163Ho experiments for neutrinomass determination
Loredana Gastaldo
Kirchhoff Institute for Physics
Heidelberg University

Outline• Electron capture in 163Ho and neutrino mass
ECHo & HOLMES• Experimental challenges
163Ho Source
Detectors
readout• From R&D to large scale experiments• Conclusions

1 meV



Electron capture in 163Ho
163
67

ee‐e‐*Ho163
66 Dy   e
163
66

e‐

np
p pn
pn

e‐e‐e‐e‐

Dy* 163
66 Dy  ECnp
npn
pne‐e‐• 1/2  4570 years (2*1011 atoms for 1 Bq)• QEC = (2.833  0.030stat  0.015syst) keV
S. Eliseev et al., Phys. Rev. Lett. 115 (2015) 062501

Electron capture in 163Ho – QEC‐value
16367

ee‐e‐*Ho16366 Dy   e16366e‐npp pnpn

QEC  m(163 Ho)  m(163 Dy)
AME 2017

Dy* 16366 Dy  EC
Penning Trap Mass Spectroscopy

e‐e‐e‐e‐@TRIGA TRAP (Uni‐Mainz) ()

np
npn
pn

@SHIPTRAP (GSI – Darmstadt) ()AME 2012

e‐e‐Future goal: 1 eV precision:
PENTATRAP @MPIK, Heidelberg (*)• 1/2  4570 years (2*1011 atoms for 1 Bq)

1CHIP‐TRAP @CMU Mount Pleasant (US) (**)• QEC = (2.833  0.030stat  0.015syst) keV
S. Eliseev et al., Phys. Rev. Lett. 115 (2015) 062501() F. Schneider et al., Eur. Phys. J. A 51 (2015) 89() S. Eliseev et al., Phys. Rev. Lett. 115 (2015) 062501(*) J. Repp et al., Appl. Phys. B 107 (2012) 983(*) C. Roux et al., Appl. Phys. B 107 (2012) 997(**) M. Redshaw et al Nucl.Instrum.Meth. B376 (2016) 302‐306Electron capture in 163Ho – Spectrum
16367

ee‐e‐*
Ho16366 Dy   e
163
66e‐

npp pnpn

Atomic de‐excitation:

Dy  Dy  EC*163
66• X‐ray emission• Auger electrons• Coster‐Kronig transitions

e‐e‐e‐e‐

np
npn
pne‐

e‐

• 1/2  4570 years (2*1011 atoms for 1 Bq)• QEC = (2.833  0.030stat  0.015syst) keV
S. Eliseev et al., Phys. Rev. Lett. 115 (2015) 062501

Electron capture in 163Ho – Spectrum
16367

ee‐e‐*
Ho16366 Dy   e16366

e‐

np
p pn
pn

Atomic de‐excitation:

Dy  Dy  EC
*16366• X‐ray emission• Auger electrons• Coster‐Kronig transitions

e‐e‐e‐e‐npnpnpne‐e‐m( e )  225 eV• 1/2  4570 years (2*1011 atoms for 1 Bq)• QEC = (2.833  0.030stat  0.015syst) keV
S. Eliseev et al., Phys. Rev. Lett. 115 (2015) 062501

P. T. Springer, C. L. Bennett, and P. A. Baisden Phys. Rev. A 35 (1987) 679

Electron capture in 163Ho – Spectrum
16367ee‐e‐*Ho163
66 Dy   e
163
66

e‐

npp pnpn

Atomic de‐excitation:

Dy  Dy  EC
*e16366• X‐ray emission

e• Auger electrons• Coster‐Kronig transitions

e‐e‐e‐e‐

npnpnpne‐e‐• 1/2  4570 years (2*1011 atoms for 1 Bq)• QEC = (2.833  0.030stat  0.015syst) keV
S. Eliseev et al., Phys. Rev. Lett. 115 (2015) 062501

Calorimetric measurement

Source = Detector

A. De Rujula and M. Lusignoli, Phys. Lett. 118B (1982)

eElectron capture in 163Ho – Spectrum
16367

ee‐e‐*
Ho16366 Dy   e
163
66

e‐

np
p pn
pn

Atomic de‐excitation:

Dy  Dy  EC
*e

163
66

• X‐ray emission

e• Auger electrons• Coster‐Kronig transitions

e‐e‐e‐e‐np
npn
pne‐e‐• 1/2  4570 years (2*1011 atoms for 1 Bq)• QEC = (2.833  0.030stat  0.015syst) keV
S. Eliseev et al., Phys. Rev. Lett. 115 (2015) 062501

Calorimetric measurement

Source = Detector

P. C.‐O. Ranitzsch et al., Phys. Rev. Lett. 119 (2017) 122501

eElectron capture in 163Ho – Spectrum
16367

e

e‐

e‐

*Ho16366 Dy   e
163
66

e‐

npp pnpn

Atomic de‐excitation:

