The MEG II experiment is being carried out in the PSI, piE5 area in the experimental hall west. The MEG II aims to search for the charged lepton flavor violation process, $\mu^{+}\rightarrow e^{+}\gamma$. The physics run started in 2021 and will be planned by the end of 2026 with the target sensitivity of branching ratio of $6\times10^{-14}$). In 2025, we published the result with the data...
A large enhancement of parity-violation via the weak interaction has been observed in nuclear reactions for several nuclei [1]. The enhancement is explained by the mixing of parity-unfavored partial amplitudes in the entrance channel of the compound nuclear states, s-p mixing [2]. The s-p mixing occurs between resonances with the same spin. Therefore, the spin of resonances is an important...
The nEDM Collaboration at PSI presents a novel method for extracting the energy spectrum of ultracold neutrons from magnetically induced spin depolarization measurements using the n2EDM apparatus. This method is also sensitive to the storage properties of the materials used to trap ultracold neutrons, specifically, how specular or diffuse is the surface. We highlight the sensitivity of this...
We present a detailed analytic evaluation of the soft-photon bremsstrahlung radiative corrections to the unpolarized elastic lepton-proton scattering cross-section within the framework of low-energy chiral effective field theory. Our study is motivated by the precision goals of the MUSE experiment, which aims to resolve the proton radius puzzle via simultaneous measurements of $e^\pm p$ and...
Abstract
The analysis of the heavy and very heavy nuclei with, particularly, an extension into the domain of exotic and superheavy nuclei is in the center of the contemporary research in low energy subatomic physics. This research program, currently going on the biggest laboratories in the world, is motivated from the theoretical calculations which predict the existence of an island of...
The spectroscopy of light muonic atoms offers a powerful tool for probing nuclear structure with high precision. By studying X-ray transitions, particularly low-lying states such as the 2pโ1s transitions, it is possible to extract absolute nuclear charge radii with high accuracy.
However, measuring these transitions for low-Z nuclei in the 20โ150 keV energy range remains challenging,...
A Multi-Pixel Photon Counter (MPPC) sensitive to vacuum ultraviolet (VUV) light, called VUV-MPPC, is used in the liquid xenon (LXe) gamma-ray detector for the MEG II experiment. In the MEG II runs with high intensity muon beam, the degradation of VUV-MPPC's photon detection efficiency (PDE) to VUV light was observed. The cause of PDE degradation is considered due to a surface damage of...
The concept of โmirror matterโ has been postulated in various terms since the 1950s. The modern formulation supposes that every Standard Model particle has a partner with opposite chirality, in order to restore parity symmetry in the weak interaction. Neutrons are of particular interest because their lack of electric charge allows for the possibility of mixing between the ordinary and mirror...
Medium-energy, short-baseline neutrino experiments play a crucial role in testing both the Standard Model and physics beyond it. In recent years, pulsed neutron spallation sources have emerged as promising venues for such investigations. The Swiss Spallation Neutron Source (SINQ) at PSI presents another bright neutrino source, however, with almost continuous neutrino production due to the 50...
The impact of earth's gravity onย neutral mesons dynamics is analyzed. The main effect of a Newtonian potential is to couple the strangeness and bottomness flavor oscillations with the quarks zitterbewegung oscillations (arXiv:2503.09465). This coupling is responsible of the observed CP violations in the three types of experiments analyzed here: (i)indirect violation in the mixing, (ii) direct...
The muEDM collaboration is aiming at measuring the electric dipole moment of the muon with unprecedented sensitivity of $\sigma (d_\mu) = 6 \cdot 10 ^{23} \space \mathrm{e\space cm}$ at the Paul Scherrer Institute. The experiment uses the frozen-spin technique inside a 3-T superconducting solenoid magnet. One of the key parts of the experiment is the superconducting injection channels. They...
Positronium, a bound state composed of an electron and a positron, is a pure lepton system. Depending on the total spin, there are para-positronium (p-Ps) and ortho-positronium (o-Ps), which eventually annihilate into two photons and three photons, respectively. Due to minimal hadronic effects, experimental measurement of the continuous spectrum of three-photon annihilation of o-Ps can be used...
