Science with Ultracold Neutrons at the MLZ

8 Oct 2025, 08:00 → 9 Oct 2025, 18:20 Europe/Berlin

UYG 02 22 - Pforte (MLZ)

Andreas Frei (FRM II - TUM), Bastian Märkisch (Physik-Department, TUM), Peter Fierlinger (TUM)

Science with Ultracold Neutrons at the MLZ

The construction of the UCN source at the FRM II in Garching has finally reached critical milestones in terms of regulation, testing, and procurement and production. The aim of this workshop is to initiate discussion of a future science program with UCN at this source with a small group of experts. A report on the results of this workshop will advise the MLZ directorate.

Programme

On the first day, we will discuss the design, status, and performance of the UCN source, and the role it will play in the field of physics with UCN also in comparison to other sources. We will visit the non-nuclear testing facilities, where a copy of the source is in operation, and the space available for experiments in the guide hall east of the FRM II.

On the second day, we aim to openly discuss a potential science program, including but not limited to EDM, neutron lifetime, gravitationally bound neutrons, decay correlations - also in the light of alternative options.

A. Frei -- The source for ultra-cold neutrons at the FRM II

Wednesday 8 October

09:00 → 09:15 Welcome

09:00 Welcome

Speakers: Dr Andreas Frei (FRM II - TUM), Bastian Märkisch (Physik-Department, TUM), Peter Fierlinger (TUM)

09:15 → 11:00 UCN Sources

09:15 The Munich UCN source

In this talk the current status of the UCN source project at the FRM II will be presented. Expected values for UCN density and UCN flux will be discussed. Further steps to install the source and take it into operation will be shown.

Speaker: Dr Andreas Frei (FRM II - TUM)

The Munich UCN Source.pdf

10:00 UCN intensity at the PSI UCN source

I will report on different measurements which were conducted over many years to understand operation and UCN output of the PSI UCN source.
This was done also with simulation analysis of neutron production and UCN transport.

Speaker: Bernhard Lauss (Paul Scherrer Institut)

10:30 PULSTAR UCN source and SFnEDM test bed

First part of my talk will be an update on status of the PULSTAR UCN source commissioning at NC State University. Last year we verified expected thermal neutron flux with a real source assembly and tested gamma shielding. This year we are assembling source for the final installation in the thermal column enclosure. A first test of UCN production has been approved by the reactor and university safety administration and installation is planned for October, 2025. The second part of the talk will discuss testbed for the new generation of nEDM as a possible experiment for FRM-II UCN source.

Speaker: Ekaterina Korobkina (NC State University)

PULSTAR UCN source Munich-MLZ-2025 pdf.pdf

11:00 → 11:15 Coffee

11:15 → 12:15 UCN Sources

11:15 First ultracold neutrons from the new TUCAN source at TRIUMF

The TUCAN collaboration is developing a next-generation spallation-based ultracold neutron (UCN) source at TRIUMF to supply high-density UCNs for fundamental physics experiments. The source's design leverages protons from TRIUMF's 500-MeV cyclotron and a large flux of cold neutrons created by a room-temperature heavy water moderator and a liquid deuterium shell, which then feed a superfluid liquid helium-4 volume at ~1 K. The unique properties of the superfluid allow for the efficient production and extraction of UCNs with a long storage lifetime.

Construction of the source was completed in 2025, and it is currently undergoing commissioning with beam. Following successful cryogenic commissioning, the first ultracold neutrons were produced from the spallation target's irradiation. Initial tests, conducted without the liquid deuterium moderator, demonstrated a significant UCN yield, with approximately 900,000 UCNs detected after a 60-second irradiation. We anticipate that the liquid deuterium moderator will increase this yield by an order of magnitude, up to a factor of 50.

This presentation will detail the source's innovative design, highlight the key milestones of its construction and commissioning, and discuss these exciting initial results.

Speaker: Ruediger Picker (TRIUMF)

2025-10 TUCAN UCN source, MLZ.pptx

11:45 SuperSUN

Speaker: Skyler Degenkolb (Universität Heidelberg)

SuperSUN.pdf

12:15 → 13:00 Lunch

13:00 → 14:45 Site visits: Visit to the UCN source testing facility

14:45 → 15:00 Coffee

15:00 → 16:00 Site visits: Visit to the guide hall east

16:00 → 17:00 UCN Sources: Discussion

19:00 → 21:00 Dinner

Thursday 9 October

09:00 → 10:30 Science with UCN: Science with UCN - EDM

09:00 The n2EDM experiment at PSI

The n2EDM experiment, which is currently being commissioned by the international nEDM collaboration at the Paul Scherrer Institute, aims to search for a non-vanishing electric dipole moment of the neutron with a sensitivity of 1x10^-27 e cm in the baseline setup. An overview of the experimental setup and the current status of the experiment will be presented.

