Review of Direct Measurements of Neutrino Masses

Review of Direct Measurements of Neutrio Masses Loredana Gastaldo Kirchhoff Institute for Physics Heidelberg University Knowing neutrino mass scale…. Particle Physics Neutrino mass generation Astrophysics Supernova neutrinos Cosmology Matter distribution in the Universe 0  m 0  m 1 Status of the art ෍𝑚𝑖<0.072eVat95%C.L. Cosmology ෍ 1=1 3𝑈𝑒𝑖 2𝑚𝑖<ቐ0.079−0.180eV90%C.L.76Ge 0.070−0.240eV90%C.L.130Te 0.036−0.156eV90%C.L.136Xe ෍𝑖=1 3𝑈𝑒𝑖2𝑚𝑖2<൝0.45eV90%C.L.3H−𝑚(ҧ𝜈𝑒) 15eV90%C.I.163Ho−𝑚(𝜈e) Neutrinoless double beta decay Kinematic approach 2 DESI Coll., JCAP 02 (2025) 021 M. Agostini et al., Phys. Rev. Lett. 125, 252502 (2020) D. Q. Adams et al., arXiv:2404.04453 [nucl-ex] (2024) S. Abe et al., Phys. Rev. Lett. 130, 051801 (2023) KATRIN Coll., Science 338 (2025) ECHo Coll., arXiv:2509.03423v1 [hep-ex] Status of the art ෍𝑚𝑖<0.072eVat95%C.L. Cosmology Model independent Neutrinoless double beta decay Kinematic approach ෍𝑖=1 3𝑈𝑒𝑖2𝑚𝑖2<൝0.45eV90%C.L.3H−𝑚(ҧ𝜈𝑒) 15eV90%C.I.163Ho−𝑚(𝜈e) Neutrino mass determination via kinematic approach •will play major role in understanding the evolution of the Universe •will guide the design of future DBD experiments F. Capozzi et al. Phys. Rev. D 111 (2025) 0930062 ෍ 1=1 3𝑈𝑒𝑖 2𝑚𝑖<ቐ0.079−0.180eV90%C.L.76Ge 0.070−0.240eV90%C.L.130Te 0.036−0.156eV90%C.L.136Xe pn n eee  epn p •1/2 12.3 years •Q= 18 592.01(7) eV (4*108atoms for 1 Bq) E.G. Myers et al., Phys. Rev. Lett. 114 (2015) 013003 e e    HeH33 •1/2 4570 years •QEC = (2863.2 0.6) eV (2*1011 atoms for 1 Bq) C 163 66 *163 66 e *163 66 163 67 DyDy DyHo E   3H 3He -163Ho 163Dy EC e  * Beta decay and electron capture Ch. Schweiger et al., Nat. Phys. 20, 921–927 (2024) 3 pn n eee  epn p e e    HeH33 C 163 66 *163 66 e *163 66 163 67 DyDy DyHo E   e  * Beta decay and electron capture 4 3H-based experiments –KATRIN Most stringent limit on the effective neutrino mass: 𝑚𝛽<0.45eV90%C.L. Achievable limit for KATRIN: 𝑚𝛽<0.3eV90%C.L KATRIN Collaboration, Science 388, 180 (2025) 5 3H-based experiments –KATRIN 5 Most stringent limit on the effective neutrino mass: 𝑚𝛽<0.45eV90%C.L. Achievable limit for KATRIN: 𝑚𝛽<0.3eV90%C.L KATRIN Collaboration, Science 388, 180 (2025) what’s next? 3H-based experiments –KATRIN ++ Differential spectrum ++ better use of acquired events •Time of Flight (electron tagging) •Microcalorimeters as focal plane detectors Kovac et al. 2025, arXiv:2502.05975 Atomic 3H source Avoid broadening (~ 1 eV) Avoid limiting systematics of T2 6 Phase III: Neutrino mass sensitivity 𝑚𝛽≥ 100 meV • Atomic source development T2molecules need to be broken System with a particular magnetic field configuration for transport and to avoid molecular recombination • Large-volume CRES Cavity-Based CRES Experiment Cavity at 26 GHz: using TE01 mode in 1 T MRI magnet Low frequency apparatus: feasibility of CRES in large volume and low fields (frequencies) 3H-based experiments –Project 8 Atomic source 11 m 9 Phase III: Neutrino mass sensitivity 𝑚𝛽≥ 100 meV • Atomic source development T2molecules need to be broken System with a particular magnetic field configuration for transport and to avoid molecular recombination • Large-volume CRES Cavity-Based CRES Experiment Cavity at 26 GHz: using TE01 mode in 1 T MRI magnet Same frequency as Phase II: same RF setup, waveguide L = 14 cm, R = 0.7 cm, V ∼20 cm3 Low frequency apparatus: feasibility of CRES in