Workshop on "Determination of the Absolute Electron (Anti-)Neutrino Mass"

Apr 13, 2026, 8:30 AM → Apr 16, 2026, 7:00 PM Europe/Berlin

KIT Campus South

Kathrin Valerius (Karlsruhe Institute of Technology), Magnus Schlösser (Tritium Laboratory Karlsruhe - Institute of Astroparticle Physics)

Overview

We are pleased to announce that the next iteration of the Neutrino Mass Workshop (NuMass 2026), titled “Determination of the Absolute Electron (Anti-)Neutrino Mass”, will take place in Karlsruhe, Germany, from April 13–16, 2026.

The NuMass workshop series is dedicated to the direct determination of the neutrino mass and has established itself as a central forum for the exchange of ideas between experimentalists and theorists working in this field. NuMass 2026 continues this tradition by providing an international platform to discuss the latest experimental results, technological developments, and theoretical advances related to absolute neutrino mass measurements.

Directly following the NuMass 2026 workshop, a celebration symposium will be held in honor of the KATRIN experiment reaching its target of 1000 days of neutrino mass measurements, hosted at the Karlsruhe Institute of Technology (KIT), Campus North. This symposium will highlight the achievements of KATRIN and reflect on its impact on the global neutrino physics landscape. Every participant is invited to join. More information Here!

The KATRIN experiment, designed for the direct determination of the effective electron anti-neutrino mass, has recently achieved a sub-eV upper limit and has accumulated more than 1000 days of beta-scanning marking a major milestone in the field. At the same time, new direct neutrino mass experiments using tritium, such as Project 8, PTOLEMY, and QTNM, as well as experiments based on electron capture in Ho-163, including ECHo and HOLMES, are completing their research and development phases and reporting new experimental results and novel ideas.

The goal of this international workshop is to fully exploit the scientific potential of current and future direct neutrino mass experiments and to foster in-depth discussions of experimental techniques and theoretical interpretations in a synergistic environment.

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Scientific Topics

The workshop will cover, but is not limited to, the following topics:

• Neutrino mass experimental overviews:
  neutrinoless double beta decay, cosmology, neutrino oscillations, sterile neutrinos, and the cosmic neutrino background

• Direct neutrino mass measurements:
  beta decay and electron capture (EC) end-point studies

• Experimental aspects:
  detector technologies, read-out electronics, data acquisition systems

• Data analysis:
  signal processing, statistical analysis, background studies, calibration methods, detector modeling

• Theory:
  theoretical description of beta-decay and electron-capture spectra

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Modus Operandi

NuMass 2026 is organized to maximize scientific exchange and cross-collaboration between different approaches to neutrino mass determination:

• Researchers from all neutrino mass–related fields are invited to participate.

• All participants are encouraged to contribute a poster, providing a broad overview of ongoing activities and recent results.

• All oral contributions are "on invitation only".

• Review talks will cover adjacent and complementary fields, such as cosmology, neutrinoless double-beta decay, and neutrino theory, to place direct neutrino mass measurements in a wider scientific context. 

• Collaboration overview talks will be given, with one dedicated overview presentation for each major experimental collaboration.

• The workshop will feature focused topical sessions (e.g. data analysis, detector technology, R&D, and experimental strategy).
  These sessions are organized by small, cross-collaboration working groups and consist of concerted contributions resulting in a joint presentation. Each presentation will introduce the topic, summarize recent developments across experiments, and serve as a basis for extended and structured discussion.

 

This format is designed to strengthen cooperation between experiments and to identify common challenges, synergies, and future directions in the quest for the absolute neutrino mass.

 

Silver Sponsors

 

Bronze Sponsors

 

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Mon, April 13

8:30 AM → 9:00 AM Registration

Registration for conference and retrieval of conference bag.

9:00 AM → 9:30 AM Announcements and introducions: Welcome and introduction

Welcome-Wed2.pdf

9:30 AM → 10:30 AM Overview: Collaboration overview talks - I

Overview talks by the neutrino mass collaborations (presentation duration: 50 min + 10 min discussion)

9:30 AM ECHo Overview

Speaker: Loredana Gastaldo (Kirchhoff Institute for Physics, Heidelberg University, Heidelberg, Germany)

10:30 AM → 11:00 AM Coffee break

Coffee and refreshments are served in the Gaede Lecture Theater Foyer.

11:00 AM → 1:00 PM Overview: Collaboration overview talks - II

Overview talks by the neutrino mass collaborations (presentation duration: 50 min + 10 min discussion)

11:00 AM HOLMES Overview

Speaker: A. Nucciotti

holmes_numass2026_nucciotti.pdf

12:00 PM Project8 Overview

Speaker: Dr Hannah Binney (Massachussets Institute of Technology)

NuMass_Project8_Overview_2026_draft_withbackup.pdf

NuMass_Project8_Overview_2026_draft_withbackup.pptx

1:00 PM → 2:30 PM Lunch break

In your conference bag you will find a voucher for eating in the canteen / mensa. However, you are also free to go to Karlsruhe Inner City to find something to eat there. The latter is not covered in the conference feed.

2:30 PM → 4:30 PM Overview: Collaboration overview talks - III

Overview talks by the neutrino mass collaborations (presentation duration: 50 min + 10 min discussion)

2:30 PM KATRIN Overview

Speaker: Chloe Goupy (MPIK)

NuMass2026_KATRINOverview.pdf

3:30 PM QTNM Overview

Speaker: Seb Jones (University College London)

numass2026_qtnm.pdf

4:30 PM → 5:00 PM Coffee break

Coffee and refreshments are served in the Gaede Lecture Theater Foyer.

5:00 PM → 6:30 PM Posters: Poster session I

5:00 PM Ab initio calculations of the electron capture spectrum in Ho

The ECHo experiment aims to determine the electron neutrino mass from electron capture in $^{163}$Ho. This requires an accurate theoretical description of the differential decay rate as a function of how the total decay energy is shared between the neutrino and the electronic excitations.
We achieve this using multireference methods previously developed for core-level X-ray spectroscopy. Bound states are calculated with a state-selected restricted active-space configuration-interaction solver, yielding distinct open core–valence multiplets and bound-to-bound Auger–Meitner side peaks. The linewidth is treated ab initio through an energy-dependent self-energy that describes the coupling of bound states to unbound states with a continuous energy spectrum, including photons, charge-transfer excitations in the host material, and free electrons emitted in the Auger–Meitner process.
The dominant broadening mechanism is Coulomb scattering between electrons, which couples discrete atomic states to final states with free electrons. A key result for neutrino-mass determination is that the resonance line shapes are not Lorentzian but show an exponential decay at high energy. This behavior can be used to extract the neutrino mass from the endpoint region.
In addition, we discuss the deviations between theory and experiment and describe our plans to improve the theoretical calculation.

Speaker: Vera Butz (Institute for Theoretical Physics, Heidelberg University)

5:01 PM Cold sources of atomic hydrogen and its isotopes

We present experimental results on loading a large Ioffe-Pritchard trap with atomic hydrogen gas at temperatures around 100 mK. Dissociation of molecular hydrogen is performed in a cryogenic RF dissociator operating below 1 K. We demostrate that atomic fluxes close to $10^{14}$ atoms/s are obtained with the average RF power in the dissociator of several mW. We propose modifications of this source for operation with heavier hydrogen isotopes: deuterium and tritium. In the latter case, the T gas exiting from the dissociator will be cooled by the buffer gas of $^4$He or $^3$He and transported to the magetic trap with a dedicated magnetic guide. Magnetic field of 1-2 T at the walls of the guide will prevent collisions of atoms with the walls of the guide covered by superfluid helium film and suppress recombination.