Dy  Dy  EC
*e

163
66

• X‐ray emission

e• Auger electrons• Coster‐Kronig transitions

e‐e‐e‐e‐np
npn
pne‐e‐• 1/2  4570 years (2*1011 atoms for 1 Bq)• QEC = (2.833  0.030stat  0.015syst) keV
S. Eliseev et al., Phys. Rev. Lett. 115 (2015) 062501

Ab‐initio calculations foresee a smooth shapeat the endpoint region

Calorimetric measurement

Source = Detector

M. Braß and M. W. Haverkort, New J. Phys. 22 (2020) 093018

eParameters for  mass sub‐eV sensitivity
Statistics in the end point region•Nev > 1014 → A ≈ 1 MBq
Unresolved pile‐up (fpu ~ a  r)•fpu < 10‐5•
r < 1 µs  a ~ 10 Bq•
105 pixels
Precision characterization of the endpoint region• EFWHM < 3 eV
Background level•< 10‐6 events/eV/det/day

fpu = 10‐6 EFWHM = 2 eV
ADR, ML 1982

Parameters for  mass sub‐eV sensitivity
Statistics in the end point region•Nev > 1014 → A ≈ 1 MBq
Unresolved pile‐up (fpu ~ a  r)•fpu < 10‐5•r < 1 µs  a ~ 10 Bq•105 pixels

ADR, ML 1982

~ 1.3

1014 163Ho events

Precision characterization of the endpoint region• EFWHM < 3 eV
Background level•< 10‐6 events/eV/det/day

Improved sensitivity for a given number of 163Ho events due tolarger count‐rate in the endpoint region

MB, MWH 2020

Parameters for  mass sub‐eV sensitivity
Statistics in the end point region•
Nev > 1014 → A ≈ 1 MBq

ADR, ML 1982

Unresolved pile‐up (fpu ~ a  r)•fpu < 10‐5•r < 1 µs  a ~ 10 Bq•
105 pixels

1014 163Ho events

Precision characterization of the endpoint region• EFWHM < 3 eV
Background level•< 10‐6 events/eV/det/day

European (strong Germangroup) collaboration
Funded to ~eV sensitivity
The ECHo Collaboration EPJ‐ST 226 8 (2017) 1623

European/US collaboration
Funded to ~eV sensitivity
B. Alpert et al, Eur. Phys. J. C 75 (2015) 112

MB, MWH 2020Experimental challenges

Experimental challenges 1: 163Ho source
Required activity in the detectors: Final experiment  >106 Bq  >1017 atoms
 Neutron irradiation(n,)‐reaction on 162Er

Radioactive contaminants

Excellent chemical separation
95% efficiency
ECHo at Mainz University

Counts/ChannelHigh cross‐section

HOLMES at PSI Zurich

163Ho available for each experimentECHo 2  1018 atoms (10 MBq)

HOLMES  2  1019 atoms (110 MBq)

EnergyS. Heinitz et al., PLoS ONE 13(8): e0200910
H. Dorrer et al, Radiochim. Acta 106(7) (2018) 535–48
J.W. Engle et al., Nucl. Instrum. Meth. B 311 (2013) 131

Experimental challenges 2: high resolution detectors
Low temperature microcalorimeters for the measurement of the 163Ho spectrum
163HoΔT Ctot
GT

TE
Ctot
C
τ = tot
GThermal batht• Very small volume• Working temperature below 100 mK
small specific heatsmall thermal noise• Very sensitive temperature sensor

F. Gatti et al., Physics Letters B 398 (1997) 415

Experimental challenges 2: high resolution detectors
Low temperature microcalorimeters for the measurement of the 163Ho spectrum
163HoΔT Ctot
GTECtot
Detector arrays produced at NIST(Boulder US)

TC
τ = tot
GThermal batht

A. Giachero et al., IEEE Transactions on Applied Superconductivity
31 (2021) 2100205• Very small volume• Working temperature below 100 mK
small specific heatsmall thermal noise• Very sensitive temperature sensor

not implanted

implanted
150 μm
165 μm180 μm

F. Gatti et al., Physics Letters B 398 (1997) 415

Detector arrays produced at KIP,Heidelberg University

Experimental challenges 2: high resolution detectors
Low temperature microcalorimeters for the measurement of the 163Ho spectrum
163HoΔT Ctot
GTECtot
Detector arrays produced at NIST(Boulder US)

TC
τ = totG

Thermal batht• Very small volume• Working temperature below 100 mK
small specific heatsmall thermal noise• Very sensitive temperature sensor

F. Gatti et al., Physics Letters B 398 (1997) 415

Detector arrays produced at KIP,
Heidelberg University

Experimental challenges 2: high resolution detectors
Low temperature microcalorimeters for the measurement of the 163Ho spectrum
163HoΔT Ctot
GTECtot
Detector arrays produced at NIST(Boulder US)

