Dear colleagues,

The IMPACT project at PSI is gaining momentum. Of its two subprojects, HIMB and TATTOOS, HIMB will be realized first. Because of long delivery times for critical components, the HIPA shutdown, originally planned for 2027/28, will now be shifted to 2028/29. This allows full pre-assembly and testing of the most critical components to guarantee smooth installation and operation.

The HIPA accelerators and the user facilities CHRISP, SμS and SINQ will be in shutdown from the end of 2027 until early September 2029. For some beamlines in the WEHA experimental hall an earlier shutdown is planned, presently for piM1 (18 October 2027, CHRISP), piM3 (22 November 2027, SμS instruments GPS and FLAME) and muE4 (15 November 2027, SμS instrument LEM). 

Great news for muon science at large was the decision of the Swiss federal government to fund the National Centre of Competence in Research NCCR Muoniverse. This community will be ‘power users’ of the CHRISP and SμS facilities, greatly benefiting from the additional year of operation in 2027, which will allow them to achieve crucial milestones before the HIPA shutdown. Many other users have also appreciated the additional time in 2027 to achieve important results. While we are aware that the shift is causing some issues, we are confident that mitigating the risk of an extended shutdown due to missing components will pay off in the long run.

Andreas Knecht and Klaus Kirch, CNM Laboratory for Particle Physics, for the HIMB project and the NCCR Muoniverse

An overview of all proposal submission deadlines of the PSI facilities can be found here.

Many biological materials have outstanding properties owing to their hierarchical structure. Take bones: they are extremely hard yet elastic enough to withstand lateral forces without breaking easily, as they feature different structures on different scales. Examining such hierarchically structured materials in detail has traditionally required the use of several different instruments, such as electron and optical microscopes. Now, PSI scientists have refined an X-ray diffraction technique to enable the characterization of materials on scales from nanometres to millimetres simultaneously, by pushing the speed of small-angle X-ray scattering tensor tomography (SAS-TT), a technique originally developed at PSI some ten years ago. To demonstrate the efficiency of the improved method, the researchers performed measurements to reveal the alignment of collagen fibres in a human ossicle known as the incus, or anvil. They achieved an acquisition time of 6 hours per megavoxel at a voxel size of 25 µm³ — 15 times faster than the first measurements in 2014, with a complete scan now taking only about an hour instead of a whole day. In the future, this method could be valuable in areas such as the study of complex tissue, the analysis of bone diseases and the optimization of implant designs.

C. Appel et al., Small Methods 10, 2500162 (2026)
DOI: 10.1002/smtd.202500162

Much of the behaviour of matter arises not from electrons acting alone, but from the ways they influence each other. From chemical systems to advanced materials, their interactions shape how molecules rearrange, how materials conduct or insulate and how energy flows. In many quantum technologies information is stored in delicate patterns of these interactions, known as coherences. Learning how to understand and ultimately control such fleeting states is one of the major challenges facing quantum technologies today. Although many techniques make it possible to study how individual electrons behave, researchers have largely been blind to coherences. Now, scientists from PSI and the Swiss Federal Institute of Technology in Lausanne (EPFL), in collaboration with the Max Planck Institute of Nuclear Physics in Germany and the University of Bern, have demonstrated a way to access coherences using X-ray four-wave mixing. The experiment, performed at SwissFEL on gaseous neon, achieves what had long been theoretically envisioned but never experimentally realized: coherent, background-free X-ray four-wave mixing signals arising from doubly resonant Raman processes involving core-shell electrons. This achievement should open up a wide range of experiments for studying localized electron dynamics, in systems ranging from biomolecules to correlated quantum materials.

A. S. Morillo-Candas et al., Nature 649, 590 (2026)
DOI: 10.1038/s41586-025-09911-1

Whether used to treat bone fractures, replace teeth or act as pacemakers, metallic implants have become an irreplaceable part of modern medicine. A new avenue being explored in the field is designing titanium–magnesium hybrid implants that combine key advantages of both materials. Titanium is used for its high strength, and the magnesium component dissolves over time and helps stimulate bone growth. However, during magnesium degradation, hydrogen gas is released and can ingress into the titanium part, causing lattice expansion and potentially leading to embrittlement. To study this process on the microscopic scale, a research team led by the Helmholtz-Zentrum Hereon in collaboration with the Heinz Maier-Leibnitz Zentrum (MLZ) combined neutron tomography at SINQ, synchrotron X-ray tomography and diffraction at DESY, and several laboratory techniques. After exposing hybrid samples of titanium and magnesium alloys to a saline solution designed to mimic body fluids, they observed how hydrogen penetrated the titanium as the magnesium began to degrade. The detailed understanding now obtained should inform the design of hybrid implants and also provide insight into unwanted effects when a new temporary implant is placed near an existing permanent Ti-based implant.