Speaker: Sergey Vasiliev (University of Turku)

5:03 PM A graphene-based atomic hydrogen sensor

David Frese, Marcus Lai, Genrich Zeller, Caroline Rodenbeck, Magnus Schlösser for the TLK ATS Team

The current world leading upper limit on the neutrino mass is provided by the KATRIN Experiment with $m_\nu<0.45\,$eV/c$^2$. To improve the sensitivity on the neutrino mass by at least one order of magnitude new technologies are necessary. In addition to new detector technologies, transitioning from a molecular tritium source to an atomic tritium source is required. The Karlsruhe Mainz Atomic Tritium Experiment (KAMATE) collaboration aims to find the most suitable technology to dissociate T$_2$ and cool and trap T. For this, dedicated tools for atomic tritium beam diagnostics are being investigated. Alongside to a Quadrupole Mass Spectrometer (QMS) and a wire detector, graphene-based atomic sensor is currently under development.

In this work, a graphene-setup is presented to investigate a nonradioactive hydrogen-beam emitted from a plasma-based dissociator. In contrast to molecular hydrogen, atomic hydrogen (and tritium) can chemisorb to graphene. This leads to sp³-bounds in the graphene lattice. This effect is investigated in a twofold manner: By analyzing the D'/D ratio in ex-situ Raman microscopy sp³-type defects can be distinguished from vacancy defects. In addition, in-situ sheet resistance measurements are conducted. By heating the graphene sample to 300°C, atoms desorb whereas vacancies remain which allows to measure the atomic adsorption as well. The poster will present Raman scans of loaded graphene samples, the contacting setup for the resistivity measurements and the first loading and heating results.

Speaker: David Frese

5:05 PM Characterization of a Mass Spectrometer for Atomic Tritium Source Studies

Knowledge of the electron antineutrino mass is crucial for further advancements in cosmology and particle physics. Although the KATRIN collaboration has already confined the possible parameter space below 0.45 eV by investigating the beta decay spectrum of tritium, the sensitivity of this method is physically limited by the excitation spectrum of decayed tritium molecules. Therefore, developing sources to produce atomic tritium is indispensable to increase experimental sensitivity.

Finding a suitable dissociator is the first step for the development of an atomic tritium source, and efforts to run a commercially available thermal atom dissociator with tritium – for the first time ever – are in progress at the Tritium Laboratory Karlsruhe. The experimental hardware is operational by now, and a by a factor of five miniaturized KATRIN tritium supply loop has been assembled as well. At this moment, we are working to establish a quadrupole mass spectrometer as a fit device to study the yield of said thermal dissociator before the system can be loaded with tritium.

The poster will present our current efforts to establish the mass spectrometer as suitable tool and illustrate our latest experimental results. Additionally, an overview of the hardware, including the spectrometer itself as well as the vacuum system, the thermal dissociator and the supply loop will be provided.

Speaker: Daniel de Vincenz (TLK / IAP)

5:07 PM Electron backscattering at the Focal Plane Detector (FPD) of KATRIN

The KATRIN experiment has put the most stringent model-independent upper limit on the electron antineutrino mass. The goal is to limit it to < 0.3 eV. To achieve this, a large amount of tritium beta-electrons need to be analyzed using a MAC-E-filter type spectrometer.

One systematic effect on the neutrino mass measurement is the detector backscattering. We are using simulations describing the electron scattering in the silicon waver to estimate the effect on the neutrino mass to be $2\cdot 10^{-3}\, \mathrm{eV}^2$. In order to verify this, we performed an in-situ measurement using time-of-flight spectroscopy. With it, the electron energy loss due to plasmon excitations inside the detector can be resolved. This measurement can help to better understand the FPD response model, which allows the ab initio calculation of several systematic effects on the neutrino mass, enabling their inclusion in the analysis, and thereby minimizing their impact on the neutrino mass uncertainty.

I will present the analysis of the measurement, featuring various improvements, including a rigorous investigation of the impact of fluctuations of the electrical potentials, improved electric and magnetic field simulations using Kassiopeia, as well as more in-depth time-of-flight simulations.

In the future, this measurement principle and the analysis framework can be adapted for the TRISTAN phase of KATRIN, where understanding the escape spectrum from backscattered electrons is of greater importance than for KATRIN.

Speaker: Philipp Lingnau (KIT)

5:09 PM The Tritium Laboratory Karlsruhe for Neutrino Mass Research

The Tritium Laboratory Karlsruhe (TLK) of the Institute for Astroparticle Physics (IAP) located at KIT Campus North contributed in advancing the understanding of the radioactive hydrogen isotope tritium and its technical use for applications in nuclear fusion, astroparticle physics and beyond. Two of its outstanding features are its license to handle up to 40 grams of tritium, and its unique closed tritium cycle that allows reprocessing of tritiated gases. During its three decades of operation, the TLK has gained extensive knowledge in tritium handling. It is continuously maintained and upgraded, enabling it to provide a world-leading state-of-the-art research facility within the Helmholtz Association.
One of TLK’s outstanding achievements is operating the tritium source of the KATRIN experiment, the world-leading endeavor for direct measurement of the neutrino mass based on tritium beta decay. At TLK the closed tritium loop for KATRIN was developed and is running smoothly since 2018. Its successful operation enabled the measurements leading to the currently best upper limit on the neutrino mass. The IAP and TLK are committed to the future of tritium neutrino research and we are pursuing R&D towards generating and handling atomic tritium. Currently, the infrastructure for a atomic tritium pathfinder which consists of a >12 m train of gloveboxes, tritium retention systems and a tritium circulation loop are being installed. This modular installation will benefit global efforts for atomic tritium development.
In this contribution, we present the TLK and its unique infrastructure contributing to ongoing and future neutrino experiments.

Speakers: Beate Bornschein (Karlsruhe Institute of Technology, Institute for Astroparticle Physics), Michael Sturm

5:11 PM Sterile-neutrino search based on 259 days of KATRIN data

Light sterile neutrinos with a mass on the eV-scale could explain several anomalies observed in short-baseline oscillation experiments. The Karlsruhe Tritium Neutrino (KATRIN) experiment is designed to directly determine the effective electron anti-neutrino mass by measuring the tritium beta decay spectrum. The measured spectrum can also be investigated for the signature of light sterile neutrinos.
With this poster we present the result of the light sterile neutrino analysis of the first five KATRIN measurement campaigns. To handle the computational challenge, a neural network is used. The obtained result is compared to results from other experiments and anomalies in the field of light sterile neutrinos.

Speakers: Dr Christoph Köhler (MPIK), Xaver Stribl (MPIK/TUM)

2026-04-13_NuMass_SterilePoster-1.pdf

5:13 PM Magnetic Field Simulations for the Next-Generation MMC-Based KATRIN Experiment

The KATRIN experiment aims to determine the effective mass of the electron antineutrino using kinematics of the electrons from tritium $\beta$ decay. The current upper limit determined by the KATRIN experiment is $m_\nu<0.45\,\mathrm{eV}$ at 90\% confidence level (KATRIN Collaboration et al., Direct neutrino-mass measurement based on 259 days of KATRIN data. Science 388, 180-185 (2025). https://doi.org/10.1126/science.adq9592). A next-generation tritium-based experiment aims to reach sensitivity to the inverted neutrino mass ordering. For this purpose, a novel detector system based on metallic magnetic calorimeters (MMCs) is being proposed as a promising technology. To perform MMC-based spectroscopy of an electron beam, the electrons must be guided windowlessly through the main spectrometer at room temperature to a cryostat at $\mathrm{mK}$, where the $4\,\mathrm{cm^2}$ MMC-based detector will sit. Metallic microcalorimeters (MMCs) are cryogenic quantum sensors that rely on a calorimetric detection principle for single particles. The MMC-based detector is extremely sensitive to changes in the magnetic field in the $\mathrm{mT}$ region and will not work if it is exposed to temperatures exceeding the $\mathrm{mK}$ regime, as it is based on superconductivity. The development of a magnetic chicane with thermal shielding layers is necessary to guide electrons losslessly from the main spectrometer at room temperature and and rather large magnetic fields towards the MMC-based detector at $\mathrm{mK}$ and a low magnetic field on the order of $\mathrm{mT}$. Such a windowless connection between a room temperature region and a $\mathrm{mK}$ region has never been achieved. This highly motivates the design of such a chicane.

