avignone Harry Miley Majorana 0.5 ton of 86% enriched 76Ge Very well known and 5 yr in a US undegr lab <m> ~ 0.03 eV successful technology Segmented detectors using pulse shape discrimination to improve background rejection. Prototype ready to go this autumn/winter. (14 crystals, 1 enriched) 100% efficient Can do excited state decay. GErmanium NItrogen Underground Setup - GENIUS MPI, Heidelberg Kurchatov Inst., Moscow Inst. Of Radiophysical Research, Nishnij Novgorod Braunschweig und Technische Universität, Braunschweig U. of L'Aquila, Italy Spokesperson Int. Center for Theor. Physics, Trieste Hans Klapdor-Kleingrothaus JINR, Dubna MPI Northeastern U., Boston U. of Maryland, USA University of Valencia, Spain Texas A & M U. GENIUS GENIUS 1 ton, ~86% enriched 76Ge Naked Ge crystals in LN Very little material near Ge. 1.4x106 liters LN 40 kg test facility is approved. 100% efficient 5 yr in Gran Sasso: <m> ~ 0.02 eV Enriched Xenon Observatory EXO U. of Alabama Caltech IBM Almaden ITEP Moscow U. of Neuchatel INFN Padova SLAC Stanford U. U. of Torino U. of Trieste WIPP Carlsbad Spokesperson Giorgio Gratta Stanford EXO 10 ton, ~70% enriched 136Xe 70% effic., ~10 atm gas TPC or LXe chamber Optical identification of Ba ion. Drift ion in gas to laser path or extract on cold probe to trap. 100-200-kg enrXe prototype (no Ba ID) Isotope in hand 5 yr in a US underground lab <m> ~ 0.05 eV Future bb projects sensitivity (5 yr exposure) Experiment Source and Mass Sensitivity to T1/2 (y) Sensitivity to <m> (eV)* Majorana 76Ge, 500kg 3×1027 0.03 – 0.07 GENIUS 76Ge. 1000kg 5×1027 0.02 – 0.05 CUORE 130Te, 2×1026 0.04 – 0.17 8×1026 0.05 – 0.12 2×1026 0.04 – 0.11 750kg(nat) EXO 136Xe 1 ton SuperNEMO 82Se(or other) 100 kg * 5 different latest NME calculations Summary Great progress over past decade: <m> < 0.3-1 eV Oscillation expts: at least one neutrino 0.05 eV Next generation bb experiments will reach 0.03 – 0.1 eV (good if inverted hierarchy) Start in ~2008 The next after next generation will address 0.01 eV Nuclear theory input needed Exciting time for bb decay Things to read… S.R. Elliott, P. Vogel, Annu. Rev. Nucl. Part. Sci. 52(2002) hep-ph/0202264 BACKUP SLIDES The Controversy. 20 16 15 14 Locations of claimed peaks 10 10 Counts Counts 12 8 6 4 5 2 0 2000 2000 2020 2040 2060 Energy (keV) 0 2020 2040 2060 2080 Mod. Phys. Lett. A16, 2409 (2001) Energy (keV) If one had to summarize the controversy in a short statement: Consider two extreme background models: 1. Entirely flat in 2000-2080 keV region. 2. Many peaks in larger region, only bb peak in small region. These 2 extremes give very different significances for peak at 2039 keV. KDHK chose Model 2 but did not consider a systematic uncertainty associated with that choice. 2080