The Majorana Experiment

1. The Majorana Experiment Ryan Martin for the LBNL Majorana Group NSD Monday Morning Meeting 26 April 2010

2. Outline • Neutrinoless double-beta decay • The use of 1 tonne of Germanium • The Majorana Demonstrator • Technology Developments at LBNL Ryan Martin, LBNL, MMM, 4/26/2010

3. 2 0 104 0 Neutrinoless Double-Beta Decay Isotope Q % • Neutrinoless double beta decay is a very rare process that can occur in isotopes where beta-decay is energetically forbidden • Observing this requires excellent energy resolution Ryan Martin, LBNL, MMM, 4/26/2010 G. Gratta

4. disfavored by 0 Klapdor-Kleingrothaus et al. claimed signal Tonne Scale Disfavored by cosmology Experimental Searches for 0nbb Klapdor-Kleingrothaus’ 6.4s claim (Mod. Phys. Lett. A 21, 1547 (2006) Phase Space Nuclear Matrix Element T½0ν=( G0ν|M0ν|2〈mββ〉2 )-1 〈mββ〉 ≡ Ue12m1+ Ue22m2eif2 + Ue32m3eif3 PMNS Matrix Majorana Phases • The half life for 2nbb is of order 1020 years, so 0nbb is very rare if it exists • A tonne scale experiment is required to probe mbb of order the atmospheric mass-squared difference Ryan Martin, LBNL, MMM, 4/26/2010

5. Impact of detecting 0nbb • Only practical way to see if neutrinos are Majorana particles • Sets the scale for neutrino masses • Allows for leptogenesis as a way to solve the matter/anti-matter asymmetry in the Universe Ryan Martin, LBNL, MMM, 4/26/2010

6. Arguments for using Germanium • There are several reasons for using Germanium diode detectors (HPGe): • Source is detector • Can be enriched in 76Ge to 86% • Low level of radio-impurities • Technology is well understood • Energy resolution is excellent (~0.2% at 2039keV) • Easy to operate (LN temperature, volume is small) Ryan Martin, LBNL, MMM, 4/26/2010

7. Towards a 1Tonne Experiment • In order to build a 1 tonne Ge experiment, one must demonstrate that the required background levels can be achieved with a technology that can scale • The Majorana and GERDA collaborations are both working to demonstrate different technologies to reduce and remove radioactive backgrounds in Ge detector arrays • There is a cooperative agreement between the two collaborations to share information and come together to build an international 1 tonne Ge experiment that uses the best features from the two technologies Ryan Martin, LBNL, MMM, 4/26/2010

8. Challenges in detecting 0nbb • The main challenges in detecting 0nbb are backgrounds, backgrounds and backgrounds • One aims to have backgrounds of the level of 1 count per tonne per year within a 4keV Region Of Interest (ROI) around 2039keV to be sensitive to the atmospheric mass scale • Need to enrich Ge to have significant quantities of 76Ge Ryan Martin, LBNL, MMM, 4/26/2010

9. Main backgrounds • Natural radioactivity in detector components (U, Th) • Surface contaminants (a, b) • Low-energy backgrounds (Ge isotopes, 65Zn, 73As,3H; low-E compton from K, U, Th; 210Pb brem; …) • Cosmogenic radioactivity (68Ge, 60Co) • Muons, fast neutrons • 2nbb decay • Neutrino scattering (reactor, solar, atm., geo, SN…) Use clean materials Go deep underground Not much you can do! Ryan Martin, LBNL, MMM, 4/26/2010

10. LN Dewar Pb/Cu Shield Cu Cryostat 2m Lift The Majorana Demonstrator • The Majorana experiment is a US-led effort that will be deployed at the Sanford lab in South Dakota • The design focuses on the use of high purity material and will use a Pb/Cu shield • The experiment will be run in phases and will culminate with the use of 60 kg of Ge (30kg of which will be enriched) Ryan Martin, LBNL, MMM, 4/26/2010

11. Technologies used in Majorana • Electroformed copper • Low-noise electronics and DAQ • Stringent materials assays • Point contact Ge detectors tests • Low background detector mounts • Monte Carlo simulations • Various analysis techniques LBNL strongly involved! Ryan Martin, LBNL, MMM, 4/26/2010

