arXiv subjects

K. M. Heeger

Publications and source records attributed to K. M. Heeger.

At least 109 records · Page 6Linked to original sources

arXiv2018

First Results from CUORE: A Search for Lepton Number Violation via $0νββ$ Decay of $^{130}$Te

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: $^{130}$Te neutrinoless double-beta decay. Examining a total TeO$_2$ exposure of 86.3 kg$\cdot$yr, characterized by an effective energy resolution of (7.7 $\pm$ 0.5) keV FWHM and a background in the region of interest of (0.014 $\pm$ 0.002) counts/(keV$\cdot$kg$\cdot$yr), we find no evidence for neutrinoless double-beta decay. The median statistical sensitivity of this search is $7.0\times10^{24}$ yr. Including systematic uncertainties, we place a lower limit on the decay half-life of $T^{0ν}_{1/2}$($^{130}$Te) > $1.3\times 10^{25}$ yr (90% C.L.). Combining this result with those of two earlier experiments, Cuoricino and CUORE-0, we find $T^{0ν}_{1/2}$($^{130}$Te) > $1.5\times 10^{25}$ 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 $m_{ββ}<(110 - 520)$ meV, where the range reflects the nuclear matrix element estimates employed.

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arXiv2018

Cosmogenic neutron production at Daya Bay

Neutrons produced by cosmic ray muons are an important background for underground experiments studying neutrino oscillations, neutrinoless double beta decay, dark matter, and other rare-event signals. A measurement of the neutron yield in the three different experimental halls of the Daya Bay Reactor Neutrino Experiment at varying depth is reported. The neutron yield in Daya Bay's liquid scintillator is measured to be $Y_n=(10.26\pm 0.86)\times 10^{-5}$, $(10.22\pm 0.87)\times 10^{-5}$, and $(17.03\pm 1.22)\times 10^{-5}~μ^{-1}~$g$^{-1}~$cm$^2$ at depths of 250, 265, and 860 meters-water-equivalent. These results are compared to other measurements and the simulated neutron yield in Fluka and Geant4. A global fit including the Daya Bay measurements yields a power law coefficient of $0.77 \pm 0.03$ for the dependence of the neutron yield on muon energy.

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arXiv2018

Study of Rare Nuclear Processes with CUORE

TeO2 bolometers have been used for many years to search for neutrinoless double beta decay in 130-Te. CUORE, a tonne-scale TeO2 detector array, recently published the most sensitive limit on the half-life, $T_{1/2}^{0ν} > 1.5 \times 10^{25}\,$yr, which corresponds to an upper bound of $140-400$~meV on the effective Majorana mass of the neutrino. While it makes CUORE a world-leading experiment looking for neutrinoless double beta decay, it is not the only study that CUORE will contribute to in the field of nuclear and particle physics. As already done over the years with many small-scale experiments, CUORE will investigate both rare decays (such as the two-neutrino double beta decay of 130-Te and the hypothesized electron capture in 123-Te), and rare processes (e.g., dark matter and axion interactions). This paper describes some of the achievements of past experiments that used TeO2 bolometers, and perspectives for CUORE.

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arXiv2018

Seasonal Variation of the Underground Cosmic Muon Flux Observed at Daya Bay

The Daya Bay Experiment consists of eight identically designed detectors located in three underground experimental halls named as EH1, EH2, EH3, with 250, 265 and 860 meters of water equivalent vertical overburden, respectively. Cosmic muon events have been recorded over a two-year period. The underground muon rate is observed to be positively correlated with the effective atmospheric temperature and to follow a seasonal modulation pattern. The correlation coefficient $α$, describing how a variation in the muon rate relates to a variation in the effective atmospheric temperature, is found to be $α_{\text{EH1}} = 0.362\pm0.031$, $α_{\text{EH2}} = 0.433\pm0.038$ and $α_{\text{EH3}} = 0.641\pm0.057$ for each experimental hall.

physics.ins-det↗

arXiv2017

Low Energy Analysis Techniques for CUORE

CUORE is a tonne-scale cryogenic detector operating at the Laboratori Nazionali del Gran Sasso (LNGS) that uses tellurium dioxide bolometers to search for neutrinoless double-beta decay of $^{130}$Te. CUORE is also suitable to search for low energy rare events such as solar axions or WIMP scattering, thanks to its ultra-low background and large target mass. However, to conduct such sensitive searches requires improving the energy threshold to 10 keV. In this paper, we describe the analysis techniques developed for the low energy analysis of CUORE-like detectors, using the data acquired from November 2013 to March 2015 by CUORE-0, a single-tower prototype designed to validate the assembly procedure and new cleaning techniques of CUORE. We explain the energy threshold optimization, continuous monitoring of the trigger efficiency, data and event selection, and energy calibration at low energies in detail. We also present the low energy background spectrum of CUORE-0 below 60keV. Finally, we report the sensitivity of CUORE to WIMP annual modulation using the CUORE-0 energy threshold and background, as well as an estimate of the uncertainty on the nuclear quenching factor from nuclear recoils in CUORE-0.