The MEG II experiment, conducted at PSI from 2021 and planned through 2026, targets a $\mu\to e\gamma$ search with a sensitivity of $6\times 10^{-14}$ to the muon branching ratio. While the experiment has already demonstrated the potential to reach the target sensitivity, improvements in the reconstruction and analysis techniques will enhance the sensitivity beyond the target value.
This...
McMule (Monte Carlo for Muons and other Leptons) is a powerful tool for fully differential higher-order QED calculations of scattering and decay processes involving leptons. It provides different type of observables such as cross-sections and branching ratios.
In this work, we use McMule to study the process of lepton-proton scattering up to and including next-to-next-to-leading order (NNLO)...
The decay of free neutrons is a powerful tool for precision tests of the Standard Model of particle physics. Correlation coefficients - such as the beta asymmetry $A$ and the Fierz interference term $b$ - serve as input for the determination of the CKM matrix element $V_{ud}$ and for searches for (effective) scalar and tensor as well as right-handed couplings.
The neutron decay spectrometer...
The search for neutrinoless double beta decay (0ฮฝฮฒฮฒ) is fundamental for investigating lepton-number violation, probing new physics beyond the Standard Model, and determining whether neutrinos are Majorana particles. CUORE, a cryogenic calorimetric experiment at LNGS, studies 0ฮฝฮฒฮฒ in $^{130}$Te using 988 TeOโ crystals, reaching a tonne-scale mass and operating below 15 mK. Since 2017, CUORE has...
BRAND is a precision experiment that will investigate free polarized neutron beta-decay [1] at the PF1B cold neutron beamline of the Institut Laue-Langevin (ILL), which offers the worldโs highest cold neutron flux [2]. The experiment will perform simultaneous measurements of 11 correlation coefficients in neutron beta-decay [3], including five that have never been measured before. This enables...
The process $\mu \to e\gamma$ is a charged lepton flavor violating (CLFV) decay that is forbidden in the Standard Model, but its measurable branching ratio is predicted by several new physics models. The current experimental limit on this decay has been set by the MEG II experiment at PSI, which will continue data collection until the end of 2026 with the target sensitivity of $Br < 6 \times...
The BRAND experiment is designed to search for hints of physics beyond the Standard Model. This objective is achieved through the precise study of neutron beta decay. Generally, in neutron beta decay, the emitted electron is longitudinally polarized due to the vector and axial couplings inherent in the Weak decay theory. Any deviation from the electron's longitudinal polarization...
The Mu3e experiment at the Paul Scherrer Institute (PSI) will search for the charged lepton flavour violating decay ยตโบ โ eโบeโปeโบ, improving the current best limit set by the SINDRUM experiment by four orders of magnitude.
Mu3e will be conducted in two phases. Phase I, currently under construction at the ฯE5 beamline at PSI, will utilise an intense DC surface muon beam of 10โธ ยตโบ/s to reach a...
The Mu3e experiment, searching for charged lepton flavor violation in the ยตโบ โ eโบeโปeโบ channel with 2*10^-15 sensitivity in Phase I, is under commissioning at PSI PiE5 beamline. To achieve this, Mu3e, operating with the worldโs most intense continuous muon beam, must handle multi-terabit-per-second data streams from millions of detector channels. Meeting this challenge requires a triggerless...
Ultracold neutron (UCN) experiments suffer from low counting statistics, especially in precision measurements such as searches for the neutron electric dipole moment (nEDM). In-situ experimental designs, where all measurement and detection steps occur within a superthermal UCN source, have the potential to significantly increase the usable UCN density. Such approaches require novel detector...
The P2 Experiment at the new Mainz Energy-Recovering Superconducting Accelerator (MESA), which is currently under construction in Mainz, will measure the weak mixing angle in elastic electron-proton scattering at low momentum transfer with unprecedented precision.
A key parameter for the analysis, the momentum transfer Qยฒ, is measured by a tracking detector designed for high rates,...
At PSI a high-precision experiment is being set up to search for the muon electric dipole moment (muEDM) employing the frozen-spin technique. A muEDM larger than the Standard Model prediction would be a sign of new physics. The search will eventually improve the current best direct limit by three orders of magnitude to $6\cdot 10^{-23}$ e$\cdot$cm. The EDM signal is measured by detecting the...
