arXiv subjects

H. W. Wilschut

Publications and source records attributed to H. W. Wilschut.

At least 19 recordsLinked to original sources

arXiv2016

Test of Lorentz invariance in $β$ decay of polarized $^{20}\text{Na}$

We search for a dependence of the lifetime of $^{20}\text{Na}$ nuclei on the nuclear spin direction. Such a directional dependence would be evidence for Lorentz-invariance violation in weak interactions. A difference in lifetime between nuclei that are polarized in the east and west direction is searched for. This difference is maximally sensitive to the rotation of the Earth, while the sidereal dependence is free from most systematic errors. The experiment sets a limit of $2\times 10^{-4}$ at 90 % C.L. on the amplitude of the sidereal variation of the relative lifetime differences, an improvement by a factor 15 compared to an earlier result.

nucl-ex↗

arXiv2016

Question of Lorentz invariance in muon decay

Possibilities to test the Lorentz invariance of the weak interaction in muon decay are considered. We derive the direction-dependent muon-decay rate with a general Lorentz-violating addition to the W-boson propagator. We discuss measurements of the directional and boost dependence of the Michel parameters and of the muon lifetime as a function of absolute velocity. The total muon-decay rate in the Lorentz-violating Standard Model Extension is addressed. Suggestions are made for dedicated (re)analyses of the pertinent data and for future experiments.

hep-ph↗

arXiv2016

A gas cell for stopping, storing and polarizing radioactive particles

A radioactive beam of 20Na is stopped in a gas cell filled with Ne gas. The stopped particles are polarized by optical pumping. The degree of polarization that can be achieved is studied. A maximum polarization of 50% was found. The dynamic processes in the cell are described with a phenomenological model.

physics.ins-det↗

arXiv2015

Concurrent tests of Lorentz invariance in $β$-decay experiments

Modern experiments on neutron and allowed nuclear $β$ decay search for new semileptonic interactions, beyond the ``left-handed'' electroweak force. We show that ongoing and planned $β$-decay experiments, with isotopes at rest and in flight, can be exploited as sensitive tests of Lorentz invariance. The variety of correlations that involve the nuclear spin, the direction of the emitted $β$ particle, and the recoil direction of the daughter nucleus allow for relatively simple experiments that give direct bounds on Lorentz violation. The pertinent observables are decay-rate asymmetries and their dependence on sidereal time. We discuss the potential of several asymmetries that together cover a large part of the parameter space for Lorentz violation in the gauge sector. High counting statistics is required.

hep-ph↗

arXiv2015

Symmetry violations in nuclear and neutron $β$ decay

The role of $β$ decay as a low-energy probe of physics beyond the Standard Model is reviewed. Traditional searches for deviations from the Standard Model structure of the weak interaction in $β$ decay are discussed in the light of constraints from the LHC and the neutrino mass. Limits on the violation of time-reversal symmetry in $β$ decay are compared to the strong constraints from electric dipole moments. Novel searches for Lorentz symmetry breaking in the weak interaction in $β$ decay are also included, where we discuss the unique sensitivity of $β$ decay to test Lorentz invariance. We end with a roadmap for future $β$-decay experiments.

hep-ph↗

arXiv2015

Measurement of the branching ratio for beta-delayed alpha decay of 16N

While the 12C(a,g)16O reaction plays a central role in nuclear astrophysics, the cross section at energies relevant to hydrostatic helium burning is too small to be directly measured in the laboratory. The beta-delayed alpha spectrum of 16N can be used to constrain the extrapolation of the E1 component of the S-factor; however, with this approach the resulting S-factor becomes strongly correlated with the assumed beta-alpha branching ratio. We have remeasured the beta-alpha branching ratio by implanting 16N ions in a segmented Si detector and counting the number of beta-alpha decays relative to the number of implantations. Our result, 1.49(5)e-5, represents a 24% increase compared to the accepted value and implies an increase of 14% in the extrapolated S-factor.