Speaker: Dieter Ries (Paul Scherrer Institute)

DRies_MLZUCN2025.pdf

09:30 EDM landscape

Speaker: Skyler Degenkolb (Universität Heidelberg)

EDM_landscape.pdf

10:00 Future EDM

Speaker: Peter Fierlinger (TUM)

10:30 → 10:50 Coffee

10:50 → 11:50 Science with UCN: Science with UCN - GRS

10:50 Gravity Resonance Spectroscopy: UCNs bound at ILL

Gravity Resonance Spectroscopy (GRS) investigates the energy states of Ultra-Cold Neutrons using an equivalent of Ramsey's method of separated oscillating fields. The manipulation of states is realized using mechanical oscillations instead of EM fields. This allows direct investigation of some "beyond-Riemann" gravity models as well as specific DM and DE candidates. An overview of current status and results from the ILL is given. Experimental challenges for a successful measurement campaign are discussed.

Speaker: Jakob Micko (Universitaet Bern)

qbounce20250910.pdf

11:20 TUCAN EDM and PENeLOPE

Ultracold neutrons are indispensable probes for precision experiments in fundamental physics, providing unique opportunities to search for new physics beyond the Standard Model. This presentation will cover the principles and current status of two key experiments poised to utilize high-yield UCN sources: the TUCAN EDM experiment and the PENeLOPE neutron lifetime experiment.

The TUCAN EDM experiment aims to measure the electric dipole moment of the neutron, a quantity directly linked to the universe's matter-antimatter asymmetry. Using a state-of-the-art magnetically shielded room, a double-cell arrangement at room temperature and the TUCAN high-yield UCN source, the experiment is projected to achieve a statistical sensitivity of 10−27 ecm (1-sigma) within 400 days of beam time.

The PENeLOPE experiment addresses the long-standing 4-sigma discrepancy between beam and trap measurements of the neutron lifetime, a crucial parameter for Big Bang nucleosynthesis and the CKM quark mixing matrix. Over the last decade, we have designed and constructed a superconducting magnetic trap with a large storage volume of ~800 liters. This system, commissioned in 2020 at the Technical University of Munich, was transferred to TRIUMF in 2024 to begin its first series of measurements at the new TUCAN UCN source. The design allows for both traditional counting of remaining neutrons and real-time detection of decay protons, enabling a precise measurement with a focus on minimizing systematic uncertainties.

This talk will provide a detailed overview of both experiments, highlighting their potential to contribute to the future scientific program with a high-yield UCN source like the one at the MLZ.

Speaker: Ruediger Picker (TRIUMF)

2025-10 PENeLOPE and TUCAN EDM, MLZ.pptx

12:00 → 13:00 Lunch

13:00 → 14:00 Science with UCN: Science with UCN - Neutron decay

13:00 tauSpect Neutron Lifetime

Speaker: Martin Fertl (Johannes Gutenberg Universität Mainz)

2025-10-09_tSPECT_MLZ2025.pdf

13:30 UCNA+: an upgraded experiment to measure the beta-asymmetry with polarized ultracold neutrons

Angular correlation measurements can provide high precision values for the axial coupling constant in neutron decay, a fundamental input in the determination of the beta decay rate predicted by the Standard Model of particle physics. Completed in 2018, the UCNA experiment was designed to utilize polarized ultracold neutrons to perform a high precision measurement of the beta asymmetry -- the angular correlation between the polarization vector of the neutron and the momentum of the emitted electron. The achieved precision for the axial coupling constant of 0.16% ultimately was limited by a combination of statistics and uncertainties in the detector response. An effort is underway at the Area B UCN Source in the Los Alamos Neutron Science Center to upgrade the UCNA experiment. This upgrade, called UCNA+, is based on exploiting the improved UCN densities available at Los Alamos after the source upgrade in 2016 and a scintillator detector system (developed by R. Pattie at Eastern Tennessee State University) with improved light-collection and lower thresholds for detection of decay electrons. When combined with improved source scanning systems, thinner end-cap foils, and dedicated scattering measurements to accurately benchmark Monte Carlo calculations of scattering, roughly a factor of 3 or more improvement appears feasible over the previous results of UCNA. At this precision level, UCNA+ would make a significant contribution to the global uncertainties for the axial coupling constant, contributing to a value for the CKM unitarity constant Vud potentially competitive with the precision established by the superallowed nuclear decays.

Speaker: Albert Young (North Carolina State University/Triangle Universities Nuclear Laboratory)

Munich-2025-small.pdf

14:00 → 14:20 Coffee

14:20 → 15:50 Science with UCN: Discussion

15:50 → 16:10 Coffee

16:10 → 17:30 Wrap-Up: Summary