12. Electroformed copper • The use of electroformed copper removes impurities and significantly reduces backgrounds; goal is 0.3 µBq 232Th and 238U/kg Cu (~0.08 x 10-12 g/gCu) • The copper is electroformed on steel mandrels that have the same diameter as the cryostats • A total of 16 baths will be deployed underground. The material from the electroformed cylinders will be machined into various components Ryan Martin, LBNL, MMM, 4/26/2010

13. Low Noise Electronics Copper “mount” for the board FET Amorphous Ge resistor Fused-silica board Au/Cr pads FET Parylene cable • Paul Luke has developed a “low mass front end” (LMFE) board that allows one to have an amplification stage close to the Ge diode and thus reduce the noise in the signal from capacitance • The resistive feedback configuration for this pre-amplier is achieved by using amorphous Germanium and the intrinsic capacitance between the pads. The large resistor also reduces noise in the signal, allowing for a low threshold • Our group is testing and characterizing various implementations for this design Ryan Martin, LBNL, MMM, 4/26/2010

14. Electronics Development • LBNL is playing a leading role in the development of the electronics for the Majorana Demonstrator: • LMFE board • Cable Characterization • Preamplifier design • Digitizer Card Characterization (Gretina and Struck cards) • Low noise power source Ryan Martin, LBNL, MMM, 4/26/2010

15. Materials Assays • In order to determine which materials are suitable to go into the experiment, one needs to be able to assay the radio purity of materials - Several techniques and facilities are being used by the collaboration: • Gamma counting • Accurate but slow and needs large samples ~ 50-100ppt U,Th at Oroville • Can determine activity from all parts of a decay chain and unexpected contaminants • Neutron Activation Analysis • Accurate and can use small samples • Can determine activity from all parts of a decay chain and unexpected contaminants • ICP-MS (Inductively coupled plasma mass spectroscopy) • accurate and can (must!) do small samples ~ <1ppt U, Th at PNNL • Can only determine contributions from top parts of decay chain • LBNL is responsible for the assay and characterization of the components for the low mass front end board Ryan Martin, LBNL, MMM, 4/26/2010

16. Point contact Ge detector Point contact Ge detector allow multi-site events to be identified- invented by Paul Luke (LBNL) coax Ge PC Ge Ryan Martin, LBNL, MMM, 4/26/2010

17. Pulse Shape Analysis • The use of point contact detectors allows one to use pulse shape analysis to distinguish Multi-Site Events (MSE, background-like) from Single Site Events (SSE, signal-like) 232Th source data Red: all events Blue: PSA-selected events 208Tl DEP 9/30/09 Radford, RedTeam Review Ryan Martin, LBNL, MMM, 4/26/2010

18. Segmented PPC Prototype – SPPC Segment waveform Point-contact waveform LDRD (Amman, Luke, Chan, Lesko) • Combination of point contact and segment detector • Idea is to read out both electrodes to determine the position of the events Ryan Martin, LBNL, MMM, 4/26/2010

19. Mini-PPC Detector To cold finger Pin contact Contact pressure adjust Crystal mount Temp Ref plate • The main purpose of the mini PPC was to study surface passivation in a conventional setup (shown here) • The detector was also to used to study the low mass front end board (different configuration, not shown) as well as help to characterize the digitizing boards To sensor/heater IR shield base-plate Ryan Martin, LBNL, MMM, 4/26/2010

20. Low Background Detector Mounts my watch Front end board Detector “blank” Cold plate Cryostat “Mercedes” mount PTFE blocks to support crystal • The Majorana experiment will employ detector mounts fabricated from electroformed copper in order to reduce backgrounds • These are being tested at LBNL Ryan Martin, LBNL, MMM, 4/26/2010

21. Detector Simulation • The Majorana and GERDA collaborations have worked on the MaGe Monte Carlo simulation package (using Geant4 and ROOT) • O(5) publications • Pulse shape calculations also implemented • Simulation and Analysis task lead is at LBNL Example: 60Co in cryostat granularity PPC PSA Ryan Martin, LBNL, MMM, 4/26/2010