nucl-ex↗

arXiv2015

Testing Lorentz invariance in orbital electron capture

Searches for Lorentz violation were recently extended to the weak sector, in particular neutron and nuclear $β$ decay [1]. From experiments on forbidden $β$-decay transitions strong limits in the range of $10^{-6}$-$10^{-8}$ were obtained on Lorentz-violating components of the $W$-boson propagator [2]. In order to improve on these limits strong sources have to be considered. In this Brief Report we study isotopes that undergo orbital electron capture and allow experiments at high decay rates and low dose. We derive the expressions for the Lorentz-violating differential decay rate and discuss the options for competitive experiments and their required precision.

hep-ph↗

arXiv2014

Measurement of the half-life of the T=$\frac{1}{2}$ mirror decay of $^{19}$Ne and its implication on physics beyond the standard model

The $\frac{1}{2}^+ \rightarrow \frac{1}{2}^+$ superallowed mixed mirror decay of $^{19}$Ne to $^{19}$F is excellently suited for high precision studies of the weak interaction. However, there is some disagreement on the value of the half-life. In a new measurement we have determined this quantity to be $T_{1/2}$ = $17.2832 \pm 0.0051_{(stat)}$ $\pm 0.0066_{(sys)}$ s, which differs from the previous world average by 3 standard deviations. The impact of this measurement on limits for physics beyond the standard model such as the presence of tensor currents is discussed.

nucl-ex↗

arXiv2014

Exploration of Lorentz violation in neutral-kaon decay

The KLOE collaboration recently reported bounds on the directional dependence of the lifetime of the short-lived neutral kaon $K^0_S$ with respect to the dipole anisotropy of the cosmic microwave background. We interpret their results in an effective field theory framework developed to probe the violation of Lorentz invariance in the weak interaction and previously applied to semileptonic processes, in particular $β$ decay. In this approach a general Lorentz-violating tensor $χ^{μν}$ is added to the standard propagator of the $W$ boson. We perform an exploratory study of the prospects to search for Lorentz violation in nonleptonic decays. For the kaon, we find that the sensitivity to Lorentz violation is limited by the velocity of the kaons and by the extent to which hadronic effects can be calculated. In a simple model we derive the $K^0_S$ decay rate and calculate the asymmetry for the lifetime. Using the KLOE data, limits on the values of $χ^{μν}$ are determined.

hep-ph↗

arXiv2013

Lorentz violation in neutron and allowed nuclear beta decay

We explore the possibility that the weak interaction violates Lorentz, and in particular rotational, invariance in neutron and allowed nuclear beta decay. A broad class of Lorentz-violating effects is considered, in which the standard propagator of the W-boson acquires an additional Lorentz-violating tensor. The general decay rate for allowed beta decay that incorporates such a modified propagator is derived. The resulting Lorentz-violating signals are discussed for the different types of beta-decay transitions, Fermi, Gamow-Teller, and mixed. We study the implications of our formalism for dedicated beta-decay experiments. We give a short overview of the few relevant experiments that have been performed or are ongoing.

hep-ph↗

arXiv2013

Nuclear beta decay with Lorentz violation

We consider the possibility of Lorentz-invariance violation in weak-decay processes. We present a general approach that entails modifying the W-boson propagator by adding a Lorentz-violating tensor to it. We describe the effects of Lorentz violation on nuclear beta decay in this scenario. In particular we show the expression for a first-forbidden transition with a spin change of two. Using data from an old experiment on the rotational invariance of yttrium-90, we derive several bounds on the Lorentz-violating parameters of the order of 10^(-6)-10^(-8).

hep-ph↗

arXiv2013

First Test of Lorentz Invariance in the Weak Decay of Polarized Nuclei

A new test of Lorentz invariance in the weak interactions has been made by searching for variations in the decay rate of spin-polarized 20Na nuclei. This test is unique to Gamow-Teller transitions, as was shown in the framework of a recently developed theory that assumes a Lorentz symmetry breaking background field of tensor nature. The nuclear spins were polarized in the up and down direction, putting a limit on the amplitude of sidereal variations of the form |(Γ_{up} - Γ_{down})| / (Γ_{up} + Γ_{down}) < 3 * 10^{-3}. This measurement shows a possible route toward a more detailed testing of Lorentz symmetry in weak interactions.

