Search

We report the results of a search for neutrinoless double-beta decay in a 9.8 kg yr exposure of ${}^{130}\mathrm{Te}$ using a bolometric detector array, CUORE-0. The characteristic detector energy resolution and background level in the region of interest are $5.1\pm 0.3\mathrm{keV}$ FWHM and $0.058\pm 0.004(\text{stat})\pm 0.002(\text{syst})\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$, respectively. The median 90% C.L. lower-limit half-life sensitivity of the experiment is $2.9\times {10}^{24}\mathrm{yr}$ and surpasses the sensitivity of previous searches. We find no evidence for neutrinoless double-beta decay of ${}^{130}\mathrm{Te}$ and place a Bayesian lower bound on the decay half-life, $T_{1/2}^{0\nu }>2.7\times {10}^{24}\mathrm{yr}$ at 90% C.L. Combining CUORE-0 data with the 19.75 kg yr exposure of ${}^{130}\mathrm{Te}$ from the Cuoricino experiment we obtain $T_{1/2}^{0\nu }>4.0\times {10}^{24}\mathrm{yr}$ at 90% C.L. (Bayesian), the most stringent limit to date on this half-life. Using a range of nuclear matrix element estimates we interpret this as a limit on the effective Majorana neutrino mass, $m_{\beta \beta }<270–760\mathrm{meV}$.

The LUX-ZEPLIN (LZ) experiment is a dark matter detector centered on a dual-phase xenon time projection chamber. We report searches for new physics appearing through few-keV-scale electron recoils, using the experiment’s first exposure of 60 live days and a fiducial mass of 5.5 t. The data are found to be consistent with a background-only hypothesis, and limits are set on models for new physics including solar axion electron coupling, solar neutrino magnetic moment and millicharge, and electron couplings to galactic axionlike particles and hidden photons. Similar limits are set on weakly interacting massive particle (WIMP) dark matter producing signals through ionized atomic states from the Migdal effect.

The LUX-ZEPLIN (LZ) experiment is a dual-phase xenon time project chamber operating in the Sanford Underground Research Facility in South Dakota, USA. We report on the results of a relativistic extension to the nonrelativistic effective field theory (NREFT) from a 5.5 t fiducial mass and 60 live days of exposure. We present constraints on couplings from covariant interactions arising from the coupling of vector, axial currents, and electric dipole moments of the nucleon to the magnetic and electric dipole moments of the weakly interacting massive particle which cannot be described by recasting previous results described by an NREFT. Using a profile-likelihood ratio analysis, in an energy region between $0{\mathrm{keV}}_{\mathrm{nr}}$ to $270{\mathrm{keV}}_{\mathrm{nr}}$, we report 90% confidence level exclusion limits on the coupling strength of five interactions in both the isoscalar and isovector bases.

We report results of a search for nuclear recoils induced by weakly interacting massive particle (WIMP) dark matter using the LUX-ZEPLIN (LZ) two-phase xenon time projection chamber. This analysis uses a total exposure of $4.2\pm 0.1$ tonne-years from 280 live days of LZ operation, of which $3.3\pm 0.1$ tonne-years and 220 live days are new. A technique to actively tag background electronic recoils from ${}^{214}\mathrm{Pb}$ $\beta$ decays is featured for the first time. Enhanced electron-ion recombination is observed in two-neutrino double electron capture decays of ${}^{124}\mathrm{Xe}$, representing a noteworthy new background. After removal of artificial signal-like events injected into the dataset to mitigate analyzer bias, we find no evidence for an excess over expected backgrounds. World-leading constraints are placed on spin-independent (SI) and spin-dependent WIMP-nucleon cross sections for masses $\ge 9\mathrm{GeV}/c^2$. The strongest SI exclusion set is $2.2\times {10}^{-48}{\mathrm{cm}}^2$ at the 90% confidence level and the best SI median sensitivity achieved is $5.1\times {10}^{-48}{\mathrm{cm}}^2$, both for a mass of $40\mathrm{GeV}/c^2$.

Dark matter lighter than $10\mathrm{GeV}/c^2$ encompasses a promising range of candidates. A conceptual design for a new detector, DarkSide-LowMass, is presented, based on the DarkSide-50 detector and progress toward DarkSide-20k, optimized for a low-threshold electron-counting measurement. Sensitivity to light dark matter is explored for various potential energy thresholds and background rates. These studies show that DarkSide-LowMass can achieve sensitivity to light dark matter down to the solar neutrino fog for GeV-scale masses and significant sensitivity down to $10\mathrm{MeV}/c^2$ considering the Migdal effect or interactions with electrons. Requirements for optimizing the detector’s sensitivity are explored, as are potential sensitivity gains from modeling and mitigating spurious electron backgrounds that may dominate the signal at the lowest energies.

