arXiv subjects

C. J. Davis

Publications and source records attributed to C. J. Davis.

At least 37 records · Page 2Linked to original sources

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.

physics.ins-det↗

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.

nucl-ex↗

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.

physics.ins-det↗

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.

physics.ins-det↗

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.

nucl-ex↗

arXiv2017

The JCMT Gould Belt Survey: A First Look at IC 5146

We present 450 and 850 micron submillimetre continuum observations of the IC5146 star-forming region taken as part of the JCMT Gould Belt Survey. We investigate the location of bright submillimetre (clumped) emission with the larger-scale molecular cloud through comparison with extinction maps, and find that these denser structures correlate with higher cloud column density. Ninety-six individual submillimetre clumps are identified using FellWalker and their physical properties are examined. These clumps are found to be relatively massive, ranging from 0.5to 116 MSun with a mean mass of 8 MSun and a median mass of 3.7 MSun. A stability analysis for the clumps suggest that the majority are (thermally) Jeans stable, with M/M_J < 1. We further compare the locations of known protostars with the observed submillimetre emission, finding that younger protostars, i.e., Class 0 and I sources, are strongly correlated with submillimetre peaks and that the clumps with protostars are among the most Jeans unstable. Finally, we contrast the evolutionary conditions in the two major star-forming regions within IC5146: the young cluster associated with the Cocoon Nebula and the more distributed star formation associated with the Northern Streamer filaments. The Cocoon Nebula appears to have converted a higher fraction of its mass into dense clumps and protostars, the clumps are more likely to be Jeans unstable, and a larger fraction of these remaining clumps contain embedded protostars. The Northern Streamer, however, has a larger number of clumps in total and a larger fraction of the known protostars are still embedded within these clumps.

astro-ph.GA↗

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.

physics.ins-det↗

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.

physics.ins-det↗

arXiv2016

The disappearing act: A dusty wind eclipsing RW Aur

RW Aur is a young binary star that experienced a deep dimming in 2010-11 in component A and a second even deeper dimming from summer 2014 to summer 2016. We present new unresolved multi-band photometry during the 2014-16 eclipse, new emission line spectroscopy before and during the dimming, archive infrared photometry between 2014-15, as well as an overview of literature data. Spectral observations were carried out with the Fibre-fed RObotic Dual-beam Optical Spectrograph on the Liverpool Telescope. Photometric monitoring was done with the Las Cumbres Observatory Global Telescope Network and James Gregory Telescope. Our photometry shows that RW Aur dropped in brightness to R = 12.5 in March 2016. In addition to the long-term dimming trend, RW Aur is variable on time scales as short as hours. The short-term variation is most likely due to an unstable accretion flow. This, combined with the presence of accretion-related emission lines in the spectra suggest that accretion flows in the binary system are at least partially visible during the eclipse. The equivalent width of [O I] increases by a factor of ten in 2014, coinciding with the dimming event, confirming previous reports. The blue-shifted part of the $Hα$ profile is suppressed during the eclipse. In combination with the increase in mid-infrared brightness during the eclipse reported in the literature and seen in WISE archival data, and constraints on the geometry of the disk around RW Aur A we arrive at the conclusion that the obscuring screen is part of a wind emanating from the inner disk.

astro-ph.SR↗

arXiv2016

CUORE-0 detector: design, construction and operation

The CUORE experiment will search for neutrinoless double-beta decay of $^{130}$Te with an array of 988 TeO$_2$ bolometers arranged in 19 towers. CUORE-0, the first tower assembled according to the CUORE procedures, was built and commissioned at Laboratori Nazionali del Gran Sasso, and took data from March 2013 to March 2015. In this paper we describe the design, construction and operation of the CUORE-0 experiment, with an emphasis on the improvements made over a predecessor experiment, Cuoricino. In particular, we demonstrate with CUORE-0 data that the design goals of CUORE are within reach.

