Milano, 10/11/2006

Double Beta Decay in ILIAS-next

Andrea Giuliani

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Main objective

develop specific aspects of various detector technologies (both classical and innovative) aiming at improving the sensitivity in the search for rare events

ameliorate existing experiments

set the bases for new projects

increase the value of the infrastructures which normally host these searches, i.e. the

underground laboratories

impact on key aspects of astroparticle physics: neutrino physics dark matter discovery and identification rare event searches in general

Four Work Packages

WP1Very low temperature solid state detectors

WP2Noble liquid and

gas detectors

WP3Advanced semiconductor

detectors with active and passive background control

WP4Scintillation detectors

optimized for rare event search

1.1 New scintillating crystals for Double Beta Decay and Dark Matter searchesObjective: develop novel scintillating bolometers for rare event searchesTasks:(i) select compounds for scintillating crystals of potential interest for Double Beta Decay and Dark Matter(ii) characterize the light yield at low temperatures of the selected crystals(iii) operate the crystals as bolometers with double read-out configuration(iv) test preliminarily the background in the relevant energy regions

1.2 Single-photon light detectors operated at very low temperatures Objective: realize light detectors suitable to be operated in the 10-100 mK range, to be used in dark matter search with very low threshold scintillation+heat bolometers(i) select the optimal materials for bolometric light detectors(ii) develop phonon sensor technology for bolometric light detectors(iii) study coating methods to widen the sensitive band(iv) exploit the so-called "Luke effect" to approach single optical photon sensitivity

1.3 Fast microcalorimeters for direct measurement of neutrino mass Objective: realize detectors at keV energies with time response in the microsecond range in order to measure single beta decay with minimization of pulse pile-up(i) study of magnetic microcalorimeters(ii) development of transition edge sensors(iii) realization of kinetic inductance detectors

(iv) develop synergies with CMB and astrophysical X-ray detection techniques

WP1…

1.4 Macro-bolometers with event localization capability for background identificationObjective: develop macrobolometers capable to identify alpha and beta particles absorbed at the surface (i) advanced study of pulse formation (heat, ionization and light channels)(ii) optimization of thin film sensors sensitive to athermal phonons(iii) events localization through pulse shape analysis (phonon and ionization), and development of simulation tools(iv) event localization by exploiting the dynamics of heat flow in composite bolometers

1.5 Improvement of charge collection in heat+ionization detectorsObjective : Improve the charge collection efficiency for surface events in heat and ionization detectors(i) advanced study of charge collection and charge trapping in semiconductors at very low temperatures in low electric field (ii) optimization of amorphous Ge and Si sublayers under the electrodes and minimization of trapping at the surfaces(iii) development of simulation tools

1.6 High energy resolution microcalorimeters operated in medium – high magnetic fieldsObjective: to operate a low-temperature high-energy-resolution calorimeter in a few T magnetic field, in view of an advanced KATRIN’s detector system(i) characterize phonon sensors in medium-high magnetic field, in particular of NTD Ge and implanted Si thermistors, in terms of R-T behaviour and of electron-phonon decoupling(ii) realize a single pixel calorimetric detector operating in a few T magnetic field(iii) study and design a dilution refrigerator able to host a low temperature calorimeter in a few T field and suitable to be matched to the KATRIN’s main spectrometer

… WP1

2.1 Advanced methods of charge readout Objective: to develop and qualify advanced low background micro-pattern charge readout technology for TPCs to be used in rare event searchTasks: (i) Technical comparison of state of the art in GEMs, LEMs and Micromegas(ii) Optimization of position resolution and gain at low energies (iii) Optimisation of quench gases and gas mixtures for single and two phase operation(iv) Development of improved electronics, HV and software including imaging(v) Low background material selection

2.2 Advanced methods of light readoutObjective: to develop low background, UV sensitive, low temperature photon sensors of large area for TPCs to be used in rare event searchTasks:(i) Technical comparison of state of the art in PMTs, Si-PMTs and APDs(ii) Development of improved light collection - large area photocathodes, CsI coatings, UV wavelength shifters, liquid-PMT coupling including flanges. (iii) Development of fiducialisation and position sensitivity techniques(iv) Optimisation for robustness and long-term, low noise operation in gas and liquid(v) Low background material selection

WP2…

2.3 Target medium purification and isotopic separationObjective: to develop gas and liquid target materials with optimum low background, isotopic, purity and optimum electron or photon transport propertiesTasks:(i) Production of "dead argon" (argon free of 39Ar)(ii) Krypton, tritium and radon removal and control(iii) Recirculation and pumping technology including cartridge purity

(iv) isotopic enrichment

2.4 Ionisation and scintillation processes at keV energiesObjective: to improve understanding of the fundamental processes of particle interactions in gases and liquids at keV energiesTasks:(i) New measurements of quench factors at low energy using neutron beams including systematic measurements for different elements, purity, temperature and pressure using the same chambers and electronics(ii) Cooperation with condensed matter community on relevant low energy ionisation physics and new measurement techniques in Noble liquids and gases (inc. Hitachi)(iii) Improved understanding of non-statistical ionisation and scintillation

fluctuations

…WP2…

2.5 Event reconstruction and imagingObjective: to establish improved software and techniques for reconstruction, fiducialisation and imaging of events in TPCsTasks:(i) Study of lateral and transverse diffusion, timing and position resolution in TPC gases - influence on detector designs(ii) Development of optimised event positioning concepts(iii) Development of optimised track reconstruction procedures for low energy ionisation events in gases for directional detectors