This poster will show the first ideas to realise such a magnetic chicane and will focus on the guidance of the electrons through that magnetic chicane using the simulation software Kassiopeia (https://github.com/KATRIN-Experiment/Kassiopeia.git). The software can simulate the movement of charged particles through magnetic and electric fields. Here the guidance of electrons generated by an e-gun and the tritium source used in KATRIN are analysed. These simulations are crucial for the design of the magnetic chicane.

Speaker: Carlotta Buchner (Karlsruhe Institute of Technology – Institute for Astroparticle Physics (KIT-IAP))

PosterNuMass_CarlottaBuchner_MagneticFieldSimulationsForTheNextGenerationMMCBasedKATRINExperiment.pdf

5:15 PM Measurement of the Source Electric Potential in the KATRIN Experiment

The determination of the neutrino mass in the KATRIN experiment relies on the magnetic adiabatic collimation with electrostatic filtering (MAC-E filter) technique. A precise knowledge of the electric potential in the source region is essential for achieving the experiment’s targeted sensitivity. Metastable krypton-83 (83mKr) is used as a calibration source to probe and characterize the source electric potential. Accurate extraction of the source potential model parameters requires a detailed understanding of the krypton conversion electron spectrum. In this poster, we present recent measurements and analysis results from calibration campaigns using 83mKr, focusing on the determination of the KATRIN source electric potential and its impact on the experiment’s systematic uncertainties.

Speakers: Jaroslav Storek (IAP), Karo Erhardt

NuMassPoster_Plasma_v2.pdf

5:17 PM High-precision $Q$-value measurements for neutrino physics

Among the most important quantities in fundamental physics for cosmology and beyond standard model theories is the effective mass of the electron (anti-)neutrino, $m_{\nu}$. To date, the most constraining, least model-dependent upper limit on $m_{\nu}$ is set by the KATRIN collaboration with $<450\,\mathrm{meV}/\mathrm{c}^2$ [1]. In complementary experiments by the ECHo [2] and HOLMES [3] collaborations the kinematics of the electron capture decay in $^{163}\mathrm{Ho}$ is investigated by means of microcalorimetry. Ultimately, these experiments anticipate sub-eV limits on $m_{\nu}$, where the exclusion of possible systematic uncertainties is crucial and achieved by a comparison of the calorimetrically measured $Q$-value of the decay to an independently measured one on the same level of uncertainty.
For $^{163}\mathrm{Ho}$ an uncertainty of $0.6 \mathrm{eV}/\mathrm{c}^2$ was achieved in a direct, ultra-precise $Q$-value measurement using the Penning-trap mass spectrometer PENTATRAP which is more than a factor 50 more precise than the previously best measurement [4]. This technique is based on measuring the ratio of the free-space cyclotron frequencies of highly charged ions (HCIs) of the mother and daughter nuclides, the synthetic radioisotope $^{163}\mathrm{Ho}$ and stable $^{163}\mathrm{Dy}$, respectively. In this frequency measurement an unprecedented fractional uncertainty of $3\cdot 10^{-12}$ was reached. The $Q$-value is finally determined from the ratio of the measured cyclotron frequencies and precise atomic physics calculations of the electronic binding energies of the missing electrons in the HCIs.
The poster will focus on the measurement of the electron capture $Q$-value in $^{163}\mathrm{Ho}$ and give an outlook on future measurements that include the nuclides $^{241}\mathrm{Pu}$ and $^{7}\mathrm{Be}$ whose decay spectra are investigated by the Magneto-$\nu$ [5] and BeEST [6] collaborations, respectively, with the aim of placing stringent bounds on the existence of sterile neutrinos.

[1] Aker, M. et al., Science 388, 180 (2025)
[2] Adam, F. et al., arXiv 2509.03423 (2025)
[3] Alpert, B.K. et al., Phys. Rev. Lett. 135, 141801 (2025)
[4] Schweiger, Ch., et al., Nat. Phys. 20, 921, (2024)
[5] Leach, K.G. et al., J. Low. Temp. Phys. 209, 796 (2022)
[6] Lee, C. et al., Phys. Rev. C, accepted (2026)

Speaker: Christoph Schweiger (Max-Planck-Institut für Kernphysik, Heidelberg, Germany)

5:19 PM Extended range measurement of the KATRIN energy loss function up to 200 eV

The KATRIN experiment aims to determine the mass of the neutrino by scanning the electron energy spectrum near the endpoint. However, electrons can scatter off tritium molecules in the source of the experiment and lose energy in the process. Therefore, the energy loss function, i.e. the probability for an electron to loose a certain amount of energy in a scattering reaction, must be measured with high precision. A monoenergetic and monoangular photoelectron source mounted in the rear section of the KATRIN beamline is used to determine this function in dedicated experimental runs using both a time-of-flight and an integral measurement method.
While previous measurements covered energy losses up to 60 eV, corresponding to the region of interest for neutrino mass fits, this poster will present energy-loss results from measurements in an extended range of up to 200 eV energy loss, which is relevant for the analysis of regular column density measurements performed at the KATRIN tritum source. With this data, we developed a preliminary energy loss model for electron scattering off tritium molecules up to 200 eV surplus energy that also includes the effect of non-Poissonian scattering probabilities.
This work is supported by BMFTR under the contract number 05A23PMA

Speaker: Justus Beisenkötter (Uni Münster)

NuMass2026_Poster_KATRINeloss.pdf

5:21 PM Test setup for a potential electron tagger at KATRIN

The neutrino mass experiment KATRIN has effectively collected 1000 days of tritium beta decay data, allowing to achive a sensitivity for an upper limit on the electron neutrino mass of m < 300 meV at 90% C.L.. After searching for sterile keV neutrinos with the TRISTAN detector at KATRIN a potential next generation experiment labeled KATRIN++ aims to go beyond this limit and probe the inverted mass ordering range down to neutrino masses m < 50 meV. Besides the necessary development of an atomic tritium source, achieving the required sensitivity requires a new differential method with a sub-eV energy resolution. This may be possible through direct time-of-flight spectroscopy of beta-decay electrons. This approach requires detecting the electron start time when entering the KATRIN spectrometer with minimal change of its energy. In this talk, the concept of electron tagging using the image current technique is discussed. Here, the electrons are detected by measuring tiny currents induced by the motion of passing electrons on a nearby electrode structure. A cryogenic test setup has recently been developed at the University Münster to investigate the feasibility of this method and will be presented in this talk. This work is supported by BMFTR under contract number 05A23PMA.

Speaker: Patrick Alexander Unkhoff (University Münster)

eTagger_numass_Unkhoff.pdf

5:23 PM Studies on Ho implantation efficiency and upgrades for the HOLMES+ experiment

The HOLMES experiment aims to measure the neutrino mass by investigating the electron capture decay spectrum of $^{163}$Ho using Transition Edge Sensor (TES) microcalorimeters. The final design foresees arrays implanted with about 30 Bq per detector of the selected isotope.
To perform the implantation and separate $^{163}$Ho contaminants, a dedicated mass-separator beamline has been implemented at the Genoa laboratory, enabling the production of an array with an average activity of 0.27 Bq per detector. This milestone enabled the first neutrino mass measurement by HOLMES.
From this experience, it emerged that the main limitation of the implantation procedure lies in the sputter ion source low efficiency and limited control on beam. The system is therefore being upgraded starting from a completely new design of the ion source, and adding some new beam line elements, including an electrostatic quadrupole, a steering magnet and some diagnostic tools. All these items are deployed with the goal of reaching O(10) Bq per detector and enhancing the total implantation efficiency. This work presents the status of these upgrades, the simulations guiding the new design, and the data collected from a preliminary beamline, all aimed at improving implantation efficiency and increasing the implanted activity.

