29 research outputs found
Experimental demonstration of the stability of Berry's phase for a spin-1/2 particle
The geometric phase has been proposed as a candidate for noise resilient
coherent manipulation of fragile quantum systems. Since it is determined only
by the path of the quantum state, the presence of noise fluctuations affects
the geometric phase in a different way than the dynamical phase. We have
experimentally tested the robustness of Berry's geometric phase for spin-1/2
particles in a cyclically varying magnetic field. Using trapped polarized
ultra-cold neutrons it is demonstrated that the geometric phase contributions
to dephasing due to adiabatic field fluctuations vanish for long evolution
times.Comment: 4 pages, 4 figure
Diffraction of slow neutrons by holographic SiO_2 nanoparticle-polymer composite gratings
Diffraction experiments with holographic gratings recorded in SiO
nanoparticle-polymer composites have been carried out with slow neutrons. The
influence of parameters such as nanoparticle concentration, grating thickness
and grating spacing on the neutron-optical properties of such materials has
been tested. Decay of the grating structure along the sample depth due to
disturbance of the recording process becomes an issue at grating thicknesses of
about 100 microns and larger. This limits the achievable diffraction efficiency
for neutrons. As a solution to this problem, the Pendell\"{o}sung interference
effect in holographic gratings has been exploited to reach a diffraction
efficiency of 83% for very cold neutrons.Comment: 7 pages, 3 figures, submitted to Phys. Rev.
Diffuse reflection of ultracold neutrons from low-roughness surfaces
We report a measurement of the reflection of ultracold neutrons from flat, large-area plates of different Fermi potential materials with low surface roughness. The results were used to test two diffuse reflection models, the well-known Lambert model and the micro-roughness model which is based on wave scattering. The Lambert model fails to reproduce the diffuse reflection data. The surface roughness b and correlation length w , obtained by fitting the micro-roughness model to the data are in the range 1 b 3 nm and 10 w 120 nm, in qualitative agreement with independent measurements using atomic force microscop
An Improved Search for the Neutron Electric Dipole Moment
A permanent electric dipole moment of fundamental spin-1/2 particles violates
both parity (P) and time re- versal (T) symmetry, and hence, also charge-parity
(CP) symmetry since there is no sign of CPT-violation. The search for a neutron
electric dipole moment (nEDM) probes CP violation within and beyond the Stan-
dard Model. The experiment, set up at the Paul Scherrer Institute (PSI), an
improved, upgraded version of the apparatus which provided the current best
experimental limit, dn < 2.9E-26 ecm (90% C.L.), by the RAL/Sussex/ILL
collaboration: Baker et al., Phys. Rev. Lett. 97, 131801 (2006). In the next
two years we aim to improve the sensitivity of the apparatus to sigma(dn) =
2.6E-27 ecm corresponding to an upper limit of dn < 5E-27 ecm (95% C.L.), in
case for a null result. In parallel the collaboration works on the design of a
new apparatus to further increase the sensitivity to sigma(dn) = 2.6E-28 ecm.Comment: APS Division for particles and fields, Conference Proceedings, Two
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An Improved Neutron Electric Dipole Moment Experiment
A new measurement of the neutron EDM, using Ramsey's method of separated
oscillatory fields, is in preparation at the new high intensity source of
ultra-cold neutrons (UCN) at the Paul Scherrer Institute, Villigen, Switzerland
(PSI). The existence of a non-zero nEDM would violate both parity and time
reversal symmetry and, given the CPT theorem, might lead to a discovery of new
CP violating mechanisms. Already the current upper limit for the nEDM
(|d_n|<2.9E-26 e.cm) constrains some extensions of the Standard Model.
The new experiment aims at a two orders of magnitude reduction of the
experimental uncertainty, to be achieved mainly by (1) the higher UCN flux
provided by the new PSI source, (2) better magnetic field control with improved
magnetometry and (3) a double chamber configuration with opposite electric
field directions.
