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Z. Y. Zhang

Publications and source records attributed to Z. Y. Zhang.

At least 37 records · Page 2Linked to original sources
arXiv2022

Constraints on Sub-GeV Dark Matter--Electron Scattering from the CDEX-10 Experiment

We present improved germanium-based constraints on sub-GeV dark matter via dark matter--electron ($χ$-$e$) scattering using the 205.4 kg$\cdot$day dataset from the CDEX-10 experiment. Using a novel calculation technique, we attain predicted $χ$-$e$ scattering spectra observable in high-purity germanium detectors. In the heavy mediator scenario, our results achieve 3 orders of magnitude of improvement for $m_χ$ larger than 80 MeV/c$^2$ compared to previous germanium-based $χ$-$e$ results. We also present the most stringent $χ$-$e$ cross-section limit to date among experiments using solid-state detectors for $m_χ$ larger than 90 MeV/c$^2$ with heavy mediators and $m_χ$ larger than 100 MeV/c$^2$ with electric dipole coupling. The result proves the feasibility and demonstrates the vast potential of a new $χ$-$e$ detection method with high-purity germanium detectors in ultralow radioactive background.

hep-ex↗
arXiv2022

Constraints on sub-GeV dark matter boosted by cosmic rays from the CDEX-10 experiment at the China Jinping Underground Laboratory

We present new constraints on light dark matter boosted by cosmic rays (CRDM) using the 205.4 kg day data of the CDEX-10 experiment conducted at the China Jinping Underground Laboratory. The Monte Carlo simulation package CJPL\_ESS was employed to evaluate the Earth shielding effect. Several key factors have been introduced and discussed in our CRDM analysis, including the contributions from heavier CR nuclei than proton and helium, the inhomogeneity of CR distribution, and the impact of the form factor in the Earth attenuation calculation. Our result excludes the dark matter--nucleon elastic scattering cross-section region from $1.7\times 10^{-30}$ to $10^{-26}~\rm cm^2$ for dark matter of 10 keV$/c^2$ to 1 GeV$/c^2$.

hep-ex↗
arXiv2022

Search for Neutrinoless Double-Beta Decay of $^{76}$Ge with a Natural Broad Energy Germanium Detector

A natural broad energy germanium (BEGe) detector is operated in the China Jinping Underground Laboratory (CJPL) for a feasibility study of building the next generation experiment of the neutrinoless double-beta (0{$νββ$}) decay of $^{76}$Ge. The setup of the prototype facility, characteristics of the BEGe detector, background reduction methods, and data analysis are described in this paper. A background index of 6.4$\times$10$^{-3}$ counts/(keV$\cdot$kg$\cdot$day) is achieved and 1.86 times lower than our previous result of the CDEX-1 detector. No signal is observed with an exposure of 186.4 kg$\cdot$day, thus a limit on the half life of $^{76}$Ge 0$νββ$ decay is set at T$_{1/2}^{0ν}$ $>$ 5.62$\times$10$^{22}$ yr at 90% C.L.. The limit corresponds to an effective Majorana neutrino mass in the range of 4.6 $\sim$ 10.3 eV, dependent on the nuclear matrix elements.

nucl-ex↗
arXiv2022

Studies of the Earth shielding effect to direct dark matter searches at the China Jinping Underground Laboratory

Dark matter direct detection experiments mostly operate at deep underground laboratories. It is necessary to consider shielding effect of the Earth, especially for dark matter particles interacting with a large cross section. We analyzed and simulated the Earth shielding effect for dark matter at the China Jinping Underground Laboratory (CJPL) with a simulation package, CJPL Earth Shielding Simulation code (CJPL\_ESS), which is applicable to other underground locations. The further constraints on the $χ$-N cross section exclusion regions are derived based on the studies with CDEX experiment data.

hep-ex↗
arXiv2021

First experimental constraints on WIMP couplings in the effective field theory framework from CDEX

We present weakly interacting massive particles (WIMPs) search results performed using two approaches of effective field theory from the China Dark Matter Experiment (CDEX), based on the data from both CDEX-1B and CDEX-10 stages. In the nonrelativistic effective field theory approach, both time-integrated and annual modulation analyses were used to set new limits for the coupling of WIMP-nucleon effective operators at 90% confidence level (C.L.) and improve over the current bounds in the low $m_χ$ region. In the chiral effective field theory approach, data from CDEX-10 were used to set an upper limit on WIMP-pion coupling at 90% C.L. We for the first time extended the limit to the $m_χ<$ 6 GeV/$c^2$ region.