The n2EDM experiment of an international collaboration at the Paul Scherrer Institute (PSI) aims to improve the sensitivity of the measurement of the neutron electric dipole moment by a factor of ten with respect to its predecessor. A most efficient neutron spin transport is vital to achieve such a sensitivity. We present an overview of the spin transport coil system, the three main channels...
The Mu3e experiment is designed to search for
the lepton flavor violating decay $\mu^+ \rightarrow e^+e^-e^+$.
The aim of the experiment
is to reach a branching ratio sensitivity of $10^{-16}$.
The experiment is located at the Paul Scherrer Institute (Switzerland)
and an existing beam line providing $10^8$ muons per second will allow
to reach a sensitivity of a few $10^{-15}$ in the...
Charge conjugation symmetry (C symmetry) still remains a fundamental symmetry in the realm of physics. It is well-known to be maximally violated in weak interactions. However, its validity is yet to be tested in Electromagnetic (EM) and Strong interactions. With the aim to test this symmetry in EM interactions, the forbidden decay channel of the triplet Positronium state - the...
Designing high-precision particle physics experiments involves optimizing over complex, computationally expensive simulations, often under significant uncertaintyโparticularly in inputs such as magnetic field maps. In the Muon EDM experiment at PSI โ which aims to measure the Electric Dipole Moment (EDM) of the muon using the frozen spin technique โ the injection of muons into the experiment...
Observables of neutron decay are, among others, the $\beta$-asymmetry $A$ and the Fierz interference term $b$. Through precision measurements of $A$ we have access to the CKM matrix element $V_{ud}$, while a non-zero Fierz term $b$ would imply the existence of scalar or tensor interactions beyond the V-A theory of the Standard Model.
The currently most precise direct determinations of $A$...
Nuclear charge radii can be determined utilizing muonic atom spectroscopy. Muonic atoms are easily formed by directly stopping negative muons inside a material. Muons are 207 times heavier than electrons and consequently orbit 207 times closer to the nucleus, making them highly sensitive to nuclear properties.
The muX experiment aims to determine the absolute nuclear charge radius of...
The PanEDM experiment, coupled to the new ultracold neutron source SuperSUN at the Institut Laue-Langevin, aims to measure the neutron electric dipole moment (nEDM) with a sensitivity of $4 \times 10^{-27}$ eยทcm after 100 beam-days in its first phase.
The search for a CP-violating electric dipole moment is among the most powerful and long-standing precision tests of the Standard Model, and...
The goal of the Mu3e experiment is to search for charged LFV in the muon decay $\mu^+ \to e^+ e^- e^+$. The improvement of the sensitivity by 4 orders of magnitude compared to the limit set by the PSI SINDRUM collaboration 40 years ago, drives the need to suppress all sources of backgrounds to a level well below $10^{-16}$. Accidental backgrounds can be strongly rejected by requiring very...
The neutron storage experiment $\tau$SPECT aims to measure the free neutron lifetime, an essential input for precision tests of the Standard Model of particle physics and the Big-Bang nucleosynthesis, by confining ultracold neutrons (UCNs) in a three-dimensional magnetic trap. In contrast to material bottles, magnetic storage avoids interactions with the trap wall, eliminating systematic...
The MEG II experiment at PSI searches for the charged lepton flavor violating decay, $\mu\to e\gamma$. The physics run commenced in 2021 and is planned to continue until the end of 2026, aiming at a target sensitivity on the branching ratio of $6\times 10^{โ14}$. Based on data from 2021 and 2022, we have set the most stringent upper limit to date on the branching ratio at BR($\mu\to e\gamma$)...
The $\tau$SPECT experiment measures the free neutron lifetime by confining ultracold neutrons (UCN) in magnetic field gradients and counting the remaining neutrons after varying storage times. There are statistical and systematical changes in the yield and energy of the UCN produced by the neutron source, therefore the amount of neutrons filled into the trap in each filling cycle has to be...
Commonly used UCN beam polarizers employ the longitudinal Stern-Gerlach effect due to a strong magnetic field, or spin dependent neutron transmission through a thin magnetized foil, exploiting the combination of the spin independent neutron optical potential and the spin dependent magnetic potential. In contrast to commonly used iron foils, the commercial alloy Hiperco50, consisting of 49%...
