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Status of the MARE project

Neutrino in Particles, in Nuclear and in Astrophysics Trento, ECT*, 20 th November 2008. Andrea Giuliani. University of Insubria, Como, and INFN Milano. Status of the MARE project.

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Status of the MARE project

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  1. Neutrino in Particles, in Nuclear and in Astrophysics Trento, ECT*, 20th November 2008 Andrea Giuliani University of Insubria, Como, and INFN Milano Status of the MARE project MAREis a project aiming to determine the neutrino mass through the measurement of the beta spectrum of 187Re with calorimetric techniques at low temperatures

  2. Outline of the talk • Spectrometers and microcalorimeters for direct mn measurements • Microcalorimeter technology and precursors experiments • MARE: a challenging project in two phases • MARE-1 [2 eV sensitivity]: techniques, detectors and achievable limits • MARE-2 [0.2 eV sensitivity]: requirements and new detector technologies • Conclusions

  3. Outline of the talk • Spectrometers and microcalorimeters for direct mn measurements • Microcalorimeter technology and precursors experiments • MARE: a challenging project in two phases • MARE-1 [2 eV sensitivity]: techniques, detectors and achievable limits • MARE-2 [0.2 eV sensitivity]: requirements and new detector technologies • Conclusions

  4. The modified part of the beta spectrum is over a range of the order of [Q – mnc2 , Q] The count fraction laying in this range is  (mn/Q)3 low Q are preferred Tritium as an example E – Q [eV] Effects of a finite neutrino mass on the beta decay

  5. source separate from detector (the source is T - Q=18.6 keV) Electron analyzer Electron counter Source T2 high activity • high efficiency • low background Spectrometers • determine electron energy by means of a selection on the beta electrons operated by proper electric and magnetic fields • measurement of the electron energy out of the source • magnetic and electrostatic spectrometers high energy resolution integral spectrum: select Ee > Eth • present achieved sensitivity:  2 eV • future planned sensitivity:  0.2 eV

  6. n 187Re excitation energies electron source  detector (calorimetric approach) (the source is 187Re - Q=2.5 keV) Microcalorimeters Spectrometers and micro-calorimeters have completely different systematic uncertainties • determine all the “visible” energy of the decay with a high resolution low energy “nuclear” detector high energy resolution differential spectrum: dN/dE bolometer • measurement of the neutrino energy • cryogenic microcalorimeters When in presence of decays to excited states, the calorimeter measures both the electron and the de-excitation energy • present achieved sensitivity:  15 eV • future aimed sensitivity:  0.2 eV

  7. Calorimetry: pros and cons pure b spectrum pile-up spectrum energy [eV] • Drawback • background and systematics induced by pile-up effects • Advantages • no backscattering • no energy loss in the source • no excited final state problem • no solid state excitation Pile-up fraction fpp (dN/dE)exp=[(dN/dE)theo+ Atr(dN/dE)theo(dN/dE)theo]  R(E) generates “background” at the end-point energy region relevant for neutrino mass DE

  8. Calorimeter requirements Requirements for a sensitive calorimetric measurement: • precise determination of the b energy • high statistics • low pile-up fraction • short pulse-pair resolving time • fractionate the whole detector • in many independent elements 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 • high reproducibility of the single element • possibility of multiplexing

  9. Microcalorimeters are chasing spectrometers 0.2 eV 2 eV 20 eV 1990 1995 2000 2005 2010 2015 2.2 eV MAINZ 20-10 eV KATRIN TROITZK 2.2 eV magnetic spectrometers electrostatic spectrometers Spectrometers Calorimeters 26 eV MANU MARE-1 MARE-2 Sandro Vitale 1985 187Re 15 eV MIBETA 20 eV 2 eV 0.2 eV 1995 2005 1990 2000 2010 2015

  10. Outline of the talk • Spectrometers and microcalorimeters for direct mn measurements • Microcalorimeter technology and precursors experiments • MARE: a challenging project in two phases • MARE-1 [2 eV sensitivity]: techniques, detectors and achievable limits • MARE-2 [0.2 eV sensitivity]: requirements and new detector technologies • Conclusions