large volumes and low fields (frequencies) B ≈ 0.035 T, fc≈ 1 GHz, V ~ 0.3m3 Phase IV: Neutrino mass measurement if 𝑚𝛽≥ 40 meV 3H-based experiments –Project 8 10 3H-based experiments –QTMN •Quantum noise limited microwave sensors at ~18GHz (corresponding to 0.7T field) •3D B-field mapping with ≲1 𝜇T precision, using H-atoms as quantum sensors (Rydberg Magnetometry) •Production and confinement of H-atoms, ≥ 1012 cm-3 Technology Demonstration (2021-2025): CRESDA-0 = CRES Demonstration Apparatus Funded as part of the Quantum Technologies for Fundamental Physics programme Neutrino mass measurement from atomic 3H β-decay via Cyclotron Radiation Emission Spectroscopy using latest advances in quantum technologies. A.A.S. Amad et al., New Journal of Physics, DOI 10.1088/1367-2630/adc624 11 3H-based experiments –QTMN Funded as part of the Quantum Technologies for Fundamental Physics programme •Cryogenic (30K) pulsed supersonic source •H2/D2/T2dissociation using DC discharge seeded •Atomic beam characterisation using Resonance Enhanced Multi Photon Ionisation (REMPI) H/D/T-atoms confinement with storage ring 12 3H-based experiments –QTMN •NbN, Nb, Al, Ti paramps fabricated and tested at 18 GHz •Robust and repeatable fabrication, quantum-noise limited performance •Can be operated at 4K –potential for two-stage amplification Supercond. Sci. Technol. 36 105010 (2023), arXiv:2406.02455v2 (2024) Funded as part of the Quantum Technologies for Fundamental Physics programme Kinetic inductance parametric amplifiers 13 3H-based experiments –QTMN Funded as part of the Quantum Technologies for Fundamental Physics programme Quantum Technologies for Neutrino Mass (QTNM) 14 1081091010 1011 1012 1013 1014 T atom number density [cm−3] 10−2 10−1 100 90% CL sensitivity on mβ[eV/c2] 10−3m3 ⇥ 1year,σB/B=10−6 10 m3 ⇥ 10 years, σB/B=10−6 10 m3 ⇥ 10 years, σB/B=10−7 0.05m3 ⇥ 1year,σB/B=10−6 mmin β(IO) KATRIN (current) KATRIN (final sensitivity) Figure 3: Dependence of the sensitivity of a CRES experiment to mβ,on the T atom number density in themeasurement volume. Theset of di↵erent volumesconsidered are indicated. In each case, thecoloured bandsrepresent therangeof sensitivitiesexpected from a frequency measurement precision set by the Cram´er-Rao bound (equation 10, continuouscurve) to that set by t−1 obs (dashed-dotted curve). In all cases the magnetic field strength was chosen tobe1 T (seetext for details). Horizontal lines denoting the current, and ultimateprojected limit of theKATRIN experimentwith T2molecules[15], and theminimally allowed valueof mβfor IO neutrinos, i.e., mmin β(IO), arealso shown. decay events. For atom number densitiesabove1011 cm−3,therateat which a radiating electron scattersfrom the background gasof neutral Tatoms plays an increasingly significant role, due to the limits that this scattering process imposes on the maximal valueof tobs. In this regime, the precision with which the cyclotron frequency can be recovered according to the Cram´er-Rao bound o↵ers a higher sensitivity to mβ,for any given atom number density, than the precision set by t−1 obs.At densities above ⇠ 1013 cm−3, thescatteringratetightly restricts, and ultimately leadstoareduction in, theachievable sensitivity. *** Thereseemsto belittledistinction between sensitivity, precision and accuracy. We need to check for consistency*** The upper three curves (green, violet andorange) in