49 research outputs found
A test of local Lorentz invariance with Compton scattering asymmetry
We report on a measurement of the constancy and anisotropy of the speed of
light relative to the electrons in photon-electron scattering. We used the
Compton scattering asymmetry measured by the new Compton polarimeter in Hall~C
at Jefferson Lab to test for deviations from unity of the vacuum refractive
index (). For photon energies in the range of 9 - 46 MeV, we obtain a new
limit of . In addition, the absence of sidereal
variation over the six month period of the measurement constrains any
anisotropies in the speed of light. These constitute the first study of Lorentz
invariance using Compton asymmetry. Within the minimal standard model extension
framework, our result yield limits on the photon and electron coefficients
, and .
Although, these limits are several orders of magnitude larger than the current
best limits, they demonstrate the feasibility of using Compton asymmetry for
tests of Lorentz invariance. Future parity violating electron scattering
experiments at Jefferson Lab will use higher energy electrons enabling better
constraints.Comment: 7 pages, 5 figure
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}
Blinding for precision scattering experiments: The MUSE approach as a case study
Human bias is capable of changing the analysis of measured data sufficiently
to alter the results of an experiment. It is incumbent upon modern experiments,
especially those investigating quantities considered contentious in the broader
community, to blind their analysis in an effort to minimize bias. The choice of
a blinding model is experiment specific, but should also aim to prevent
accidental release of results before an analysis is finalized. In this paper,
we discuss common threats to an unbiased analysis, as well as common quantities
that can be blinded in different types of nuclear physics experiments. We use
the Muon Scattering Experiment as an example, and detail the blinding scheme
used therein.Comment: 6 pages, 3 figure
Statistical sensitivity of the nEDM apparatus at PSI to n - n' oscillations
The neutron and its hypothetical mirror counterpart, a sterile state degenerate in mass, could spontaneously mix in a process much faster than the neutron β-decay. Two groups have performed a series of experiments in search of neutron - mirror-neutron (n − n')oscillations. They reported no evidence, thereby setting stringent limits on the oscillation time τnn. Later, these data sets have been further analyzed by Berezhiani et al.(2009-2017), and signals, compatible with n - n' oscillations in the presence of mirror magnetic fields, have been reported. The Neutron Electric Dipole Moment Collaboration based at the Paul Scherrer Institute performed a new series of experiments to further test these signals. In this paper, we describe and motivate our choice of run configurations with an optimal filling time of 29 s, storage times of 180 s and 380 s, and applied magnetic fields of 10 µT and 20 µT. The choice of these run configurations ensures a reliable overlap in settings with the previous efforts and also improves the sensitivity to test the signals. We also elaborate on the technique of normalizing the neutron counts, making such a counting experiment at the ultra-cold neutron source at the Paul Scherrer Institute possible. Furthermore, the magnetic field characterization to meet the requirements of this n − n oscillation search is demonstrated. Finally, we show that this effort has a statistical sensitivity to n − n' oscillations comparable to the current leading constraints for B' = 0
Timing detectors with SiPM read-out for the MUSE experiment at PSI
The Muon Scattering Experiment at the Paul Scherrer Institute uses a mixed beam of electrons, muons, and pions, necessitating precise timing to identify the beam particles and reactions they cause. We describe the design and performance of three timing detectors using plastic scintillator read out with silicon photomultipliers that have been built for the experiment. The Beam Hodoscope, upstream of the scattering target, counts the beam flux and precisely times beam particles both to identify species and provide a starting time for time-of-flight measurements. The Beam Monitor, downstream of the scattering target, counts the unscattered beam flux, helps identify background in scattering events, and precisely times beam particles for time-of-flight measurements. The Beam Focus Monitor, mounted on the target ladder under the liquid hydrogen target inside the target vacuum chamber, is used in dedicated runs to sample the beam spot at three points near the target center, where the beam should be focused
Search for ultralight axion dark matter in a side-band analysis of a 199Hg free-spin precession signal
Ultra-low-mass axions are a viable dark matter candidate and may form a
coherently oscillating classical field. Nuclear spins in experiments on Earth
might couple to this oscillating axion dark-matter field, when propagating on
Earth's trajectory through our Galaxy. This spin coupling resembles an
oscillating pseudo-magnetic field which modulates the spin precession of
nuclear spins. Here we report on the null result of a demonstration experiment
searching for a frequency modulation of the free spin-precession signal of
\magHg in a \SI{1}{\micro\tesla} magnetic field. Our search covers the axion
mass range
and achieves a peak sensitivity to the axion-nucleon coupling of .Comment: 18 pages, 4 images, submitted to SciPost Physic
Search for axionlike dark matter through nuclear spin precession in electric and magnetic fields
We report on a search for ultra-low-mass axion-like dark matter by analysing the ratio of the spinprecession frequencies of stored ultracold neutrons and 199Hg atoms for an axion-induced oscillating electric dipole moment of the neutron and an axion-wind spin-precession effect. No signal consistent with dark matter is observed for the axion mass range 1024 eV ma 10 17 eV. Our null result sets the first laboratory constraints on the coupling of axion dark matter to gluons, which improve on astrophysical limits by up to 3 orders of magnitude, and also improves on previous laboratory constraints on the axion coupling to nucleons by up to a factor of 40
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