  11. Microcalorimeters for 187Re spectroscopy 187Re 187Os + e- + ne • Calorimeters measure the entire spectrum at once • use low Q beta decaying isotopes to achieve enough statistic close to Q • best choice: 187Re – Q = 2.47 keV vs. 3x10-10 for T beta spectrum event fraction in the last 10 eV: 1.3x10-7 5/2+ 1/2– unique first forbidden (computable S(Ee)) General structure of a microcalorimeter Re-based crystal coupling coupling heat sink ~ 50 mK sensor A proper sensor convert excitation number to an electrical signal • Beta decays produce very low • energy (~ meV) excitations • phonons • quasiparticles A heat sink at the necessary low temperatures

  12. Bolometric detectors of particles: basic concepts Thermal coupling read-out wires m-machined legs Si3N4 membrane basic parameter: G Energy absorber crystal containing Re M ~ 0.25 - 1 mg ~1 mg ↔ ~1Bq basic parameter: C Heat sink T ~ 50 mK dilution refrigerator Thermal coupling Special epoxy Film deposition Sensor 1. semiconductor thermistors 2. transition edge sensors 3. magnetic microcalorimeters 4. kinetic inductance detectors 3 - 4 eV energy resolution with optimized absorbers 10-20 eV energyresolution obtained with Re-based absorber

  13. Thermistors • Si-implanted thermistors • high sensitivity • many parameters to play with • high reproducibility  array • possibility of m-machining • Energy absorbers • AgReO4 single crystals • 187Re activity  0.54 Hz/mg • M  0.25 mg  A  0.13 Hz typically, array of 10 detectors lower pile up & higher statistics ~ 1 mm MIBETA (Milano/Como) experiment: the detectors

  14. total Kurie – plot ~ 365 mg  day 6.2 x 106 187Re decays above 700 eV K(E) Q = 2466.1 0.8 stat  1.5 syseV t½ = 43.2 0.2 stat  0.1 sysGy E (keV) MIBETA experiment: the Kurie - plot

  15. Fit parameters single gaussian: DEFWHM = 27.8 eV fitting interval: 0.8 – 3.5 keV free constant background: 6 x 10-3 c/keV/h free pile-up fraction: 1.7 x 10-4 Mb2 = -141  211 stat  90 sys eV2 Mb< 15.6 eV (90% c.l.) MIBETA experiment: the neutrino mass

  16. MIBETA experiment: agreement between limit and sensitivity limit sensitivity evaluation with Monte Carlo

  17. Similar technique as MIBETA • One detector only • Metallic Rhenium • DEFWHM = 96 eV • Q = 2470  1  4 eV • t ½ = 41.2  0.02 0.11 Gy detector scheme spectrum Mb< 26 eV (95 % c.l.) MANU experiment (Genoa)

  18. BEFS: effect due to the quantum interference between outgoing electron waves emitted by the decaying atom and ingoing electron waves backscattered by nearby atoms Fractional residuals Oscillatory patterns in the low energy part of the beta spectrum Energy (eV) More evident in metallic Re than in AgReO4 Fractional residuals Energy (keV) The Beta Environmental Fine Structure (BEFS)

  19. Outline of the talk • Spectrometers and microcalorimeters for direct mn measurements • Microcalorimeter technology and precursors experiments • MARE: a challenging project in two phases • MARE-1 [2 eV sensitivity]: techniques, detectors and achievable limits • MARE-2 [0.2 eV sensitivity]: requirements and new detector technologies • Conclusions

  20. The experimental challenge Energy resolution  4 Q3DE s(mn)  A TM Live time measurement Total source activity Total statistics

  21. 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 MARE-1 transition edge sensors (TES) (GE) semiconductor thermistors (MI/CO) and TES or magnetic calorimeters or kinetic inductance detectors ~ 50000 elements ~ 300 elements Activity/element ~ 0.25 Hz Activity/element ~ 1-5 Hz TR ~ 100 - 500 ms TR ~ 1 - 10 ms DEFWHM ~ 10-30 eV DEFWHM ~ 5 eV 0.2 eV mn sensitivity 2-4 eV mn sensitivity

