H. Abele

Study of the neutron quantum states in the gravity field

We have studied neutron quantum states in the potential well formed by the earths gravitational field and a horizontal mirror. The estimated characteristic sizes of the neutron wave functions in the two lowest quantum states correspond to expectations with an experimental accuracy. A position-sensitive neutron detector with an extra-high spatial resolution of ~2 microns was developed and tested for this particular experiment, to be used to measure the spatial density distribution in a standing neutron wave above a mirror for a set of some of the lowest quantum states. The present experiment can be used to set an upper limit for an additional short-range fundamental force. We studied methodological uncertainties as well as the feasibility of improving further the accuracy of this experiment.

A measurement of the beta asymmetry A in the decay of free neutrons

Abstract We have measured the beta asymmetry A in the decay of free polarized neutrons, using the 4π superconducting spectrometer PERKEO II. The asymmetry parameter is A0 = −0.1189(12) corresponding to g A g V = −1.274(3) . This value differs by three standard deviations from the one given by the Particle Data Group 1996. Our result contradicts earlier speculation on the existence of right-handed currents in neutron decay.

Quantum motion of a neutron in a waveguide in the gravitational field

We study theoretically the quantum motion of a neutron in a horizontal waveguide in the gravitational field of the Earth. The waveguide in question is equipped with a mirror below and a rough surface absorber above. We show that such a system acts as a quantum filter, i.e. it effectively absorbs quantum states with sufficiently high transversal energy but transmits low-energy states. The states transmitted are determined mainly by the potential well formed by the gravitational field of the Earth and the mirror. The formalism developed for quantum motion in an absorbing waveguide is applied to the description of the recent experiment on the observation of the quantum states of neutrons in the Earths gravitational field.

A Clean, bright, and versatile source of neutron decay products

Abstract We present a case study on a new type of beam station for the measurement of angular correlations in the β-decay of free neutrons. This beam station, called proton and electron radiation channel (PERC), is a cold-neutron guide that delivers at its open end, instead of neutrons, a beam of electrons and protons from neutron decays that take place far inside the guide. These charged neutron-decay products are magnetically guided to the end of the neutron guide, where they are separated from the cold-neutron beam. In this way, a general-purpose source of neutron decay products is obtained which can be operated as a user facility for a variety of different experiments in neutron decay correlation spectroscopy that may be installed at this beam station. The angular distribution of the emitted charged particles depends on the magnetic field configuration and can be chosen freely, according to the need of the experiment being carried out. A gain in phase space density of several orders of magnitude can be achieved with PERC, as compared to existing neutron decay spectrometers. Detailed calculations show that the spectra and angular distributions of the emerging electrons and protons will be distortion- and background-free on the level of 10−4, more than 10 times better than that achieved today.

Search for quantum states of the neutron in a gravitational field: gravitational levels

Abstract The neutron could occupy quantum stationary states if it is trapped between the Earths gravitational field on one side and the Fermi quasi-potential of a mirror on the other side. The quantum states cause a strong variation in neutron density, both for separate energy levels and for a mixture of low-energy states. The use of a position sensitive UCN (ultracold neutron) detector allows simultaneous measurement of the position probability density distribution in the total range of interest and increases significantly the statistics, making possible such an experiment. In this article we describe a specially developed neutron spectrometer and a method of measurement of such quantum states.

A quantum mechanical description of the experiment on the observation of gravitationally bound states

Quantum states in the earth’s gravitational field have been observed, with ultra-cold neutrons falling under gravity. The experimental results can be described by the quantum mechanical scattering model presented here. We also discuss other geometries of the experimental setup, which correspond to the absence or the reversion of gravity. Since our quantum mechanical model quantitatively describes, particularly, the experimentally realized situation of reversed gravity, we can practically rule out alternative explanations of the quantum states, in terms of pure confinement effects.

Quark mixing, CKM unitarity

Abstract.In the Standard Model of elementary particles, quark-mixing is expressed in terms of a 3 x 3 unitary matrix V, the so called Cabibbo-Kobayashi-Maskawa (CKM) matrix. Significant unitarity checks are so far possible for the first row of this matrix. This article reviews the experimental and theoretical information on these matrix elements. On the experimental side, we find a 2.2

Ramsey's method of separated oscillating fields and its application to gravitationally induced quantum phase shifts

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Measurement of the proton asymmetry parameter in neutron beta decay.

to 2.7

The Standard Model and the neutron β-decay

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