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arXiv2017

Search for Neutrinoless $β^{+}\hspace{-0.2em}EC$ Decay of $^{120}$Te with CUORE-0

We have performed a search for neutrinoless $β^{+}\hspace{-0.2em}EC$ decay of $^{120}$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 $T_{1/2}>1.6\cdot10^{21}$ yr at $90\%$ CI. Combining this with results from Cuoricino, a predecessor experiment, we obtain the strongest limit to date, corresponding to $T_{1/2}>2.7\cdot10^{21}$ yr at $90\%$ CI.

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arXiv2017

The projected background for the CUORE experiment

The Cryogenic Underground Observatory for Rare Events (CUORE) is designed to search for neutrinoless double beta decay of 130Te with an array of 988 TeO2 bolometers operating at temperatures around 10 mK. The experiment is currently being commissioned in Hall A of Laboratori Nazionali del Gran Sasso, Italy. The goal of CUORE is to reach a 90\% C.L. exclusion sensitivity on the \tect decay half-life of 9$\times$10$^{25}$ years after 5\,years of data taking. The main issue to be addressed to accomplish this aim is the rate of background events in the region of interest, which must not be higher than 10$^{-2}$\,counts/keV/kg/y. We developed a detailed Monte Carlo simulation, based on results from a campaign of material screening, radioassays, and bolometric measurements, to evaluate the expected background. This was used over the years to guide the construction strategies of the experiment and we use it here to project a background model for CUORE. In this paper we report the results of our study and our expectations for the background rate in the energy region where the peak signature of neutrinoless double beta decay of 130Te is expected.

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arXiv2017

CUORE Sensitivity to $0νββ$ Decay

We report a study of the CUORE sensitivity to neutrinoless double beta ($0νββ$) decay. We used a Bayesian analysis based on a toy Monte Carlo (MC) approach to extract the exclusion sensitivity to the $0νββ$ decay half-life ($T_{1/2}^{0ν}$) at $90\%$ credibility interval (CI) -- i.e. the interval containing the true value of $T_{1/2}^{0ν}$ with $90\%$ probability -- and the $3 σ$ discovery sensitivity. We consider various background levels and energy resolutions, and describe the influence of the data division in subsets with different background levels. If the background level and the energy resolution meet the expectation, CUORE will reach a $90\%$ CI exclusion sensitivity of $2\cdot10^{25}$ yr with $3$ months, and $9\cdot10^{25}$ yr with $5$ years of live time. Under the same conditions, the discovery sensitivity after $3$ months and $5$ years will be $7\cdot10^{24}$ yr and $4\cdot10^{25}$ yr, respectively.

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arXiv2017

Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay

The Daya Bay experiment has observed correlations between reactor core fuel evolution and changes in the reactor antineutrino flux and energy spectrum. Four antineutrino detectors in two experimental halls were used to identify 2.2 million inverse beta decays (IBDs) over 1230 days spanning multiple fuel cycles for each of six 2.9 GW$_{\textrm{th}}$ reactor cores at the Daya Bay and Ling Ao nuclear power plants. Using detector data spanning effective $^{239}$Pu fission fractions, $F_{239}$, from 0.25 to 0.35, Daya Bay measures an average IBD yield, $\barσ_f$, of $(5.90 \pm 0.13) \times 10^{-43}$ cm$^2$/fission and a fuel-dependent variation in the IBD yield, $dσ_f/dF_{239}$, of $(-1.86 \pm 0.18) \times 10^{-43}$ cm$^2$/fission. This observation rejects the hypothesis of a constant antineutrino flux as a function of the $^{239}$Pu fission fraction at 10 standard deviations. The variation in IBD yield was found to be energy-dependent, rejecting the hypothesis of a constant antineutrino energy spectrum at 5.1 standard deviations. While measurements of the evolution in the IBD spectrum show general agreement with predictions from recent reactor models, the measured evolution in total IBD yield disagrees with recent predictions at 3.1$σ$. This discrepancy indicates that an overall deficit in measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes $^{235}$U, $^{239}$Pu, $^{238}$U, and $^{241}$Pu. Based on measured IBD yield variations, yields of $(6.17 \pm 0.17)$ and $(4.27 \pm 0.26) \times 10^{-43}$ cm$^2$/fission have been determined for the two dominant fission parent isotopes $^{235}$U and $^{239}$Pu. A 7.8% discrepancy between the observed and predicted $^{235}$U yield suggests that this isotope may be the primary contributor to the reactor antineutrino anomaly.

