Free Neutron Beta Decay Research Articles

A flexible data acquisition system architecture for the Nab experiment

The Nab experiment will measure the electron–neutrino correlation and Fierz interference term in free neutron beta decay to test the Standard Model and probe Beyond the Standard Model physics. Using National Instrument’s PXIe-5171 Reconfigurable Oscilloscope module, we have developed a data acquisition system that is not only capable of meeting Nab’s specifications, but flexible enough to be adapted in situ as the experimental environment dictates. The L1 and L2 trigger logic can be reconfigured to optimize the system for coincidence event detection at runtime through configuration files and LabVIEW controls. This system is capable of identifying L1 triggers at a rate of at least 1MHz, while reading out a peak signal rate of approximately 2GB/s. During the commissioning phase of the experiment, the system ran at a sustained readout rate of 400MB/s of detector signal data originating from roughly 6kHz L2 triggers, well within the peak performance of the system.

About a Test of the Relativity Principle in a Free Neutron Beta-Decay

About a Test of the Relativity Principle in a Free Neutron Beta-Decay

Study of neutron beta decay with the Nab experiment

The current three sigma tension in the unitarity test of the Cabbibo-Kobayashi-Maskawa (CKM) matrix is a notable problem with the Standard Model of elementary particle physics. A long-standing goal of the study of free neutron beta decay is to better determine the CKM element Vud through measurements of the neutron lifetime and a decay correlation parameter. The Nab collaboration intends to measure a, the neutrino-electron correlation, with accuracy sufficient for a competitive evaluation of Vud based on neutron decay data alone. This paper gives a status report and an outlook.

The Nab experiment: A precision measurement of unpolarized neutron beta decay

Neutron beta decay is one of the most fundamental processes in nuclear physics and provides sensitive means to uncover the details of the weak interaction. Neutron beta decay can evaluate the ratio of axial-vector to vector coupling constants in the standard model, λ = gA/gV, through multiple decay correlations. The Nab experiment will carry out measurements of the electron-neutrino correlation parameter a with a precision of δa/a = 10−3 and the Fierz interference term b to δb = 3 × 10−3 in unpolarized free neutron beta decay. These results, along with a more precise measurement of the neutron lifetime, aim to deliver an independent determination of the ratio λ with a precision of δλ/λ = 0.03% that will allow an evaluation of Vud and sensitively test CKM unitarity, independent of nuclear models. Nab utilizes a novel, long asymmetric spectrometer that guides the decay electron and proton to two large area silicon detectors in order to precisely determine the electron energy and an estimation of the proton momentum from the proton time of flight. The Nab spectrometer is being commissioned at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source at Oak Ridge National Lab. We present an overview of the Nab experiment and recent updates on the spectrometer, analysis, and systematic effects.

NoMoS: AnR × Bdrift momentum spectrometer for beta decay studies

The beta decay of the free neutron provides several probes to test the Standard Model of particle physics as well as to search for extensions thereof. Hence, multiple experiments investigating the decay have already been performed, are under way or are being prepared. These measure the mean lifetime, angular correlation coefficients or various spectra of the charged decay products (proton and electron). NoMoS, theneutron decay productsmo___mentumspectrometer, presents a novel method of momentum spectroscopy: it utilizes theR×Bdrift effect to disperse charged particles dependent on their momentum in an uniformly curved magnetic field. This spectrometer is designed to precisely measure momentum spectra and angular correlation coefficients in free neutron beta decay to test the Standard Model and to search for new physics beyond. With NoMoS, we aim to measure inter alia the electron-antineutrino correlation coefficientaand the Fierz interference termbwith an ultimate precision of Δa/a< 0.3% and Δb< 10−3respectively. In this paper, we present the measurement principles, discuss measurement uncertainties and systematics, and give a status update.

New precision measurements of free neutron beta decay with cold neutrons

Precision measurements in free neutron beta decay serve to determine the coupling constants of beta decay, and offer several stringent tests of the standard model. This paper describes the free neutron beta decay program planned for the Fundamental Physics Beamline at the Spallation Neutron Source at Oak Ridge National Laboratory, and puts it into the context of other recent and planned measurements of neutron beta decay observables.

Physics Beyond Standard Model in Neutron Beta Decay

Limits from neutron beta decay on parameters describing physics beyond the Standard Model are presented. New Physics is described by the most general Lorentz invariant effective Hamiltonian involving vector, scalar and tensor operators and Standard Model fields only. Two-parameter fits to the decay parameters measured in free neutron beta decay have been done, in some cases indicating rather big dependence of the results on g_A/g_V ratio of nucleon form factors at zero four-momentum transfer.

