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

 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

 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

Tools for the investigation of the mass scale 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

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

 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

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

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

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

 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

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. 3x 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

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  

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

MIBETA Kurie plot Q =  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 = eV 2  M     26 eV (95% c.l.)

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 ~ 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 ~  s  E FWHM ~ 20 eV Activity/element ~ 1-10 Hz T R ~  s  E FWHM ~ 5 eV

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

 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

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

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

Best energy resolution: 19 eV 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

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

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

risetime: 160  s Energy resolution 11 eV 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

 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

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 element array “kit” development of several “kits” groups involved in detector developments for future X-ray mission are working for us!

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

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

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

MARE: statistical sensitivity channels in 5 y detectors deployed per year

 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

 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 eV in 10 y scale  Unlike spectrometers, microcalorimeter technology can be expanded further