We investigate the influence of a strong laser electromagnetic field on the α-decay rate by using the Hennenberger frame of reference. We introduce an adimensional parameter D=S_{0}/R_{0}, where ...R_{0} is the geometrical nuclear radius and S_{0}∼sqrtI/ω^{2} is a length parameter depending on the laser intensity I and frequency ω. We show that the barrier penetrability has a strong increase for intensities corresponding to D>D_{crit}=1, due to the fact that the resulting Coulomb potential becomes strongly anisotropic even for spherical nuclei. As a consequence, the contribution of the monopole term increases the barrier penetrability by 2 orders of magnitude, while the total contribution has an effect of 6 orders of magnitude at D∼3D_{crit}. In the case of deformed nuclei, the electromagnetic field increases the penetrability by an additional order of magnitude for a quadrupole deformation β_{2}∼0.3. The influence of the electromagnetic field can be expressed in terms of a shifted Geiger-Nuttal law by a term depending on S_{0} and deformation.
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We show that the current search for Lorentz invariance violation (LIV) in the summed energy spectra of electrons in 2νββ decay can be extended by investigating the single electron spectra and the ...angular correlation between the emitted electrons. We derive and calculate the LIV contributions to these spectra associated with the isotropic part of the countershaded operator and controlled through the coefficient ∘a(3)of and discuss possible signatures that may be probed in experiments. First, we show that some distortion occurs in the single electron spectrum, maximal at small electron energies. Then, we show that other LIV effects may be highlighted by analyzing the angular correlation spectra and the ratio between the Standard Model extension electron spectra and their Standard Model forms. We found that these LIV signatures depend on the magnitude of ∘a(3)of, manifest differently for positive and negative values of this coefficient, and become more pronounced as the electron energy approaches the Q value. Finally, we propose an alternative, new method to constrain ∘a(3)of through the measurement of the angular correlation coefficient. Using this method, and considering only statistical uncertainties, we obtain bounds of ∘a(3)of at the level of present ones, obtained from summed energy spectra. We show that future experiments can improve these limits significantly. Our study is performed for 100Mo, but the results hold qualitatively for other nuclei that undergo a double-beta decay. We hope our results will provide additional motivation for the LIV analyses performed in DBD experiments.
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A
bstract
A search for the
K
+
→
π
+
X
decay, where
X
is a long-lived feebly interacting particle, is performed through an interpretation of the
K
+
→
π
+
ν
ν
¯
analysis of data collected in 2017 by ...the NA62 experiment at CERN. Two ranges of
X
masses, 0–110 MeV
/c
2
and 154–260 MeV
/c
2
, and lifetimes above 100 ps are considered. The limits set on the branching ratio, BR(
K
+
→
π
+
X
), are competitive with previously reported searches in the first mass range, and improve on current limits in the second mass range by more than an order of magnitude.
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