arXiv subjects

R. Wang

Publications and source records attributed to R. Wang.

At least 73 records · Page 4Linked to original sources

arXiv2020

Symmetry-Protected Topological Triangular Weyl Complex

Weyl points are often believed to appear in pairs with opposite chirality. In this work, we show by first-principles calculations and symmetry analysis that single Weyl phonons with linear dispersion and double Weyl phonons with quadratic dispersion are simultaneously present between two specific phonon branches in realistic materials with trigonal or hexagonal lattices. These phonon Weyl points are guaranteed to locate at high-symmetry points due to the screw rotational symmetry, forming a unique triangular Weyl complex. In sharp contrast to conventional Weyl systems with surface arcs terminated at the projections of a pair of Weyl points with opposite chirality, the phonon surface arcs of the unconventional triangular Weyl complex connect the projections of one double Weyl point and two single Weyl points. Importantly, the phonon surface arcs originating from the triangular Weyl complex are extremely long and span the entire surface Brillouin-zone. Furthermore, there are only nontrivial phonon surface states across the iso-frequency surface, which facilitates their detection in experiments and further applications. Our work not only offers the promising triangular phonon Weyl complex but also provides guidance for exploring triangular Weyl bosons in both phononic and photonic systems.

cond-mat.mtrl-sci↗

arXiv2020

An ALMA survey of the brightest sub-millimetre sources in the SCUBA-2 COSMOS field

We present an ALMA study of the ~180 brightest sources in the SCUBA-2 map of the COSMOS field from the S2COSMOS survey, as a pilot study for AS2COSMOS - a full survey of the ~1,000 sources in this field. In this pilot we have obtained 870-um continuum maps of an essentially complete sample of the brightest 182 sub-millimetre sources (S_850um=6.2mJy) in COSMOS. Our ALMA maps detect 260 sub-millimetre galaxies (SMGs) spanning a range in flux density of S_870um=0.7-19.2mJy. We detect more than one SMG counterpart in 34+/-2 per cent of sub-millimetre sources, increasing to 53+/-8 per cent for SCUBA-2 sources brighter than S_850um>12mJy. We estimate that approximately one-third of these SMG-SMG pairs are physically associated (with a higher rate for the brighter secondary SMGs, S_870um>3mJy), and illustrate this with the serendipitous detection of bright [CII] 157.74um line emission in two SMGs, AS2COS0001.1 & 0001.2 at z=4.63, associated with the highest significance single-dish source. Using our source catalogue we construct the interferometric 870um number counts at S_870um>6.2mJy. We use the extensive archival data of this field to construct the multiwavelength spectral energy distribution of each AS2COSMOS SMG, and subsequently model this emission with MAGPHYS to estimate their photometric redshifts. We find a median photometric redshift for the S_870um>6.2mJy AS2COSMOS sample of z=2.87+/-0.08, and clear evidence for an increase in the median redshift with 870-um flux density suggesting strong evolution in the bright-end of the 870um luminosity function.

astro-ph.GA↗

arXiv2020

Space Charge Effects in the S$π$RIT Time Projection Chamber

Time projection chambers (TPCs) are widely used in nuclear and particle physics. They are particularly useful when measuring reaction products from heavy ion collisions. Most nuclear experiments at low energy are performed in a fixed target configuration, in which the unreacted beam will pass through the detection volume. As the beam intensity increases, the buildup of positive ions created from the ionization of the detector gas by the beam creates the main source of space charge, distorting the nominal electric field of the TPC. This has a profound effect on the accuracy of the measured momenta of the emitted particles. In this paper we will discuss the magnitude of the effects and construct an observable more appropriate for fixed target experiments to study the effects. We also will present an algorithm for correcting the space charge and some of the implications it has on the momentum determination.

physics.ins-det↗

arXiv2020

Search for proton decay into three charged leptons in 0.37 megaton-years exposure of the Super-Kamiokande

A search for proton decay into three charged leptons has been performed by using 0.37$\,$Mton$\cdot$years of data collected in Super-Kamiokande. All possible combinations of electrons, muons and their anti-particles consistent with charge conservation were considered as decay modes. No significant excess of events has been found over the background, and lower limits on the proton lifetime divided by the branching ratio have been obtained. The limits range between $9.2\times10^{33}$ to $3.4\times10^{34}$ years at 90$\,$% confidence level, improving by more than an order of magnitude upon limits from previous experiments. A first limit has been set for the $p\rightarrowμ^-e^+e^+$ mode.

