Experiments in nuclear and particle physics often use magnetic fields to guide charged reaction products to a detector. Due to their gyration in the guide field, the particles hit the detector within an area that can be considerably larger than the d
iameter of the source where the particles are produced. This blurring of the image of the particle source on the detector surface is described by a suitable point spread function (PSF), which is defined as the image of a point source. We derive simple analytical expressions for such magnetic PSFs, valid for any angular distribution of the emitted particles that can be developed in Legendre polynomials. We investigate this rather general problem in the context of neutron beta decay spectrometers and study the effect of limited detector size on measured neutron decay correlation parameters. To our surprise, insufficient detector size does not affect much the accuracy of such measurements, even for rather large radii of gyration. This finding can considerably simplify the layout of the respective spectrometers.
Experiments with cold and ultracold neutrons have reached a level of precision such that problems far beyond the scale of the present Standard Model of particle physics become accessible to experimental investigation. Due to the close links between p
article physics and cosmology, these studies also permit a deep look into the very first instances of our universe. First addressed in this article, both in theory and experiment, is the problem of baryogenesis ... The question how baryogenesis could have happened is open to experimental tests, and it turns out that this problem can be curbed by the very stringent limits on an electric dipole moment of the neutron, a quantity that also has deep implications for particle physics. Then we discuss the recent spectacular observation of neutron quantization in the earths gravitational field and of resonance transitions between such gravitational energy states. These measurements, together with new evaluations of neutron scattering data, set new constraints on deviations from Newtons gravitational law at the picometer scale. Such deviations are predicted in modern theories with extra-dimensions that propose unification of the Planck scale with the scale of the Standard Model ... Another main topic is the weak-interaction parameters in various fields of physics and astrophysics that must all be derived from measured neutron decay data. Up to now, about 10 different neutron decay observables have been measured, much more than needed in the electroweak Standard Model. This allows various precise tests for new physics beyond the Standard Model, competing with or surpassing similar tests at high-energy. The review ends with a discussion of neutron and nuclear data required in the synthesis of the elements during the first three minutes and later on in stellar nucleosynthesis.
We present a case study on a new type of cold neutron beam station for the investigation of angular correlations in the beta-decay of free neutrons. With this beam station, called PERC, the active decay volume lies inside the neutron guide, and the c
harged neutron decay products are magnetically guided towards the end of the neutron guide. Hence, the guide delivers at its exit a beam of decay electrons and protons, under well-defined and precisely variable conditions, which can be well separated from the cold neutron beam. In this way a general-purpose source of neutron decay products is obtained which can be used for various different experiments in neutron decay correlation spectroscopy. A gain in phase space density of several orders of magnitude can be achieved with PERC, as compared to existing neutron decay spectrometers. Neutron beam related background is separately measurable in PERC, and magnetic mirror effects on the charged neutron decay products and edge effects in the active neutron beam volume are both strongly suppressed. Therefore the spectra and angular distributions of the emerging decay particles will be distortion-free on the level of 10^-4, more than 10 times better than achieved today.
