Mixing the stimulus list in bilingual lexical decision turns cognate facilitation effects into mirrored inhibition effects

To test the BIA+ and Multilink models’ accounts of how bilinguals process words with different degrees of cross-linguistic orthographic and semantic overlap, we conducted two experiments manipulating stimulus list composition. Dutch-English late bilinguals performed two English lexical decision tasks including the same set of cognates, interlingual homographs, English control words, and pseudowords. In one task, half of the pseudowords were replaced with Dutch words, requiring a ‘no’ response. This change from pure to mixed language list context was found to turn cognate facilitation effects into inhibition. Relative to control words, larger effects were found for cognate pairs with an increasing cross-linguistic form overlap. Identical cognates produced considerably larger effects than non-identical cognates, supporting their special status in the bilingual lexicon. Response patterns for different item types are accounted for in terms of the items’ lexical representation and their binding to ‘yes’ and ‘no’ responses in pure vs mixed lexical decision

Ft\mathcal{F}t values of the mirror β transitions and the weak-magnetism-induced current in allowed nuclear β decay

The precision of correlation measurements in neutron and nuclear β decay has now reached the level of about 1% and better. At this level of precision, higher-order corrections such as recoil-order corrections induced by the strong interaction and radiative corrections cannot necessarily be neglected anymore. We provide here an update of the $\mathcal{F}t$ values of the isospin T = 1/2 mirror β decays including the neutron, of interest to determine the V$_{ud}$ quark-mixing matrix element. We also provide an overview of current experimental and theoretical knowledge of the most important recoil term, weak magnetism, for both these mirror β decays and a large set of β decays in higher isospin multiplets. The matrix elements determining weak magnetism were calculated in the nuclear shell model and cross-checked against experimental data, showing overall good agreement. We show that the neutron and the mirror nuclei now effectively contribute to the value of V$_{ud}$, but we also stress the need for further work on the radiative correction $\Delta_{R}^{V}$. Our results provide new insight into the size of weak magnetism, extending the available information to nuclei with masses up to A = 75. This provides important guidance for planning and improved sensitivity for interpreting correlation measurements in searches for new physics or to extract V$_{ud}$ in mirror β decays. It can also be of interest for further theoretical work related to the reactor neutrino problem

A first extraction of the weak magnetism form factor and Fierz interference term from the 114^{114}In →\rightarrow114^{114}Sn Gamow-Teller transition

International audienceSpectrum shape measurements in nuclear $\beta$ decay can be used to test physics beyond the Standard Model with results being complementary to high-energy collider experiments. In particular, Beyond Standard Model sensitivity of the weak interaction is expressed through the so-called Fierz interference term. Additionally, the $\beta$ spectrum shape is a useful tool to probe Standard Model effects, among which the most prominent is \textit{weak magnetism}, a higher-order recoil correction induced by nuclear pion exchange. To study effects in the $\beta$ spectrum shape at a precision level competitive with the LHC, a new spectrometer was designed and built. It consists of a 3D low-pressure gas electron tracker and a plastic scintillator used for triggering the data acquisition and recording the $\beta$ particle energy. In this Letter, the results from $\beta$ spectrum shape measurements on the allowed Gamow-Teller transition $^{114}\text{In} \rightarrow ^{114}\text{Sn}$ are presented, including a first extraction of the weak magnetism form factor in the high nuclear mass range and a new estimate of the $90\%$ confidence interval for the Fierz interference term

A first extraction of the weak magnetism form factor and Fierz interference term from the 114^{114}In →\rightarrow114^{114}Sn Gamow-Teller transition

International audienceSpectrum shape measurements in nuclear $\beta$ decay can be used to test physics beyond the Standard Model with results being complementary to high-energy collider experiments. In particular, Beyond Standard Model sensitivity of the weak interaction is expressed through the so-called Fierz interference term. Additionally, the $\beta$ spectrum shape is a useful tool to probe Standard Model effects, among which the most prominent is \textit{weak magnetism}, a higher-order recoil correction induced by nuclear pion exchange. To study effects in the $\beta$ spectrum shape at a precision level competitive with the LHC, a new spectrometer was designed and built. It consists of a 3D low-pressure gas electron tracker and a plastic scintillator used for triggering the data acquisition and recording the $\beta$ particle energy. In this Letter, the results from $\beta$ spectrum shape measurements on the allowed Gamow-Teller transition $^{114}\text{In} \rightarrow ^{114}\text{Sn}$ are presented, including a first extraction of the weak magnetism form factor in the high nuclear mass range and a new estimate of the $90\%$ confidence interval for the Fierz interference term

Beta spectrum shape measurements using a multi-wire drift chamber and a plastic scintillator

Spectrum shape measurements in nuclear $\beta$ decay are a versatile observable. They can be used to test physics beyond the Standard Model with results being complementary to high energy collider experiments. In addition, the $\beta$ spectrum shape is a useful tool to probe Standard Model effects. One of those effects is called Weak Magnetism and is induced by QCD interactions between quarks in the nucleon. In order to study effects on the order of $10^{-3} - 10^{-2}$ in the $\beta$ spectrum shape, a new prototype spectrometer, named miniBETA, was designed and built. It consists of a 3D low-pressure gas tracker, i.e. a multi-wire drift chamber with hexagonal cells, and a plastic scintillator for triggering the data acquisition and recording the $\beta$ particle energy. Results of the miniBETA spectrometer characterization, supported by Monte Carlo simulations in Geant4 and Garfield++, are reported here. In addition, the preliminary results from $\beta$ spectrum shape measurements on the allowed Gamow-Teller transition $^{114}\textrm{In}\rightarrow ^{114}\textrm{Sn}$ are presented, including an extraction of the Weak Magnetism form factor

WISArD : Weak Interaction Studies with 32^{32}Ar Decay

International audienceThe WISArD experiment is probing the possible existence of exotic currents in the electroweak sector using nuclear $\beta$ decay, to improve the constraints on beyond Standard Model physics. The setup of the experiment underwent a full upgrade between 2018 and 2021 in preparation of a second run of data taking at ISOLDE, CERN, scheduled for October 2021. The detector stage was completely renewed to improve statistics and minimize the main systematic effects identified in a proof-of-principle run in 2018. With this upgrade, the objective is to reach the per-mil level of uncertainty on the angular correlation coefficent $a$ and on the Fierz interference term $b$, in a pure Fermi transition. In this case, both parameters are directly sensitive to the possible contribution of exotic scalar currents