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arXiv2017

First search for a dark matter annual modulation signal with NaI(Tl) in the Southern Hemisphere by DM-Ice17

We present the first search for a dark matter annual modulation signal in the Southern Hemisphere conducted with NaI(Tl) detectors, performed by the DM-Ice17 experiment. Nuclear recoils from dark matter interactions are expected to yield an annually modulated signal independent of location within the Earth's hemispheres. DM-Ice17, the first step in the DM-Ice experimental program, consists of 17 kg of NaI(Tl) located at the South Pole under 2200 m.w.e. overburden of Antarctic glacial ice. Taken over 3.6 years for a total exposure of 60.8 kg yr, DM-Ice17 data are consistent with no modulation in the energy range of 4-20 keV, providing the strongest limits on weakly interacting massive particle dark matter from a direct detection experiment located in the Southern Hemisphere. The successful deployment and stable long-term operation of DM-Ice17 establishes the South Pole ice as a viable location for future dark matter searches and in particular for a high-sensitivity NaI(Tl) dark matter experiment to directly test the DAMA/LIBRA claim of the observation of dark matter.

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arXiv2017

Measurement of the Two-Neutrino Double Beta Decay Half-life of $^{130}$Te with the CUORE-0 Experiment

We report on the measurement of the two-neutrino double beta decay half-life of $^{130}$Te with the CUORE-0 detector. From an exposure of 33.4 kg$\cdot$y of TeO$_2$, the half-life is determined to be $T_{1/2}^{2ν}$ = [8.2 $\pm$ 0.2 (stat.) $\pm$ 0.6 (syst.)] $\times$ 10$^{20}$y. This result is obtained after a detailed reconstruction of the sources responsible for the CUORE-0 counting rate, with a specific study of those contributing to the $^{130}$Te neutrinoless double beta decay region of interest.

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arXiv2017

Improved Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay

A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9~GW$_{\mathrm{th}}$ nuclear reactors and detected by eight antineutrino detectors deployed in two near (560~m and 600~m flux-weighted baselines) and one far (1640~m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be $0.946\pm0.020$ ($0.992\pm0.021$) for the Huber+Mueller (ILL+Vogel) model. A 2.9~$σ$ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4-6~MeV was found in the measured spectrum, with a local significance of 4.4~$σ$. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.

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arXiv2016

The CUORE and CUORE-0 experiments at LNGS

The Cryogenic Underground Observatory for Rare Events (CUORE) is a 1-ton scale bolometric experiment devoted to the search of the neutrinoless double-beta decay (0ν\b{eta}\b{eta}) in 130Te. The CUORE detector consists of an array of 988 TeO2 crystals operated at 10 mK. CUORE-0 is the CUORE demonstrator: it has been built to test the performance of the upcoming CUORE experiment and represents the largest 130Te bolometric setup ever operated. CUORE-0 has been running at Laboratori Nazionali del Gran Sasso (Italy) from 2013 to 2015. The final CUORE-0 analysis on 0ν\b{eta}\b{eta} and the corresponding detector performance are presented. The present status of the CUORE experiment, now in its final construction and commissioning phase, are discussed. The results from assembly of the detector and the commissioning of the cryostat are reported.

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arXiv2016

The detector calibration system for the CUORE cryogenic bolometer array

The Cryogenic Underground Observatory for Rare Events (CUORE) is a ton-scale cryogenic experiment designed to search for neutrinoless double-beta decay of $^{130}$Te and other rare events. The CUORE detector consists of 988 TeO$_2$ bolometers operated underground at 10 mK in a dilution refrigerator at the Laboratori Nazionali del Gran Sasso. Candidate events are identified through a precise measurement of their energy. The absolute energy response of the detectors is established by the regular calibration of each individual bolometer using gamma sources. The close-packed configuration of the CUORE bolometer array combined with the extensive shielding surrounding the detectors requires the placement of calibration sources within the array itself. The CUORE Detector Calibration System is designed to insert radioactive sources into and remove them from the cryostat while respecting the stringent heat load, radiopurity, and operational requirements of the experiment. This paper describes the design, commissioning, and performance of this novel source calibration deployment system for ultra-low-temperature environments.