  22. Precursors (MANU, MIBETA) s(Mb) ~ 20 eV Single element Array of 10 elements Statistics: N = 106 events Semiconductors s(Mb) ~ 2 eV MARE-1 – starting – DE ~ 10 – 30 eV – tR ~ 100 ms Transition Edge Sensors Semiconductors Arrays of 300 elements Statistics: N = 1010 events s(Mb) ~ 0.2 eV Transition Edge Sensors Magnetic calorimeters Kinetic Inductance Det, MARE-2 – 4 years for R&D – DE ~ 5 - 10 eV – tR ~ 1 – 10 ms Arrays of 50000 elementi Statistics: N = 1013 events The MARE roadmap

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

  24. Outline of the talk • Spectrometers and microcalorimeters for direct mn measurements • Microcalorimeter technology and precursors experiments • MARE: a challenging project in two phases • MARE-1 [2 eV sensitivity]: techniques, detectors and achievable limits • MARE-2 [0.2 eV sensitivity]: requirements and new detector technologies • Conclusions

  25. Two lines SEMICONDUCTORS U. Milano Bicocca / INFN Mi-Bicocca U. Insubria / INFN Milano Bicocca Itc-IRST / INFN Padova U. Madison, Wisconsin NASA Goddard TRANSITION EDGE SENSORS U. Genova / INFN Genova University of Miami Array of 300 elements Innovative technology for the sensor Superconductive crystals of metallic Re Array of 288 elements Well tested technology for the sensor Dielectric crystals of AgReO4 MARE - 1 Based on a ready-to -use technology and on the already acquired experiences Purposes: • High statistics measurement • Reach a few eVsensitivity • Cross check on the spectrometer results • Investigate systematicsand orient the choices in view of MARE-2

  26. The two approaches to the phonon sensor Semiconductor R MW T 100 mK Rs R C R JFET SQUID C R T 100 mK TES mW

  27. MARE-1 / semiconductor thermistors Three options in parallel, in all cases micromachined arrays: Si doped thermistors realized by NASA/Wisconsin collaboration Si doped thermistors realized by ITC-irst, Trento NTD Ge thermistors (LBL, Berkeley) on Si3N4 membranes single pixel 0.3  0.3 mm AgReO4 crystals 36 elements

  28. MARE-1 / AgReO4 crystals In the past, serious problems connected to the quality of the crystals have determined uncertainties and delays. Today, after a long but fruitful interaction with the producers (MATEK company, Germany) most of the problems were solved and the arrays are ready to be assembled. The crystals are geometrically very regular and, unlike the former MIBETA case, present plane and parallel sides.

  29. MARE-1 / Thermistors Energy [keV]

  30. MARE-1 / semiconductor thermistors – cryogenic setup Cu shielding for environmental radioactivity Detector holder Pb shielding for calibration source JFET box

  31. MARE-1 / semiconductor thermistors - status Prospects Oct 2008 Cryo-mechanical assembly completed including cold electronics MARE-1 will take data within an few weeks! Nov 2008 Assembly of 72 element array, including the delicate operation of sensor-absorber coupling Dec 2008 Cool-down and data taking

  32. MARE-1 / semiconductor thermistors – sensitivity progress

  33. MARE-1 / TES Single crystal of metallic Re • TES on SiN membranes • Cubic crystals of metallic Re side 0.5 mm • Array of 16 elements is operating Re Si spacer TES SiN suspended membrane

  34. MARE-1 / TES – single element performance Energy resolution 11 eV FWHM @ 5.9 keV risetime: 160 ms READ-OUT with SQUID Problems in performance reproducibility • Read-out with transformers • Noise pick-up

  35. MARE-1 / TES – sensitivity 300 elementi

  36. Phase I - systematic uncertainties Several potential systematic uncertainty sources were considered and work is in progress to evaluate their impact on sensitivity for both phases • spectral shape (nuclear factor) we rely on a single very old calculation W. Buhring, Nucl Phys. 61 (1965) 190 • solid state BEFS effect • detector response function now reasonably well known • shape of the pile-up spectrum • shape of the radioactive background under the end-point • energy scale • beta electron escape