physics.ins-det↗

arXiv2016

The JCMT Gould Belt Survey: A First Look at Southern Orion A with SCUBA-2

We present the JCMT Gould Belt Survey's first look results of the southern extent of the Orion A Molecular Cloud ($δ\leq -5\mathrm{:}31\mathrm{:}27.5$). Employing a two-step structure identification process, we construct individual catalogues for large-scale regions of significant emission labelled as islands and smaller-scale subregions called fragments using the 850 $μ$m continuum maps obtained using SCUBA-2. We calculate object masses, sizes, column densities, and concentrations. We discuss fragmentation in terms of a Jeans instability analysis and highlight interesting structures as candidates for follow-up studies. Furthermore, we associate the detected emission with young stellar objects (YSOs) identified by Spitzer and Herschel. We find that although the population of active star-forming regions contains a wide variety of sizes and morphologies, there is a strong positive correlation between the concentration of an emission region and its calculated Jeans instability. There are, however, a number of highly unstable subregions in dense areas of the map that show no evidence of star formation. We find that only $\sim$72\% of the YSOs defined as Class 0+I and flat-spectrum protostars coincide with dense 850 $μ$m emission structures (column densities $>3.7\times10^{21}\mathrm{\:cm}^{-2}$). The remaining 28\% of these objects, which are expected to be embedded in dust and gas, may be misclassified. Finally, we suggest that there is an evolution in the velocity dispersion of young stellar objects such that sources which are more evolved are associated with higher velocities.

astro-ph.SR↗

arXiv2016

The JCMT Gould Belt Survey: Evidence for Dust Grain Evolution in Perseus Star-forming Clumps

The dust emissivity spectral index, $β$, is a critical parameter for deriving the mass and temperature of star-forming structures, and consequently their gravitational stability. The $β$ value is dependent on various dust grain properties, such as size, porosity, and surface composition, and is expected to vary as dust grains evolve. Here we present $β$, dust temperature, and optical depth maps of the star-forming clumps in the Perseus Molecular Cloud determined from fitting SEDs to combined Herschel and JCMT observations in the 160 $μ$m, 250 $μ$m, 350 $μ$m, 500 $μ$m, and 850 $μ$m bands. Most of the derived $β$, and dust temperature values fall within the ranges of 1.0 - 2.7 and 8 - 20 K, respectively. In Perseus, we find the $β$ distribution differs significantly from clump to clump, indicative of grain growth. Furthermore, we also see significant, localized $β$ variations within individual clumps and find low $β$ regions correlate with local temperature peaks, hinting at the possible origins of low $β$ grains. Throughout Perseus, we also see indications of heating from B stars and embedded protostars, as well evidence of outflows shaping the local landscape.

astro-ph.GA↗

arXiv2016

The JCMT Gould Belt Survey: Evidence for radiative heating and contamination in the W40 complex

We present SCUBA-2 450μm and 850μm observations of the W40 complex in the Serpens-Aquila region as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) of nearby star-forming regions. We investigate radiative heating by constructing temperature maps from the ratio of SCUBA-2 fluxes using a fixed dust opacity spectral index, β = 1.8, and a beam convolution kernel to achieve a common 14.8" resolution. We identify 82 clumps ranging between 10 and 36K with a mean temperature of 20{\pm}3K. Clump temperature is strongly correlated with proximity to the external OB association and there is no evidence that the embedded protostars significantly heat the dust. We identify 31 clumps that have cores with densities greater than 105cm{^{-3}}. Thirteen of these cores contain embedded Class 0/I protostars. Many cores are associated with bright-rimmed clouds seen in Herschel 70 μm images. From JCMT HARP observations of the 12CO 3-2 line, we find contamination of the 850μm band of up to 20 per cent. We investigate the free-free contribution to SCUBA-2 bands from large-scale and ultracompact H ii regions using archival VLA data and find the contribution is limited to individual stars, accounting for 9 per cent of flux per beam at 450 μm or 12 per cent at 850 μm in these cases. We conclude that radiative heating has potentially influenced the formation of stars in the Dust Arc sub-region, favouring Jeans stable clouds in the warm east and fragmentation in the cool west.

astro-ph.GA↗

arXiv2016

Analysis Techniques for the Evaluation of the Neutrinoless Double-Beta Decay Lifetime in $^{130}$Te with CUORE-0

We describe in detail the methods used to obtain the lower bound on the lifetime of neutrinoless double-beta ($0νββ$) decay in $^{130}$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 $0νββ$ 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 $0νββ$ decay 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 $0νββ$ decay peak and catalog the main sources of systematic uncertainty. Finally, we derive the $0νββ$ decay half-life limits previously reported for CUORE-0, $T^{0ν}_{1/2}>2.7\times10^{24}$ yr, and in combination with the Cuoricino limit, $T^{0ν}_{1/2}>4.0\times10^{24}$ yr.