The CUORE experiment, a ton-scale cryogenic bolometer array, recently began operation at the Laboratori Nazionali del Gran Sasso in Italy. The array represents a significant advancement in this technology, and in this work we apply it for the first time to a high-sensitivity search for a lepton-number-violating process: ${}^{130}\mathrm{Te}$ neutrinoless double-beta decay. Examining a total ${\mathrm{TeO}}_2$ exposure of 86.3 kg yr, characterized by an effective energy resolution of $(7.7\pm 0.5)\mathrm{keV}$ FWHM and a background in the region of interest of $(0.014\pm 0.002)\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$, we find no evidence for neutrinoless double-beta decay. Including systematic uncertainties, we place a lower limit on the decay half-life of $T_{1/2}^{0\nu }({}^{130}\mathrm{Te})>1.3\times {10}^{25}\mathrm{yr}$ (90% C.L.); the median statistical sensitivity of this search is $7.0\times {10}^{24}\mathrm{yr}$. Combining this result with those of two earlier experiments, Cuoricino and CUORE-0, we find $T_{1/2}^{0\nu }({}^{130}\mathrm{Te})>1.5\times {10}^{25}\mathrm{yr}$ (90% C.L.), which is the most stringent limit to date on this decay. Interpreting this result as a limit on the effective Majorana neutrino mass, we find $m_{\beta \beta }<(110-520)\mathrm{meV}$, where the range reflects the nuclear matrix element estimates employed.

Searches for dark matter with liquid xenon time projection chamber experiments have traditionally focused on the region of the parameter space that is characteristic of weakly interacting massive particles, ranging from a few $\mathrm{GeV}/c^2$ to a few $\mathrm{TeV}/c^2$. Models of dark matter with a mass much heavier than this are well motivated by early production mechanisms different from the standard thermal freeze-out, but they have generally been less explored experimentally. In this work, we present a reanalysis of the first science run of the LZ experiment, with an exposure of $0.9\text{tonne}\times \mathrm{yr}$, to search for ultraheavy particle dark matter. The signal topology consists of multiple energy deposits in the active region of the detector forming a straight line, from which the velocity of the incoming particle can be reconstructed on an event-by-event basis. Zero events with this topology were observed after applying the data selection calibrated on a simulated sample of signal-like events. New experimental constraints are derived, which rule out previously unexplored regions of the dark matter parameter space of spin-independent interactions beyond a mass of ${10}^{17}\mathrm{GeV}/c^2$.

Following the first science results of the LUX-ZEPLIN (LZ) experiment, a dual-phase xenon time projection chamber operating from the Sanford Underground Research Facility in Lead, South Dakota, USA, we report the initial limits on a model-independent nonrelativistic effective field theory describing the complete set of possible interactions of a weakly interacting massive particle (WIMP) with a nucleon. These results utilize the same 5.5 t fiducial mass and 60 live days of exposure collected for the LZ spin-independent and spin-dependent analyses while extending the upper limit of the energy region of interest by a factor of 7.5 to 270 keV. No significant excess in this high energy region is observed. Using a profile-likelihood ratio analysis, we report 90% confidence level exclusion limits on the coupling of each individual nonrelativistic WIMP-nucleon operator for both elastic and inelastic interactions in the isoscalar and isovector bases.

We report results from searches for new physics models through electron recoils using data collected by the LUX-ZEPLIN experiment during its first two science runs, with a total exposure of $4.2\mathrm{tonne}\text{−}\mathrm{years}$. The observed data are consistent with a background-only hypothesis. Constraints are derived for electromagnetic interactions of solar neutrinos, solar axionlike particles (ALPs), mirror dark matter, and the absorption of bosonic dark matter candidates. The inverse Primakoff process for ${}^{57}\mathrm{Fe}$ deexcitation solar ALPs is considered for the first time. These results represent the most stringent constraints to date on keV-scale Primakoff and ${}^{57}\mathrm{Fe}$ solar ALPs, bosonic dark matter, mirror dark matter, and neutrino millicharge, while remaining competitive for the other signal models investigated.

We have performed a search for neutrinoless ${\beta }^{{}^{+}}\text{EC}$ decay of ${}^{120}\mathrm{Te}$ using the final CUORE-0 data release. We describe a new analysis method for the simultaneous fit of signatures with different event topology, and of data subsets with different signal efficiency, obtaining a limit on the half-life of the decay of $T_{1/2}>1.6\times {10}^{21}$ yr at $90\%$ credibility interval (CI). Combining this with results from Cuoricino, a predecessor experiment, we obtain the strongest limit to date, corresponding to $T_{1/2}>2.7\times {10}^{21}$ yr at $90\%$ CI.