The n2EDM experiment at the Paul Scherrer Institute (PSI) aims to improve the sensitivity to the neutron electric dipole moment (nEDM) by an order of magnitude relative to the current best limit ($1.8 \times 10^{-26}~e\cdot\mathrm{cm}$). A key requirement to achieve this goal is the generation and precise control of a highly homogeneous static magnetic field $ B_0 $ within the precession...
The n2EDM experiment at the Paul Scherrer Institute aims to measure the neutron electric dipole moment with a sensitivity of below 1Eโ27 eโ cm by observing neutron spin precession in a near perfectly uniform magnetic field. Precise control of systematic effects, particularly those caused by magnetic field non-uniformities, is crucial for achieving this sensitivity. To address this, an array of...
The Mu3e experiment aims to search for the charged lepton flavour violating decay ฮผโบ โ eโบeโปeโบ with an ultimate sensitivity of 10โปยนโถ. Its Vertex Detector employs ultra-thin
MuPix11 sensors to provide precise tracking with minimal material. During our beam time at PSI this year, we successfully commissioned the detector.
Through Time over Threshold calibration, signal transmission tuning, and...
The $\tau$SPECT experiment aims to measure the free neutron lifetime
with an uncertainty goal of sub-second by storing ultra-cold neutrons (UCNs)
in a fully magnetic bottle using a spin-flip loading technique. Monte Carlo (MC) simulations of neutron dynamics in the experiment are a key element to study and understand systematic effects, reduce uncertainties, and improve the experimental...
The PIONEER experiment intends to measure rare pion decays at the PSI PiE5 beamline to achieve the most precise test of lepton flavor universality to date. To achieve the necessary statistics for PIONEER, a pion stop rate of more than 300 kHz must be employed; such high beam rates result in significant pileup in the calorimeter used to differentiate between pion and muon decay products, which...
Precision storage ring experiments, such as those testing fundamental symmetries and investigating nuclear structure, rely on precise control of electric and magnetic fields to guide, focus and probe charged particles. This is achieved using various techniques, generally involving distributed systems across large scale rings [1-4].
The frozen-spin technique is a yet-undemonstrated approach...
Understanding the matter-dominated universe requires the discovery of CP violation beyond the Standard Model. A promising approach is to search for time-reversal invariance violation (TRIV), which is equivalent to CP violation, using polarized neutron and polarized target nuclear reactions. Neutron transmission experiments are expected to be a particularly sensitive probe of TRIV effects by...
Ultracold neutrons (UCNs) can be stored in material vessels and magnetic field gradients. This property allows for long observation times and thereby precision measurements of fundamental neutron properties. In the presented detector design, UCNs are converted into an electrical signal by employing a $^{10}\text{B}$ conversion layer stacked with a ZnS(Ag) scintillation layer. The neutron...
We present the performance characterization of a Magnetically Shielded Room (MSR) designed to meet the stringent magnetic requirements of next-generation $^3$He/$^{129}$Xe co-magnetometer experiments, in particular the search for a permanent electric dipole moment (EDM) of $^{129}$Xe. The Xenon EDM experiment aims to probe new sources of CP violation beyond the Standard Model with...
The study of cold antihydrogen for CPT symmetry tests began in 2010 with the first successful demonstration of trapping individual antihydrogen atoms [1]. In the ALPHA experiment, antihydrogen is produced via a three-body recombination process involving one antiproton and two positrons [2]. Antihydrogen is formed by combining cold plasmas of positrons and antiprotons in a specialized...
The n2EDM experiment at the Paul Scherrer Institute searches for the electric dipole moment (EDM) of the neutron with a baseline sensitivity of approximately $1ร10^{โ27}$ eยทcm. Precise monitoring of the average magnetic field experienced by the neutrons is essential to prevent systematic shifts in the EDM measurement that cannot be otherwise mitigated. This magnetic field monitoring is...
The LEMING experiment is designing the next generation of laser spectroscopy and gravity experiments using a novel atomic beam of muonium (Mu = ฮผโบ + eโป). Cold atomic muonium beams are generated in vacuum and subsequently undergo self-interference using newly engineered, self-aligned diffraction gratings. The setup allows for nanometer-sensitive measurements of muonium displacements due to...