22. Pulse Shape Simulation • LBNL group has done work on modelling the electric field to determine pulse shapes • BEGe detector from Canberra shown here Geometry of BEGe simulated pulses Electric field and potential Point contact Ryan Martin, LBNL, MMM, 4/26/2010

23. Digital Energy Filter Development Filter Pulse • New energy digital filter was developed to correct for possible changes in the response of the front end electronics (varying pole zero correction) and improve the energy resolution • Individual pulses are fit to determine the pole zero correction and the energy Ryan Martin, LBNL, MMM, 4/26/2010

24. Discreet Wavelet Analysis Can be used to tag SSE and MSE Can be used for de-noising • The Discreet Wavelet Transform (DWT) is a reversible transformation (like the Fourier Transform) that can be done on a discreetly sampled signal • Unlike the Fourier Transform, the DWT contains information about the frequencies contained in a signal and when they occur Ryan Martin, LBNL, MMM, 4/26/2010

25. Majorana Sensitivity The Majorana experiment will be able to test the Klapdor claim Ryan Martin, LBNL, MMM, 4/26/2010

26. Low noise electronics and DM search • Low capacitance results in very good resolution and low noise • Can look for low energy events (Dark Matter searches) The CoGeNT collaboration, has recently published a paper showing the energy spectrum in a low-threshold point contact Ge detector (http://arxiv.org/abs/1002.4) 2 CDMS Events DAMA/LIBRA Ryan Martin, LBNL, MMM, 4/26/2010

27. Summary • 0nbb discovery would be a very compelling result • 1 tonne of Ge would allow one to explore mass scales beyond the inverted mass hierarchy • The Majorana Demonstrator will soon start to evaluate the feasibility of a tonne scale 76Ge experiment as well as test the Klapdor claim • LBNL is leading the detector development and analysis tasks for the Majorana Demonstrator and will continue to play a leadership role in the experiment Ryan Martin, LBNL, MMM, 4/26/2010

28. Backup Slides Ryan Martin, LBNL, MMM, 4/26/2010

29. http://ilias.in2p3.fr/ilias_site/meetings/documents/ILIAS_3rd_Annual_Meeting/Parallel_DBD_Exp_Zuzel.pdfhttp://ilias.in2p3.fr/ilias_site/meetings/documents/ILIAS_3rd_Annual_Meeting/Parallel_DBD_Exp_Zuzel.pdf The GERDA Exeperiment • The GERDA experiment is a European experiment that is in the final phases of construction at LNGS • The Ge diodes are immersed in LAr inside a stainless steel tank, surrounded by an instrumented tank of water • The first phase of the experiment uses ~18kg of enriched Ge from the IGEX and Heidelberg Moscow experiments - in the second phase, they will have a total of 35-40kg of enriched Ge Ryan Martin, LBNL, MMM, 4/26/2010

30. Towards a 1 tonne Ge experiment Sensitivity depends on energy resolution, background rate and exposure: energy resolution background rate live-time active mass A 1 tonne experiment is well suited for exploring mass scales down to the atmospheric neutrino oscillation mass-squared difference. Ryan Martin, LBNL, MMM, 4/26/2010

31. 3 2 mass mass 1 2 1 3 Neutrino Mass • We know from neutrino oscillation experiments that neutrinos have mass, but: • We do not know the hierarchy • We do not know the absolute mass scale • We do not know if the neutrinos have a Majorana mass term (the only particle that could) ? (solar, reactor) (atmospheric, LBL) ? ? Ryan Martin, LBNL, MMM, 4/26/2010 Normal hierarchy ? Inverted hierarchy ?

32. Other Experiments Ryan Martin, LBNL, MMM, 4/26/2010

33. Nuclear Matrix Elements Ryan Martin, LBNL, MMM, 4/26/2010

34. The Majorana and Advanced Detector Development at LBNL • Staff Scientists: Alan Poon, Yuen-Dat Chan, Brian Fujikawa, Kai Vetter • Engineers: Paul Luke, Harold Yaver, Sergio Zimmerman • Postdocs: Jason Detwiler, James Loach, Jing Qian, Ryan Martin • Undergraduate Student: Justin Tang • Summer Students through mentoring program Ryan Martin, LBNL, MMM, 4/26/2010