figure 3 are the results of calculations in which the fractional uncertainty in the st rengthof the magnet ic field experienced by theradiating electron isσB/B=10−6:σB=1µTin theparticular case considered. Under these conditions, a compact CRESapparatus with an instrumented volume of 10−3m3is expected to provide a sensitivity below 1 eV/c2for T atom number densities between 1012 and 1013 cm−3.Bearing in mind the characteristics and specifications of currently available H atom sources that could be operated to Preferred Location: Culham Centre for Fusion Energy CRESDA-0 → CRESDA+Tritium → 100 meV → 50 meV → 10 meV (2020 - 2025) (2026 - 2030) (2030 – 2040….) 14 3H-based experiments –PTOLEMY PonTecorvo Observatory for Light Early-universe Massive-neutrino Yield Designed for the detection of relic neutrinos 𝜈𝑒+3𝐻→𝑒−+3𝐻𝑒 Monochromatic peak at Q+m Neutrino mass as by-product AG.Cocco, G.Mangano, M.Messina JCAP 06(2007)015 15 3H-based experiments –PTOLEMY PTOLEMY Coll., JCAP 07 (2019) 047 AG.Cocco, G.Mangano, M.Messina JCAP 06(2007)015 15 PonTecorvo Observatory for Light Early-universe Massive-neutrino Yield Designed for the detection of relic neutrinos 𝜈𝑒+3𝐻→𝑒−+3𝐻𝑒 Monochromatic peak at Q+m Neutrino mass as by-product 3H-based experiments –PTOLEMY Prototype set-up in construction at LNGS M.G. Betti et al., Nano Lett. 22, 7 (2022) 2971 C. Pepe et al., Phys.Rev.Applied 22 (2024) 4, L041007 A. Apponi et al., JINST 17 (2022) 05, P05021 PTOLEMY Coll., arXiv:2503.10025 PTOLEMY Coll., JCAP 07 (2019) 047 16 3H-based experiments –PTOLEMY First goal: demonstrate feasibility with moderate 3H source on graphite substrate full loading: 𝜌=0.2mg/m2 1 µg 716 MBq •Weakly dependent upon energy resolution (for e< 400 meV –0.94 eV FWHM) •1 μg: competitive with the forthcoming generation •100 μg (0.5 m2) close to probe the IO scenario 17 ECHo-1k HOLMES 200 million events from 100 eV to 5000 eV 60 million events above 300 eV EFWHM = (6.59 0.16) eV EFWHM = (6 1) eV number of events in [2900 –5000] eV = 80 b= (9.1 1.3) × 10−6 /eV/pixel/day b= (1.7 ± 0.1) × 10−4/eV/pixel/day 163Ho-based experiments –Proof of Concept Experiments 24 ECHo-1k HOLMES 𝑑𝑁 𝑑𝐸=𝐶× 𝐴(𝐸)×𝐹𝑃𝑆(𝑄,𝐸) ⊗𝑔𝐸,𝜎 +𝑏(𝐸) •No analytical function is available to describe A(E), the probability to create excited states with a given energy in the 163Dy atom •In M. Braß et al., New J. Phys. 22 (2020) 093018 it is stated that A(E) is very smooth •Test of different functions has been performed 𝐹𝑃𝑆= 𝑄−𝐸 𝑄−𝐸2−𝑚𝛽 2 25 163Ho-based experiments –Proof of Concept Experiments ECHo-1k HOLMES Q= 2862(4) eV Q = 2848−6 +7eV 𝑚𝜈<15eV/c2(90% C.I.) 𝑚𝜈<27eV/c2(90% C.L) BK. Alpert et al. (HOLMES Coll.), arXiv:2503.19920v2 [hep-ex] accepted in PRL 26 F. Adam et al. (ECHo Coll.), arXiv:2509.03423v1 [hep-ex] submitted to PRL 163Ho-based experiments –Proof of Concept Experiments ECHo-1k HOLMES Q= 2862(4) eV Q = 2848−6 +7eV 𝑚𝜈<15eV/c2(90% C.I.) 