R. Kumar et al., RSC Advances 15, 4472 (2025)
DOI: 10.1039/D4RA08586H

Muonium — a purely leptonic atom consisting of a positive muon and an electron — is uniquely suited to precision tests of quantum electrodynamics (QED) as nuclear structure effects and finite-size contributions are absent. While the ground-state transitions have been the subject of several experimental efforts, measurements in the n = 2 manifold remain scarce. Now, the Mu-MASS collaboration at PSI has determined the 2S_1/2 – 2P_3/2 fine-structure transition in muonium with a fivefold improvement in precision over the only previous measurement, performed more than three decades ago. In the experiment, metastable muonium atoms in the 2S state undergo microwave-driven transitions to the short-lived 2P_3/2 state. By scanning the microwave frequency and recording the depletion of the 2S population, the team measured a transition frequency of 9871.0 ± 7.0 MHz. This value agrees with the QED prediction within one standard deviation. Combined with the recent Lamb shift result from the same collaboration, the measurement also yields an improved value for the 2S_1/2 – 2P_3/2 splitting. The result establishes a foundation for future measurements targeting sub-MHz precision — a regime that will become accessible with the High-Intensity Muon Beams (HIMB) upgrade at PSI — and paves the way for searches for Lorentz violation and muon-specific new physics.

P. Blumer et al., Physical Review A 113, 012817 (2026)
DOI: 10.1103/f1z4-xzq2

Muon Spectroscopy School 2026

From 14 to 21 January, the PSI Laboratory for Muon Spin Spectroscopy (LMU), the ISIS Muon Group and KTH Stockholm held the Muon Spectroscopy School 2026 for PhD students and postdocs in Rigi-Kaltbad, Switzerland. 39 participants — chosen from more than 90 applicants — heard about various aspects of muon spectroscopy and complementary techniques in lectures, workshops and discussion groups with 26 expert lecturers from muon/neutron research centres and universities. Participants introduced themselves in evening poster sessions, and during their free time they enjoyed the beautiful landscape of Mount Rigi or relaxed in the nearby spa. On the last day of the school, a tour of the neutron and muon facilities at PSI was offered, bringing the successful and stimulating school to a close. 

CHRISP Users Meeting BVR57

The 2026 edition of the Users Meeting for the CHRISP facility, the 57^th of its kind, was held from 3 to 5 February 2026. The first day was dedicated to detailed reviews of the Mu3e, HyperMu, PIONEER and muEDM experiments. On the second day, the Open CHRISP Users Meeting BVR57 took place, with strong in-person attendance. After some news from PSI and an update on the status of the High-Intensity Muon Beams (HIMB) project, two new proposals and a letter of intent were presented and discussed. Progress reports on the four experiments reviewed on the first day were also publicly presented. These and all other progress reports and requests for beamtime were discussed in the closed sessions of the Research Committee for Particle Physics at the Ring Cyclotron on the second and the third day. The meeting concluded with the oral feedback and recommendations to the projects by the president of the committee and the presentation of the beamtime allocations.

SLS — A new endstation for high-resolution soft X-ray ptychography

Soft X-ray ptychography is rapidly becoming a key synchrotron-based imaging technique, enabling routine acquisition of high-resolution images across fields ranging from condensed matter physics to chemistry, environmental science and life sciences. To achieve a resolution at the theoretical limits of the technique, special attention needs to be dedicated to the positioning precision of the sample while allowing for flexibility in the sample mounting to accommodate the requirements of the user community. The Soft X-ray Ptychography Highly Integrated Endstation (SOPHIE) was developed to meet both goals. The endstation was designed and assembled at PSI and commissioned at the SoftiMAX beamline of Max IV during the SLS 2.0 upgrade shutdown. The quality of the acquired ptychography images has exceeded design expectations, enabling routine imaging of nanoparticle samples with sub-5-nm spatial resolution. SOPHIE is now back at SLS and will be installed and commissioned at the SIM beamline, with the goal of opening it for user beamtime applications from the second half of 2026. The design and performance overview of the endstation was recently published in the Review of Scientific Instruments.

