Studies of Quantum-Mechanical Coherency Effects in Neutrino-Nucleus Elastic Scattering

Neutrino-nucleus elastic scattering ($ u {rm A}_{el}$) provides a unique laboratory to study the quantum-mechanical (QM) coherency effects in electroweak interactions. The deviations of the cross-sections from those of completely coherent systems can be quantitatively characterized through a coherency parameter $alpha ( q^2 )$. The relations between $alpha$ and the underlying nuclear physics in terms of nuclear form factors are derived. The dependence of cross-section on $alpha ( q^2 )$ for the various neutrino sources is presented. The $alpha ( q^2 )$-values are evaluated from the measured data of the COHERENT CsI and Ar experiments. Complete coherency and decoherency conditions are excluded by the CsI data with $p {=} 0.004$ at $q^2 {=} 3.1 {times} 10^{3} ~ {rm MeV^2}$ and with $p {=} 0.016$ at $q^2 {=} 2.3 {times} 10^{3} ~ {rm MeV^2}$, respectively, verifying that both QM superpositions and nuclear many-body effects contribute to $ u {rm A}_{el}$ interactions.

The Exposure-Background Duality in the Searches of Neutrinoless Double Beta Decay

Tremendous efforts are required to scale the summit of observing neutrinoless double beta decay ($0 u beta beta$). This article quantitatively explores the interplay between exposure (target mass X data taking time) and background levels in $0 u beta beta$ experiments. In particular, background reduction can substantially alleviate the necessity of unrealistic large exposure as the normal mass hierarchy (NH) is probed. The non-degenerate (ND)-NH can be covered with an exposure of O(100) ton-year, which is only an order of magnitude larger than those planned for next generation projects - provided that the background could be reduced by 0($10^{-6}$) relative to the current best levels. It follows that background suppression will be playing increasingly important and investment-effective, if not determining, roles in future $0 u beta beta$ experiments with sensitivity goals of approaching and covering ND-NH.

Neutron background measurements with a hybrid neutron detector at the Kuo-Sheng Reactor Neutrino Laboratory

We report in situ neutron background measurements at the Kuo-Sheng Reactor Neutrino Laboratory (KSNL) by a hybrid neutron detector (HND) with a data size of 33.8 days under identical shielding configurations as during the neutrino physics data taking. The HND consists of BC-501A liquid and BC-702 phosphor powder scintillation neutron detectors, which is sensitive to both fast and thermal neutrons, respectively. Neutron-induced events for the two channels are identified and differentiated by pulse shape analysis, such that background of both are simultaneously measured. The fast neutron fluxes are derived by an iterative unfolding algorithm. Neutron induced background in the germanium detector under the same fluxes, both due to cosmic-rays and ambient radioactivity, are derived and compared with the measurements. The results are valuable to background understanding of the neutrino data at the KSNL. In particular, neutron-induced background events due to ambient radioactivity as well as from reactor operation are negligible compared to intrinsic cosmogenic activity and ambient $gamma$-activity. The detector concept and analysis procedures are applicable to neutron background characterization in similar rare-event experiments.

Circumstellar ammonia in oxygen-rich evolved stars

The circumstellar ammonia (NH$_3$) chemistry in evolved stars is poorly understood. Previous observations and modelling showed that NH$_3$ abundance in oxygen-rich stars is several orders of magnitude above that predicted by equilibrium chemistry. In this article, we characterise the spatial distribution and excitation of NH$_3$ in the O-rich circumstellar envelopes (CSEs) of four diverse targets: IK Tau, VY CMa, OH 231.8+4.2, and IRC +10420 with multi-wavelength observations. We observed the 1.3-cm inversion line emission with the Very Large Array (VLA) and submillimetre rotational line emission with the Heterodyne Instrument for the Far-Infrared (HIFI) aboard Herschel from all four targets. For IK Tau and VY CMa, we observed the rovibrational absorption lines in the $ u_2$ band near 10.5 $mu$m with the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). We also attempted to search for the rotational transition within the $v_2=1$ state near 2 mm with the IRAM 30m Telescope towards IK Tau. Non-LTE radiative transfer modelling, including radiative pumping to the vibrational state, was carried out to derive the radial distribution of NH$_3$ in these CSEs. Our modelling shows that the NH$_3$ abundance relative to molecular hydrogen is generally of the order of $10^{-7}$, which is a few times lower than previous estimates that were made without considering radiative pumping and is at least 10 times higher than that in the C-rich CSE of IRC +10216. Incidentally, we also derived a new period of IK Tau from its $V$-band light curve. NH$_3$ is again detected in very high abundance in O-rich CSEs. Its emission mainly arises from localised spatial-kinematic structures that are probably denser than the ambient gas. Circumstellar shocks in the accelerated wind may contribute to the production of NH$_3$. (Abridged abstract)

An XMM-Newton Study of the Mixed-Morphology Supernova Remnant G346.6-0.2

We present an X-ray imaging and spectroscopic study of the molecular cloud interacting mixed-morphology (MM) supernova remnant (SNR) G346.6-0.2 using XMM-Newton. The X-ray spectrum of the remnant is well described by a recombining plasma that most likely arises from adiabatic cooling, and has sub-solar abundances of Mg, Si, and S. Our fits also suggest the presence of either an additional power-law component with a photon index of $sim$2, or an additional thermal component with a temperature of $sim$2.0 keV. We investigate the possible origin of this component and suggest that it could arise from either the Galactic ridge X-ray emission, an unidentified pulsar wind nebula or X-ray synchrotron emission from high-energy particles accelerated at the shock. However, deeper, high resolution observations of this object are needed to shed light on the presence and origin of this feature. Based on its morphology, its Galactic latitude, the density of the surrounding environment and its association with a dense molecular cloud, G346.6-0.2 most likely arises from a massive progenitor that underwent core-collapse.