The first stage of the experiment will use an upgrade of the RAL/Sussex/ILL
group's apparatus (which has produced the current best result) moved from
Institut Laue-Langevin to PSI. The final accuracy will be achieved in a further
step with a new spectrometer, presently in the design phase.Comment: Flavor Physics & CP Violation Conference, Taipei, 200
Gravitational depolarization of ultracold neutrons: comparison with data
We compare the expected effects of so-called gravitationally enhanced depolarization of ultracold neutrons to measurements carried out in a spin-precession chamber exposed to a variety of vertical magnetic-field gradients. In particular, we have investigated the dependence upon these field gradients of spin-depolarization rates and also of shifts in the measured neutron Larmor precession frequency. We find excellent qualitative agreement, with gravitationally enhanced depolarization accounting for several previously unexplained features in the data
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}
Dynamic stabilization of the magnetic field surrounding the neutron electric dipole moment spectrometer at the Paul Scherrer Institute
The Surrounding Field Compensation (SFC) system described in this work is installed around the four-layer Mu-metal magnetic shield of the neutron electric dipole moment spectrometer located at the Paul Scherrer Institute. The SFC system reduces the DC component of the external magnetic field by a factor of about 20. Within a control volume of approximately 2.5 m × 2.5 m × 3 m, disturbances of the magnetic field are attenuated by factors of 5–50 at a bandwidth from 10−3 Hz up to 0.5 Hz, which corresponds to integration times longer than several hundreds of seconds and represent the important timescale for the neutron electric dipole moment measurement. These shielding factors apply to random environmental noise from arbitrary sources. This is achieved via a proportional-integral feedback stabilization system that includes a regularized pseudoinverse matrix of proportionality factors which correlates magnetic field changes at all sensor positions to current changes in the SFC coils
Observation of gravitationally induced vertical striation of polarized ultracold neutrons by spin-echo spectroscopy
We describe a spin-echo method for ultracold neutrons (UCNs) confined in a precession chamber and exposed to a |B 0 |=1 μT magnetic field. We have demonstrated that the analysis of UCN spin-echo resonance signals in combination with knowledge of the ambient magnetic field provides an excellent method by which to reconstruct the energy spectrum of a confined ensemble of neutrons. The method takes advantage of the relative dephasing of spins arising from a gravitationally induced striation of stored UCNs of different energies, and also permits an improved determination of the vertical magnetic-field gradient with an exceptional accuracy of 1.1 pT/cm . This novel combination of a well-known nuclear resonance method and gravitationally induced vertical striation is unique in the realm of nuclear and particle physics and should prove to be invaluable for the assessment of systematic effects in precision experiments such as searches for an electric dipole moment of the neutron or the measurement of the neutron lifetime
The neutron and its role in cosmology and particle physics
Experiments with cold and ultracold neutrons have reached a level of
precision such that problems far beyond the scale of the present Standard Model
of particle physics become accessible to experimental investigation. Due to the
close links between particle physics and cosmology, these studies also permit a
deep look into the very first instances of our universe. First addressed in
this article, both in theory and experiment, is the problem of baryogenesis ...
The question how baryogenesis could have happened is open to experimental
tests, and it turns out that this problem can be curbed by the very stringent
limits on an electric dipole moment of the neutron, a quantity that also has
deep implications for particle physics. Then we discuss the recent spectacular
observation of neutron quantization in the earth's gravitational field and of
resonance transitions between such gravitational energy states. These
measurements, together with new evaluations of neutron scattering data, set new
constraints on deviations from Newton's gravitational law at the picometer
scale. Such deviations are predicted in modern theories with extra-dimensions
that propose unification of the Planck scale with the scale of the Standard
Model ... Another main topic is the weak-interaction parameters in various
fields of physics and astrophysics that must all be derived from measured
neutron decay data. Up to now, about 10 different neutron decay observables
have been measured, much more than needed in the electroweak Standard Model.
This allows various precise tests for new physics beyond the Standard Model,
competing with or surpassing similar tests at high-energy. The review ends with
a discussion of neutron and nuclear data required in the synthesis of the
elements during the "first three minutes" and later on in stellar
nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic