K.F. Smith

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.

A new measurement of the neutron lifetime

Abstract We have measured the mean lifetime τ of the free neutron by counting decay protons stored in an electromagnetic trap. Neutron density determination was by activation of calibrated boron foils. The result, based on five independent measurements for various experimental conditions, is τ = 937 ± 18 s.

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.

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.

Apparatus for measurement of the electric dipole moment of the neutron using a cohabiting atomic-mercury magnetometer

A description is presented of apparatus used to carry out an experimental search for an electric dipole moment of the neutron, at the Institut Laue-Langevin (ILL), Grenoble. The experiment incorporated a cohabiting atomic-mercury magnetometer in order to reduce spurious signals from magnetic field fluctuations. The result has been published in an earlier letter [1]; here, the methods and equipment used are discussed in detail.

Reply to Comment on An 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 |d(n)|< 2.9 x 10(-26)e cm (90% C.L.).

Precision field averaging NMR magnetometer for low and high fields, using flowing water.

The separated oscillatory field magnetic resonance technique (Ramsey technique) has been employed with flowing water as a volume averaging magnetometer. Polarization and detection were performed in high fields, external to the volume over which the magnetic field was to be averaged. An accuracy of a few parts in 10(7) at a nominal field of 18 G was obtained. The technique is applicable, using standard equipment, for the measurement of fields ranging from kilogauss down to milligauss.

A measurement of the neutron to 199Hg magnetic moment ratio

The neutron gyromagnetic ratio has been measured relative to that of the 199Hg atom with an uncertainty of 0.8 ppm. We employed an apparatus where ultracold neutrons and mercury atoms are stored in the same volume and report the result γn/γHg=3.8424574(30).

Minimum variance of frequency estimations for a sinusoidal signal with low noise

Consideration is given to frequency estimates for continuous data trains of a fixed length amounting to at least five oscillations of a sinusoidal signal of constant frequency accompanied by low-level noise. The minimum variance of the frequency estimation is derived in terms of the noise spectral density at frequencies close to that of the signal. The extent to which several practical methods of frequency measurement can reach this limit is analysed. The case in which the frequency of the signal source may vary slightly within each data train is also included.