Projected sensitivity of the LUX-ZEPLIN experiment to the two-neutrino and neutrinoless double $\ensuremath{\beta}$ decays of $^{134}\mathrm{Xe}$

Projected sensitivity of the LUX-ZEPLIN experiment to the two-neutrino and neutrinoless double $β$ decays of ${}^{134}{Xe}$

D. S. Akerib et al. (The LUX-ZEPLIN Collaboration)

Phys. Rev. C 104, 065501 – Published 10 December 2021

Abstract

The projected sensitivity of the LUX-ZEPLIN (LZ) experiment to two-neutrino and neutrinoless double $β$ decay of ${}^{134}{Xe}$ is presented. LZ is a 10-tonne xenon time-projection chamber optimized for the detection of dark matter particles and is expected to start operating in 2021 at Sanford Underground Research Facility, USA. Its large mass of natural xenon provides an exceptional opportunity to search for the double $β$ decay of ${}^{134}{Xe}$ , for which xenon detectors enriched in ${}^{136}{Xe}$ are less effective. For the two-neutrino decay mode, LZ is predicted to exclude values of the half-life up to $1.7 \times 10^{24}$ years at 90% confidence level (CL) and has a three-sigma observation potential of $8.7 \times 10^{23}$ years, approaching the predictions of nuclear models. For the neutrinoless decay mode LZ, is projected to exclude values of the half-life up to $7.3 \times 10^{24}$ years at 90% CL.

Received 19 May 2021
Accepted 19 November 2021

DOI:https://doi.org/10.1103/PhysRevC.104.065501

Physics Subject Headings (PhySH)

Double beta decay Neutrinoless double beta decay

90 ≤ A ≤ 149

Spectrometers & spectroscopic techniques

Nuclear PhysicsParticles & Fields

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Vol. 104, Iss. 6 — December 2021

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Figure 1
Cutaway view of the LZ experiment.
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Figure 2
(top left) Sensitivity to $T_{1 / 2}^{2 ν}$ of ${}^{134}{Xe}$ as a function of $r$ , for $z_{\min} = 25$ cm and $z_{\max} = 125$ cm. (top right) Sensitivity to $T_{1 / 2}^{2 ν}$ of ${}^{134}{Xe}$ as a function of $z_{\min}$ and $z_{\max}$ , for $r = 68.8$ cm. (bottom left) Sensitivity to $T_{1 / 2}^{0 ν}$ of ${}^{134}{Xe}$ as a function of $r$ , with $z_{\min} = 25$ cm and $z_{\max} = 125$ cm. (bottom right) Sensitivity to $T_{1 / 2}^{0 ν}$ of ${}^{134}{Xe}$ as a function of $z_{\min}$ and $z_{\max}$ , for $r = 65$ cm.
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Figure 3
(left) Sensitivity to the $2 ν 2 β$ decay of ${}^{134}{Xe}$ as a function of the live time of the detector (black), along with the respective statistical uncertainty at $1 σ$ (green band). The horizontal lines show the predictions for IBM-2 [7], assuming $g_{A} = 1.269$ (continuous blue) and $g_{A} = 1$ (dashed blue), and QRPA [8] (dotted red). The current best limit, set by EXO-200 [9], is $8.7 \times 10^{20}$ years at 90% CL, and therefore lies below the minimum of the vertical axis. (right) Sensitivity to the $0 ν 2 β$ decay of ${}^{134}{Xe}$ as a function of the live time of the detector (black), along with the respective statistical uncertainty at $1 σ$ (green band). The horizontal line (blue) shows the current best limit, set by EXO-200 [9].
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Figure 4
Energy spectra of the $2 ν 2 β$ (left) and $0 ν 2 β$ (right) decays of ${}^{134}{Xe}$ , along with those of the background categories described in Sec. 3. In each case the signal assumes the respective 90% CL half-life obtained in this study. The spectra were obtained using the event selection described in Sec. 5 along with the respective optimal FV found in Sec. 6. The curves show the signal (continuous light gray) and the total background (continuous dark gray), along with the partial contributions from the $2 ν 2 β$ decay of ${}^{136}{Xe}$ (dashed red), solar neutrinos (dotted green), the $β$ decay of ${}^{85}{Kr}$ (dashed orange), the decay chains of ${}^{222}{Rn}$ (continuous blue) and ${}^{220}{Rn}$ (continuous cyan), and $γ$ rays from the contamination in the detector components and the cavern walls (magenta).
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Figure 5
Dependence of the sensitivity to the $2 ν 2 β$ decay of ${}^{134}{Xe}$ with the level of ${}^{85}{Kr}$ contamination in LXe (left), and dependence of the sensitivity to the $0 ν 2 β$ decay of ${}^{134}{Xe}$ with the energy resolution at $Q = 825.8$ keV (right). The gray dashed line indicates the values assumed in this work, namely 0.3 ppt g/g ${}^{nat}{Kr / Xe}$ and 1.62%, respectively.
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Figure 6
Dependence of the sensitivity to the $2 ν 2 β$ (left) and $0 ν 2 β$ (right) decays of ${}^{134}{Xe}$ with the isotopic abundance of ${}^{136}{Xe}$ . The gray dashed line indicates the natural isotopic abundance of ${}^{136}{Xe}$ , namely, 8.87%.
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Physical Review C

covering nuclear physics

Projected sensitivity of the LUX-ZEPLIN experiment to the two-neutrino and neutrinoless double $β$ decays of ${}^{134}{Xe}$

D. S. Akerib et al. (The LUX-ZEPLIN Collaboration)

Phys. Rev. C 104, 065501 – Published 10 December 2021

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Physical Review C

covering nuclear physics

Projected sensitivity of the LUX-ZEPLIN experiment to the two-neutrino and neutrinoless double β decays of Xe134

D. S. Akerib et al. (The LUX-ZEPLIN Collaboration)

Phys. Rev. C 104, 065501 – Published 10 December 2021

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Projected sensitivity of the LUX-ZEPLIN experiment to the two-neutrino and neutrinoless double $β$ decays of ${}^{134}{Xe}$