22 research outputs found
Measurement of the permanent electric dipole moment of the neutron
We present the result of an experiment to measure the electric dipole moment EDM) of the neutron at the Paul Scherrer Institute using Ramsey's method of separated oscillating magnetic fields with ultracold neutrons (UCN). Our measurement stands in the long history of EDM experiments probing physics violating time reversal invariance. The salient features of this experiment
were the use of a Hg-199 co-magnetometer and an array of optically pumped cesium vapor magnetometers to cancel and correct for magnetic field changes. The statistical analysis was performed on blinded datasets by two separate groups while the estimation of systematic effects profited from an
unprecedented knowledge of the magnetic field. The measured value of the neutron EDM is d_{\rm n} = (0.0\pm1.1_{\rm stat}\pm0.2_{\rmsys})\times10^{-26}e\,{\rm cm}
The very large n2EDM magnetically shielded room with an exceptional performance for fundamental physics measurements.
We present the magnetically shielded room (MSR) for the n2EDM experiment at the Paul Scherrer Institute, which features an interior cubic volume with each side of length 2.92 m, thus providing an accessible space of 25 m3. The MSR has 87 openings of diameter up to 220 mm for operating the experimental apparatus inside and an intermediate space between the layers for housing sensitive signal processing electronics. The characterization measurements show a remanent magnetic field in the central 1 m3 below 100 pT and a field below 600 pT in the entire inner volume, up to 4 cm to the walls. The quasi-static shielding factor at 0.01 Hz measured with a sinusoidal 2 μT peak-to-peak signal is about 100 000 in all three spatial directions and increases rapidly with frequency to reach 108 above 1 Hz
Search for an interaction mediated by axion-like particles with ultracold neutrons at the PSI
We report on a search for a new, short-range, spin-dependent interaction
using a modified version of the experimental apparatus used to measure the
permanent neutron electric dipole moment at the Paul Scherrer Institute. This
interaction, which could be mediated by axion-like particles, concerned the
unpolarized nucleons (protons and neutrons) near the material surfaces of the
apparatus and polarized ultracold neutrons stored in vacuum. The dominant
systematic uncertainty resulting from magnetic-field gradients was controlled
to an unprecedented level of approximately 4 pT/cm using an array of
optically-pumped cesium vapor magnetometers and magnetic-field maps
independently recorded using a dedicated measurement device. No signature of a
theoretically predicted new interaction was found, and we set a new limit on
the product of the scalar and the pseudoscalar couplings (95% C.L.) in a range of for the monopole-dipole interaction. This new result confirms
and improves our previous limit by a factor of 2.7 and provides the current
tightest limit obtained with free neutrons
Optically pumped Cs magnetometers enabling a high-sensitivity search for the neutron electric dipole moment
An array of 16 laser-pumped scalar Cs magnetometers was part of the neutron electric dipole moment (nEDM) experiment taking data at the Paul Scherrer Institute in 2015 and 2016. It was deployed to measure the gradients of the experiment's magnetic field and to monitor their temporal evolution. The originality of the array lies in its compact design, in which a single near-infrared diode laser drives all magnetometers that are located in a high-vacuum chamber, with a selection of the sensors mounted on a high-voltage electrode. We describe details of the Cs sensors' construction and modes of operation, emphasizing the accuracy and sensitivity of the magnetic-field readout. We present two applications of the magnetometer array directly beneficial to the nEDM experiment: (i) the implementation of a strategy to correct for the drift of the vertical magnetic-field gradient and (ii) a procedure to homogenize the magnetic field. The first reduces the uncertainty of the nEDM result. The second enables transverse neutron spin relaxation times exceeding 1500 s, improving the statistical sensitivity of the nEDM experiment by about 35% and effectively increasing the rate of nEDM data taking by a factor of 1.8
A New Cryogenic Apparatus to Search for the Neutron Electric Dipole Moment
A cryogenic apparatus is described that enables a new experiment, nEDM@SNS,
with a major improvement in sensitivity compared to the existing limit in the