High precision corrections to the neutron beta decay rate and electron asymmetry and current determination of Vud

The goal of the present analysis is to find, in the free neutron beta decay, the expressions for the decay rate and the electron asymmetry that contain all the theoretical effects at the 10−4 level. This accuracy is better than the current experimental precision that modern experiments allow. For this aim it is necessary to study the strong interaction effects, the radiative corrections and the recoil of the proton. A conceptual problem that we discuss in detail is the Fermi function additivity. The model dependence in the radiative corrections yields important effects which must be incorporated. We show that this is the only source of uncertainty that is out of control still at the mentioned order. As an application, we compare the values of the CKM matrix element |Vud | from this decay with the values both from the superallowed Fermi transition beta decays and the unitarity of the CKM matrix. We discuss the relevance of the observed discrepancies.

THE ELECTRON–ANTINEUTRINO ANGULAR CORRELATION IN FREE NEUTRON DECAY

Free neutron beta decay is the simplest nuclear beta decay and the prototype charged-current semileptonic decay. It has some theoretical advantage over other nuclear decay systems in that there are no nuclear structure corrections, and it is the only mixed Fermi/Gamow–Teller beta decay for which the relative matrix elements can be directly calculated. The status of the electron–antineutrino angular correlation (a-coefficient) in neutron beta decay and its role in elucidating fundamental properties of the weak interaction are reviewed, with an emphasis on experiments. A new generation of experiments intended to reduce the uncertainty in the a-coefficient to less than 1% is described.

A method for an improved measurement of the electron–antineutrino correlation in free neutron beta decay

The angular correlation between the beta electron and antineutrino in nuclear beta decay is characterized by the dimensionless parameter a . The value of a for free neutron decay, when combined with other neutron decay parameters, can be used to determine the weak vector and axial vector coupling constants g V and g A and test the validity and self-consistency of the Electroweak Standard Model. Previous experiments that measured a in neutron decay relied on precise proton spectroscopy and were limited by systematic effects at about the 5% level. We present a new approach to measuring a for which systematic uncertainties promise to be much smaller.

New limit on T violation in free neutron decay

Time reversal invariance violation beyond the Standard model mechanism can be tested in free neutron beta decay. The triple correlation between neutron spin and the momenta of electron and antineutrino ( D coefficient) tests T violating phases in non-standard couplings. We present a new preliminary limit for this correlation which was obtained by the Trine experiment: D preliminary = (−3.1 ± 6.2 stat ± 4.7 syststat) · 10 −4.

Possible contribution of an intermediate-leptoquark-boson mechanism to free-neutron beta decay

A possible mechanism of the virtual intermediate-scalar-leptoquark-boson exchange associated with the contribution of right-handed nucleon currents to free-neutron beta decay is demonstrated. The hypothesis can be extended by considering the realization of the same mechanism in beta decay via the emission of right-handed neutrinos (left-handed antineutrinos). It is shown that a hypothesis of this kind leads to the appearance of scalar and tensor terms in the effective Hamiltonian of weak interaction and that these terms include the right-handed neutrinos. Relevant experimental data are discussed.

A method for precise neutron beam polarisation analysis using an opaque spin filter

Free neutron beta decay provides sensitive tests of the Standard Model of electroweak interaction. A particular class of experiments has now reached a limit set by the imperfect knowledge of the neutron polarisation and of the efficiency of a spin flipper. Standard techniques of polarisation analysis reach a precision of ≥0.25%. In a recent experiment it was shown that an accuracy on the level of a few times 10 −4 can be reached within a classical scheme of polarisation analysis, using an opaque spin filter as analyser. In this letter a new scheme is given which takes advantage of a natural degree of freedom of spin filters, resulting in a more sensitive and simpler measurement of neutron polarisation and flipper efficiency.

Tests of the standard model with free neutron beta decay

I review recent measurements of neutron beta decay data. Implications of these measurements for CVC, the unitarity of the KM matrix, SU(3) flavour symmetry, right-handed currents, solar physics and big bang cosmology are investigated.

Particle physics with slow neutrons at the institute Laue-Langevin

We give an overview over the particle and fundamental physics program at the European High Flux Reactor of the Institut Max von Laue-Paul Langevin at Grenoble, France. The experiments on neutron-antineutron oscillations, the neutron electric dipole moment, and on free neutron beta decay are reviewed in more detail.