hep-ex↗

arXiv2020

Charged particle track reconstruction with S$π$RIT Time Projection Chamber

In this paper, we present a software framework, S$π$RITROOT, which is capable of track reconstruction and analysis of heavy-ion collision events recorded with the S$π$RIT time projection chamber. The track-fitting toolkit GENFIT and the vertex reconstruction toolkit RAVE are applied to a box-type detector system. A pattern recognition algorithm which performs helix track finding and handles overlapping pulses is described. The performance of the software is investigated using experimental data obtained at the Radioactive Isotope Beam Facility (RIBF) at RIKEN. This work focuses on data from $^{132}$Sn + $^{124}$Sn collision events with beam energy of 270 AMeV. Particle identification is established using $\left $ and magnetic rigidity, with pions, hydrogen isotopes, and helium isotopes.

physics.ins-det↗

arXiv2019

Constraints on high-J CO emission lines in $z\sim 6$ quasars

We present Atacama Large Millimiter/submillimiter Array (ALMA) observations of eight highly excited CO (J$_{\rm up}>8$) lines and continuum emission in two $z\sim6$ quasars: SDSS J231038.88+185519.7 (hereafter J2310), for which CO(8-7), CO(9-8), and CO(17-16) lines have been observed, and ULAS J131911.29+095951.4 (J1319), observed in the CO(14-13), CO(17-16) and CO(19-18) lines. The continuum emission of both quasars arises from a compact region ($< 0.9$ kpc). By assuming a modified black-body law, we estimate dust masses of Log$(M_{\rm dust}/M_{\odot})=8.75\pm0.07$ and Log$(M_{\rm dust}/M_{\odot})=8.8\pm0.2$ and dust temperatures of $T_{\rm dust}=76\pm3~{\rm K}$ and $T_{\rm dust}=66^{+15}_{-10}~{\rm K}$, respectively for J2310 and J1319. Only CO(8-7) and CO(9-8) in J2310 are detected, while $3σ$ upper limits on luminosities are reported for the other lines of both quasars. The CO line luminosities and upper limits measured in J2310 and J1319 are consistent with those observed in local AGN and starburst galaxies, and other $z\sim 6$ quasars, except for SDSS J1148+5251 (J1148), the only quasar at $z=6.4$ with a previous CO(17-16) line detection. By computing the CO SLEDs normalised to the CO(6-5) line and FIR luminosities for J2310, J1319, and J1149, we conclude that different gas heating mechanisms (X-ray radiation and/or shocks) may explain the different CO luminosities observed in these $z\sim6$ quasar. Future J$_{\rm up}>8$ CO observations will be crucial to understand the processes responsible for molecular gas excitation in luminous high-$z$ quasars.

astro-ph.GA↗

arXiv2019

Localization transitions and mobility edges in quasiperiodic ladder

We investigate localization properties in a two-coupled uniform chains with quasiperiodic modulation on interchain coupling strength. We demonstrate that this ladder is equivalent to a Aubry-Andre (AA) chain when two legs are symmetric. Analytical and numerical results indicate the appearance of mobility edges for asymmetric ladder. We also propose an easily engineered quasiperiodic ladder system which is a moiré superlattice system consisting of two-coupled uniform chains. An irrational lattice constant difference results in quasiperiodic structure. Numerical simulations show that such a system supports mobility edge. Additionally, we find that the mobility edge can be detected by a dynamic method, which bases on the measurement of surviving probability in the presence of a single imaginary negative potential as a leakage. The result provides insightful information about the localization transitions and mobility edge in experiment.

cond-mat.dis-nn↗

arXiv2019

The East Asian Observatory SCUBA--2 survey of the COSMOS field: unveiling 1147 bright sub-millimeter sources across 2.6 square degrees