SwissFEL — Synchronizing ultrashort X-ray pulses

Scrutinizing fast atomic and molecular processes in action requires bright and short X-ray pulses — a task in which free-electron lasers such as SwissFEL excel. However, within these X-ray pulses the light is internally disordered: its temporal structure is randomly distributed and varies from shot to shot, limiting the accuracy of certain experiments. To tame this inherent randomness, a team of PSI researchers has implemented a technique to generate trains of pulses that are coherent in time. Writing in Physical Review Letters, they report the first experimental demonstration of mode-locked self-amplified spontaneous emission (SASE), which generates periodic trains of phase-locked sub-femtosecond pulses — thereby providing an X-ray analogue of the optical frequency comb. This advance represents a significant step towards the generation of tailored attosecond X-ray pulses and enables a range of new experiments that are only possible with precisely timed, synchronized light pulses.

SINQ — Isotope effects matter in operando neutron studies of hydrogen electrolysers

Neutron imaging is a powerful tool for studying water distribution inside proton exchange membrane water electrolysers (PEMWEs) during operation. Because hydrogen scatters neutrons strongly while deuterium does not, researchers often replace ordinary water (H₂O) with heavy water (D₂O) to improve image contrast — but the electrochemical consequences of this substitution have received little attention. A team led by the University of Southern Denmark, in collaboration with PSI, has now systematically studied the effects of replacing H₂O with D₂O in operating PEMWE cells. Using operando neutron radiography at SINQ alongside electrochemical characterization, they found that D₂O imposes a substantial performance penalty, due to slower reaction kinetics and lower ionic conductivity. Neutron imaging further revealed that H₂O permeates through the membrane more than twice as fast as D₂O at high current densities, consistent with the stronger bonding of D₂O to the membrane and its higher viscosity. The results carry a clear practical message: the isotope substitution commonly used to simplify neutron imaging can substantially alter the physics being studied and should be accounted for in the interpretation of operando experiments.

SμS — Major step towards muon spin spectroscopy using Si pixel detectors

A milestone has been achieved in the development of MuSiP (Muon Spin Spectroscopy using Si Pixel detectors) at PSI. During the 2025 beam campaigns, the MuPix11 silicon pixel chips were successfully operated in high vacuum (~10^-6 mbar) and in close proximity to a cryostat reaching a base temperature of 4 K. The fully assembled spectrometer — integrating vacuum chamber, cold-finger cryostat and compact magnet — was commissioned as a modular unit ready for beamline installation. Despite the heat load of ~1 W per chip and only millimetres of clearance to the cryostat radiation shield, stable multi-day operation with reduced noise was achieved. In addition, plastic scintillator detectors read out by the MuTRiG ASIC were integrated and successfully operated in vacuum, providing timing resolutions of 230–280 ps. This hybrid Si-pixel/scintillator configuration enables vertex-reconstructed µSR (vx-µSR) with unprecedented lateral resolution and significantly enhanced rate capability. These developments represent crucial steps towards a fully Si-pixel-based µSR spectrometer, designed to exploit the future High-Intensity Muon Beams (HIMB) and to enable measurements on millimetre-scale samples and beyond.

CHRISP — An advanced neutron lifetime experiment at the UCN source

Neutrons provide an ideal testing ground for investigating the weak interaction by measuring the free neutron decay lifetime. A precise and accurate determination of this lifetime is the goal of the 𝜏SPECT experiment, which uses stored ultracold neutrons (UCNs). Co-led by Martin Fertl from the Johannes Gutenberg University Mainz and Dieter Ries from PSI, 𝜏SPECT has been developed at Mainz and is now installed at PSI. Physics data taking started in 2025. The setup pioneers a unique spin-flip scheme to load UCNs in a fully magnetic trap, which reduces systematic uncertainties due to wall interactions. Recently, the ERC Consolidator Grant “NuLife” was awarded to Prof. Fertl to support the development of a next-generation neutron lifetime experiment, also anticipated to be located at the PSI UCN source. The ERC grant makes it possible to start designing a new apparatus with a much larger and deeper trap volume, accepting the full available phase space to maximize counting statistics. The NuLife developments should enable the determination of the neutron lifetime with an uncertainty below 0.1 s.

Guesthouse and catering updates for PSI users

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