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تسجيل مستخدم جديدNeutrinoless Double Beta Decay with Germanium Detectors: 10$^{26}$ yr and Beyond
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In the global landscape of neutrinoless double beta ($0 ubetabeta$) decay search, the use of semiconductor germanium detectors provides many advantages. The excellent energy resolution, the negligible intrinsic radioactive contamination, the possibility of enriching the crystals up to 88% in the $^{76}$Ge isotope as well as the high detection efficiency, are all key ingredients for highly sensitive $0 ubetabeta$ decay search. The MAJORANA and GERDA experiments successfully implemented the use of germanium (Ge) semiconductor detectors, reaching an energy resolution of $2.53 pm 0.08$ keV at the Q$_{betabeta}$ and an unprecedented low background level of $5.2 times 10^{-4}$ cts/(keV$cdot$kg$cdot$yr), respectively. In this paper, we will review the path of $0 ubetabeta$ decay search with Ge detectors from the original idea of E. Fiorini et al. in 1967, to the final recent results of the GERDA experiment setting a limit on the half-life of $^{76}$Ge $0 ubetabeta$ decay at $T_{1/2} > 1.8 times 10^{26}$ yr (90% C.L.). We will then present the LEGEND project designed to reach a sensitivity to the half-life up to $10^{28}$ yr and beyond, opening the way to the exploration of the normal ordering region.
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The nEXO neutrinoless double beta decay experiment is designed to use a time projection chamber and 5000 kg of isotopically enriched liquid xenon to search for the decay in $^{136}$Xe. Progress in the detector design, paired with higher fidelity in i
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nation of the novel experimental design, the careful material selection for radio-purity and the active/passive shielding techniques result in a very low residual background at the Q-value of the decay, about 1e-3 counts/(keV kg yr). This makes GERDA the first experiment in the field to be background-free for the complete design exposure of 100 kg yr. A search for neutrinoless double beta decay was performed with a total exposure of 47.7 kg yr: 23.2 kg yr come from the second phase (Phase II) of the experiment, in which the background is reduced by about a factor of ten with respect to the previous phase. The analysis presented in this paper includes 12.4 kg yr of new Phase II data. No evidence for a possible signal is found: the lower limit for the half-life of Ge76 is 8.0e25 yr at 90% CL. The experimental median sensitivity is 5.8e25 yr. The experiment is currently taking data. As it is running in a background-free regime, its sensitivity grows linearly with exposure and it is expected to surpass 1e26 yr within 2018.
The Gerda experiment designed to search for the neutrinoless double beta decay in 76Ge has successfully completed the first data collection. No signal excess is found, and a lower limit on the half life of the process is set, with T1/2 > 2.1x10^25 yr
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