The muEDM experiment aims to measure the electric dipole moment (EDM) of the muon with unprecedented sensitivity, providing a powerful probe for physics beyond the Standard Model. Utilizing the frozen spin technique, the experiment is designed to isolate EDM-induced spin precession while suppressing magnetic moment (gโ2) effects. This poster presents a technical overview of the experimental...
The HyperMu experiment at PSI aims at the first measurement of the ground state hyperfine splitting in muonic hydrogen (ฮผp) with 1 ppm precision using pulsed laser spectroscopy. This accuracy allows for a precise extraction of the proton structure contributions, including the Zemach radius and the proton polarizability.
To measure the ground state hyperfine splitting in ฮผp, we are...
The PanEDM experiment aims to measure the neutron electric dipole moment, using ultracold neutrons (UCN) produced by the superfluid-helium UCN source SuperSUN at the Institut Laue-Langevin (ILL). UCN will be stored in double-chamber spectrometer for spin-precession measurements, with a sensitivity of $4 \times 10^{-27}\,e \,\mathrm{cm}$ anticipated after 100 days of measurement time.
A...
The qBounce experiment investigates the quantum states of ultracold neutrons in the gravitational field of the Earth. This offers a unique opportunity to study gravity at a microscopic level with great accuracy. When neutrons are confined above a horizontal mirror, ultracold neutrons form discrete quantum energy levels arising from the interplay between gravitational and quantum effects. This...
The n2EDM experiment at the Paul Scherrer Institut seeks to measure the neutron electric dipole moment with a sensitivity below 10^(โ27) e . cm, which demands an extremely well-controlled magnetic environment. To track down tiny magnetic contaminants that could mimic an EDM signal, we built a mobile gradiometer based on optically pumped cesium magnetometers operating in the Mx configuration....
The Muon $g-2$ experiment at Fermilab has measured the anomalous magnetic moment of the muon ($a_{\mu} \equiv (g_{\mu} -2)/2$) to a precision of 127 parts-per-billion. During the experiment, `fills' of $\mathcal{O}\left( 10^5 \right)$ $3.1\,\text{GeV}/\text{c}$ muons were injected into the $g-2$ storage ring, of which $\approx 5{\small,}000$ muons were stored and decay over the course of...
The Mu3e experiment is designed to search for the Charged Lepton Flavor Violation (cLFV) through the rare decay ฮผ+ โ e+eโe+, targeting a branching ratio sensitivity of 10^-15 using the PSI piE5 beamline in Phase I, scheduled for 2026.
To cope with the exceptionally high muon rate of 10^8/s (equivalent to ~80 Gbps raw data rate), a triggerless, GPU-based online event selection algorithm is...
for the nEDM Collaboration at PSI
The n2EDM project, aiming for a most sensitive measurement of the electric dipole moment of the neutron hosted by PSI, takes advantage of extensive Monte Carlo simulations of the ultracold neutron storage and transport. This includes modelling of the UCN spin transport system, which also allows the study of depolarization effects in the guides during...
We provide an overview of the capabilities of the modernized Ultra-Cold and Very-Cold Neutron beam ports of the PF2 instrument at the Institut Laue-Langevin.
Experiments using UCN and VCN are important tools to investigate fundamental physics and beyond. Experiments range from dark sector searches over cross-section measurements to neutron instrumentation.
The PF2 instrument serves as...
We describe a concept for a quantum computer based on an abundant number of energy eigenstates. These states form Q-bits or, ad libitum, higher dimensional Q-Nits with N > 2, allowing gate operations according to the quantum computing requirements of DiVincenzo. This system with higher dimensional Q-Nits offers potential advantages over traditional Q-Bit-based quantum computing. It provides a...
Neutron Interferometry was introduced by H. Rauch and U. Bonse in 1974. It opened the path to matter wave interferometry, allowing many direct precision tests of quantum mechanics and fundamental physics and the precise measurement of scattering lengths. A thermal neutron interferometer uses perfect crystals as optical elements (beam splitters, mirrors, and recombiner), where all acting...
The ``neutron lifetime puzzle'' arises from the discrepancy between neutron lifetime measurements obtained using the beam method, which measures decay products, and the bottle method, which measures the disappearance of neutrons.
To resolve this puzzle, we conducted an experiment using a pulsed cold neutron beam at J-PARC. In this experiment, the neutron lifetime is determined from the ratio...