search for a neutron Electric Dipole Moment (EDM). It uses superfluid He to
produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a
suitably coated pair of measurement cells. The experiment, to be operated at
the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized
He from an Atomic Beam Source injected into the superfluid He and
transported to the measurement cells as a co-magnetometer. The superfluid
He is also used as an insulating medium allowing significantly higher
electric fields, compared to previous experiments, to be maintained across the
measurement cells. These features provide an ultimate statistical uncertainty
for the EDM of e-cm, with anticipated systematic
uncertainties below this level
Johnson-Nyquist noise effects in neutron electric-dipole-moment experiments
Magnetic Johnson-Nyquist noise (JNN) originating from metal electrodes, used to create a static electric field in neutron electric-dipole-moment (nEDM) experiments, may limit the sensitivity of measurements. We present here a dedicated study on JNN applied to a large-scale long-measurement-time experiment with the implementation of a comagnetometry. In this study, we derive surface- and volume-averaged root-mean-square normal noise amplitudes at a certain frequency bandwidth for a cylindrical geometry. In addition, we model the source of noise as a finite number of current dipoles and demonstrate a method to simulate temporal and three-dimensional spatial dependencies of JNN. The calculations are applied to estimate the impact of JNN on measurements with the new apparatus, n2EDM, at the Paul Scherrer Institute. We demonstrate that the performances of the optically pumped Cs133 magnetometers and Hg199 comagnetometers, which will be used in the apparatus, are not limited by JNN. Further, we find that, in measurements deploying a comagnetometer system, the impact of JNN is negligible for nEDM searches down to a sensitivity of 4×10-28ecm in a single measurement; therefore, the use of economically and mechanically favored solid aluminum electrodes is possible
The design of the n2EDM experiment: nEDM Collaboration
We present the design of a next-generation experiment, n2EDM, currently under construction at the ultracold neutron source at the Paul Scherrer Institute (PSI) with the aim of carrying out a high-precision search for an electric dipole moment of the neutron. The project builds on experience gained with the previous apparatus operated at PSI until 2017, and is expected to deliver an order of magnitude better sensitivity with provision for further substantial improvements. An overview is of the experimental method and setup is given, the sensitivity requirements for the apparatus are derived, and its technical design is described
The `n2EDM MSR' -- a very large magnetically shielded room with an exceptional performance for fundamental physics measurements
We present the magnetically shielded room (MSR) for the n2EDM experiment at the Paul Scherrer Institute which features an interior cubic volume with each side of length 2.92m, thus providing an accessible space of 25m3. The MSR has 87 openings up to 220mm diameter to operate the experimental apparatus inside, and an intermediate space between the layers for sensitive signal processing electronics. The characterization measurements show a remanent magnetic field in the central 1m3 below 100pT, and a field below 600pT in the entire inner volume, up to 4 cm to the walls. The quasi-static shielding factor at 0.01 Hz measured with a sinusoidal 2muT peak-to-peak signal is about 100,000 in all three spatial directions and rises fast with frequency to reach 10^8 above 1Hz
The `n2EDM MSR' -- a very large magnetically shielded room with an exceptional performance for fundamental physics measurements
We present the magnetically shielded room (MSR) for the n2EDM experiment at the Paul Scherrer Institute which features an interior cubic volume with each side of length 2.92m, thus providing an accessible space of 25m3. The MSR has 87 openings up to 220mm diameter to operate the experimental apparatus inside, and an intermediate space between the layers for sensitive signal processing electronics. The characterization measurements show a remanent magnetic field in the central 1m3 below 100pT, and a field below 600pT in the entire inner volume, up to 4 cm to the walls. The quasi-static shielding factor at 0.01 Hz measured with a sinusoidal 2muT peak-to-peak signal is about 100,000 in all three spatial directions and rises fast with frequency to reach 10^8 above 1Hz