2.6 Advanced study of pulse shape properties of LAr scintillation lightObjective: to develop improved pulse shape discrimination techniques for particle discrimination methods in liquid argon applicable in dark matter detection Tasks:(i) Study of the time distribution of scintillation photons in response to , , and neutron radiation and its dependence on chemical impurities and on electrical fields.(ii) Development of optimized front-end and digital electronics for pulse shape analysis purpose (iii) Development of novel numerical analysis tools for discrimination of -, -, - events and recoil events

2.7 Propagation of XUV photons in liquid argonObjective: to study the propagation of 128 nm XUV scintillation photons in liquid argon and to develop MC simulation tools for detector modellingTasks:(i) Study of elastic and inelastic scattering of XUV photons in liquid argon and the dependence on chemical trace impurities(ii) Development of Monte Carlo tools for the simulation of XUV light propagation including wavelength shifting processes to model the detector response of large liquid argon detectors.

…WP2

3.1 Ultra-low background Ge array for material selectionObjective: development of an ultra-low background Ge detector array for material assay at the 1 Bq/kg level in underground laboratoriesTasks:(i) Simulation and optimization of geometry of array with passive and/or active shielding system(ii) Design, development and calibration of system

3.2 Electrode segmentation in Ge detectors for event identification Objective: to study the discrimination of multi-site from single-site events (i.e. background events from double beta decay signal) using electrode segmentation in low-background Ge detectorsTasks: (i) Study of the operation of segmented bare Ge detectors with low-background contacts in liquid argon(ii) Localization and event reconstruction using mirror charges(iii) Comparison of background reduction factors of calibration data with MC simulations

3.3 Novel liquid argon active veto system for Ge detectorsObjective: to study background suppression of bare Ge detectors submerged in liquid argon by using the scintillation light of liquid argon. Detectors both with segmented and unsegmented electrodes will be investigated Tasks:(i) Operation of bare Ge detectors in a liquid argon with scintillation light read out at an underground laboratory(ii) Development of full MC description of a LArGe hybrid detector system (iii) Study of orthogonality of background reduction of segmentation and LAr active veto (iv) Study of LArGe system sensitivity for double beta decay and sample counting

WP3…

3.4 Advanced pulse shape analysis in Ge and LArGe hybrid detectorsObjective: exploit time structure of charge signals from Ge detectors and LArGe hybrid detectors for event recognition and background reduction in double beta decayTask:(i) Study of the time structures for various event classes in Ge (segmented, unsegmented, coaxial, true-coaxial) and LArGe hybrid detectors(ii) Modelling of characteristic time distribution of events in Ge detectors and LArGe hybrid detectors including the scintillation signal for various event classes and comparison with experimental data

3.5 Pixellization in CdZnTe detectors for particle identificationObjective: explore pixel pattern in CdZnTe semiconductor detectors to identify different particles as active background reduction in double beta decay(i) Model various particles (alpha, betas and gamma) as well as double beta decay events in pixellated CdZnTe detectors to explore their characteristic features and optimise pixel size.(ii) Study such a detector underground to prove the expected performance after extensive calibration on the surface.

3.6 Advanced Pulse shape analysis in CPG CdZnTe Objective: explore pulse shape of each of the two electrodes in coplanar grid CdZnTe detectors for vertex determination and extension of eventsTask:(i) Develop readout of individual grids by modifying available preamplifier and study pulse rise-times(ii) Use high energy gamma sources for pair production as an approximation to

double beta events and low energy sources for point-like charge depositions.

…WP3…

3.7 Performance of CdZnTe semiconductors in liquid scintillator Objective: run CdZnTe semiconductors with a minimum of material within a Liquid Scintillator acting as an active veto for background reductionTask:(i) Find reasonable scintillators, materials and run a naked CdZnTe detector in it

…WP3

4.1 Liquid scintillators for low energy neutrino detection Objective: to improve the low background, the scintillation yield and attenuation length of liquid scintillators Tasks:(i) Production of new liquid scintillators formulation highly doped with metallic compounds(ii) Improvement of the radiopurity level by removing noble gas radioactive isotopes (iii) Optimisation of the chemical compatibility with other plastics including optical fibers and plastic scintillators

(iv) Simulation of the light propagation

4.2 Solid organic scintillators Objective: to improve the production and collection of the light, the transparency and the stability of the plastic scintillatorsTasks:(i) Development of scintillators polymer base (ii) Study of new backlight reflectors for the scintillator wrapping(iii) Simulation of the light propagation

4.3 High-efficiency low-radioactivity photomultipliers Objective: to develop high quantum efficiency and very low radioactivity PMT and to be able to survey the gain of the PMT with very high accuracyTasks:(i) Development of new low background glasses and ceramics(ii) Selection of radiopure PMT materials (iii) Optimisation of photocathodes and dynodes characteristics for photoelectrons production and collection(iv) Development of PMT gain survey with very high precision

WP4

Budget considerations

Number of subtasks Subtotals Budget for each subtask

WP1 6 720 120

WP2 7 840

WP3 7 840

WP4 3 360

Total 2760