G. Konrad

Impact of Neutron Decay Experiments on non-Standard Model Physics

This paper gives a brief overview of the present and expected future limits on physics beyond the Standard Model (SM) from neutron beta decay, which is described by two parameters only within the SM. Since more than two observables are accessible, the problem is over-determined. Thus, precise measurements of correlations in neutron decay can be used to study the SM as well to search for evidence of possible extensions to it. Of particular interest in this context are the search for right-handed currents or for scalar and tensor interactions. Precision measurements of neutron decay observables address important open questions of particle physics and cosmology, and are generally complementary to direct searches for new physics beyond the SM in high-energy physics. Free neutron decay is therefore a very active field, with a number of new measurements underway worldwide. We present the impact of recent developments.

Neutron Decay with PERC: a Progress Report

The PERC collaboration will perform high-precision measurements of angular correlations in neutron beta decay at the beam facility MEPHISTO of the Forschungs-Neutronenquelle Heinz Maier-Leibnitz in Munich, Germany. The new beam station PERC, a clean, bright, and versatile source of neutron decay products, is designed to improve the sensitivity of neutron decay studies by one order of magnitude. The charged decay products are collected by a strong longitudinal magnetic field directly from inside a neutron guide. This combination provides the highest phase space density of decay products. A magnetic mirror serves to perform precise cuts in phase space, reducing related systematic errors. The new instrument PERC is under development by an international collaboration. The physics motivation, sensitivity, and applications of PERC as well as the status of the design and preliminary results on uncertainties in proton spectroscopy are presented in this paper.

Cold and Ultra-cold Neutrons as Probes of New Physics

Despite the great success of the Standard Model, many key questions in particle physics, astrophysics, and cosmology are unanswered. In particular, more than 95% of the universe consists of unknown dark matter and dark energy. Today, a major goal of particle physics is to look for evidence of new physics beyond the Standard Model. Collider searches for new physics are well suited to the direct production of new high-mass particles, whereas low-energy precision experiments search for traces that new particles leave in known processes. Direct and indirect evidence of new physics are highly complementary. High-precision experiments with extremely slow, cold and ultra-cold neutrons address some of the unanswered questions, for instance, on the nature of the fundamental forces and underlying symmetries, the origin, evolution, and fate of the universe, or on the nature of the gravitational force at very small distances. For example, the limit on the electric dipole moment of the neutron constrains the CP violating phases, the lifetime of the neutron determines the relative helium abundance in the universe, and neutrons bouncing over a mirror probe dark matter and dark energy. New facilities and technological developments now give window for significant improvement in precision by one to two orders of magnitude. In this paper, we will give an overview of current and planned facilities and experiments, as well as an overview of some of the applications of neutrons to astrophysics, cosmology, and physics beyond the Standard Model.

NoMoS: Beyond the Standard Model Physics in Neutron Decay

The newly established New Frontiers Group ’NoMoS: Beyond the Standard Model Physics in Neutron Decay’ of the Austrian Academy of Sciences aims to search for traces of new physics in neutron beta decay with novel experimental techniques. The NoMoS group is hosted at the Stefan-Meyer-Institute for Subatomic Physics in Vienna. Precision measurements in neutron decay allow searching for physics beyond the Standard Model of particle physics. An accuracy of 10−4 in the observables corresponds to energy scales of 1−100 TeV for new particles and interactions. In order to achieve this accuracy, a new experimental technique is developed: R×B spectroscopy. An R×B spectrometer measures the momentum of charged particles by their drift in a circular magnetic field. This new, accurate method of spectroscopy will be applied to determine several correlation coefficients in neutron decay. The construction of the first R×B spectrometer, NoMoS, is part of the New Frontiers Group. For measurements at ultimate statistics, the R×B spectrometer will be installed at PERC, a new facility at the FRM II in Garching/Germany that collects electrons and protons from a large neutron decay volume. A final goal is to measure or to set limits on the Fierz interference term. This term is forbidden in the Standard Model and has not yet been measured with neutrons. A non-zero value would indicate that yet unknown charged Higgs bosons, sleptons, or leptoquarks were exchanged instead of the Standard Model W boson. Besides the physics motivation, the measurement concept and physics programme of NoMoS are presented in this paper.

The Proton Spectrum in Neutron Beta Decay: First Results with the aSPECT spectrometer

First measurements with the aSPECT spectrometer have been performed in a beam time at the beam line MEPHISTO of the neutron research reactor FRM‐II. In this paper we give a short description of the spectrometer. The data analysis is still underway.