Speaker: Federico Bianco (Università La Sapienza, INFN sezione Genova)

2026-04-13-ImplanterAbstractNuMass.pdf

5:25 PM KAMELEON: a montecarlo and analytical approach to simulating electrons in the KATRIN beamline

This year the KATRIN experiment will shift from the neutrino mass measurement to the search for keV-scale sterile neutrinos.
For this purpose, the experiment will be equipped with a new detector system, called TRISTAN, which will be able to handle the increased count rates and provide high energy resolution.
Due to the high count rates of the detector and the possibility of a very small sterile neutrino signal, a precise understanding of the detector response is crucial for the success of the experiment.
Therefore, a fast and accurate simulation of the beamline and detector response is needed to understand and model the expected signal and background in the TRISTAN detector.
That is why KAtrin Montecarlo ELEctron simulatiON (KAMELON) was developed, which is a fast and accurate simulation tool for the KATRIN experiment combining both Kassiopeia, a particle tracking software developed for the KATRIN experiment, and Geant4, a widely used toolkit for the simulation of the passage of particles through matter.
KAMELON allows for the simulation of the entire KATRIN beamline, including the source, transport section, and detector, providing a comprehensive understanding of the expected signal and background in the TRISTAN detector.
In this poster, we will present the KAMELON simulation tool and its application to the search for keV-scale sterile neutrinos in the KATRIN experiment as well as its use in furthering our understanding of the current neutrino mass measurement.

Speakers: Giulio Gagliardi (University of Milano-Bicocca), Tom Geigle (KIT)

5:27 PM Sensitivities beyond KATRIN: first steps towards a next-generation neutrino mass experiment

After completing 1000 days of data taking at the KATRIN experiment, the collaboration expects to reach a final sensitivity on the effective electron neutrino mass below 300 meV. However, from the neutrino oscillation experiments, we know that neutrino mass can be as low as 50 meV or 9 meV, depending on the mass ordering. Taking the next step in direct neutrino-mass searches includes probing the region of inverted mass hierarchy, which requires substantial increase in statistics, improvement in energy resolution, and background suppression.

Within the framework of KATRIN++, several novel experimental concepts are being investigated to extend the sensitivity of such a next-generation experiment.
The two key strategies we're focussing on are:
(1) implementation of differential detection techniques with sub-eV energy resolution, such as quantum-sensor-based detector arrays or time-of-flight spectroscopy, and
(2) development of a high-luminosity atomic tritium source.

The combination of these approaches would allow for high statistics to be acquired quickly and with ultra-high energy resolution. In this poster presentation, we show the sensitivity of such an experiment and investigate the technological requirements and fundamental physics limitations for pushing the neutrino mass limits below the inverted mass ordering regime.

Speakers: Chloe Goupy (MPIK), Neven Kovac (Institute for Astroparticle Physics, Karlsruhe Institute of Technology), Svenja Heyns

5:29 PM Neutrino mass absolute scale sensitivity studies for Holmium-based experiments

Several experiments --- HOLMES, ECHo, and NUMECS --- have begun investigating the electron-capture decay of $^{163}\mathrm{Ho}$ to determine the neutrino mass. They studied this process using low-temperature microcalorimetry, in which the decaying Holmium is embedded directly into the absorber of cryogenic detectors, typically a few hundred micrometers in size. This configuration enables high-resolution spectroscopy of the total energy released in the decay, with the only missing component being the energy carried away by the neutrino.

Recent measurements with HOLMES detectors have produced a high-statistics $^{163}\mathrm{Ho}$ spectrum [1,2]. To obtain an accurate phenomenological description of the EC spectrum, the data are first corrected for detector effects using Bayesian iterative unfolding, which accounts for the different energy resolutions across the array. The unfolded spectrum is then fitted with a phenomenological model including asymmetric Breit--Wigner resonances at the electron binding energies, shake-up and shake-off (SU/SOF) processes, and third order processes. The measured spectrum exhibits clear deviations from the simple single-hole theoretical description. The region near the endpoint appears smooth and featureless, with a signal rate larger than predicted by first-order models. These observations motivate updated studies of the neutrino-mass sensitivity for future Ho-based experiments.

These sensitivity studies are performed by generating simulated spectra, using the phenomenological model [1], under different experimental conditions, varying parameters such as energy resolution, total statistics, detector activity, pile-up fraction, and background. For each configuration, the sensitivity is evaluated by generating an ensemble of simulated spectra, each spectrum being Poisson-fluctuated and independently fitted. The simulated spectra are fitted in the endpoint region using a Bayesian framework, with posterior sampling performed via Hamiltonian Markov Chain Monte Carlo implemented in \texttt{Stan}. This procedure yields an ensemble of posterior distributions and upper limits on $m_\beta$; the final sensitivity is defined as the mean of these upper limits, while their standard deviation quantifies the associated uncertainty. Additional optimization studies investigate the impact of binning choices and region-of-interest selection on the inferred values of $m_\beta$, the $Q$ value, and the overall computational cost of the analysis pipeline. Further tests examine the influence of different prior choices for $m_\beta$, in particular comparing uniform priors in $m_\beta$ and in $m_\beta^2$.

The impact of several systematic effects is also assessed, including detector-to-detector resolution variations, non-Gaussian energy response, and non-linear energy calibration. hese results inform the design of next‑generation Ho‑based neutrino‑mass‑experiment detector modules and help define the experimental conditions required to achieve sub‑eV sensitivity to the neutrino mass.
[1] F. Ahrens, B. K. Alpert, D. T. Becker, D. A. Bennett, E. Bogoni, M. Borghesi, P. Campana, R. Carobene, A. Cattaneo,
A. Cian, H. H. Corti, N. Crescini, M. De Gerone, W. B. Doriese, M. Faverzani, L. Ferrari Barusso, E. Ferri, J. Fowler,
G. Gallucci, S. Gamba, J. D. Gard, H. Garrone, F. Gatti, A. Giachero, M. Gobbo, A. Irace, U. K¨oster, D. Labranca,
M. Lusignoli, F. Malnati, F. Mantegazzini, B. Margesin, J. A. B. Mates, E. Maugeri, E. Monticone, R. Moretti, A. Nucciotti,
G. C. O’Neil, L. Origo, G. Pessina, S. Ragazzi, M. Rajteri, C. D. Reintsema, D. R. Schmidt, D. S. Swetz, Z. Talip, J. N.
Ullom, and L. R. Vale. Phenomenological modeling of the 163ho calorimetric electron capture spectrum from the holmes
experiment, 2025.
[2] B. K. Alpert, M. Balata, D. T. Becker, D. A. Bennett, M. Borghesi, P. Campana, R. Carobene, M. De Gerone, W. B. Doriese,
M. Faverzani, L. Ferrari Barusso, E. Ferri, J. W. Fowler, G. Gallucci, S. Gamba, J. D Gard, F. Gatti, A. Giachero, M. Gobbo,
U. K¨oster, D. Labranca, M. Lusignoli, P. Manfrinetti, J. A. B. Mates, E. Maugeri, R. Moretti, S. Nisi, A. Nucciotti, G. C.
O’Neil, L. Origo, G. Pessina, S. Ragazzi, C. D. Reintsema, D. R. Schmidt, D. Schumann, D. S Swetz, Z. Talip, J. N. Ullom,
and L. R. Vale. Most stringent bound on electron neutrino mass obtained with a scalable low-temperature microcalorimeter
array. Phys. Rev. Lett., 135:141801, Sep 2025.