nucl-ex↗

arXiv2013

Limits on Lorentz violation in neutral-Kaon decay

The KLOE collaboration recently reported bounds on the directional dependence of the lifetime of the short-lived neutral kaon K_S with respect to the cosmic microwave background dipole anisotropy. We interpret their results in a general framework developed to probe Lorentz violation in the weak interaction. In this approach a Lorentz-violating tensor χ_{μν} is added to the standard propagator of the W boson. We derive the K_S decay rate in a naive tree-level model and calculate the asymmetry for the lifetime. By using the KLOE data the real vector part of χ_{μν} is found to be smaller than 10^-2. We briefly discuss the theoretical challenges concerning nonleptonic decays.

hep-ph↗

arXiv2013

Limits on Lorentz violation from forbidden beta decays

Forbidden (slow) beta decays offer new opportunities to test the invariance of the weak interaction under Lorentz transformations. Within a general effective field theory framework we analyze and reinterpret the only two relevant experiments, performed in the 1970s, dedicated to search for a preferred direction in space in first- and second-forbidden beta decays. We show that the results of these experiments put strong and unique limits on Lorentz violation, and in particular on the presence of several interactions in the modern Lorentz-violating Standard Model extension. We discuss prospects to improve on these limits.

hep-ph↗

arXiv2013

A new approach to test Lorentz invariance

Lorentz invariance in the weak interaction has been tested rather poorly compared to the electromagnetic interaction. In this work we show which tests on the weak interaction should be considered. We focus on one particular test that explores the spin degree of freedom in β decay. To connect various phenomenological tests of Lorentz invariance in the weak interaction, we exploit a new theoretical model that may provide a framework that relates the different tests.

nucl-ex↗

arXiv2011

Isotope Shifts of the $6d\,^2$D$_{3/2}\,$ - $7p\,^2$P$_{1/2}\,$ Transition in Trapped Short-Lived $^{209-214}$Ra$^+$

Laser spectroscopy of short-lived radium isotopes in a linear Paul trap has been performed. The isotope shifts of the $6d\,^2$D$_{3/2}\,$ - $7p\,^2$P$_{1/2}\,$ transition in $^{209-214}$Ra$^+$ were measured, which are sensitive to the short range part of the atomic wavefunctions. The results are essential experimental input for improving the precision of atomic structure calculation. This is indispensable for parity violation in Ra$^+$ aiming at the determination of the weak mixing angle.

physics.atom-ph↗

arXiv2011

Radium single-ion optical clock

We explore the potential of the electric quadrupole transitions $7s\,^2S_{1/2}$ - $6d\,^2D_{3/2}$, $6d\,^2D_{5/2}$ in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive $^A$Ra$^+$ candidates with $A=$ 223 - 229 are identified. In particular, we show that the transition $7s\,^2S_{1/2}\,(F=2,m_F=0)$ - $6d\,^2D_{3/2}\,(F=0,m_F=0)$ at 828 nm in $^{223}$Ra$^+$, with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of $10^{-17}$. With more experimental effort, the $^{223,225,226}$Ra$^+$ clocks could be pushed to a projected performance reaching the $10^{-18}$ level.

physics.atom-ph↗

arXiv2010

Emission patterns of neutral pions in 40 A MeV Ta+Au reactions

Differential cross sections of neutral pions emitted in 181Ta + 197Au collisions at a beam energy of 39.5A MeV have been measured with the photon spectrometer TAPS. The kinetic energy and transverse momentum spectra of neutral pions cannot be properly described in the framework of the thermal model, nor when the reabsorption of pions is accounted for in a phenomenological model. However, high energy and high momentum tails of the pion spectra can be well fitted through thermal distributions with unexpectedly soft temperature parameters below 10 MeV.

nucl-ex↗