Dark matter detection experiments using liquid argon rely on a precise characterization of the ionization response to nuclear recoils, especially in the keV energy range relevant for light dark matter interactions. In this work, we present a comprehensive analysis that combines new measurements from the ReD setup, part of the DarkSide experimental program, with calibration data from DarkSide-50, as well as results from the ARIS and SCENE experiments. These combined datasets enable improved constraints on atomic screening effects in the modeling of the ionization response of liquid argon to nuclear recoils. The analysis is performed within the Thomas-Imel recombination framework adopted in previous DarkSide studies, and is here further constrained by the inclusion of ReD data, which allow the screening function to be determined from calibration measurements. By including the updated ionization model into the DarkSide-50 analysis framework, we obtain stronger exclusion limits on low-mass weakly interacting massive particle (WIMP) interactions, setting new world-leading constraints in the $1–3\mathrm{GeV}/{\mathrm{c}}^2$ WIMP mass range. Finally, we recast the sensitivity projections for the upcoming DarkSide-20k detector, demonstrating a significantly enhanced discovery potential for low-mass dark matter candidates.

LUX-ZEPLIN is a dark matter detector expected to obtain world-leading sensitivity to weakly-interacting massive particles interacting via nuclear recoils with a $\sim 7$-tonne xenon target mass. This paper presents sensitivity projections to several low-energy signals of the complementary electron recoil signal type: 1) an effective neutrino magnetic moment, and 2) an effective neutrino millicharge, both for $pp$-chain solar neutrinos, 3) an axion flux generated by the Sun, 4) axionlike particles forming the Galactic dark matter, 5) hidden photons, 6) mirror dark matter, and 7) leptophilic dark matter. World-leading sensitivities are expected in each case, a result of the large 5.6 t 1000 d exposure and low expected rate of electron-recoil backgrounds in the $<100\mathrm{keV}$ energy regime. A consistent signal generation, background model and profile-likelihood analysis framework is used throughout.

The projected sensitivity of the LUX-ZEPLIN (LZ) experiment to two-neutrino and neutrinoless double $\beta$ decay of ${}^{134}\mathrm{Xe}$ 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 $\beta$ decay of ${}^{134}\mathrm{Xe}$, for which xenon detectors enriched in ${}^{136}\mathrm{Xe}$ 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.

Electron-capture decays of ${}^{125}\mathrm{Xe}$ and ${}^{127}\mathrm{Xe}$, and double-electron-capture decays of ${}^{124}\mathrm{Xe}$, are backgrounds in searches for weakly interacting massive particles (WIMPs) conducted by dual-phase xenon time projection chambers such as LUX-ZEPLIN (LZ). These decays produce signals with more light and less charge than equivalent-energy $\beta$ decays and correspondingly overlap more with WIMP signals. We measure three electron-capture charge yields in LZ: the 1.1 keV M-shell, 5.2 keV L-shell, and 33.2 keV K-shell at drift fields of 193 and $96.5\mathrm{V}/\mathrm{cm}$. The LL double-electron-capture decay of ${}^{124}\mathrm{Xe}$ exhibits even more pronounced shifts in charge and light. We provide a first model of double-electron-capture charge yields using the link between ionization density and electron-ion recombination, and identify a need for more accurate calculations. Finally, we discuss the implications of the reduced charge yield of these decays and other interactions creating inner-shell vacancies for future dark matter searches.

We describe in detail the methods used to obtain the lower bound on the lifetime of neutrinoless double-beta ($0\nu \beta \beta$) decay in ${}^{130}\mathrm{Te}$ and the associated limit on the effective Majorana mass of the neutrino using the CUORE-0 detector. CUORE-0 is a bolometric detector array located at the Laboratori Nazionali del Gran Sasso that was designed to validate the background reduction techniques developed for CUORE, a next-generation experiment scheduled to come online in 2016. CUORE-0 is also a competitive $0\nu \beta \beta$ decay search in its own right and functions as a platform to further develop the analysis tools and procedures to be used in CUORE. These include data collection, event selection and processing, as well as an evaluation of signal efficiency. In particular, we describe the amplitude evaluation, thermal gain stabilization, energy calibration methods, and the analysis event selection used to create our final $0\nu \beta \beta$ search spectrum. We define our high level analysis procedures, with emphasis on the new insights gained and challenges encountered. We outline in detail our fitting methods near the hypothesized $0\nu \beta \beta$ decay peak and catalog the main sources of systematic uncertainty. Finally, we derive the $0\nu \beta \beta$ decay half-life limits previously reported for CUORE-0, $T_{1/2}^{0\nu }>2.7\times {10}^{24}\mathrm{yr}$, and in combination with the Cuoricino limit, $T_{1/2}^{0\nu }>4.0\times {10}^{24}\mathrm{yr}$.

