Systematic effects in the search for the muon electric dipole moment using the frozen-spin technique

At the Paul Scherrer Institute (PSI) we are developing a high precision instrument to measure the muon electric dipole moment (EDM). The experiment is based on the frozen-spin method in which the spin precession induced by the anomalous magnetic moment is suppressed, thus increasing the signal-to-noise ratio for EDM signals to achieve a sensitivity otherwise unattainable using conventional $g-2$ muon storage rings. The expected statistical sensitivity for the EDM after a year of data taking is $6\times 10^{-23} e\cdot$cm with the $p = 125$ MeV/c muon beam available at the PSI. Reaching this goal necessitates a comprehensive analysis on spurious effects that mimic the EDM signal. This work discusses a quantitative approach to study systematic effects for the frozen-spin method when searching for the muon EDM. Equations for the motion of the muon spin in the electromagnetic fields of the experimental system are analytically derived and validated by simulation.Comment: 7 pages, 2 figures, conference proceedin

PicoTesla absolute field readings with a hybrid 3He/87Rb magnetometer

We demonstrate the use of a hybrid 3He/87 magnetometer to measure absolute magnetic fields in the pT range. The measurements were undertaken by probing time-dependent 3He magnetisation using 87Rb zero-field magnetometers. Measurements were taken to demonstrate the use of the magnetometer in cancelling residual fields within a magnetic shield. It was shown that the absolute field could be reduced to the 10 pT level by using field readings from the magnetometer. Furthermore, the hybrid magnetometer was shown to be applicable for the reduction of gradient fields by optimising the effective 3He T2 time. This procedure represents a convenient and consistent way to provide a near zero magnetic field environment which can be potentially used as a base for generating desired magnetic field configurations for use in precision measurements

Electric dipole moments and the search for new physics

Static electric dipole moments of nondegenerate systems probe mass scales for physics beyond the Standard Model well beyond those reached directly at high energy colliders. Discrimination between different physics models, however, requires complementary searches in atomic-molecular-and-optical, nuclear and particle physics. In this report, we discuss the current status and prospects in the near future for a compelling suite of such experiments, along with developments needed in the encompassing theoretical framework.Comment: Contribution to Snowmass 2021; updated with community edits and endorsement

The search for the neutron electric dipole moment at PSI

International audienceThe existence of a nonzero permanent electric dipole moment (EDM) of the neutron would reveal a new source of CP violation and shed light on the origin of the matter--antimatter asymmetry of the Universe. The sensitivity of current experiments using stored ultracold neutrons (UCN) probes new physics beyond the TeV scale. Using the UCN source at the Paul Scherrer Institut, the nEDM collaboration has performed the most sensitive measurement of the neutron EDM to date, still compatible with zero ($|d_n|<1.8\times 10^{-26} \, e {\rm cm}$, C.L.90%). A new experiment designed to improve the sensitivity by an order of magnitude, n2EDM, is currently in construction

Search for electric dipole moments

Searches for permanent electric dipole moments of fundamental particles and systems with spin are the experiments most sensitive to new CP violating physics and a top priority of a growing international community. We briefly review the current status of the field emphasizing on the charged leptons and lightest baryons

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 cm for Phase I and cm for Phase II. Going beyond cm will enable us to probe various Standard Model extensions.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

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 × 10^(-23) e·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

Time-of-flight spectroscopy of ultracold neutrons at the PSI UCN source

The ultracold neutron (UCN) source at the Paul Scherrer Institute (PSI) provides high intensities of storable neutrons for fundamental physics experiments. The neutron velocity spectrum parallel to the beamline axis was determined by time-of-flight spectroscopy using a neutron chopper. In particular, the temporal evolution of the spectrum during neutron production and UCN storage in the source storage volume was investigated and compared to Monte Carlo simulation results. A softening of the measured spectrum from a mean velocity of 7.7(1)–5.1(1) ms-1 occurred within the first 30 s after the proton beam pulse had impinged on the spallation target. A spectral hardening was observed over longer time scales of one measurement day, consistent with the effect of surface degradation of the solid deuterium moderator.ISSN:1434-6001ISSN:1434-601

Superconducting shield for the injection channel of the muEDM experiment at PSI

At the Paul Scherrer Institute (PSI), we are setting up an experiment to search for the electric dipole moment (EDM) of the muon using the frozen-spin technique. The discovery of a muon EDM would indicate violation of charge conjugation parity symmetry (CP-violation) and lepton flavor universality, beyond the Standard Model. The experiment aims to achieve a sensitivity of σ(dμ) ≤ 6 × 10$^{-23}$ e · cm.This study is taking place during the first phase of the experiment and it focuses on the off-axis injection of muons into a 3 T storage solenoid. Muons need to be transported from the exit of the PSI beamline, a low magnetic-field region, into the strong magnetic-field of the solenoid. For this purpose, two magnetically shielded channels are being developed. In the direct vicinity of the injection helix inside the solenoid bore, we will use superconducting (SC) shielding to avoid any hysteresis effect, while farther away in the fringe field we will use iron tubes. Three prototypes of SC injection tubes will be produced: the first will use a commercial high temperature superconducting (HTS) tape wrapped around a hollow copper tube, the second will utilize several Nb-Ti/Nb/Cu sheets obtained from CERN, wrapped and mechanically clamped around another hollow copper tube, while the third will consist of a commercial cast Bi-2223 superconducting tube coiled with HTS tape. To evaluate the effectiveness of the different SC-shields, we will measure their shielding factors and determine the muon injection efficiency from the beamline into the solenoid