Speaker: Sara Gamba

1776114200131_bitmap (1).pdf

abstract_poster_numass (3).pdf

5:31 PM Search for Local Relic Neutrino Overdensities with the KATRIN experiment

The cosmic neutrino background is one of the remaining predictions of Big Bang cosmology that has yet to be directly observed.
The Karlsruhe Tritium Neutrino (KATRIN) experiment, primarily designed to probe the effective electron anti-neutrino mass, performs a high-precision measurement of the tritium beta-decay spectrum near its kinematic endpoint.
This data also enables us to search for local relic neutrino overdensities by including the rate contribution from neutrino capture on tritium.
Assuming relic neutrinos behave as a fully degenerate Fermi gas significantly changes the capture spectrum at high overdensities.
Moreover, it impacts the tritium beta-decay spectrum via Pauli blocking.
In this work, we present the latest results from this updated model, including a comparison to the previous analysis published in PRL 129, 011806 (2022).

Speaker: Alessandro Schwemmer (Max-Planck-Institut für Kernphysik)

5:33 PM Measurement of the Electron Backscattering on the KATRIN Rear Wall

Currently, the tightest constraints on the absolute scale of neutrino mass from a direct, model-independent approach, are obtained by the KATRIN experiment, giving an upper limit on the mass of the electron anti-neutrino of 0.45 eV (https://doi.org/10.48550/arXiv.2406.13516), with final projected sensitivity below 0.3 eV.
Reaching these ambitious goals requires proper treatment of all systematic effects, with the scattering related systematics currently dominating the systematics budget. In particular, backscattering of electrons on the gold-coated surface of the KATRIN rear wall results in an additional spectrum, shifted in energy due to energy loss of electrons scattering on gold and tritium gas molecules. If unaccounted for, this systematic effects would bias the neutrino mass and therefore needs to be quantified and taken into account in the final analysis.
With this poster, we will discuss the proposed measurements to quantify the backscattering ratio and show the results of our first measurement campaign.

Speakers: Justus Beisenkötter (Uni Münster), Neven Kovac (Institute for Astroparticle Physics, Karlsruhe Institute of Technology), Dr Rudolf Sack (Karlsruhe Institut für Technologie)

6:30 PM → 9:00 PM Evening activities: Barbecue

Tue, April 14

8:50 AM → 9:00 AM Announcements and introducions: Announcements for the day

Welcome-Wed2.pdf

9:00 AM → 10:00 AM Overview: Collaboration overview talks - IV

Overview talks by the neutrino mass collaborations (presentation duration: 50 min + 10 min discussion)

9:00 AM PTOLEMY Overview

Speaker: Francesca Maria Pofi (GSSI)

NuMass.pdf

10:00 AM → 11:15 AM Focused Topical Session: Background and systematics

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

11:15 AM → 11:45 AM Coffee break

11:45 AM → 1:00 PM Focused Topical Session: Holumium source

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

1:00 PM → 2:30 PM Lunch break

In your conference bag you will find a voucher for eating in the canteen / mensa. However, you are also free to go to Karlsruhe Inner City to find something to eat there. The latter is not covered in the conference feed.

2:30 PM → 3:45 PM Focused Topical Session: Front-end electronics

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

2:30 PM TRISTAN and KATRIN Frontend

Speaker: Marco Carminati (Politecnico di Milano & INFN)

2:45 PM Project 8 Frontend

Speaker: Noah Oblath (PNNL)

3:00 PM Multiplexing schemes

Speaker: Marco Faverzani (INFN and University of Milano-Bicocca)

3:15 PM ECHo electron fro µMUX readout

Speaker: Timo Muscheid (KIT)

NuMass_ECHoDAQ_final.pdf

3:30 PM QUBIC, X-IFU readout and multiplexing

Speaker: Damien Prêle (APC CNRS/Université Paris Cité)

3:45 PM → 4:15 PM Coffee break

4:15 PM → 5:05 PM Focused Topical Session: Tritiated graphene

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

4:15 PM Graphene theory

Speaker: Angelo Esposito (Sapienza University of Rome)

4:30 PM Graphene loading

Speaker: Alice Apponi

4:45 PM Tritium graphene

Speaker: Genrich Zeller (KIT-TLK)

5:05 PM → 6:35 PM Posters: Poster session II

5:05 PM Why a solid tritium source was not an option for KATRIN

The design of the KATRIN experiment was based on the successful predecessor experiments in Mainz and Troitsk, which collected data in the 1990s and early 2000s. While both experiments used the same principle for analyzing the energy of tritium decay electrons — the MAC-E filter — the tritium sources were of very different types.
In Troitsk, a gaseous molecular tritium source was used, a concept previously employed by the group in Los Alamos; in Mainz, a novel concept was employed, namely a quench-condensed molecular tritium source at temperatures as low as 1.9 K. Although the quench-condensed source requires 100,000 times less tritium than the gaseous source to achieve a similar luminosity, and handling is therefore much simpler, the KATRIN experiment opted for a gaseous source due to an effect discovered by the Mainz group in 1997—the self-charging of quench-condensed tritium films. This contribution serves as a reminder of the Effect, published in 2003, and its impact on neutrino mass measurements.

Speaker: Lutz Bornschein (IAP-KIT)

5:07 PM Characterization of Tritium Retention in Solid Samples

The KATRIN experiment determines the absolute neutrino mass via high-precision electron spectroscopy of the tritium β-decay spectrum. Recently, an upper limit of 0.45 eV (90% C.L.) was achieved, with a target sensitivity of 0.3 eV. As KATRIN and next-generation experiments advance, the demand for solid-state tritium sources and targets continues to grow. Promising candidate materials include graphene, which can chemisorb atomic tritium, and Ti-based metal samples, where the titanium acts as a tritium getter. The PTOLEMY experiment investigates the use of atomic tritium bound on graphene as a target material for the detection of cosmic relic neutrinos. In the KATRIN experiment, both tritiated graphene and Ti-based samples are explored as potential low-activity, solid sources of β-electrons. One application of such samples is the characterization of new detector technologies, e.g., metallic magnetic calorimeters (MMCs). Additionally, they could be used as calibration sources for already established detection techniques like beta-induced X-ray spectroscopy (BIXS).

In this work, we present first quantitative measurements of tritium retention for both sample types, obtained at the Tritium Laboratory Karlsruhe (TLK). We determine the total adsorbed activity and track how stable the retained tritium remains during long-term storage. We also quantify outgassing by directly measuring the activity released from the samples into their storage containers. These results provide a systematic basis for assessing the suitability of tritium-loaded solids for neutrino mass experiments and tritium-related research.

Speakers: Moritz Hellmann (KIT-TLK), Genrich Zeller (KIT-TLK)

5:09 PM Atomic Hydrogen Beam Characterization Techniques for the KAMATE Collaboration

To overcome statistical and systematic limitations arising from the rovibrational final-state distribution of molecular tritium, future precision mass-measurement experiments are pursuing atomic tritium sources. Within the Karlsruhe Mainz Atomic Tritium Effort (KAMATE), we investigate the dissociation fraction of thermal effusive atomic sources. In these sources, molecular gas is directed through a thin tungsten capillary heated to ~ 2600 K, where dissociation occurs via high-temperature surface and gas-phase processes. Due to the radioactive nature of tritium, initial R&D work for the source and diagnostic tools development is carried out with hydrogen.

The dissociation efficiency is governed primarily by the gas flow rate and the temperature at the capillary exit. In this poster, we present quadrupole mass spectrometer ionization-scan measurements of the resulting atomic beam and thermal-radiation spectrometry measurements of the capillary temperature to determine the dissociation efficiency of these thermal sources.

