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Determining the neutrino mass:

Determining the neutrino mass:. The search for the neutrinoless double beta decay. Outline. Introduction Theory Dirac vs Majorana neutrino Neutrino mass mixing Nuclei undergoing double beta decay Experiments Heidelberg-Moscow experiment GerDA CUORE Enriched Xenon Observatory

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Determining the neutrino mass:

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  1. Determining the neutrino mass: The search for the neutrinoless double beta decay Tobias Bode

  2. Outline • Introduction • Theory • Dirac vsMajorana neutrino • Neutrino mass mixing • Nuclei undergoing double beta decay • Experiments • Heidelberg-Moscow experiment • GerDA • CUORE • Enriched Xenon Observatory • Conclusion and outlook Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  3. Introduction • Why look for neutrinoless double beta decay (0νββ)? • Dirac or Majorana neutrino? • Physics beyond the Standard Model? • ΔL≠0 ? • Determine the neutrino mass Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  4. Introduction • Feynman graph of hypothetical neutrinoless double beta decay (0νββ) • 2nd order processes of weak interaction • 4th order in GWS-model • 0νββ forbidden in SM(ΔL≠0) Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  5. ββ-decay plot • 2νββ decay is four particle decay process • Continuous electron spectrum • 0νββ is two particle decay process • Sharp peak at Q-value in energy sum spectrum energy sum spectrum Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  6. Dirac vsMajorana neutrino • Dirac neutrino • Charge conjugation changes the neutrino to an antineutrino • Majorana neutrino • neutrino is charge self-conjugated → its own antiparticle Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  7. Majorana neutrino • No known majorana fermions in nature • If it exists →Physics beyond the SM • ΔL≠0 • No more neutrino/antineutrino but right-handed & left-handed neutrino Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  8. Theory • Requirements for 0νββ • Neutrino is Majorana particle • Neutrino has mass • Handedness changes due to massive ν Also possible by : • Right handed weak interaction • RH weak current couples to RH antineutrino • Other exchange particles (neutralino etc.) Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  9. ββ decay theory • ββ decay possible if the next even/even nucleus energetically lower than the mother nucleus • Decay through a continuum of virtual intermediate states odd/odd Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  10. Nuclei which undergo double beta decay • ββ decay observable only if β decay energetically forbidden • For all other isotopes : • β decay rate much higher • ββ decay is suppressed Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  11. Calculate the effective majorana mass effektive majorana mass • Assumes no right-handed weak currents • The halflife is experimentally determined • The phasespace factor is larger for 0νββ than for 2νββ due to the virtual character of the neutrino • the nuclear matrix elements are very difficult to compute • Uncertainties factor 3 • The calculated effective majorana mass depends heavily on choice of those matrix elements Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  12. Why effective neutrino mass? • Effective mass term • Majorana mass • Emission of antineutrino: • Absorption of neutrino: • elements of neutrino mass mixing matrix • Total amplitude of 0νββ decay p p n n Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  13. Effective majorana mass • In contrast to β decay majorana phases α also relevant in neutrino mass mixing • coherent sum over mass eigenstates • → destructive interference possible • Single mass eigenstates could be larger than • if CP conserved α=±1 • Only range of neutrino mass can be determined by 0νββ • asff Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  14. Experiments Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  15. Experiments • Passive targets • Source ≠ detector • ββ emitter in thin foils between detectors • Easy to change isotopes • NEMO-3 • Active targets • Source = detector(no self absorption) • Bolometer (CUORE) • Semiconductor detector(Heidelberg-Moskau, GERDA) • TPC (EXO) Ge-Diode TPC Bolometer Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  16. Semiconductor detector experiments • Active target • High energy resolution • Material: 76-Ge • High nat. abundance (7.8%) • Low Q-value of 2.04 MeV • Hard to discriminate from natural radioactive background • passive shielding & active veto counters needed • Solid shielding source of radioactivity Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  17. Heidelberg-Moscow experiment (HDMS) • Operated at Gran Sasso Underground Lab from 1990-2003 • Target & detector: 10.9kg enriched 76-Ge in 5 diodes • Lead and copper shielding Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  18. Data analysis Heidelberg-Moscow 2004 • 71.7 kg years of data • Author claims signal at Q=2039 keV • 28.75 ± 6.86 events detected (4.2σ) • Problem: background simulation, discriminate γ and β counts • Heidelberg-Moscow solution: Pulse shape analysis Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  19. Pulse shape analysis of HDMS data • 90% of ββ events are localized in a small volume in the detector (single site event) • Normal γ events are multiple site events (MSE) • Calculation of SSE Library • Comparison with all events • Rejection of identified MSE • 11±1.8 events Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  20. How to increase the sensitivity of 0νββ experiments I • a=isotope abundance • M=target mass • B=background • ΔE=energy resolution • t=measurement time • → enrichment more effective than target mass increase • Easy to enrich isotopes best suited for future experiments • If B=0 → • If B≠0 → (Poisson fluctuations) • Background reduction! • Low level shielding • Radon free environment • Selected materials • Underground labs • Detector segmentation • µ-veto, neutron veto Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  21. How to increase the sensitivity of 0νββ experiments II • Increase of target mass • HDMS=11kg • → future Ge experiment 35kg • → future Xe experiment 1t • Modular design(scaleable) Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  22. Current and future 0νββ experiments Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  23. GerDA(GERmanium Detector Array) • located at Gran Sasso • Similar to HDMS • Bare 76-Ge diodes, immersed in cryogenic fluid(LN/LAr) • No radiation from solid shielding Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  24. GerDA build-up • Phase I: 15kg HDMS Ge-diodes • background≈0.01 cts(keV kg y) • Sensitivity: =0.3-0.9 eV • Phase II: 35kg segmented new Ge-diodes • background≈0.001 cts(keV kg y) • Sensitivity: =0.09-0.29 eV Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  25. GerDA background reduction • LAr-Anticoincidence • ββ-decay localized event • If scintillation light detected in LAr at same time • Event rejected because it was a γ-event • Segmentation • ββ-decay localized event • If ionization detected in more than 1-2 segments • Event is rejected • Main goal is to further reduce external γ-background Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  26. CUORICINO • Using 62 -crystals in bolometer setup • Debye-Law : • T→ 0 : • E: deposited energy • Placed in dilution refrigerator at ≈10mK • At E=2.53MeV (Q-value) ΔT=0.18mK • 3 years, backgroundrate: 0.19 cts/(kg keV y) 5x5x5 cm³ Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  27. Cryogenic Underground Observatory for Rare Events • Next phase of CUORICINO, 750 kg • 19 towers with 53 crystals each=988 crystals Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  28. Enriched Xenon Observatory (EXO) • Liquid/gaseous Xe Time Projection Chamber • Xenon easy to purify and enrich (Russian centrifuges) • Q-value higher than nat. radioactivity • Possible to “laser-tag” Barium ions • coincidence of ion and ββ event • → reduction of background Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  29. EXO-200 • First phase: 200 kg LXe • Energy resolution not good in LXe TPC • → Combination of scintillation & ionization • Dense material → • Small volume → • Good spatial resolution • Electrons drifting to ground • Electron trajectory reconstructed by anode segmentation & drift time • Scintillation light used as timing signal for electron drift time measurement Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  30. EXO Barium tagging • 1t (10t) of enriched LXe/Gxe in full-scale EXO • Laser fluorescence will be used to identify ions to reduce background • 2νββ and 0νββ not destinguishable! Good enough energy resolution needed Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  31. Projected sensitivity of EXO • EXO also looks for 2νββ decay • Test for matrix elements • Knowledge of important for background estimates of 0νββ decay Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  32. Conclusion • Importance of different approaches to 0νββ decay • To increase sensitivity a quadratic increase in target mass is needed • International collaborations and funding is needed • If mass range is determined, it will give new impulses and limitations for theories&experiments in particle- & astrophysics Seminar talk , T. Bode, 12.06.09, Determining the netrino mass: Search for the neutrinless double beta decay

  33. Thank you

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