We present the first performance results obtained with microwave multiplexed Transition Edge Sensors prototypes specifically designed for the HOLMES experiment, a project aimed at directly measuring ...the electron neutrino mass through the calorimetric measurement of the
163
Ho electron capture spectrum. The detectors required for such an experiment feature a high energy resolution at the
Q
–value of the transition, around
∼
2.8 keV, and a fast response time combined with the compatibility to be multiplexed in large arrays in order to collect a large statistics while keeping the pile-up contribution as small as possible. In addition, the design has to be suitable for future ion-implantation of
163
Ho. The results obtained in these tests allowed us to identify the optimal detector design among several prototypes. The chosen detector achieved an energy resolution of (4.5 ± 0.3) eV on the chlorine K
α
line, at
∼
2.6 keV, obtained with an exponential rise time of 14
μ
s. The achievements described in this paper pose a milestone for the HOLMES detectors, setting a baseline for the subsequent developments, aiming to the actual ion-implantation of the
163
Ho nuclei. In the first section the HOLMES experiment is outlined along with its physics goal, while in the second section the HOLMES detectors are described; the experimental set-up and the calibration source used for the measurements described in this paper are reported in Sects.
3
and
4
, respectively; finally, the details of the data analysis and the results obtained are reported in Sect.
6
.
Time-division multiplexing (TDM) is a mature scheme for the readout of arrays of transition-edge sensors (TESs). TDM is based on superconducting-quantum-interference-device (SQUID) current ...amplifiers. Multiple spectrometers based on gamma-ray and X-ray microcalorimeters have been operated with TDM readout, each at the scale of 200 sensors per spectrometer, as have several astronomical cameras with thousands of sub-mm or microwave bolometers. Here we present the details of two different versions of our TDM system designed to read out X-ray TESs. The first has been field-deployed in two 160-sensor (8 columns
×
20 rows) spectrometers and four 240-sensor (8 columns
×
30 rows) spectrometers. It has a three-SQUID-stage architecture, switches rows every 320 ns, and has total readout noise of 0.41
μ
Φ
0
/
√
Hz. The second, which is presently under development, has a two-SQUID-stage architecture, switches rows every 160 ns, and has total readout noise of 0.19
μ
Φ
0
/
√
Hz. Both quoted noise values are non-multiplexed and referred to the first-stage SQUID. In a demonstration of this new architecture, a multiplexed 1-column
×
32-row array of NIST TESs achieved average energy resolution of
2.55
±
0.01
eV at 6 keV.
The European Research Council has recently funded HOLMES, a new experiment to directly measure the neutrino mass. HOLMES will perform a calorimetric measurement of the energy released in the decay of ...Formula: see textHo. The calorimetric measurement eliminates systematic uncertainties arising from the use of external beta sources, as in experiments with beta spectrometers. This measurement was proposed in 1982 by A. De Rujula and M. Lusignoli, but only recently the detector technological progress allowed to design a sensitive experiment. HOLMES will deploy a large array of low temperature microcalorimeters with implanted Formula: see textHo nuclei. The resulting mass sensitivity will be as low as 0.4 eV. HOLMES will be an important step forward in the direct neutrino mass measurement with a calorimetric approach as an alternative to spectrometry. It will also establish the potential of this approach to extend the sensitivity down to 0.1 eV. We outline here the project with its technical challenges and perspectives.
The high-resolution mid-infrared spectrometer instrument will fly onboard the National Aeronautics and Space Administration’s airborne stratospheric observatory for infrared astronomy in 2019. It ...will provide astronomers with a unique observing window (25–122
μ
m
) for exploring the evolution of protoplanetary disks into young solar systems. There are two focal plane detector arrays for the instrument: a high-resolution (
λ
/
Δ
λ
=
100
,
000
)
8
×
16
detector array, with a target noise-equivalent power,
NEP
≤
3
aW
/
Hz
, and a low-resolution (
λ
/
Δ
λ
=
600
–19,000)
16
×
64
detector array with a target
NEP
≤
20
aW
/
Hz
. The detectors for both of these arrays are superconducting Mo/Au bilayer transition-edge sensor bolometers on suspended single-crystal silicon membranes. We present detector characterization results for both arrays, including measurements of thermal conductance in comparison with phonon transport models, and measurements of saturation power and noise.