Speakers: Ms Aya El Boustani (University of Mainz), Ms Brunilda Mucogllava (University of Mainz)

5:11 PM Characterization of an inductively coupled plasma source for atomic hydrogen with optical emission spectroscopy

David Frese, Görkem Yavuz, Caroline Rodenbeck for the TLK ATS Team

The current world leading upper limit on the neutrino mass is provided by the KATRIN Experiment with $m_{\nu_e}<0.45\,$eV/c$^2$. To improve the sensitivity on the neutrino mass by at least one order of magnitude new technologies are necessary. In addition to new detector technologies, transitioning from a molecular tritium source to an atomic tritium source is required. Various commercial devices are available that can dissociate H$_2$ and in principle T$_2$ as well. The Karlsruhe Mainz Atomic Tritium Experiment (KAMATE) collaboration aims to investigate the most suited technology and is therefore comparing two thermal dissociators and a plasma based dissociator. The latter is an inductively coupled plasma (ICP) source.

This work presents the characterization of the ICP source with non-radioactive hydrogen by utilizing Optical Emission Spectroscopy (OES). By comparing OES measurements with theoretical calculations from collisional radiative (CR) models, plasma parameters and eventually the number of atoms can be determined. The source can be operated in an capacitive (E-) mode and an inductive (H-) mode. In this poster, results of OES measurements for both modes in terms of line stability, pressure, electron density and electron temperature are presented.

Speakers: David Frese, Görkem Yavuz

5:13 PM ELECTRON - Development of High Resolution Metallic Microcalorimeters for a Future Neutrino Mass Experiment

Metallic Magnetic Calorimeters (MMCs) are low temperature single particle detectors, whose working principle is based on quantum technology. Due to their excellent energy resolution, near linear detector response, fast signal rise time and close to 100\% quantum efficiency, MMCs outperform conventional detectors by several orders of magnitude, making them interesting for a wide range of different applications.
The aim of the ELECTRON project was to demonstrate, for the first time, that MMC based detectors can be employed for a high resolution spectroscopy of external electron sources, namely electron-gun, Kr-83m and tritium.
Technology and methods developed within the context of the ELECTRON project will pave a way for the next generation neutrino experiments with tritium, employing a differential detector based on quantum technology.
Possible future applications include the next phase of the KATRIN neutrino mass experiment, aiming at sub-200 meV sensitivity to electron (anti-)neutrino mass, as well as the detection of the cosmic neutrino background.
With this poster, we present the characterization measurements of the MMC-based detectors using external electrons, together with the measured Kr-83m spectrum.

Speaker: Neven Kovac (Institute for Astroparticle Physics, Karlsruhe Institute of Technology)

5:15 PM Search for keV sterile neutrino with the TRISTAN detector at KATRIN

Sterile neutrinos in the keV mass range are a well-motivated extension of the Standard Model and viable dark matter candidates. Their existence can be probed in laboratory experiments, as the admixture of a sterile state would induce a characteristic kink-like distortion in the β-decay electron energy spectrum. Following the completion of its neutrino mass program, KATRIN will extend its physics reach to the search for keV-scale sterile neutrinos. This effort will be enabled by the TRISTAN detector, a newly developed silicon drift detector array optimized for differential measurements at high rates and energies well below the endpoint. With four months of detector livetime, KATRIN has the statistical power to probe mixing amplitudes at the level of |Ue4|2 ~ 10-6 for sterile neutrino masses in the (4–13) keV range, significantly extending the reach of previous laboratory searches. The major experimental systematic uncertainties investigated in this work reduces the sensitivity by a factor of 10–50 over the same mass range.
In this poster, I will present an overview of this new measurement phase and the projected sensitivity of KATRIN to keV-scale sterile neutrinos.

Speaker: Dr Anthony Onillon (Max-Planck-Institut für Kernphysik)

5:17 PM Coupled Gas Dynamics Simulations and Superconducting Magnet Design for High-Flow Millikelvin Atomic Tritium

Atomic tritium is a key enabling technology for the next-generation neutrino mass experiment Project 8. However, existing technology cannot supply the high required flow rate of millikelvin atoms, making new developments essential. I will describe design and simulation work underway at Lawrence Berkeley National Laboratory (LBNL) that links large-scale collisional gas simulations at the National Energy Research Scientific Computing Center with expertise from LBNL’s Superconducting Magnet Program. This combination is uniquely suited to address the peculiar challenges of atomic tritium. These include the highly energy-dependent collisional cross sections between tritium atoms and with helium buffer-gas atoms, and the replacement of low-temperature superconductors (LTS, around 4 K) with high-temperature superconductors (HTS, around 20 K) that have not previously been applied to trapping atomic hydrogen isotopes. This minimizes the required tritium inventory by reducing freeze-out while matching or exceeding the field strength and trapping efficiency of LTS magnets. An HTS magnetic guide pairs naturally with the tight integration of a buffer gas within a magnetic guide and the method to slow an atom beam with a bent, static magnetic guide that I proposed. Coupled with a long-standing program of atom source, surface cooling, and O(100 m^3) atom trap development in Project 8, the collaboration is thus paving the way to a complete atomic tritium apparatus with a sensitivity of 40 meV.

Speaker: Alec Lindman (Johannes Gutenberg Universität Mainz)

5:19 PM Probing new light bosons with the KATRIN experiment

The Karlsruhe Tritium Neutrino (KATRIN) experiment is designed to measure the effective electron antineutrino mass with a sensitivity better than $m_\nu c^2 = 0.3\,\mathrm{eV}$ (90% CL) in a kinematic approach by applying precision electron spectroscopy to the beta decay of molecular tritium. The measurement focuses on the spectral endpoint ($E_0$) region, extending up to tens of eV below $E_0 \approx 18.6\,\mathrm{keV}$.
Light neutral scalar or vector bosons arise in various theories beyond the Standard Model. Constraints on their couplings to neutrinos or electrons can be derived from cosmological, astrophysical and laboratory observations. KATRIN complements these approaches, as the emission of an additional light state in tritium decay introduces characteristic modifications to the observed electron energy spectrum. We present the sensitivity of KATRIN to such new light bosons, based on data from 2019, corresponding to $4 \times 10^6$ electrons in the analysis interval of $[-40, +130]\,\mathrm{eV}$ around $E_0$.
This work is supported by the Helmholtz Association, by the Ministry for Education and Research BMBF (grant numbers 05A23PMA, 05A23PX2, 05A23VK2, and 05A23WO6), and the bwForCluster NEMO.

Speaker: Joscha Lauer (KIT)

5:21 PM TRIMS: The Molecular Physics of Tritium Decay

When tritium beta decay occurs within a molecule, the resulting distribution of electronic, vibrational and rotational molecular excitations modifies the shape of the beta spectrum. Experiments like KATRIN require a detailed theoretical understanding of these spectral changes in order to probe the absolute mass scale of the neutrino via TT beta decay. The Tritium Recoil Ion Mass Spectrometer (TRIMS) experiment ran in 2018 - 2019 to test the predicted probabilities of different final-state ion topologies after HT and TT decay. ??

This poster will discuss recent progress in the TRIMS analysis, including the identification of a gradual gain drift and significant improvements in isolating the TT and HT signals from mixed sources. We will also explain a new, quantitative understanding of why historical ion spectrometry measurements substantially disagreed with theoretical predictions.

Speaker: Diana Parno (Carnegie Mellon University)

5:23 PM Search for neutrino mass - 8 decades of tritium source evolution

The most sensitive way to determine the neutrino mass scale without further assumptions is to measure the shape of a tritium beta spectrum near its endpoint. Tritium is the nucleus of choice because of its low endpoint energy, superallowed decay, simple nuclear properties and simple atomic structure. Tritium beta decay experiments have been performed for 8 decades using different types of tritium sources. The poster contribution provides an overview of the various sources used during this period, discussing pros and cons of the different types.