hep-ex↗
arXiv2021

Improved limits on solar axions and bosonic dark matter from the CDEX-1B experiment using the profile likelihood ratio method

We present the improved constraints on couplings of solar axions and more generic bosonic dark matter particles using 737.1 kg-days of data from the CDEX-1B experiment. The CDEX-1B experiment, located at the China Jinping Underground Laboratory, primarily aims at the direct detection of weakly interacting massive particles using a p-type point-contact germanium detector. We adopt the profile likelihood ratio method for analysis of data in the presence of backgrounds. An energy threshold of 160 eV was achieved, much better than the 475 eV of CDEX-1A with an exposure of 335.6 kg-days. This significantly improves the sensitivity for the bosonic dark matter below 0.8 keV among germanium detectors. Limits are also placed on the coupling $g_{Ae} < 2.48 \times 10^{-11}$ from Compton, bremsstrahlung, atomic-recombination and de-excitation channels and $g^{eff}_{AN} \times g_{Ae} < 4.14 \times 10^{-17}$ from a $^{57}$Fe M1 transition at 90\% confidence level.

hep-ex↗
arXiv2021

New $α$-Emitting Isotope $^{214}$U and Abnormal Enhancement of $α$-Particle Clustering in Lightest Uranium Isotopes

A new $α$-emitting isotope $^{214}$U, produced by fusion-evaporation reaction $^{182}$W($^{36}$Ar, 4n)$^{214}$U, was identified by employing the gas-filled recoil separator SHANS and recoil-$α$ correlation technique. More precise $α$-decay properties of even-even nuclei $^{216,218}$U were also measured in reactions of $^{40}$Ar, $^{40}$Ca with $^{180, 182, 184}$W targets. By combining the experimental data, improved $α$-decay reduced widths $δ^2$ for the even-even Po--Pu nuclei in the vicinity of magic neutron number $N=126$ were deduced. Their systematic trends are discussed in terms of $N_{p}N_{n}$ scheme in order to study the influence of proton-neutron interaction on $α$ decay in this region of nuclei. It is strikingly found that the reduced widths of $^{214,216}$U are significantly enhanced by a factor of two as compared with the $N_{p}N_{n}$ systematics for the $84 \leq Z \leq 90$ and $N<126$ even-even nuclei. The abnormal enhancement is interpreted by the strong monopole interaction between the valence protons and neutrons occupying the $π1f_{7/2}$ and $ν1f_{5/2}$ spin-orbit partner orbits, which is supported by a large-scale shell model calculation.

nucl-ex↗
arXiv2020

The chemical structure of young high-mass star-forming clumps: (II) parsec-scale CO depletion and deuterium fraction of $\rm HCO^+$

The physical and chemical properties of cold and dense molecular clouds are key to understanding how stars form. Using the IRAM 30 m and NRO 45 m telescopes, we carried out a Multiwavelength line-Imaging survey of the 70 $μ$m dark and bright clOuds (MIAO). At a linear resolution of 0.1--0.5 pc, this work presents a detailed study of parsec-scale CO depletion and $\rm HCO^+$ deuterium (D-) fractionation toward four sources (G11.38+0.81, G15.22-0.43, G14.49-0.13, and G34.74-0.12) included in our full sample. In each source with $\rm T<20$ K and $n_{\rm H}\rm\sim10^4$--$\rm 10^5 cm^{-3}$, we compared pairs of neighboring 70 $μ$m bright and dark clumps and found that (1) the $\rm H_2$ column density and dust temperature of each source show strong spatial anticorrelation; (2) the spatial distribution of CO isotopologue lines and dense gas tracers, such as 1--0 lines of $\rm H^{13}CO^+$ and $\rm DCO^+$, are anticorrelated; (3) the abundance ratio between $\rm C^{18}O$ and $\rm DCO^+$ shows a strong correlation with the source temperature; (4) both the $\rm C^{18}O$ depletion factor and D-fraction of $\rm HCO^+$ show a robust decrease from younger clumps to more evolved clumps by a factor of more than 3; and (5) preliminary chemical modeling indicates chemical ages of our sources are ${\sim}8\times10^4$ yr, which is comparable to their free-fall timescales and smaller than their contraction timescales, indicating that our sources are likely dynamically and chemically young.

astro-ph.GA↗
arXiv2020

Direct Detection Constraints on Dark Photons with CDEX-10 Experiment at the China Jinping Underground Laboratory