  37. Phase I - effect of BEFS Nevent = 1010 fpp = 10-4 DE = 20 eV

  38. Phase I - effect of uncertainty on response function Gaussian symmetric response function, with uncertainty s(DE) on the width DE Nevent = 1010 fpp = 10-4

  39. Outline of the talk • Spectrometers and microcalorimeters for direct mn measurements • Microcalorimeter technology and precursors experiments • MARE: a challenging project in two phases • MARE-1 [2 eV sensitivity]: techniques, detectors and achievable limits • MARE-2 [0.2 eV sensitivity]: requirements and new detector technologies • Conclusions

  40. simplified assumption: pile-up is the only background source • fix reasonable pulse-pair resolving time tR for next generation microcalorimeters groups involved in detector developments for future X-ray mission are working for us! • fix reasonable energy resolution DEFWHM • evaluate the total statistics required to reach the assumed sensitivity goal • convert the total statistics into (number of channel)  (measuring time) tR 1-10 ms guideline for R&D on single pixel: goals DEFWHM  5 eV multiplexing scheme 10000 element array “kit” guideline for R&D on set-up: goals development of several “kits” The future in bolometric experiments: MARE phase II Sensitivity goal: 0.2 eV

  41. Pile-up: simplified discussion (1) The pile-up problem can be analyzed analytically or with Monte Carlo We are following both approaches 1. The Monte Carlo analysis is in progress 2. Semi-quantitative significant results can be obtained with the analytical approach Fraction of counts close to the end-point finite neutrino mass 0 neutrino mass

  42. accepted rejected kept Pile-up: simplified discussion (2) The event fraction close to the end-point is compared with the one due to pile-up Pile-up parameter:tR pulse pair resolving time If two pulses are separated by T > tR  recognized as double tR If two pulses are separated by T <tR  misinterpreted as a single one with sum amplitude Fraction of counts due to pile-up close to E0

  43. pure b spectrum pile-up spectrum energy [eV] DE Pile-up: simplified discussion (3) region relevant for n mass

  44. Pile-up: simplified discussion (4) this ratio must be ~ 1.7 for 90 % c.l. limit

  45. total background dominating pile-up negligible pile-up ~10-5 for Re-based LT microcalorimeters DE ~ 2  DEFWHM extreme pile-up condition Ab ~ 1 / tR increase statistics without making pile-up dominate  fractionate the detector in multiple elements unpractical in thermal detectors Pile-up: simplified discussion (5)

  46. DE improve energy resolution DEFWHM dual read-out ? improve detector rise time TR tR improve algorithms to reject pile-up on the rise time state-of-the-arte Rhenium-based detectors with semiconductor thermistor technology Optimized thermal microcalorimeters with TES, magnetic sensors, MKIDs TR ~ 1 - 10 ms DEFWHM ~ 3 eV Critical parameters for the single elementtR and DE with TES or MMC Activity ~ 0.25 Hz TR ~ 500 ms DEFWHM ~ 20 eV

  47. MMC TES NIST Boulder Kirkhoff Institute of Physics, Heidelberg 450 mm Bi absorber 250 mm Magnetic MicroCalorimeter Mo/Cu TES Si3N4 membrane 55Mn 3.4 eV FWHM Available technologies

  48. A superconductive strip below the critical temperature has a surface inductance proportional to the penetration depth l ( ~ 50 nm) of an external magnetic field Ls= m0l Zs = Rs + iwLs The impedance is Absorption of quasiparticles changes both Rs and Ls If the strip is part of a resonant circuit, both width and frequency of the resonance are abruptly changed phase variation signal New available technology MKID Multiplexed kinetic inductance detectors Roma, ITC-irst, Cardiff

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

  50. (1 Hz, 10 ms) (Ab,tR) = (10 Hz, 1 ms) Required total statistics 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 target statistics

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