Speaker: Beate Bornschein (Karlsruhe Institute of Technology, Institute for Astroparticle Physics)

5:25 PM Qualification measurements towards a new KATRIN Rear Wall

In 2026, the Karlsruhe Tritium Neutrino (KATRIN) experiment is undergoing an upgrade to enable the search for keV sterile neutrinos. This upgrade also introduces new systematic uncertainties that must be addressed. The dominant systematic effect arises from electron backscattering at the end of the source, the so-called Rear Wall. This effect can be mitigated by replacing the gold-coated Rear Wall with an alternative material. Two promising candidates with low electron backscattering probability are beryllium and microstructured silicon.
To qualify as a suitable Rear Wall material, several requirements must be met: low tritium accumulation, efficient UV-ozone decontamination, and resistance to this treatment.
This poster presents qualification measurements of a new Rear Wall material performed at the Tritium Laboratory Karlsruhe (TLK). Surface activity after contamination and subsequent decontamination is measured using beta-induced X-ray spectrometry (BIXS). To assess the resistance to UV-ozone treatment, Auger Electron Spectroscopy (AES) is employed to investigate possible oxide layer growth and surface charge-up effects.

Speaker: Kerstin Trost (KIT IAP-TLK)

2026_NuMass_Poster_Trost.pdf

5:27 PM KATRIN-like MINI-MAC-E Filter with a tritium source for the advanced physics lab course

To provide students with hands-on insight into modern neutrino mass experiments, a scaled laboratory setup of KATRIN has been developed for the advanced physics lab course at KIT. With an approximate scale of 1:20, the experiment reproduces the essential components of KATRIN, including a tritium source, an adjustable high-voltage spectrometer of the MAC-E filter type, a high-resolution detector, and magnetic guiding fields. In contrast to KATRIN, the source utilizes exchangeable implanted disks containing tritium and 83mKr within an ultra-high-vacuum chamber. This poster presents the design of the Mini-MAC-E laboratory setup. The project is supported by KIT’s Research Infrastructure in Research-Oriented Teaching (RIRO) program.

Speaker: Sarah Untereiner

Mini-MAC-EPoster_NuMass_SU.pdf

5:29 PM Measurement of the Tritium Column Density at the KATRIN Experiment

Currently, the tightest constraints on the absolute scale of neutrino mass from a direct, model-independent approach, are obtained by the KATRIN experiment, giving an upper limit on the mass of the electron anti-neutrino of 0.45 eV (https://doi.org/10.48550/arXiv.2406.13516), with final projected sensitivity below 0.3 eV. Reaching this ambitious goal requires proper treatment of all systematic effects, with the scattering related systematics currently being the dominant contribution. In particular, the determination of the tritium gas density for each scientific run, usually expressed in terms of column density, is of great importance. With this poster, we will show the column density measurement procedure including the calibration methods that allow to obtain gas density on the β-scan level.

Speakers: Christoph Köhler (Max-Planck-Institut für Kernphysik), Neven Kovac (Institute for Astroparticle Physics, Karlsruhe Institute of Technology)

5:31 PM MAGNETIC-FIELD COMPATIBILITY AND LONGTERM-STABILITY OF TRISTAN DETECTORS FOR THE KATRIN keV STERILE NEUTRINO SEARCH

At the Karlsruhe Institute of Technology (KIT), a full-scale replica of the KATRIN experiment’s detector system was developed to pretest the innovative TRISTAN detector modules. This replica enables comprehensive testing and calibration of up to nine TRISTAN detector modules under controlled conditions, ensuring optimal performance before their integration into the KATRIN beamline in 2026. This upgrade aims to enhance KATRIN’s sensitivity in the search for keV-scale sterile neutrinos. Preliminary results demonstrate that the TRISTAN modules deliver exceptional high-resolution for beta spectroscopy, which is essential for precise neutrino mass measurements and the exploration of potential new physics.

During operation in the KATRIN beamline, the detector modules will be exposed to a strong magnetic field. To investigate its influence on critical detector parameters, dedicated measurements were performed using the TRISTAN replica setup. In addition, long-term stability studies of the detector performance were conducted over extended data-taking periods.

The poster will show these results and highlight the excellent properties of the TRISTAN detector modules, the stable detector response and calibration behavior.

Speakers: Ms Fiona Braun (KIT - IAP), Simon Gentner (KIT - IAP)

5:33 PM Atomic Tritium Analytics for Future Neutrino Experiments

For the next generation neutrino mass experiment KATRIN++, atomic tritium will be used.
The advantage of using atomic tritium compared to the previously used molecular tritium (T$_2$) lies in the avoidance of molecular excitations in the $^3$HeT$^+$ daughter molecule, which would otherwise lead to a smearing of the beta spectrum and thus limit the maximum achievable sensitivity. To use atomic tritium for beta spectroscopy, it must be cooled down to a few mK and magnetically trapped. Neither a source of atomic tritium which can provide the required high flux, nor a tritium compatible beam cooling device are readily available and must therefore be developed. To develop an atomic beam source, analysis methods for the beam are necessary.
This poster shows a method for characterizing the particle velocity distribution inside of the beam based on a time-of-flight (ToF) setup and an optical method for mapping the particle density of the atomic beam.
Using a chopper, continuous particle beams are segmented into particle bunches, which can then be analyzed with a quadrupole mass spectrometer to infer the velocity distribution.
The method for characterizing the beam density profile is based on laser Rayleigh scattering. By measuring the intensity of the scattered light with a sensitive camera, the particle density can be mapped.
In this contribution, the conceptual design, the experimental setup, and the challenges encountered during the first implementation of the experimental apparatus for the Time of Flight setup as well as the challenge of stray light suppression and results of a first experimental stray light suppression study for Rayleigh scattering are presented.

Speaker: Tobias Geier (IAP-TLK)

5:35 PM Simulation of electron energy loss in the KATRIN source

Electrons from tritium beta decay can lose significant energy through inelastic scattering on gas molecules in the KATRIN source. Accurate modeling of the scattering probabilities and the energy loss distribution is crucial to achieve the desired sensitivity to the electron anti-neutrino mass.
In this poster we present a method based on Monte Carlo simulations to quantify the impact of energy-dependent scattering probabilities on the reproducibility of the energy loss distribution and source gas density obtained from dedicated KATRIN calibration measurements, and their propagation to the determination of the electron anti-neutrino mass.

Speakers: Chloe Goupy (MPIK), Xaver Stribl

5:37 PM Search for keV-Scale Sterile Neutrinos with TRISTAN at KATRIN Using Neural Simulation-Based Inference

Following the completion of its neutrino mass measurement program at the end of 2025, the KATRIN experiment aims to probe keV-scale sterile neutrinos by analyzing the full tritium beta decay spectrum with a novel detector system, TRISTAN. Leveraging KATRIN’s high source activity, this search is sensitive to mixing amplitudes at the parts-per-million level. However, extracting a potential sterile neutrino signature is challenging, as it relies on detailed modeling of the the observed tritium spectrum and requires computationally intensive Monte Carlo simulations. To address this challenge, we implement neural simulation-based inference using normalizing flows to approximate the underlying probability density of the physics simulation. We demonstrate that continuous normalizing flows trained via conditional flow-matching enable highly efficient modeling of experimental spectra. This approach opens up the possibility of a fast surrogate model for rapid sampling and generates a continuous, unbinned representation of the KATRIN beamline response, accelerating and enabling the analysis pipeline.

Speaker: Luca Fallböhmer (MPIK)

numass26_poster.pdf

5:39 PM Analysis strategies for determining the neutrino mass with the final KATRIN data set

The KArlsruhe TRItium Neutrino (KATRIN) experiment probes the effective electron anti-neutrino mass by a precision measurement of the tritium beta-decay spectrum near the endpoint. Using data from the first five measurement campaigns, KATRIN has established a world-leading upper limit of 0.45$\,$eV/c$^2$ (90% C.L.). After 1000days of measurement and 19 campaigns, the data taking was concluded in October 2025. The available statistics of the full data set has increased by more than a factor six compared to the previous dataset.