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arXiv2016

Limits on Active to Sterile Neutrino Oscillations from Disappearance Searches in the MINOS, Daya Bay, and Bugey-3 Experiments

Searches for a light sterile neutrino have been performed independently by the MINOS and the Daya Bay experiments using the muon (anti)neutrino and electron antineutrino disappearance channels, respectively. In this Letter, results from both experiments are combined with those from the Bugey-3 reactor neutrino experiment to constrain oscillations into light sterile neutrinos. The three experiments are sensitive to complementary regions of parameter space, enabling the combined analysis to probe regions allowed by the LSND and MiniBooNE experiments in a minimally extended four-neutrino flavor framework. Stringent limits on $\sin^2 2θ_{μe}$ are set over 6 orders of magnitude in the sterile mass-squared splitting $Δm^2_{41}$. The sterile-neutrino mixing phase space allowed by the LSND and MiniBooNE experiments is excluded for $Δm^2_{41} < 0.8$ eV$^2$ at 95% CL$_s$.

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arXiv2016

Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment

A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GW$_{\rm th}$ nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of $\overlineν_{e}$'s. Comparison of the $\overlineν_{e}$ rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors ($\sim$1500-1950 m) relative to detectors near the reactors ($\sim$350-600 m) allowed a precise measurement of $\overlineν_{e}$ disappearance. More than 2.5 million $\overlineν_{e}$ inverse beta decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (Dec. 2011--Jul. 2012) with a subsequent 1013 days using the complete configuration of eight detectors (Oct. 2012--Jul. 2015). The $\overlineν_{e}$ rate observed at the far detectors relative to the near detectors showed a significant deficit, $R=0.949 \pm 0.002(\mathrm{stat.}) \pm 0.002(\mathrm{syst.})$. The energy dependence of $\overlineν_{e}$ disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle $\sin^22θ_{13}=0.0841 \pm 0.0027(\mathrm{stat.}) \pm 0.0019(\mathrm{syst.})$ and the effective neutrino mass-squared difference of $\left|Δm^2_{\mathrm{ee}}\right|=(2.50 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$. Analysis using the exact three-flavor probability found $Δm^2_{32}=(2.45 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$ assuming the normal neutrino mass hierarchy and $Δm^2_{32}=(-2.56 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$ for the inverted hierarchy.

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arXiv2016

Improved Search for a Light Sterile Neutrino with the Full Configuration of the Daya Bay Experiment

This Letter reports an improved search for light sterile neutrino mixing in the electron antineutrino disappearance channel with the full configuration of the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data collected in eight antineutrino detectors, this search benefits from 3.6 times the statistics available to the previous publication, as well as from improvements in energy calibration and background reduction. A relative comparison of the rate and energy spectrum of reactor antineutrinos in the three experimental halls yields no evidence of sterile neutrino mixing in the $2\times10^{-4} \lesssim |Δm^{2}_{41}| \lesssim 0.3$ eV$^{2}$ mass range. The resulting limits on $\sin^{2}2θ_{14}$ are improved by approximately a factor of 2 over previous results and constitute the most stringent constraints to date in the $|Δm^{2}_{41}| \lesssim 0.2$ eV$^{2}$ region.

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arXiv2016

Study of the wave packet treatment of neutrino oscillation at Daya Bay

The disappearance of reactor $\barν_e$ observed by the Daya Bay experiment is examined in the framework of a model in which the neutrino is described by a wave packet with a relative intrinsic momentum dispersion $σ_\text{rel}$. Three pairs of nuclear reactors and eight antineutrino detectors, each with good energy resolution, distributed among three experimental halls, supply a high-statistics sample of $\barν_e$ acquired at nine different baselines. This provides a unique platform to test the effects which arise from the wave packet treatment of neutrino oscillation. The modified survival probability formula was used to fit Daya Bay data, providing the first experimental limits: $2.38 \cdot 10^{-17} < σ_{\rm rel} < 0.23$. Treating the dimensions of the reactor cores and detectors as constraints, the limits are improved: $10^{-14} \lesssim σ_{\rm rel} < 0.23$, and an upper limit of $σ_{\rm rel} <0.20$ is obtained. All limits correspond to a 95\% C.L. Furthermore, the effect due to the wave packet nature of neutrino oscillation is found to be insignificant for reactor antineutrinos detected by the Daya Bay experiment thus ensuring an unbiased measurement of the oscillation parameters $\sin^22θ_{13}$ and $Δm^2_{32}$ within the plane wave model.

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