nucl-ex↗

arXiv2015

The JCMT Gould Belt Survey: A First Look at Dense Cores in Orion B

We present a first look at the SCUBA-2 observations of three sub-regions of the Orion B molecular cloud: LDN 1622, NGC 2023/2024, and NGC 2068/2071, from the JCMT Gould Belt Legacy Survey. We identify 29, 564, and 322 dense cores in L1622, NGC 2023/2024, and NGC 2068/2071 respectively, using the SCUBA-2 850 micron map, and present their basic properties, including their peak fluxes, total fluxes, and sizes, and an estimate of the corresponding 450 micron peak fluxes and total fluxes, using the FellWalker source extraction algorithm. Assuming a constant temperature of 20 K, the starless dense cores have a mass function similar to that found in previous dense core analyses, with a Salpeter-like slope at the high-mass end. The majority of cores appear stable to gravitational collapse when considering only thermal pressure; indeed, most of the cores which have masses above the thermal Jeans mass are already associated with at least one protostar. At higher cloud column densities, above 1-2 x 10^23 cm^-2, most of the mass is found within dense cores, while at lower cloud column densities, below 1 x 10^23 cm^-2, this fraction drops to 10% or lower. Overall, the fraction of dense cores associated with a protostar is quite small (<8%), but becomes larger for the densest and most centrally concentrated cores. NGC 2023 / 2024 and NGC 2068/2071 appear to be on the path to forming a significant number of stars in the future, while L1622 has little additional mass in dense cores to form many new stars.

astro-ph.SR↗

arXiv2015

The JCMT Plane Survey: early results from the l = 30 degree field

We present early results from the JCMT Plane Survey (JPS), which has surveyed the northern inner Galactic plane between longitudes l=7 and l=63 degrees in the 850-μm continuum with SCUBA-2, as part of the James Clerk Maxwell Telescope Legacy Survey programme. Data from the l=30 degree survey region, which contains the massive star-forming regions W43 and G29.96, are analysed after approximately 40% of the observations had been completed. The pixel-to-pixel noise is found to be 19 mJy/beam, after a smooth over the beam area, and the projected equivalent noise levels in the final survey are expected to be around 10 mJy/beam. An initial extraction of compact sources was performed using the FellWalker method resulting in the detection of 1029 sources above a 5-σ surface-brightness threshold. The completeness limits in these data are estimated to be around 0.2 Jy/beam (peak flux density) and 0.8 Jy (integrated flux density) and are therefore probably already dominated by source confusion in this relatively crowded section of the survey. The flux densities of extracted compact sources are consistent with those of matching detections in the shallower ATLASGAL survey. We analyse the virial and evolutionary state of the detected clumps in the W43 star-forming complex and find that they appear younger than the Galactic-plane average.

astro-ph.GA↗

arXiv2015

The UWISH2 extended H2 source catalogue

We present the extended source catalogue for the UKIRT Widefield Infrared Survey for H2 (UWISH2). The survey is unbiased along the inner Galactic Plane from l \approx 357deg to l \approx 65deg and |b| < 1.5deg and covers 209 square degrees. A further 42.0 and 35.5 square degrees of high dust column density regions have been targeted in Cygnus and Auriga. We have identified 33200 individual extended H2 features. They have been classified to be associated with about 700 groups of jets and outflows, 284 individual (candidate) Planetary Nebulae, 30 Supernova Remnants and about 1300 Photo-Dissociation Regions. We find a clear decline of star formation activity (traced by H2 emission from jets and photo-dissociation regions) with increasing distance from the Galactic Centre. About 60% of the detected candidate Planetary Nebulae have no known counterpart and 25% of all Supernova Remnants have detectable H2 emission associated with them.

astro-ph.GA↗

arXiv2015

The JCMT Gould Belt Survey: SCUBA-2 observations of circumstellar disks in L 1495

We present 850$μ$m and 450$μ$m data from the JCMT Gould Belt Survey obtained with SCUBA-2 and characterise the dust attributes of Class I, Class II and Class III disk sources in L1495. We detect 23% of the sample at both wavelengths, with the detection rate decreasing through the Classes from I--III. The median disk mask is 1.6$\times 10^{-3}$M$_{\odot}$, and only 7% of Class II sources have disk masses larger than 20 Jupiter masses. We detect a higher proportion of disks towards sources with stellar hosts of spectral type K than spectral type M. Class II disks with single stellar hosts of spectral type K have higher masses than those of spectral type M, supporting the hypothesis that higher mass stars have more massive disks. Variations in disk masses calculated at the two wavelengths suggests there may be differences in dust opacity and/or dust temperature between disks with hosts of spectral types K to those with spectral type M.

astro-ph.GA↗