In this contribution, we discuss the analysis approaches employed in the KATRIN neutrino-mass measurement and provide an update on the current status of the analysis using data from all 19 measurement campaigns. We further present an outlook on the combination of the complete KATRIN dataset to obtain the final KATRIN neutrino-mass result. Finally, we discuss the potential for further statistical improvement by extending the standard analysis range of the KATRIN analysis from 40 to 60 or even 90$\,$eV below the endpoint.

This work is supported by the Helmholtz Association and by the Ministry for Education and Research BMFTR (grant numbers 05A23PMA, 05A23PX2, 05A23VK2, and 05A23WO6).

Speakers: Jan Plößner (MPIK), Karo Erhardt, Khushbakht Habib (Karlsruhe Institute of Technology), Svenja Heyns

5:41 PM Development of KICS multiplexing lines for HOLMES+ experiment

The HOLMES experiment investigates the electron neutrino mass by studying the end point of the electron-capture decay spectrum of $^{163}$Ho. The detector technology is based on transition edge sensors (TESs) microcalorimeters.

During the first phase of the experiment, the simultaneous readout of multiple detectors was performed via microwave SQUID multiplexing ($\mu$MUX). However, the high cost per detector of this multiplexing technology limits neutrino mass measurements below $0.1\,\mathrm{eV}$.

In the next phase, HOLMES+, the multiplexed readout will instead be performed with kinetic inductance current sensors (KICSs).
A KICS consists of a lumped element tunable resonator whose inductance is mainly governed by the kinetic inductance of the superconducting material. Thus, its resonance frequency can be modulated upon a current signal, thanks to the current-sensitivity of the kinetic inductance.
This novel multiplexing technology brings several advantages if compared to the $\mu$MUX approach, including ease of microfabrication, with a single lithographic layer, high yield and low costs, as well as a potentially higher multiplexing factor and temporal resolution. This will increase the number of points on the signal rising slope, allowing the distinction of signals pile-up.

In this contribution, we report our recent results in the development of KICS based on thin NbTiN films. We discuss the design and simulation of the first prototypes, with several KICSs coupled to a common transmission line, and we show their successful operation at cryogenic temperatures. We demonstrate the insertion of a persistent current in the circuit to fix an optimal working point, as well as the expected frequency response of the devices upon a current signal, achieving the detection of a test gaussian-shaped pulse.

Speaker: Sara Gamba

numass_abstract_kics (2).pdf

6:35 PM → 9:05 PM Evening activities: Black light minigolf

6:35 PM Black light minigolf

Social Activities NuMass.pdf

Wed, April 15

8:35 AM → 8:45 AM Announcements and introducions

Welcome-Wed2.pdf

8:45 AM → 9:45 AM Invited talks: Double beta decay

Invited talks outside from adjacent topics to direct neutrino mass measurements

8:45 AM Neutrinoless double beta decay overview

Speaker: Prof. Lindley Winslow (Massachussets Institute of Technology)

Review_DBD_Winslow_April2026.pdf

9:45 AM → 11:15 AM Focused Topical Session: Atomic tritum

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

9:45 AM Hot sources for atomic tritium

Speaker: Caroline Rodenbeck (Karlsruher Institut für Technologie (KIT), IAP-TLK)

10:00 AM Cryogenic sources and magentic confinement for atomic hydrogen

Speaker: Vincenzo Monachello (UCL)

10:15 AM Dissocitating hydrogen below 1 K

Speaker: Sergey Vasiliev (University of Turku)

10:30 AM Magnetic Cooling and Trapping

Speaker: Jones Ben (U Manchester)

10:45 AM Atomic tritium experiments at TLK: Facilities and Opportunities for Collaboration

Speaker: Dr Marco Roellig (IAP-TLK)

11:15 AM → 11:45 AM Coffe break

11:45 AM → 1:00 PM Focused Topical Session: RF-based methods

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

11:45 AM CRES introduction

Speaker: Ben Monreal (Case Western Reserve University)

12:00 PM Project8 - CRES

Speaker: Juliana Stachurska (Unversiteit Ghent)

12:15 PM PTOLEMY and RF

Speaker: Federico Virzi (LNGS)

12:30 PM KATRIN - Time of Flight

Speaker: Andrew Gavin (MPIK)

1:00 PM → 2:30 PM Lunch break

In your conference bag you will find a voucher for eating in the canteen / mensa. However, you are also free to go to Karlsruhe Inner City to find something to eat there. The latter is not covered in the conference fee..

2:30 PM → 3:45 PM Focused Topical Session: Calibration methods

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

2:30 PM Calibration overview

Speaker: Lorenzo Calza (KIP Heidelberg)

3:45 PM → 4:15 PM Coffee break

4:15 PM → 5:30 PM Focused Topical Session: Data analysis

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

5:30 PM → 6:30 PM Invited talks: Cryogenic detector applications in observational cosmology and astrophysics

Invited talks outside from adjacent topics to direct neutrino mass measurements

5:30 PM Cryogenic detector applications in observational cosmology and astrophysics

Speaker: Sotiris Loucatos (Irfu CEA-Saclay and APC, Paris)

6:30 PM → 9:00 PM Evening activities: Conference Dinner - Mariannes Flammkuchen

Thu, April 16

8:35 AM → 8:45 AM Announcements and introducions

Welcome-Wed2.pdf

8:45 AM → 9:45 AM Invited talks: Neutrino-mass from cosmology

Invited talks outside from adjacent topics to direct neutrino mass measurements

8:45 AM Neutrino-mass inference through cosmological probes

Cosmological observations provide powerful constraints on the neutrino mass that are complementary to terrestrial laboratory experiments. In this talk, I will survey current constraints from cosmology, with a focus on the latest measurements from DESI and CMB experiments, which have now reached a level of precision at which the inferred neutrino masses are below the lower limits derived from neutrino oscillations. After reviewing the status of this tension, I will turn to the spectrum of possible resolutions, which include new interactions in the neutrino sector and alternative models of dark energy. Other approaches will be covered that can constrain the neutrino mass independently of the CMB. I will close with prospects for further improvements enabled by surveys like Euclid, LSST, and DESI-II.

Speaker: Dr Willem Elbers (Durham University)

9:45 AM → 10:00 AM NuMass-prize session

Speakers: Kathrin Valerius (Karlsruhe Institute of Technology), Loredana Gastaldo (Kirchhoff Institute for Physics, Heidelberg University, Heidelberg, Germany), Dr Magnus Schlösser (Tritium Laboratory Karlsruhe - Institute of Astroparticle Physics)

10:00 AM → 11:40 AM Focused Topical Session: Wild Card / New Ideas

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

10:00 AM Bound-state beta decay of tritium

Speaker: Dr Evgeny Akhmedov (MPIK)

11:40 AM → 12:05 PM Coffee break

12:05 PM → 1:20 PM Focused Topical Session: Quantum sensors

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

1:20 PM → 2:50 PM Lunch break

In your conference bag you will find a voucher for eating in the canteen / mensa. However, you are also free to go to Karlsruhe Inner City to find something to eat there. The latter is not covered in the conference fee.

2:50 PM → 4:05 PM Focused Topical Session: Strategy and synergies

NuMass_Ho_Electron_Capture_Theory_Haverkort.pptx

4:05 PM → 4:35 PM Coffee break

4:35 PM → 5:15 PM Wrap-up: Wrap-up talk

5:15 PM → 5:30 PM Announcements and introducions: Goodbye

Welcome-Wed2.pdf