1. MARE Microcalorimeter Arrays for a Rhenium Experiment A DETECTOR OVERVIEW Andrea Giuliani, University of Insubria, Como, and INFN Milano on behalf of the MARE collaboration

2.  The physics case: importance of direct m measurement  Methods: spectrometers and microcalorimeters  Status of microcalorimeters and prospects  MARE-1: techniques, detectors and sensitivity  MARE-2: new detector technologies  Conclusions Outline of the talk

3.  The physics case: importance of direct m measurement  Methods: spectrometers and microcalorimeters  Status of microcalorimeters and prospects  MARE-1: techniques, detectors and sensitivity  MARE-2: new detector technologies  Conclusions Outline of the talk

4. Tools for the investigation of the mass scale 0.7 - 1 eV 0.5 eV 2.2 eV 0.1 eV 0.05 eV 0.2 eV Present sensitivity Future sensitivity (a few year scale) Cosmology (CMB + LSS) Neutrinoless Double Beta Decay Single Beta Decay Tools Model dependent Direct determination Laboratory measurements Neutrino oscillations cannot provide information about a crucial parameter in neutrino physics: the absolute neutrino mass scale

5. Effects of a finite neutrino mass on the beta decay The count fraction laying in this range is  (M  Q) 3 low Q are preferred The modified part of the beta spectrum is over range of the order of [Q – M c 2, Q] E – Q [eV] Tritium as an example

6.  The physics case: importance of direct m measurement  Methods: spectrometers and microcalorimeters  Status of microcalorimeters and prospects  MARE-1: techniques, detectors and sensitivity  MARE-2: new detector technologies  Conclusions Outline of the talk

7. Source Electron analyzerElectron counter T2T2 high activity high energy resolution  integral spectrum: select E e > E th  high efficiency  low background spectrometers spectrometers MAINZ-TROITZK  2.2 eV - KATRIN (2010)  0.2 eV  electron excitation energies When in presence of decays to excited states, the calorimeter measures both the electron and the de-excitation energy bolometer high energy resolution  differential spectrum: dN/dE microcalorimeters microcalorimeters MIBETA  15.0 eV

8. Advantages  no backscattering  no energy loss in the source  no excited final state problem  no solid state excitation Drawback  background and systematics induced by pile-up effects (dN/dE) exp =[(dN/dE) theo + A  r (dN/dE) theo  (dN/dE) theo ]  R(E) generates “background” at the end-point energy [eV] pure  spectrum pile-up spectrum EE energy region relevant for neutrino mass Calorimetry: pros and cons

9. In terms of detector technology: development of a single element with these features  extremely high energy resolution in the keV range (1 ‰)  very fast risetime (100  s  1  s)  high reproducibility of the single element  possibility of multiplexing Calorimeter requirements A sensitive measurement with the calorimetric method requires:  precise determination of the  energy  high statistics  low pile-up fraction  short pulse-pair resolving time  fractionate the whole detector in many independent elements bound on m  (  E) 1/2 bound on m  1 / (N counts ) 1/4

10.  The physics case: importance of direct m measurement  Methods: spectrometers and microcalorimeters  Status of microcalorimeters and prospects  MARE-1: techniques, detectors and sensitivity  MARE-2: new detector technologies  Conclusions Outline of the talk

11. 187 Re  187 Os + e - + e 5/2 +  1/2 – unique first forbidden (computable S(E e )) Calorimeters measure the entire spectrum at once  use low Q beta decaying isotopes to achieve enough statistic close to Q  best choice: 187 Re – Q = 2.47 keV - 1 mg natural Re  1 Bq vs. 3x10 -10 for T beta spectrum event fraction in the last 10 eV: 1.3x10 -7 Microcalorimeters for 187 Re spectroscopy Re crystal sensor heat sink ~ 100 mK beta decays produce very low energy (~ meV) excitations  phonons  quasiparticles a proper sensor convert excitation number to an electrical signal a dilution refrigerator provides the necessary low temperatures General structure of a microcalorimeter coupling

12. True microcalorimeters beta decay thermal phonons transmission to a phonon sensor (thermometer) semiconductor thermistortransition edge sensor (TES) T R 100 mK T R MM m  

13. Precursors 187 Re experiments MANU MANU (Genoa) Energy absorber  Metalllic Re single crystals  M  1.5 mg  A  1.5 Hz Phonon sensor  NTD Ge thermistors  size = 0.1 x 0.1 x 0.23 mm single crystal total collected statistics: 6. x 10 6 decays above 420 eV 1 mm MIBETA MIBETA (Milano/Como) Energy absorbers  AgReO 4 single crystals  187 Re activity  0.54 Hz/mg  M  0.25 mg  A  0.13 Hz Phonon sensors  Si-implanted thermistors  high reproducibility  array  possibility of  -machining typically, array of 10 detectors lower pile up & higher statistics total collected statistics ~ 365 mg  day 6.2 x 10 6 decays above 700 eV 1 mm

14. MIBETA Kurie plot Q = 2466.1  0.8 stat  1.5 sys eV  ½ = 43.2  0.2 stat  0.1 sys Gy  M   2 = -141  211 stat  90 sys eV 2  M     15 eV (90% c.l.)MANU beta spectrum Q = 2470  1 stat  4 sys eV  ½ = 41.2  0.02 stat  0.11 sys Gy  M   2 = - 462 + 579 - 679 eV 2  M     26 eV (95% c.l.)