TC
τ = tot
GThermal batht• Very small volume• Working temperature below 100 mK
small specific heatsmall thermal noise• Very sensitive temperature sensor

F. Gatti et al., Physics Letters B 398 (1997) 415

Detector arrays produced at KIP,
Heidelberg University

eV‐scale energy resolution achieved

Experimental challenges 3: enclosing 163Ho
163Ho ion‐implantation is used both by ECHo and HOLMES:

Mass separation and ion implantation in MMC pixels
RISIKO @ Institute of Physics, Mainz University‐ Resonant laser ion source efficiency(69 ± 5stat ± 4syst )%‐ Reduction of 166mHo in MMC
166mHo/163Ho < 4(2)10‐9

Mass seperation and ion implantation in TES pixels
Mass separator and implanter installed @ Physics
Department, Genoa University•

Argon sputter ion source•

Acceleration section  up to 50 kV

 Commissioning phase‐ Optimization of beam focalization~4 mm FWHM
Beam size

Targetchamber
F. Schneider et al., NIM B 376 (2016) 388
T. Kieck et al., Rev. Sci. Inst. 90 (2019) 053304
T. Kieck et al., NIM A 945 (2019) 162602

19

G. Gallucci et al., JLTP 194 (2019) 453

Experimental challenges 4: multiplexing
Microwave SQUID multiplexing offers the possibility to readout a large number of channels maintaining a large bandwidth
Both ECHo and HOLMES use such approach, but differently optimized

S.Kempf et al., AIP Advances 7 (2017) 015007
M. Wegner et al., J. Low Temp. Phys. 193, 462 (2018)

B. Alpert et al., EPJ C 79 (2019) 304

From R&D to large experiments
1 readout channel  ~100 detectors

n. 1

n. 6

n. 2

n. 7

1 readout channel  1 detector

...

...

...

...

...

...
n. 5

n. 10

GHzGHzECHo‐1k4‐day measurement with 4 pixels loaded with ~0.2 Bq 163Ho
Energy resolution
Background level

EFWHM = 9.2 eV
b < 1.6  10‐4 events/eV/pixel/day• QEC = (2838 ± 14) eV• m(e) < 150 eV (95% C.L.)
C. Velte et al., EPJC 79 (2019) 1026

60 MMC pixels with about 1 Bq 163Hoparallel 2‐stage SQUID readout
more that 108 163Ho events
Achievable sensitivitym(e) < 20 eV (95% C.L.)ECHo‐100k: sub‐2eV sensitivity
ECHo‐100k baseline: large arrays of metallic magnetic calorimeters
Number of detectors:
Activity per pixel:

12000
10 Bq (2  1012 163Ho atoms)

Present status:
High Purity 163Ho source:• available about 18 MBq
Ion implantation system:• demostrated on single chip next stage: wafer scale implantation
Metallic magnetic calorimeters• reliable fabrication of large MMC array next stage: ECHo‐100k wafers in production• successfull characterization of arrays with 163HoMultiplexing and data acquisition:• demostrated for 8 channels
 next stage: 163Ho spectrum and test on larger arrays
The ECHo Collaboration EPJ‐ST 226 8 (2017) 1623

Data reduction• optimized energy independent algorithm to identify spurious traces

HOLMES: sub‐2eV sensitivity
HOLMES baseline: large arrays of Transition Edge Sensors
Number of detectors:
Activity per pixel:

1000
300 Bq (6  1013 163Ho atoms)

Present status:
High Purity 163Ho source:• available about 110 MBqIon implantation system:• commissioning in 2021
Transition Edge Sensor arrays• reliable fabrication of large TES array• succesfull characterization of empty arrays• still to demonstrate performance with 300 Bq
Multiplexing and data acquisition:• completed and demonstrated for 32 channels
Data reduction• optimized algorithms to reduce unresolved pile‐up background
B. Alpert et al, Eur. Phys. J. C (2015) 75:112
A. Nucciotti, Eur. Phys. J. C (2014) 74:3161

Conclusions and outlook The determination of the electron neutrino mass with 163Ho is complementary to the determination of the electron
antineutrino mass with 3H

 Determination of the 163Ho spectral shape is indicates that the spectral shape at the endpoint region is smooth ECHo and HOLMES have already demonstrated:
production and purification of large amount of 163Ho sample
operation of large arrays of high resolution low temperature detectors

 Background identification and suppression to achieve the unresolved pile‐up limit
 HOLMES detector modules will be soon tested for 163Ho enclosure ECHo is now a running experiment on the way to provide a new limit on the electron
neutrino mass and ready for upgrades to larger arrays First multiplexed 163Ho spectra will tell us if reaching sub‐eV sensitivity is just a matter of scaling up

7 institutions
About 50 scientists

The ECHo Collaboration EPJ‐ST 226 8 (2017) 1623

6 institutions
About 40 scientists

B. Alpert et al, Eur. Phys. J. C 75 (2015) 112