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تسجيل مستخدم جديدMeasurement of the half-life of the T=$frac{1}{2}$ mirror decay of $^{19}$Ne and its implication on physics beyond the standard model
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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.
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The half-life of $^{19}$Ne has been measured using a real-time digital multiparametric acquisition system providing an accurate time-stamp and relevant information on the detectors signals for each decay event. An exhaustive offline analysis of the d
ata gave unique access to experimental effects potentially biasing the measurement. After establishing the influence factors impacting the measurement such as after-pulses, pile-up, gain and base line fluctuations, their effects were accurately estimated and the event selection optimized. The resulting half-life, $17.2569pm0.0019_{(stat)}pm0.0009_{(syst)}$~s, is the most precise up to now for $^{19}$Ne. It is found in agreement with two recent precise measurements and not consistent with the most recent one [L.J. Broussard {it et al.}, Phys. Rev. Lett. {bf112}, 212301 (2014)] by 3.0 standard deviations. The full potential of the technique for nuclei with half-lives of a few seconds is discussed.
The half-life of the neutron-rich nuclide, {fesixty} has been in dispute in recent years. A measurement in 2009 published a value of $(2.62 pm 0.04)times10^{6}$ years, almost twice that of the previously accepted value from 1984 of $(1.49 pm 0.27)tim
es10^{6}$ years. This longer half-life was confirmed in 2015 by a second measurement, resulting in a value of $(2.50 pm 0.12)times10^{6}$ years. All three half-life measurements used the grow-in of the $gamma$-ray lines in { isixty} from the decay of the ground state of $^{60}text{Co}$ (t$_{1/2}$=5.27 years) to determine the activity of a sample with a known number of {fesixty} atoms. In contrast, the work presented here measured the {fesixty} activity directly via the 58.6 keV $gamma$-ray line from the short-lived isomeric state of $^{60}text{Co}$ (t$_{1/2}$=10.5 minutes), thus being independent of any possible contamination from long-lived $^{60text{g}}text{Co}$. A fraction of the material from the 2015 experiment with a known number of {fesixty} atoms was used for the activity measurement, resulting in a half-life value of $(2.72 pm 0.16)times10^{6}$ years, confirming again the longer half-life. In addition, {fesixty}/{fe} isotopic ratios of samples with two different dilutions of this material were measured with Accelerator Mass Spectrometry (AMS) to determine the number of {fesixty} atoms. Combining this with our activity measurement resulted in a half-life value of $(2.69 pm 0.28)times 10^{6}$ years, again agreeing with the longer half-life.
We measured two-neutrino double beta decay of $^{130}$Te using an exposure of 300.7 kg$cdot$yr accumulated with the CUORE detector. Using a Bayesian analysis to fit simulated spectra to experimental data, it was possible to disentangle all the major
background sources and precisely measure the two-neutrino contribution. The half-life is in agreement with past measurements with a strongly reduced uncertainty: $T^{2 u}_{1/2} = 7.71^{+0.08}_{-0.06}mathrm{(stat.)}^{+0.12}_{-0.15}mathrm{(syst.)}times10^{20}$ yr. This measurement is the most precise determination of the $^{130}$Te 2$ ubetabeta$ decay half-life to date.
The half-life of the $^{20}$F ground state has been measured using a radioactive beam implanted in a plastic scintillator and recording $betagamma$ coincidences together with four CsI(Na) detectors. The result, $T_{1/2} = 11.0011(69)_{rm stat}(30)_{r
m sys}$~s, is at variance by 17 combined standard deviations with the two most precise results. The present value revives the poor consistency of results for this half-life and calls for a new measurement, with a technique having different sources of systematic effects, to clarify the discrepancy.
The half-life of tsups{37}K has been measured to be $1.23651(94)~mathrm{s}$, a value nearly an order of magnitude more precise than the best previously reported. The $beta^+$ decay of tsups{37}K occurs mainly via a superallowed branch to the ground-s
tate of its $T=1/2$ mirror, tsups{37}Ar. This transition has been used recently, together with similar transitions from four other nuclei, as an alternative test of CVC and method for determining $V_{ud}$, but the precision of its $ft$ value was limited by the relatively large half-life uncertainty. Our result corrects that situation. Another motivation for improving the $ft$ value was to determine the standard-model prediction for the $beta$-decay correlation parameters, which will be compared to those currently being measured by the trinat{} collaboration at triumf. The new $ft$ value, $4605(8)~mathrm{s}$, is now limited in precision by the $97.99(14)%$ ground-state branching ratio.
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