15. The future of bolometric experiments: MARE General strategy: push up bolometric technology aiming at:  multiplication of number of channels  improvement of energy resolution  decrease of pulse-pair resolving time MARE is divided in two phases MARE-2 TES or magnetic calorimeters or kinetic inductance detectors ~ 50000 elements 0.2 eV m sensitivity MARE-1 semiconductor thermistors (Mi/Co) transition edge sensors (TES) (Ge) ~ 300 elements 2-4 eV m sensitivity and Activity/element ~ 0.25 Hz T R ~ 100 - 500  s  E FWHM ~ 20 eV Activity/element ~ 1-10 Hz T R ~ 1 - 10  s  E FWHM ~ 5 eV

16. Genova NASA Heidelberg Como Milano NIST Boulder ITC-irst PTB Berlin Roma SISSA Wisconsin The collaboration

17.  The physics case: importance of direct m measurement  Methods: spectrometers and microcalorimeters  Status of microcalorimeters and prospects  MARE-1: techniques, detectors and sensitivity  MARE-2: new detector technologies  Conclusions Outline of the talk

18. target statistics Required total statistics (MARE-1) On the basis of the analytical approach to pile-up problem and on preliminary Monte Carlo studies, the sensitivity as a function of the total statistics can be determined, for assumed detector performance in terms of time/energy resolution

19. MARE-1 / semiconductor thermistors MARE-1 / semiconductor thermistors (Milano / Como) Three options in parallel, in all cases micromachined arrays:  Si doped thermistors realized by NASA/Wisconsin collaboration  Si doped thermistors realized by irst-ITC, Trento NTD Ge thermistors (LBL, Berkeley) on Si 3 N 4 membranes single pixel 0.3  0.3 mm AgReO 4 crystals 36 elements

20. Best energy resolution: 19 eV FWHM @ 1.5 keV Fastest risetime: 230  s (10%-90%) MARE-1 / semiconductor - single pixel performance Calibration spectrum obtained at 85 mK M = 0.4 mg Very promising for MARE-1 development Re spectrum

21. 288 elements gradually deployed 0.3 decays/s/element  ~ 400  s time resolution  ~ 50  s time resolution MARE-1 / semiconductor - prospects

22. MARE-1 / transition edge sensors MARE-1 / transition edge sensors (Genoa) Two searches are going on in parallel  Ag-Al superconductive hcp  phase alloy  Ir-Au film T c lowered by proximity effect Ir\Au\Ir multilayer on Si Resist pattern Ar Ion etching Final result Re crystals

23. risetime: 160  s Energy resolution 11 eV FWHM @ 5.9 keV In a few years, the present limit on neutrino mass (2.2 eV) can be approached MARE-1 / TES - single pixel performance

24.  The physics case: importance of direct m measurement  Methods: spectrometers and microcalorimeters  Status of microcalorimeters and prospects  MARE-1: techniques, detectors and sensitivity  MARE-2: new detector technologies  Conclusions Outline of the talk

25. Required total statistics (MARE-2) target statistics guideline for R&D on single pixel: goals  R  1  s  E FWHM   5 eV guideline for R&D on set-up: goals multiplexing scheme 10000 element array “kit” development of several “kits” groups involved in detector developments for future X-ray mission are working for us!

26. Candidate techniques for MARE-2 NASA-GSFC, Wisconsin, NIST Boulder 450  m 250  m Bi absorber Si 3 N 4 membrane Mo/Cu TES TES 55 Mn Kirkhoff Institute of Physics, Heidelberg Magnetic MicroCalorimeter 3.4 eV FWHM MMC

27. New available technology MKID Multiplexed kinetic inductance detectors A superconductive strip below the critical temperature has a surface inductance proportional to the penetration depth ( ~ 50 nm) of an external magnetic field L s =  0 The impedance is Z s = R s + i  L s Absorption of quasiparticles changes both R s and L s If the strip is part of a resonant circuit, both width and frequency of the resonance are abruptly changed Roma, ITC-irst, Cardiff phase variation signal

28. Aluminum strip on a Si substrateEquivalent circuit Resonance peak phase signal induced by absorption of a single 5.9 keV photon metallurgic problem: coupling of the Re crystal to the Al film MKIDs: results Nature, K. Day et al., 2003

29. MARE: statistical sensitivity 50000 channels in 5 y 10000 detectors deployed per year

30.  The physics case: importance of direct m measurement  Methods: spectrometers and microcalorimeters  Status of microcalorimeters and prospects  MARE-1: techniques, detectors and sensitivity  MARE-2: new detector technologies  Conclusions Outline of the talk

31.  Neutrino is at the frontier of particle physics Its properties have strong relevance in cosmology and astrophysics  Absolute mass scale, a crucial parameter, is not accessible via flavor oscillations  Direct measurement through single beta decay is the only genuine model independent method to investigate the neutrino mass scale  KATRIN is the only funded next generation experiment (0.2 eV)  Low temperature microcalorimeters can provide an alternate path to the sub-eV region  Microcalorimeters will develop in two phases: MARE-1 - technology already established - 2 eV in 5 y scale MARE-2 - new technologies are required - 0.2 eV in 10 y scale  Unlike spectrometers, microcalorimeter technology can be expanded further