37 research outputs found
An application of the Mossbauer effect to the study of some magnetic properties of ilmenite
The investigations described in this thesis clarify and supplement, by means of Mossbauer spectroscopy, the magnetic properties and chemical composition of natural ilmenite and its oxidation products. Natural ilmenite was found by some investigators, using a m.agnetic measurement method, to be weakly ferrimagnetic but was revealed to be in a paramagnetic state by others using Mossbauer spectroscopy. There was an uncertainty about the nature of the magnetic properties of an ilmenite sample which had been partially oxidised by heat treatment. The types of compounds existing in natural ilmenite and its oxidation products were not clearly determined
Deeply subrecoil two-dimensional Raman cooling
We report the implementation of a two-dimensional Raman cooling scheme using
sequential excitations along the orthogonal axes. Using square pulses, we have
cooled a cloud of ultracold Cesium atoms down to an RMS velocity spread of
0.39(5) recoil velocity, corresponding to an effective temperature of 30 nK
(0.15 T_rec). This technique can be useful to improve cold atom atomic clocks,
and is particularly relevant for clocks in microgravity.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
Comparison of two experiments on radiative neutron decay
Over 10 years ago we proposed an experiment on measuring the characteristics
of radiative neutron decay in papers [1, 2]. At the same time we had published
the theoretical spectrum of radiative gamma quanta, calculated within the
framework of the electroweak interactions, on the basis of which we proposed
the methodology for the future experiment [3,4]. However, because we were
denied beam time on the intensive cold neutron beam at ILL (Grenoble, France)
for a number of years, we could only conduct the experiment in 2005 on the
newly opened FRMII reactor of Technical University of Muenchen. The main result
of this experiment was the discovery of radiative neutron decay and the
measurement of its relative intensity B.R.= (3.2+-1.6)10-3 with C.L.=99.7% for
radiative gamma quanta with energy over 35 kev [5,6]. Over a year after our
first announcement about the results of the conducted experiment, "Nature" [7]
published a letter asserting that its authors have also measured the branching
ratio of radiative neutron decay B.R.= (3.13+-0.34)10-3 with C.L.=68% and gamma
quanta energy from 15 to 340 kev. This article aims to compare these two
experiments. It is shown that the use of strong magnetic fields in the NIST
(Washington, USA) experiment methodology not only prevents any exact
measurement of the branching ratio and identification of radiative neutron
decay events, but also makes registration of ordinary neutron decay events
impossible.Comment: contribution on conference ISINN-1
emiT: an apparatus to test time reversal invariance in polarized neutron decay
We describe an apparatus used to measure the triple-correlation term (\D
\hat{\sigma}_n\cdot p_e\times p_\nu) in the beta-decay of polarized neutrons.
The \D-coefficient is sensitive to possible violations of time reversal
invariance. The detector has an octagonal symmetry that optimizes
electron-proton coincidence rates and reduces systematic effects. A beam of
longitudinally polarized cold neutrons passes through the detector chamber,
where a small fraction beta-decay. The final-state protons are accelerated and
focused onto arrays of cooled semiconductor diodes, while the coincident
electrons are detected using panels of plastic scintillator. Details regarding
the design and performance of the proton detectors, beta detectors and the
electronics used in the data collection system are presented. The neutron beam
characteristics, the spin-transport magnetic fields, and polarization
measurements are also described.Comment: 15 pages, 13 figure
Sharpening Low-Energy, Standard-Model Tests via Correlation Coefficients in Neutron Beta-Decay
The correlation coefficients a, A, and B in neutron beta-decay are
proportional to the ratio of the axial-vector to vector weak coupling
constants, g_A/g_V, to leading recoil order. With the advent of the next
generation of neutron decay experiments, the recoil-order corrections to these
expressions become experimentally accessible, admitting a plurality of Standard
Model (SM) tests. The measurement of both a and A, e.g., allows one to test the
conserved-vector-current (CVC) hypothesis and to search for second-class
currents (SCC) independently. The anticipated precision of these measurements
suggests that the bounds on CVC violation and SCC from studies of nuclear
beta-decay can be qualitatively bettered. Departures from SM expectations can
be interpreted as evidence for non-V-A currents.Comment: 4 pages, REVTeX, intro. broadened, typos fixed, to appear in PR
Constraints on T-Odd, P-Even Interactions from Electric Dipole Moments
We construct the relationship between nonrenormalizable,effective,
time-reversal violating (TV) parity-conserving (PC) interactions of quarks and
gauge bosons and various low-energy TVPC and TV parity-violating (PV)
observables. Using effective field theory methods, we delineate the scenarious
under which experimental limits on permanent electric dipole moments (EDM's) of
the electron, neutron, and neutral atoms as well as limits on TVPC observables
provide the most stringent bounds on new TVPC interactions. Under scenarios in
which parity invariance is restored at short distances, the one-loop EDM of
elementary fermions generate the most severe constraints. The limits derived
from the atomic EDM of Hg are considerably weaker. When parity symmetry
remains broken at short distances, direct TVPC search limits provide the least
ambiguous bounds. The direct limits follow from TVPC interactions between two
quarks.Comment: 43 pages, 9 figure
New limit on the D coefficient in polarized neutron decay
We describe an experiment that has set new limits on the time reversal invariance violating D coefficient in neutron beta decay. The emiT experiment measured the angular correlation [J] . (p(e) x p(p)) using an octagonal symmetry that optimizes electron-proton coincidence rates. The result is D=[-0.6+/-1.2(stat)+/-0.5(syst)] x 10(-3). This improves constraints on the phase of g(A)/g(V) and limits contributions to T violation due to leptoquarks. This paper presents details of the experiment, data analysis, and the investigation of systematic effects
Searching for time reversal invariance violation in polarized neutron decay
Time reversal invariance violation is tightly constrained in the Standard Model, and the existence of a T-violating effect above the predicted level would be an indication of new physics. A sensitive probe of this symmetry in the weak interaction is the measurement of the D-coefficient in neutron decay. This parameter characterizes the triple-correlation of neutron spin, electron momentum, and neutrino (or proton) momentum, which changes sign under time reversal. The emiT experiment, now on line, attempts to improve the measurement of D,D, whose current average is 0.3±1.5Ă10â3.0.3±1.5Ă10â3. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87907/2/399_1.pd