We present sensitive 850$μ$m imaging of the COSMOS field using 640hr of new and archival observations taken with SCUBA-2 at the East Asian Observatory's James Clerk Maxwell Telescope. The SCUBA-2 COSMOS survey (S2COSMOS) achieves a median noise level of $σ_{850μ{\mathrm{m}}}$=1.2mJy/beam over an area of 1.6 sq. degree (MAIN; HST/ACS footprint), and $σ_{850μ{\mathrm{m}}}$=1.7mJy/beam over an additional 1 sq. degree of supplementary (SUPP) coverage. We present a catalogue of 1020 and 127 sources detected at a significance level of >4$σ$ and >4.3$σ$ in the MAIN and SUPP regions, respectively, corresponding to a uniform 2% false-detection rate. We construct the single-dish 850$μ$m number counts at $S_{850}$>2mJy and show that these S2COSMOS counts are in agreement with previous single-dish surveys, demonstrating that degree-scale fields are sufficient to overcome the effects of cosmic variance in the $S_{850}$=2-10mJy population. To investigate the properties of the galaxies identified by S2COSMOS sources we measure the surface density of near-infrared-selected galaxies around their positions and identify an average excess of 2.0$\pm$0.2 galaxies within a 13$''$ radius (~100kpc at $z$~2). The bulk of these galaxies represent near-infrared-selected SMGs and/or spatially-correlated sources and lie at a median photometric redshift of $z$=2.0$\pm$0.1. Finally, we perform a stacking analysis at sub-millimeter and far-infrared wavelengths of stellar-mass-selected galaxies ($M_{\star}$=10$^{10}$-10$^{12}{\rm M_{\odot}}$) from $z$=0-4, obtaining high-significance detections at 850um in all subsets (SNR=4-30), and investigate the relation between far-infrared luminosity, stellar mass, and the peak wavelength of the dust SED. The publication of this survey adds a new deep, uniform sub-millimeter layer to the wavelength coverage of this well-studied COSMOS field.

astro-ph.GA↗

arXiv2019

Electrostatic turbulence and Debye-scale structures in collisionless shocks

We present analysis of more than one hundred large-amplitude bipolar electrostatic structures in a quasi-perpendicular supercritical Earth's bow shock crossing, measured by the Magnetospheric Multiscale spacecraft. The occurrence of the bipolar structures is shown to be tightly correlated with magnetic field gradients in the shock transition region. The bipolar structures have negative electrostatic potentials and spatial scales of a few Debye lengths. The bipolar structures propagate highly oblique to the shock normal with velocities (in the plasma rest frame) of the order of the ion-acoustic velocity. We argue that the bipolar structures are ion phase space holes produced by the two-stream instability between incoming and reflected ions. This is the first identification of the ion two-stream instability in collisionless shocks. The implications for electron acceleration are discussed.

astro-ph.SR↗

arXiv2019

Scintillating crystals for the Neutral Particle Spectrometer in Hall C at JLab

This paper discusses the quality and performance of currently available PbWO$_4$ crystals of relevance to high-resolution electromagnetic calorimetry, e.g. detectors for the Neutral Particle Spectrometer at Jefferson Lab or those planned for the Electron-Ion Collider. Since the construction of the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC) and early PANDA (The antiProton ANnihilations at DArmstadt) electromagnetic calorimeter (ECAL) the worldwide availability of high quality PbWO$_4$ production has changed dramatically. We report on our studies of crystal samples from SICCAS/China and CRYTUR/Czech Republic that were produced between 2014 and 2019.

physics.ins-det↗

arXiv2019

Properties of Radial Velocities measurement based on LAMOST-II Medium-Resolution Spectroscopic Observations

The radial velocity (RV) is a basic physical quantity which can be determined through Doppler shift of the spectrum of a star. The precision of RV measurement depends on the resolution of the spectrum we used and the accuracy of wavelength calibration. In this work, radial velocities of LAMOST-II medium resolution (R ~ 7500) spectra are measured for 1,594,956 spectra (each spectrum has two wavebands) through matching with templates. A set of RV standard stars are used to recalibrate the zero point of the measurement, and some reference sets with RVs derived from medium/high-resolution observations are used to evaluate the accuracy of the measurement. Comparing with reference sets, the accuracy of our measurement can get 0.0227 km s/1 with respect to radial velocities standard stars. The intrinsic precision is estimated with the multiple observations of single stars, which can achieve to 1.36 km s/1,1.08 km s/1, 0.91 km s/1 for the spectra at signal-to-noise levels of 10, 20, 50, respectively.