We estimate the amount of ${}^{37}\mathrm{Ar}$ produced in natural xenon via cosmic-ray-induced spallation, an inevitable consequence of the transportation and storage of xenon on the Earth’s surface. We then calculate the resulting ${}^{37}\mathrm{Ar}$ concentration in a 10-tonne payload (similar to that of the LUX-ZEPLIN experiment) assuming a representative schedule of xenon purification, storage, and delivery to the underground facility. Using the spallation model by Silberberg and Tsao, the sea-level production rate of ${}^{37}\mathrm{Ar}$ in natural xenon is estimated to be $0.024\mathrm{atoms}/\mathrm{kg}/\mathrm{day}$. Assuming the xenon is successively purified to remove radioactive contaminants in 1-tonne batches at a rate of $1\mathrm{tonne}/\mathrm{month}$, the average ${}^{37}\mathrm{Ar}$ activity after 10 tons are purified and transported underground is $0.058-0.090\mu \mathrm{Bq}/\mathrm{kg}$, depending on the degree of argon removal during above-ground purification. Such cosmogenic ${}^{37}\mathrm{Ar}$ will appear as a noticeable background in the early science data, while decaying with a 35-day half-life. This newly noticed production mechanism of ${}^{37}\mathrm{Ar}$ should be considered when planning for future liquid-xenon-based experiments.

While dual-phase xenon time projection chambers have driven the sensitivity toward weakly interacting massive particles at the $\mathrm{GeV}/c^2$ to $\mathrm{TeV}/c^2$ mass scale, the scope for sub-$\mathrm{GeV}/c^2$ dark matter particles is hindered by a limited nuclear recoil energy detection threshold. One approach to probe for lighter candidates is to consider cases where they have been boosted by collisions with cosmic rays in the Milky Way, such that the additional kinetic energy lifts their induced signatures above the nominal threshold. In this Letter, we report first results of a search for cosmic ray-boosted dark matter (CRDM) with a combined $4.2\mathrm{metric}\mathrm{ton}/\mathrm{yr}$ exposure from the LUX-ZEPLIN experiment. We observe no excess above the expected backgrounds and establish world-leading constraints on the spin-independent CRDM-nucleon cross section as small as $3.9\times {10}^{-33}{\mathrm{cm}}^2$ at 90% confidence level for sub-$\mathrm{GeV}/c^2$ masses.

We report on a search for millicharged particles (mCPs) produced in cosmic ray atmospheric interactions using data collected during the first science run of the LUX-ZEPLIN experiment. The mCPs produced by two processes—meson decay and proton bremsstrahlung—are considered in this study. This search utilized a novel signature unique to liquid xenon (LXe) time projection chambers, allowing sensitivity to mCPs with masses ranging from 10 to $1000\mathrm{MeV}/{\mathrm{c}}^2$ and fractional charges between 0.001 and 0.02 of the electron charge ($e$). With an exposure of 60 live days and a 5.5 metric ton fiducial mass, we observed no significant excess over background. This represents the first experimental search for atmospheric mCPs and the first search for mCPs using an underground LXe experiment.

The LUX-ZEPLIN experiment recently reported limits on WIMP-nucleus interactions from its initial science run, down to $9.2\times {10}^{-48}{\mathrm{cm}}^2$ for the spin-independent interaction of a $36\mathrm{GeV}/{\mathrm{c}}^2$ WIMP at 90% confidence level. In this paper, we present a comprehensive analysis of the backgrounds important for this result and for other upcoming physics analyses, including neutrinoless double-beta decay searches and effective field theory interpretations of LUX-ZEPLIN data. We confirm that the in-situ determinations of bulk and fixed radioactive backgrounds are consistent with expectations from the ex-situ assays. The observed background rate after WIMP search criteria were applied was $(6.3\pm 0.5)\times {10}^{-5}\mathrm{events}/{\mathrm{keV}}_{ee}/\mathrm{kg}/\mathrm{day}$ in the low-energy region, approximately 60 times lower than the equivalent rate reported by the LUX experiment.

The LUX-ZEPLIN experiment is a dark matter detector centered on a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility in Lead, South Dakota, USA. This Letter reports results from LUX-ZEPLIN’s first search for weakly interacting massive particles (WIMPs) with an exposure of 60 live days using a fiducial mass of 5.5 t. A profile-likelihood ratio analysis shows the data to be consistent with a background-only hypothesis, setting new limits on spin-independent WIMP-nucleon, spin-dependent WIMP-neutron, and spin-dependent WIMP-proton cross sections for WIMP masses above $9\mathrm{GeV}/{\mathrm{c}}^2$. The most stringent limit is set for spin-independent scattering at $36\mathrm{GeV}/{\mathrm{c}}^2$, rejecting cross sections above $9.2\times {10}^{-48}{\mathrm{cm}}^2$ at the 90% confidence level.