We have measured the 3d→2p transition x rays of kaonic ^{3}He and ^{4}He atoms using superconducting transition-edge-sensor microcalorimeters with an energy resolution better than 6 eV (FWHM). We ...determined the energies to be 6224.5±0.4(stat)±0.2(syst) eV and 6463.7±0.3(stat)±0.1(syst) eV, and widths to be 2.5±1.0(stat)±0.4(syst) eV and 1.0±0.6(stat)±0.3(stat) eV, for kaonic ^{3}He and ^{4}He, respectively. These values are nearly 10 times more precise than in previous measurements. Our results exclude the large strong-interaction shifts and widths that are suggested by a coupled-channel approach and agree with calculations based on optical-potential models.
In recent years, the progress on low temperature detector technologies has allowed design of large scale experiments aiming at pushing down the sensitivity on the neutrino mass below 1 eV. Even with ...outstanding performances in both energy (~eV on keV) and time resolution (~ 1 μs) on the single channel, a large number of detectors working in parallel is required to reach a sub-eV sensitivity. HOLMES is a new experiment to directly measure the neutrino mass with a sensitivity as low as 2eV. HOLMES will perform a calorimetric measurement of the energy released in the electron capture (EC) decay of 163 Ho. In its final configuration, HOLMES will deploy 1000 detectors of low temperature microcalorimeters with implanted 163 Ho nuclei. The baseline sensors for HOLMES are Mo/Cu TESs (Transition Edge Sensors) on SiNx membrane with gold absorbers. The readout is based on the use of rf-SQUIDs as input devices with flux ramp modulation for linearization purposes; the rf-SQUID is then coupled to a superconducting lambda/4-wave resonator in the GHz range, and the modulated signal is finally read out using the homodyne technique. The TES detectors have been designed with the aim of achieving an energy resolution of a few eV at the spectrum endpoint and a time resolution of a few micro-seconds, in order to minimize pile-up artifacts.
Many current and future applications for superconducting transition-edge sensor (TES) microcalorimeters require significantly faster pulse response than is currently available. X-ray spectroscopy ...experiments at next-generation synchrotron light sources need to successfully capture very large fluxes of photons, while detectors at free-electron laser facilities need pulse response fast enough to match repetition rates of the source. Additionally, neutrino endpoint experiments such as HOLMES need enormous statistics, yet are extremely sensitive to pile-up effects that can distort spectra. These issues can be mitigated only by fast rising and falling edges. To address these needs, we have designed high-speed TES detectors with novel geometric enhancements to increase the thermal conductance of pixels suspended on silicon nitride membranes. This paper shows that the thermal conductivity can be precisely engineered to values spanning over an order of magnitude to achieve fast thermal relaxation times tailored to the relevant applications. Using these pixel prototypes, we demonstrate decay time constants faster than 100
μ
s, while still maintaining spectral resolution of 3 eV FWHM at 1.5 keV. This paper also discusses the trade-offs inherent in reducing the pixel time constant, such as increased bias current leading to degradation in energy resolution, and potential modifications to improve performance.
For experiments with high arrival rates, reliable identification of nearly-coincident events can be crucial. For calorimetric measurements to directly measure the neutrino mass such as HOLMES, ...unidentified pulse pile-ups are expected to be a leading source of experimental error. Although Wiener filtering can be used to recognize pile-up, it suffers from errors due to pulse shape variation from detector nonlinearity, readout dependence on subsample arrival times, and stability issues from the ill-posed deconvolution problem of recovering Dirac delta-functions from smooth data. Due to these factors, we have developed a processing method that exploits singular value decomposition to (1) separate single-pulse records from piled-up records in training data and (2) construct a model of single-pulse records that accounts for varying pulse shape with amplitude, arrival time, and baseline level, suitable for detecting nearly-coincident events. We show that the resulting processing advances can reduce the required performance specifications of the detectors and readout system or, equivalently, enable larger sensor arrays and better constraints on the neutrino mass.
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