𝑚𝜈<27eV/c2(90% C.L) BK. Alpert et al. (HOLMES Coll.), arXiv:2503.19920v2 [hep-ex] accepted in PRL 26 F. Adam et al. (ECHo Coll.), arXiv:2509.03423v1 [hep-ex] submitted to PRL what’s next? 163Ho-based experiments –Proof of Concept Experiments Aim: reach sub-eV sensitivity in next upgrade Minimal design: 20000 pixel Multiplexed readout ~10 Bq/pixel EFWHM < 5 eV fpu< 10-6 b < 10-6 /eV/detector/day Better model of 163Ho spectrum number of events = 1013 27 163Ho-based experiments–Future Perspectives Aim: reach sub-eV sensitivity in next upgrade Minimal design: 20000 pixel Multiplexed readout ~10 Bq/pixel EFWHM < 5 eV fpu< 10-6 b < 10-6 /eV/detector/day Better model of 163Ho spectrum •Fabrication arrays with EFWHM < 5 eV OK •Production & purification of the 163Ho source OK •Implantation ~10 Bq/pixel possible but not trivial •still necessary work on background reduction •Multiplexing big challenge: high energy resolution + large bandwidth 27 A. Faessler et al., J. Phys. G 42 (2015) 015108 R. G. H. Robertson, Phys. Rev. C 91, 035504 (2015) A. Faessler et al., Phys. Rev. C 91, 064302 (2015) A. Faessler and F. Simkovic, Phys. Rev. C 91, 045505 (2015) A. De Rujula and M. Lusignoli, JHEP 05 (2016) 015, A. Faessler et al., Phys. Rev. C 95, (2017) 045502 M. Braß et al., Phys. Rev. C 97 (2018) 054620 M. Braß and M. W. Haverkort, New J. Phys. 22 (2020) 093018 163Ho-based experiments–Future Perspectives Aim: reach sub-eV sensitivity in next upgrade Minimal design: 20000 pixel Multiplexed readout ~10 Bq/pixel EFWHM < 5 eV fpu< 10-6 b < 10-6 /eV/detector/day Better model of 163Ho spectrum •Fabrication arrays with EFWHM < 5 eV OK •Production & purification of the 163Ho source OK •Implantation ~10 Bq/pixel possible but not trivial •still necessary work on background reduction •Multiplexing big challenge: high energy resolution + large bandwidth •Future high statistics spectra will help to constrain model 27 A. Faessler et al., J. Phys. G 42 (2015) 015108 R. G. H. Robertson, Phys. Rev. C 91, 035504 (2015) A. Faessler et al., Phys. Rev. C 91, 064302 (2015) A. Faessler and F. Simkovic, Phys. Rev. C 91, 045505 (2015) A. De Rujula and M. Lusignoli, JHEP 05 (2016) 015, A. Faessler et al., Phys. Rev. C 95, (2017) 045502 M. Braß et al., Phys. Rev. C 97 (2018) 054620 M. Braß and M. W. Haverkort, New J. Phys. 22 (2020) 093018 F. Ahrens et al., arXiv:2507.09240 [nucl-ex] F. Ahrens et al., arXiv:2507.09240 [nucl-ex] 163Ho-based experiments–Future Perspectives ECHo-LE (2026 - 2030) Detector fabrication on going 10 wafer with pixel optimization from ECHo-100k phase Focus on microwave-SQUID multiplexing 400 channels per multiplexing line Improve energy resolution from proof of concept results HOLMES+ Improving the multiplexing less cost x channel, higher multiplexing factor Reducing the critical temperature of the TES to reduce the effect of Ho specific heat Kinetic Inductance Current Sensors (KICs) M. Neidig et al., arXiv:2509.07671v1 163Ho-based experiments –Next Steps 28 Conclusions J. Formaggio, talk @European Startegy for Particle Physics, 23.–27. Juni 2025 29 The determination of the neutrino mass scale will guide beyond Standard Model theories and support our understanding of the Universe The study of low energy electron capture and beta spectra provides a less model dependent approach for neutrino mass determination 3H is an ideal candidate for determining the neutrino mass scale. Different experimental concept have been developed and continuously improved 163Ho is gaining importance thanks to the successful R&D in ECHo and HOLMES Challenging but realistic plans for the determination of the neutrino mass scale are going to be implemented      Thanks to: Angelo Nucciotti and Matteo Borghesi for the HOLMES Collaboration Joe Formaggio and Juliana Stachurska for Project 8 Ruben Saakyan for QTNM Marcello Messina for PTOLEMY KATRIN Collaboration and ECHo Collaboration