157 research outputs found
Geometric phases in electric dipole searches with trapped spin-1/2 particles in general fields and measurement cells of arbitrary shape with smooth or rough walls
The important role of geometric phases in searches for a permanent electric
dipole moment of the neutron, using Ramsey separated oscillatory field nuclear
magnetic resonance, was first noted by Commins and investigated in detail by
Pendlebury et al. Their analysis was based on the Bloch equations. In
subsequent work using the spin density matrix Lamoreaux and Golub showed the
relation between the frequency shifts and the correlation functions of the
fields seen by trapped particles in general fields (Redfield theory). More
recently we presented a solution of the Schr\"odinger equation for spin-
particles in circular cylindrical traps with smooth walls and exposed to
arbitrary fields [Steyerl et al.] Here we extend this work to show how the
Redfield theory follows directly from the Schr\"odinger equation solution. This
serves to highlight the conditions of validity of the Redfield theory, a
subject of considerable discussion in the literature [e.g., Nicholas et al.]
Our results can be applied where the Redfield result no longer holds, such as
observation times on the order of or shorter than the correlation time and
non-stochastic systems and thus we can illustrate the transient spin dynamics,
i.e. the gradual development of the shift with increasing time subsequent to
the start of the free precession. We consider systems with rough, diffuse
reflecting walls, cylindrical trap geometry with arbitrary cross section, and
field perturbations that do not, in the frame of the moving particles, average
to zero in time. We show by direct, detailed, calculation the agreement of the
results from the Schr\"odinger equation with the Redfield theory for the cases
of a rectangular cell with specular walls and of a circular cell with diffuse
reflecting walls.Comment: 20 pages, 8 figure
Surface roughness effect on ultracold neutron interaction with a wall and implications for computer simulations
We review the diffuse scattering and the loss coefficient in ultracold
neutron reflection from slightly rough surfaces, report a surprising reduction
in loss coefficient due to roughness, and discuss the possibility of transition
from quantum treatment to ray optics. The results are used in a computer
simulation of neutron storage in a recent neutron lifetime experiment that
re-ported a large discrepancy of neutron lifetime with the current particle
data value. Our partial re-analysis suggests the possibility of systematic
effects that were not included in this publication.Comment: 39 pages, 9 figures; additional calculations include
Ultracold neutron depolarization in magnetic bottles
We analyze the depolarization of ultracold neutrons confined in a magnetic
field configuration similar to those used in existing or proposed
magneto-gravitational storage experiments aiming at a precise measurement of
the neutron lifetime. We use an extension of the semi-classical Majorana
approach as well as an approximate quantum mechanical analysis, both pioneered
by Walstrom et al. [Nucl. Instr. Meth. Phys. Res. A 599, 82 (2009)]. In
contrast with this previous work we do not restrict the analysis to purely
vertical modes of neutron motion. The lateral motion is shown to cause the
predominant depolarization loss in a magnetic storage trap. The system studied
also allowed us to estimate the depolarization loss suffered by ultracold
neutrons totally reflected on a non-magnetic mirror immersed in a magnetic
field. This problem is of preeminent importance in polarized neutron decay
studies such as the measurement of the asymmetry parameter A using ultracold
neutrons, and it may limit the efficiency of ultracold neutron polarizers based
on passage through a high magnetic field.Comment: 18 pages, 6 figure
Spin flip loss in magnetic storage of ultracold neutrons
We analyze the depolarization of ultracold neutrons confined in a magnetic
field configuration similar to those used in existing or proposed
magneto-gravitational storage experiments aiming at a precise measurement of
the neutron lifetime. We use an approximate quantum mechanical analysis such as
pioneered by Walstrom \emph{et al} [Nucl. Instrum. Methods Phys. Res. A 599, 82
(2009)]. Our analysis is not restricted to purely vertical modes of neutron
motion. The lateral motion is shown to cause the predominant depolarization
loss in a magnetic storage trap.Comment: 12 pages, 3 figures, for Proceedings of Neutron Lifetime Worksho
Comment on "Giant absorption cross section of ultracold neutrons in Gadolinium"
Rauch et al (PRL 83, 4955, 1999) have compared their measurements of the Gd
cross section for Ultra-cold neutrons with an exptrapolation of the cross
section for thermal neutrons and interpreted the discrepancy in terms of
coherence properties of the neutron. We show the extrapolation used is based on
a misunderstanding and that coherence properties play no role in absorption.Comment: 2 pages, 1 postscript figure, comment on Rauch et al, PRL 83,4955
(1999
Calculation of geometric phases in electric dipole searches with trapped spin-1/2 particles based on direct solution of the Schr\"odinger equation
Pendlebury [Phys. Rev. A , 032102 (2004)] were
the first to investigate the role of geometric phases in searches for an
electric dipole moment (EDM) of elementary particles based on Ramsey-separated
oscillatory field magnetic resonance with trapped ultracold neutrons and
comagnetometer atoms. Their work was based on the Bloch equation and later work
using the density matrix corroborated the results and extended the scope to
describe the dynamics of spins in general fields and in bounded geometries. We
solve the Schr\"odinger equation directly for cylindrical trap geometry and
obtain a full description of EDM-relevant spin behavior in general fields,
including the short-time transients and vertical spin oscillation in the entire
range of particle velocities. We apply this method to general macroscopic
fields and to the field of a microscopic magnetic dipole.Comment: 11 pages, 4 figure
Recommended from our members
Research using ultracold neutrons at the ILL
In this talk I will make no effort to give an exhaustive, detailed description of the well-published results of recent work with ultracold neutrons (UCN) at the ILL. Instead, there will be a biased selection of some topics in which author happens to be most interested, though in some cases as a spectator from a considerable distance than as an actor. The selection includes the recent lifetime experiment using a Fomblin-coated bottle, the continuing search for an electric dipole moment of the neutron and some ideas on high precision neutron optics experiments
Localization of Ultra-Cold Particles over Rough Substrates
Localization and diffusion parameters are calculated for particles adsorbed over inhomogeneous substrates for discrete and quasicontinuous spectra of the adsorbed states. The results are expressed via the angular harmonics of the correlation function of surface roughness. The problem is solved analytically in the limiting cases of longwave particles and large correlation radii of surface inhomogeneities. Elsewhere, the problem is solved numerically for Gaussian correlation of inhomogeneities. Applications to electrons on helium films, mobile adsorbed hydrogen atoms and molecules, ultra-cold neutrons in gravitational or magnetic field, etc., are discussed
Observation of Quasibound States of the Neutron in Matter
Quasistationary states of ultracold neutrons have been observed in a double-hump potential barrier. This potential barrier was created by sandwiching a thin film of aluminum between two thin copper films. Measurements of reflection from and transmission through such composite films displayed clear resonances. The resonance positions and widths are in agreement with calculations
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