arXiv subjects

Angela Papa

Publications and source records attributed to Angela Papa.

11 recordsLinked to original sources

arXiv2026

Construction and characterization of a muon trigger detector for the PSI muEDM experiment

We present the upgraded design, construction, and beam test results for the Muon Trigger Detector (MTD) developed for the muon Electric Dipole Moment (muEDM) experiment at the Paul Scherrer Institute (PSI) in Switzerland. This experiment aims to improve the sensitivity of the muon EDM measurement by more than three orders of magnitude beyond the current limit established by the BNL Muon $g-2$ experiment. Precise identification of storable incoming muons at the entrance of the storage solenoid is essential, as the MTD must rapidly trigger a pulsed magnetic kicker to confine muons in the central region of the solenoid, where a weakly focusing magnetic field is maintained. The MTD comprises two subsystems: a \SI{0.1}{mm}-thick plastic scintillator ``gate detector'' read out by four silicon photomultipliers (SiPMs), and a \SI{5}{mm}-thick CNC-machined plastic scintillator ``active aperture detector'' read out by six SiPMs. The geometry of the active aperture detector was optimized through acceptance studies to maximize both storage efficiency and background veto efficiency. Integrated fast electronics generate an LVTTL trigger signal under an anti-coincidence condition -- a muon detected in the gate but not in the aperture -- ensuring selective triggering of storable muon events for the EDM measurement. The system was tested at the PSI $\pi$E1 beamline using \SI{22.5}{MeV/\textit{c}} muons under scaled-down conditions to characterize detector response and trigger performance. A Geant4 simulation incorporating detailed optical photon transport and SiPM response modeling was developed and reproduces the measured event topologies with ${\sim}97\%$ agreement. These results validate the detector design and demonstrate the MTD's readiness for deployment in the full muEDM Phase-1 setup.

physics.ins-det↗

arXiv2025

Physics Briefing Book: Input for the 2026 update of the European Strategy for Particle Physics

The European Strategy for Particle Physics (ESPP) reflects the vision and presents concrete plans of the European particle physics community for advancing human knowledge in fundamental physics. The ESPP is updated every five-to-six years through a community-driven process. It commences with the submission of specific proposals and other input from the community at large, outlining projects envisioned for the near-, mid-, and long-term future. All submitted contributions are evaluated by the Physics Preparatory Group (PPG), and a preliminary analysis is presented at a Symposium meant to foster a broad community discussion on the scientific value and feasibility of the various ideas proposed. The outcomes of the analysis and the deliberations at the Symposium are synthesized in the current Briefing Book, which provides an important input in the deliberations of the Strategy recommendations by the European Strategy Group (ESG).

hep-ex↗

arXiv2025

Letter Of Intent for a future $\mu^+ \to \mathrm{e}^+ \gamma$ experiment at the High Intensity Muon Beam facility at PSI

Searches for charged lepton flavor violation in the muon sector stand out among the most sensitive and clean probes for physics beyond the Standard Model. Currently, $\mu^+ \to \mathrm{e}^+ \gamma$ experiments provide the best constraints in this field for a wide range of models while, in the coming years, new experiments investigating the processes of $\mu^+ \to \mathrm{e}^+ \mathrm{e}^+ \mathrm{e}^-$ and $\mu \to \mathrm{e}$ conversion in the nuclear field are anticipated to reach comparable or higher sensitivities. The High-Intensity Muon Beam (HIMB) facility at PSI, which is expected to deliver muon beam intensities up to two orders of magnitude higher than the existing beam lines, offers a unique opportunity to significantly enhance the sensitivity of $\mu^+ \to \mathrm{e}^+ \gamma$ searches. The discovery potential could be substantially boosted and a sensitivity comparable to that of all the other projects could be reestablished, which is essential for discriminating among competing new-physics scenarios should an observation occur in any of the channels. In this document, we express our interest in developing a $\mu^+ \to \mathrm{e}^+ \gamma$ experimental program at HIMB, with the goal of improving, within the next decade, the sensitivity of the $\mu^+ \to \mathrm{e}^+ \gamma$ search by more than one order of magnitude relative to the expected final result of the current leading experiment, MEG II. This effort would ensure that PSI retains its leadership in this field.

hep-ex↗

arXiv2024

Beam test performance of a prototype muon trigger detector for the PSI muEDM experiment

We report on the performance evaluation of a prototype muon trigger detector for the PSI muEDM experiment, conducted as a proof-of-principle test at the $\pi$E1 beamline of the Paul Scherrer Institute (PSI) using \SI{27.5}{MeV/c} muons. The detector is designed to identify muons within the acceptance phase space of a compact storage solenoid and activate a pulsed magnetic kicker for muon storage; it was tested without the application of a magnetic field. It comprises a telescope made up of four scintillators in anticoincidence with a gate scintillator, all read out by silicon photomultipliers. The study focused on characterizing the detector's response to various muon trajectories and the light yield of its plastic scintillators. Experimental results demonstrated strong agreement with Geant4 Monte Carlo simulations that incorporate optical photon modeling, confirming the detector's concept and its potential for meeting the stringent requirements of the muEDM experiment.

physics.ins-det↗

arXiv2023

Status of the muEDM experiment at PSI

Permanent electric dipole moments (EDMs) are excellent probes of physics beyond the Standard Model, especially on new sources of CP violation. The muon EDM has recently attracted significant attention due to discrepancies in the magnetic anomaly of the muon, as well as potential violations of lepton-flavor universality in B-meson decays. At the Paul Scherrer Institute in Switzerland, we have proposed a muon EDM search experiment employing the frozen-spin technique, where a radial electric field is exerted within a storage solenoid to cancel the muon's anomalous spin precession. Consequently, the EDM signal can be inferred from the upstream-downstream asymmetry of the decay positron count versus time. The experiment is planned to take place in two phases, anticipating an annual statistical sensitivity of $3\times10^{-21}$ $e\cdot$cm for Phase~I, and $6\times10^{-23}$ $e\cdot$cm for Phase~II. Going beyond $10^{-21}$ $e\cdot$cm will enable us to probe various Standard Model extensions.

hep-ex↗

arXiv2022

Characterization of a continuous muon source for the Muon-Induced X-ray Emission (MIXE) Technique

The toolbox for material characterization has never been richer than today. Great progress with all kinds of particles and interaction methods provide access to nearly all properties of an object under study. However, a tomographic analysis of the subsurface region remains still a challenge today. In this regard, the Muon-Induced X-ray Emission (MIXE) technique has seen rebirth fueled by the availability of high intensity muon beams. We report here a study conducted at the Paul Scherrer Institute (PSI). It demonstrates that the absence of any beam time-structure leads to low pile-up events and a high signal-to-noise ratio (SNR) with less than one hour acquisition time per sample or data point. This performance creates the perspective to open this technique to a wider audience for the routine investigation of non-destructive and depth-sensitive elemental compositions, for example in rare and precious samples. Using a hetero-structured sample of known elements and thicknesses, we successfully detected the characteristic muonic X-rays, emitted during the capture of a negative muon by an atom, and the gamma-rays resulting from the nuclear capture of the muon, characterizing the capabilities of MIXE at PSI. This sample emphasizes the quality of a continuous beam, and the exceptional SNR at high rates. Such sensitivity will enable totally new statistically intense aspects in the field of MIXE, e.g. elemental 3D-tomography and chemical analysis. Therefore, we are currently advancing our proof-of-concept experiments with the goal of creating a full fledged permanently operated user station to make MIXE available to the wider scientific community as well as industry.

physics.app-ph↗

arXiv2022

muEDM: Towards a search for the muon electric dipole moment at PSI using the frozen-spin technique

The search for a permanent electric dipole moment (EDM) of the muon is an excellent probe for physics beyond the Standard Model of particle physics. We propose the first dedicated muon EDM search employing the frozen-spin technique at the Paul Scherrer Institute (PSI), Switzerland, with a sensitivity of $6 \times 10^{-23}~e\!\cdot\!\mathrm{cm}$, improving the current best limit set by the E821 experiment at Brookhaven National Laboratory by more than three orders of magnitude. In preparation for a high precision experiment to measure the muon EDM, several R&D studies have been performed at PSI: the characterisation of a possible beamline to host the experiment for the muon beam injection study and the measurement of the multiple Coulomb scattering of positrons in potential detector materials at low momenta for the positron tracking scheme development. This paper discusses experimental concepts and the current status of the muEDM experiment at PSI.

hep-ex↗

arXiv2021

The Search for $\mu^+\to e^+ \gamma$ with 10$^{-14}$ Sensitivity: the Upgrade of the MEG Experiment

The MEG experiment took data at the Paul Scherrer Institute in the years 2009--2013 to test the violation of the lepton flavour conservation law, which originates from an accidental symmetry that the Standard Model of elementary particle physics has, and published the most stringent limit on the charged lepton flavour violating decay ${\mu}^+ \rightarrow {\rm e}^+ \gamma$: BR(${\mu}^+ \rightarrow {\rm e}^+ \gamma$) $<4.2 \times 10^{-13}$ at 90% confidence level. The MEG detector has been upgraded in order to reach a sensitivity of $6\times10^{-14}$. The basic principle of MEG II is to achieve the highest possible sensitivity using the full muon beam intensity at the Paul Scherrer Institute ($7\times10^{7}$ muons/s) with an upgraded detector. The main improvements are better rate capability of all sub-detectors and improved resolutions while keeping the same detector concept. In this paper, we present the current status of the preparation, integration and commissioning of the MEG II detector in the recent engineering runs.

hep-ex↗

arXiv2018

The Quest for $μ\to e γ$ and its Experimental Limiting Factors at Future High Intensity Muon Beams

The search for the Lepton Flavor Violating decay $μ\to e γ$ exploits the most intense continuous muon beams, which can currently deliver $\sim 10^8$ muons per second. In the next decade, accelerator upgrades are expected in various facilities, making it feasible to have continuous beams with an intensity of $10^9$ or even $10^{10}$ muons per second. We investigate the experimental limiting factors that will define the ultimate performances, and hence the sensitivity, in the search for $μ\to e γ$ with a continuous beam at these extremely high rates. We then consider some conceptual detector designs and evaluate the corresponding sensitivity as a function of the beam intensity.

hep-ex↗

arXiv2018

The WaveDAQ integrated Trigger and Data Acquisition System for the MEG II experiment

The WaveDAQ is a newly-designed digitization Trigger and Data AcQuisition system (TDAQ) allowing Multi-gigasample waveform recording on a large amount of channels (up to 16384) by using the DRS4 analog switched capacitor array as downconverting ASIC. A high bandwidth, programmable input stage has been coupled with a bias generator to allow SiPM operation without need of any other external apparatus. The trigger generation is tightly coupled within the system to limit the required depth of the analog memory, allowing faster digitization speeds. This system has been designed for the MEG experiment upgrade but also proved to be highly scalable and already found other applications.

physics.ins-det↗

arXiv2014

Muon cooling: longitudinal compression

A 10 MeV/c $μ^+$ beam was stopped in helium gas of a few mbar in a magnetic field of 5 T. The muon 'swarm' has been efficiently compressed from a length of 16 cm down to a few mm along the magnetic field axis (longitudinal compression) using electrostatic fields. The simulation reproduces the low energy interactions of slow muons in helium gas. Phase space compression occurs on the order of microseconds, compatible with the muon lifetime of 2 $μ$s. This paves the way for preparation of a high quality muon beam.

physics.acc-ph↗