J.M. Pendlebury

Improved Experimental Limit on the Electric Dipole Moment of the Neutron

An experimental search for an electric dipole moment (EDM) of the neutron has been carried out at the Institut Laue-Langevin, Grenoble. Spurious signals from magnetic-field fluctuations were reduced to insignificance by the use of a cohabiting atomic-mercury magnetometer. Systematic uncertainties, including geometric-phase-induced false EDMs, have been carefully studied. The results may be interpreted as an upper limit on the neutron EDM of |dn|

A Search for the Electric Dipole Moment of the Neutron

We report on a search for the electric dipole moment of the neutron. Using a magnetic resonance technique with stored ultra-cold neutrons we have measured the electric dipole moment of the neutron to be −(3±5)×10−26 e cm.

Revised experimental upper limit on the electric dipole moment of the neutron

We present for the first time a detailed and comprehensive analysis of the experimental results that set the current world sensitivity limit on the magnitude of the electric dipole moment (EDM) of the neutron. We have extended and enhanced our earlier analysis to include recent developments in the understanding of the effects of gravity in depolarizing ultracold neutrons; an improved calculation of the spectrum of the neutrons; and conservative estimates of other possible systematic errors, which are also shown to be consistent with more recent measurements undertaken with the apparatus. We obtain a net result of dn=−0.21±1.82×10−26  e cm, which may be interpreted as a slightly revised upper limit on the magnitude of the EDM of 3.0×10−26  e cm (90% C.L.) or 3.6×10−26  e cm (95% C.L.).

Neutron life time value measured by storing ultracold neutrons with detection of inelastically scattered neutrons

Abstract The neutron life time τ n was measured by storage of ultracold neutrons (UCN) in a material bottle covered with Fomblin oil. The inelastically scattered neutrons were detected by surrounding neutron counters monitoring the UCN losses due to upscattering at the bottle walls. Comparing traps with different surface to volume ratios the free neutron life time was deduced. Consistent results for different bottle temperatures yielded τ n sec =885.4±0.9 stat ±0.4 syst .

The interaction of Ultra-Cold Neutrons (UCN) with liquid helium and a superthermal UCN source

Abstract We discuss the interaction of Ultra-Cold and Cold Neutrons with superfluid 4He and show that this interaction has all the characteristics which are necessary for the achievement of extremely high densities of UCN.

Super-thermal sources of ultra-cold neutrons

Abstract We discuss some systems in which the steady state UCN density corresponds to ‘temperatures’ much lower than the temperature of the moderator, contrary to the generally accepted view that this cannot occur.

Search for a neutron electric dipole moment

In 1950 at a time when parity conservation was almost universally believed, PURCELL and RAMSEY [1] pointed out that such an assumption must be based on experiment and that there was little experimental evidence for the assumption at that time. We further noted that a search for a neutron electric dipole moment would provide such a test since a dipole moment is forbidden under parity symmetry and the test would be particularly sensitive since the neutron has no electric charge and is consequently not accelerated out of the observation region when a strong external electric field is applied.

The Electric Dipole Moment of the Neutron

SUMMARY. There are seemingly compelling reasons for expecting the laws of physics to be unchanged under various symmetry transformations. However, during the last fifteen years it has been discovered that many of these symmetries are in fact broken. The search for the electric dipole moment of the neutron has already made, and will continue to make, an important contribution to the understanding of this fascinating and fundamental problem. The experimental limits of sensitivity can be understood in terms of the Heisenberg uncertainty principle and the achievable limits for such things as the electric field strengths and observation times in various systems. The two experimental methods used to date are neutron beam magnetic resonance and crystal diffraction. New methods which have been proposed, such as that using bottled neutrons and further work on existing methods, promise a considerable improvement in sensitivity in the next few years. 1. Introduction Physicists have been interested in the electric dipole moment (EDM) of the neutron since about 1950. Today, 22 years later, this interest has significantly increased even though nobody has succeeded in demonstrating the existence of an EDM for the neutron or any other particle. The reason for this interest is the role that the ideas of symmetry have played and are continuing to play in physics. An EDM, if it existed, would have rather special symmetry properties and would give us information about the forces acting on the neutron and other particles. Following the pioneering experiment of Smith, Purcell and Ramsey (1957) the results of a more recent generation of experiments to search for the EDM have now been available for about four years (Shull and Nathans 1967, Cohen et al. 1969 and Baird et al. 1969). Further descriptions of these experiments have been given by Cohen (1969) and Ramsey (1969). Plans are now being made in several laboratories for a new generation of experiments. We feel that this is an appropriate time to discuss at a non-specialist level the recent history of ideas on symmetry in physics in relation to the part played by the EDM, to review the past experiments in terms of what really limits their sensitivity and to speculate on the improvements which may be achieved in the future. Although this article is concerned solely with the neutron, attempts have been made and are currently in progress to search for the EDM’s of other particles (Player and Sandars 1970, Stein et al. 1969). The detection of an EDM for any elementary particle would have the same significance as it would for the neutron and much of what we will say about the interpretation of the neutron EDM experiments will apply to the EDM’s of other particles except for some quantitative differences.

Performance of an atomic mercury magnetometer in the neutron EDM experiment

Abstract Previous measurements of the electric dipole moment (EDM) of the neutron have been limited by the systematic effect of changes in the magnetic environment. In this paper we report the performance of a newly-developed “cohabiting” magnetometer based upon measurements of the nuclear precession frequency of free mercury atoms that occupy the same volume as the neutrons. We find that we are able to observe changes as small as 10 −9 G in the volume-averaged magnetic field, allowing us to reduce the systematic errors in the EDM experiment by more than an order of magnitude in comparison with previous measurements.

Experimental search for neutron-antineutron transitions with free neutrons

Abstract The observation of neutron-antineutron transitions would be direct evidence for baryon number violation. For the first time an experiment has been carried out to search for this phenomenon with neutrons in free flight. The experiment using the research reactor at the Institut Laue-Langevin in Grenoble has set a lower limit to the oscillation time τ n n of 106 s.