Bulk and Surface Event Identification in p-type Germanium Detectors

The p-type point-contact germanium detectors have been adopted for light dark matter WIMP searches and the studies of low energy neutrino physics. These detectors exhibit anomalous behavior to events located at the surface layer. The previous spectral shape method to identify these surface events from the bulk signals relies on spectral shape assumptions and the use of external calibration sources. We report an improved method in separating them by taking the ratios among different categories of in situ event samples as calibration sources. Data from CDEX-1 and TEXONO experiments are re-examined using the ratio method. Results are shown to be consistent with the spectral shape method.

An observational study of dust nucleation in Mira ($o$ Ceti): I. Variable features of AlO and other Al-bearing species

Context: Dust is efficiently produced by cool giant stars, but the condensation of inorganic dust is poorly understood. Aims: Identify and characterize aluminum bearing species in the circumstellar gas of Mira ($o$ Ceti) in order to elucidate their role in the production of Al$_2$O$_3$ dust. Methods: Multiepoch spectral line observations at (sub-)millimeter, far-infrared, and optical wavelengths including: maps with ALMA which probe the gas distribution in the immediate vicinity of the star at ~30 mas; observations with ALMA, APEX, and Herschel in 2013-2015 for studying cycle and inter-cycle variability of the rotational lines of Al bearing molecules; optical records as far back as 1965 to examine variations in electronic transitions over time spans of days to decades; and velocity measurements and excitation analysis of the spectral features which constrain the physical parameters of the gas. Results: Three diatomic molecules AlO, AlOH, and AlH, and atomic Al I are the main observable aluminum species in Mira, although a significant fraction of aluminum might reside in other species that have not yet been identified. Strong irregular variability in the (sub-)millimeter and optical features of AlO (possibly the direct precursor of Al$_2$O$_3$) indicates substantial changes in the excitation conditions, or varying abundance that is likely related to shocks in the star. The inhomogeneous distribution of AlO might influence the spatial and temporal characteristics of dust production. Conclusions: We are unable to quantitatively trace aluminum depletion from the gas, but the rich observational material constrains time dependent chemical networks. Future improvements should include spectroscopic characterization of higher aluminum oxides, coordinated observations of dust and gas species at different variability phases, and tools to derive abundances in shock excited gas.

Resolving the extended atmosphere and the inner wind of Mira ($o$ Ceti) with long ALMA baselines

The prototypical Mira variable, $o$ Cet (Mira), has been observed as a Science Verification target in the 2014 ALMA Long Baseline Campaign with a longest baseline of 15 km. ALMA clearly resolves the images of the continuum and molecular line emission/absorption at an angular resolution of ~30 mas at 220 GHz. We image the data of the $^{28}$SiO v=0, 2 $J$=5-4 and H$_2$O $ u_2$=1 $J(K_a,K_c)$=5(5,0)-6(4,3) transitions and extract spectra from various lines-of-sight towards Miras extended atmosphere. In the course of imaging, we encountered ambiguities in the resulting images and spectra that appear to be related to the performance of the CLEAN algorithm. We resolve Miras millimetre continuum emission and our data are consistent with a radio photosphere with a brightness temperature of 2611$pm$51 K, in agreement with recent results obtained with the VLA. We do not confirm the existence of a compact region (<5 mas) of enhanced brightness. We derive the gas density, kinetic temperature, molecular abundance and outflow/infall velocities in Miras extended atmosphere by modelling the SiO and H$_2$O lines. We find that SiO-bearing gas starts to deplete beyond 4$R_star$ and at a kinetic temperature of $lesssim$600 K. The inner dust shells are probably composed of grain types other than pure silicates. During this observation, Miras atmosphere generally exhibited infall motion, with a shock front of velocity $lesssim$12 km/s outside the radio photosphere. The structures predicted by the hydrodynamical model CODEX can reproduce the observed spectra in astonishing detail; while some other models fail when confronted with the new data. Combined with radiative transfer modelling, ALMA successfully demonstrates the ability to reveal the physical conditions of the extended atmospheres and inner winds of AGB stars in unprecedented detail. (Abbreviated abstract)

Supergiant Shells and Molecular Cloud Formation in the LMC

We investigate the influence of large-scale stellar feedback on the formation of molecular clouds in the Large Magellanic Cloud (LMC). Examining the relationship between HI and 12CO(J=1-0) in supergiant shells (SGSs), we find that the molecular fraction in the total volume occupied by SGSs is not enhanced with respect to the rest of the LMC disk. However, the majority of objects (~70% by mass) are more molecular than their local surroundings, implying that the presence of a supergiant shell does on average have a positive effect on the molecular gas fraction. Averaged over the full SGS sample, our results suggest that ~12-25% of the molecular mass in supergiant shell systems was formed as a direct result of the stellar feedback that created the shells. This corresponds to ~4-11% of the total molecular mass of the galaxy. These figures are an approximate lower limit to the total contribution of stellar feedback to molecular cloud formation in the LMC, and constitute one of the first quantitative measurements of feedback-triggered molecular cloud formation in a galactic system.

Dark Matter Search with sub-keV Germanium Detectors at the China Jinping Underground Laboratory

Germanium detectors with sub-keV sensitivities open a window to search for low-mass WIMP dark matter. The CDEX-TEXONO Collaboration is conducting the first research program at the new China Jinping Underground Laboratory with this approach. The status and plans of the laboratory and the experiment are discussed.