astro-ph.SR↗

arXiv2019

Search for Astronomical Neutrinos from Blazar TXS0506+056 in Super-Kamiokande

We report a search for astronomical neutrinos in the energy region from several GeV to TeV in the direction of the blazar TXS0506+056 using the Super-Kamiokande detector following the detection of a 100 TeV neutrino from the same location by the IceCube collaboration. Using Super-Kamiokande neutrino data across several data samples observed from April 1996 to February 2018 we have searched for both a total excess above known backgrounds across the entire period as well as localized excesses on smaller time scales in that interval. No significant excess nor significant variation in the observed event rate are found in the blazar direction. Upper limits are placed on the electron and muon neutrino fluxes at 90\% confidence level as $6.03 \times 10^{-7}$ and $4.52 \times 10^{-7}$ to $9.26 \times 10^{-10}$ [${\rm erg}/{\rm cm}^2/{\rm s}$], respectively.

astro-ph.HE↗

arXiv2019

Moiré pattern of spin liquid and Neel magnet in a Kitaev chain

A moiré pattern occurs when two periodic structures in a system have a slight mismatch period, resulting the coexistence of distinct phases in different large-scale spacial regions of the same system. Two periodic structures can arise from periodic electric and magnetic fields, respectively. We investigated the moiré pattern via a dimerized Kitaev spin chain with a periodic transverse field, which can be mapped onto the system of dimerized spinless fermions with p-wave superconductivity. The exact solution for staggered field demonstrated that the ground state has two distinct phases: (i) Neel magnetic phase for nonzero field, (ii) Spin liquid phase due to the emergence of isolated flat Bogoliubov--de Gennes band for vanishing field. We computed the staggered magnetization and local density of states (\textrm{LDOS}) for the field with a slight difference period to the chain lattice. Numerical simulation demonstrated that such two phases appear alternatively along the chain with a long beat period. Additionally, we proposed a dynamic scheme to detect the Moiré fringes based on the measurement of Loschmidt echo (\textrm{LE}) in the presence of local perturbation.

cond-mat.dis-nn↗

arXiv2019

Pseudo-2D superconducting quantum computing circuit for the surface code: the proposal and preliminary tests

Of the many potential hardware platforms, superconducting quantum circuits have become the leading contender for constructing a scalable quantum computing system. All current architecture designs necessitate a 2D arrangement of superconducting qubits with nearest neighbour interactions, compatible with powerful quantum error correction using the surface code. A major hurdle for scalability in superconducting systems is the so called wiring problem, where qubits internal to a chip-set become inaccessible for external control/readout lines. Current approaches resort to intricate and exotic 3D wiring and packaging technology which is a significant engineering challenge to realize, while maintaining qubit fidelity. Here we solve this problem and present a modified superconducting scalable micro-architecture that does not require any 3D external line technology and reverts back to a completely planar design. This is enabled by a new pseudo-2D resonator network that provides inter-qubit connections via airbridges. We carried out experiments to examine the feasibility of the newly introduced airbridge component. The measured quality factor of these new inter-qubit resonators is sufficient for high fidelity gates, below the threshold for the surface code, with negligible measured cross-talk. The resulting physical separation of the external wirings and the inter-qubit connections on-chip should reduce cross-talk and decoherence as the chip-set increases in size. This result demonstrates that a large-scale, fully error corrected quantum computer can be constructed by monolithic integration technologies without additional overhead and without special packaging know-hows.

quant-ph↗

arXiv2019

Multi-wavelength properties of radio and machine-learning identified counterparts to submillimeter sources in S2COSMOS

We identify multi-wavelength counterparts to 1,147 submillimeter sources from the S2COSMOS SCUBA-2 survey of the COSMOS field by employing a recently developed radio$+$machine-learning method trained on a large sample of ALMA-identified submillimeter galaxies (SMGs), including 260 SMGs identified in the AS2COSMOS pilot survey. In total, we identify 1,222 optical/near-infrared(NIR)/radio counterparts to the 897 S2COSMOS submillimeter sources with S$_{850}$>1.6mJy, yielding an overall identification rate of ($78\pm9$)%. We find that ($22\pm5$)% of S2COSMOS sources have multiple identified counterparts. We estimate that roughly 27% of these multiple counterparts within the same SCUBA-2 error circles very likely arise from physically associated galaxies rather than line-of-sight projections by chance. The photometric redshift of our radio$+$machine-learning identified SMGs ranges from z=0.2 to 5.7 and peaks at $z=2.3\pm0.1$. The AGN fraction of our sample is ($19\pm4$)%, which is consistent with that of ALMA SMGs in the literature. Comparing with radio/NIR-detected field galaxy population in the COSMOS field, our radio+machine-learning identified counterparts of SMGs have the highest star-formation rates and stellar masses. These characteristics suggest that our identified counterparts of S2COSMOS sources are a representative sample of SMGs at z<3. We employ our machine-learning technique to the whole COSMOS field and identified 6,877 potential SMGs, most of which are expected to have submillimeter emission fainter than the confusion limit of our S2COSMOS surveys (S$_{850}$<1.5mJy). We study the clustering properties of SMGs based on this statistically large sample, finding that they reside in high-mass dark matter halos ($(1.2\pm0.3)\times10^{13}\,h^{-1}\,\rm M_{\odot}$), which suggests that SMGs may be the progenitors of massive ellipticals we see in the local Universe.

astro-ph.GA↗

arXiv2019

Anderson localization induced by complex potential

Uncorrelated disorder potential in one-dimensional lattice definitely induces Anderson localization, while quasiperiodic potential can lead to both localized and extended phases, depending on the potential strength. We investigate the Anderson localization in one-dimensional lattice with nonHermitian complex disorder and quasiperiodic potential. We present a non-Hermitian SSH chain to demonstrate that a nonzero imaginary disorder on-site potential can induce the standard Anderson localization. We also show that the non-Hermitian Aubry-Andre (AA) model exhibits a transition in parameter space, which separates the localization and delocalization phases and is determined by the self-duality of the model. It indicates that a pure imaginary quasiperiodic potential takes the same role as a real quasiperiodic potential in the transition point between localization and delocalization. Remarkably, a system with complex quasiperiodic potential exhibits interference-like pattern on the transition points.

cond-mat.dis-nn↗

arXiv2019

Sensitivity of Super-Kamiokande with Gadolinium to Low Energy Anti-neutrinos from Pre-supernova Emission

Supernova detection is a major objective of the Super-Kamiokande (SK) experiment. In the next stage of SK (SK-Gd), gadolinium (Gd) sulfate will be added to the detector, which will improve the ability of the detector to identify neutrons. A core-collapse supernova will be preceded by an increasing flux of neutrinos and anti-neutrinos, from thermal and weak nuclear processes in the star, over a timescale of hours; some of which may be detected at SK-Gd. This could provide an early warning of an imminent core-collapse supernova, hours earlier than the detection of the neutrinos from core collapse. Electron anti-neutrino detection will rely on inverse beta decay events below the usual analysis energy threshold of SK, so Gd loading is vital to reduce backgrounds while maximising detection efficiency. Assuming normal neutrino mass ordering, more than 200 events could be detected in the final 12 hours before core collapse for a 15-25 solar mass star at around 200 pc, which is representative of the nearest red supergiant to Earth, $\mathrmα$Ori (Betelgeuse). At a statistical false alarm rate of 1 per century, detection could be up to 10 hours before core collapse, and a pre-supernova star could be detected by SK-Gd up to 600 pc away. A pre-supernova alert could be provided to the astrophysics community following gadolinium loading.

astro-ph.HE↗

arXiv2019

Dissipative dynamics of atomic and molecular Rydberg gases: Avalanche to ultracold plasma states of strong coupling

Not long after metastable xenon was photoionized in a magneto-optical trap, groups in Europe and North America found that similar states of ionized gas evolved spontaneously from state-selected, high principal quantum number Rydberg gases. Studies of atomic xenon and molecular nitric oxide entrained in a supersonically cooled molecular beam subsequently showed much the same final state evolved from a sequence of prompt Penning ionization and electron-impact avalanche to plasma, well-described by coupled rate-equation simulations. But, measured over longer times, the molecular ultracold plasma was found to exhibit an anomalous combination of very long lifetime and very low apparent electron temperature. This review summarizes early developments in the study of ultracold plasmas formed by atomic and molecular Rydberg gases, and then details observations as they combine to characterize properties of the nitric oxide molecular ultracold plasma that appear to call for an explanation beyond the realm of conventional plasma physics.

physics.plasm-ph↗