We report constraints on the dark photon effective kinetic mixing parameter ($κ$) with data taken from two ${p}$-type point-contact germanium detectors of the CDEX-10 experiment at the China Jinping Underground Laboratory. The 90\% confidence level upper limits on $κ$ of solar dark photon from 205.4 kg-day exposure are derived, probing new parameter space with masses (${m_V}$) from 10 to 300 eV/${c^2}$ in direct detection experiments. Considering dark photon as the cosmological dark matter, limits at 90\% confidence level with ${m_V}$ from 0.1 to 4.0 keV/${c^2}$ are set from 449.6 kg-day data, with a minimum of ${\rm{κ=1.3 \times 10^{-15}}}$ at ${\rm{m_V=200\ eV/c^2}}$.

hep-ex↗
arXiv2019

Fine structure in the $α$ decay of $^{223}$U

Fine structure in the $α$ decay of $^{223}$U was observed in the fusion-evaporation reaction $^{187}$Re($^{40}$Ar, p3n) by using fast digital pulse processing technique. Two $α$-decay branches of $^{223}$U feeding the ground state and 244 keV excited state of $^{219}$Th were identified by establishing the decay chain $^{223}$U $\xrightarrow{α_{1}}$ $^{219}$Th $\xrightarrow{α_{2}}$ $^{215}$Ra $\xrightarrow{α_{3}}$ $^{211}$Rn. The $α$-particle energy for the ground-state to ground-state transition of $^{223}$U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62$^{+14}_{-10}$ $μ$s. Evolution of nuclear structure for $N$ = 131 even-$Z$ isotones from Po to U was discussed in the frameworks of nuclear mass and reduced $α$-decay width, a weakening octupole deformation in the ground state of $^{223}$U relative to its lighter isotones $^{219}$Ra and $^{221}$Th was suggested.

nucl-ex↗
arXiv2018

Phenomenological study on the decay widths of $Υ(nS)\rightarrow \bar{d}^{\ast}(2380)+X$

The decay widths of $Υ(nS)$ $\rightarrow$ $\bar{d}^{\ast}(2380)+X$ with $n=1,2,3$ are studied in a phenomenological way. With the help of crossing symmetry, the decay widths are obtained by investigating the imaginary part of the forward scattering amplitudes between $d^\ast$ and $Υ(nS)$. The wave functions of $d^\ast$ and deuteron obtained in previous studies are used for calculating the amplitude. The interaction between $d^{\ast}$ ($d$) and $Υ$ is governed by the quark-meson interaction where the coupling constant is determined by fitting the observed widths of $Υ(nS)$ $\rightarrow$ $\bar{d}+X$. The numerical results show that the decay widths of $Υ(nS)$ $\rightarrow$ $\bar{d}^{\ast}+X$ are about $2 - 10$ times smaller than that of $\bar{d}+X$. The calculated momentum of $\bar{d^*}$ is in the range $0.3-0.8$ GeV. Therefore, it is very likely that one can find $\bar{d}^\ast(2380)$ in these semi-inclusive decay processes.

hep-ph↗
arXiv2017

The most distant, luminous, dusty star-forming galaxies: redshifts from NOEMA and ALMA spectral scans

We present 1.3- and/or 3-mm continuum images and 3-mm spectral scans, obtained using NOEMA and ALMA, of 21 distant, dusty, star-forming galaxies (DSFGs). Our sample is a subset of the galaxies selected by Ivison et al. (2016) on the basis of their extremely red far-infrared (far-IR) colours and low {\it Herschel} flux densities; most are thus expected to be unlensed, extraordinarily luminous starbursts at $z \gtrsim 4$, modulo the considerable cross-section to gravitational lensing implied by their redshift. We observed 17 of these galaxies with NOEMA and four with ALMA, scanning through the 3-mm atmospheric window. We have obtained secure redshifts for seven galaxies via detection of multiple CO lines, one of them a lensed system at $z=6.027$ (two others are also found to be lensed); a single emission line was detected in another four galaxies, one of which has been shown elsewhere to lie at $z=4.002$. Where we find no spectroscopic redshifts, the galaxies are generally less luminous by 0.3-0.4 dex, which goes some way to explaining our failure to detect line emission. We show that this sample contains amongst the most luminous known star-forming galaxies. Due to their extreme star-formation activity, these galaxies will consume their molecular gas in $\lesssim 100$ Myr, despite their high molecular gas masses, and are therefore plausible progenitors of the massive, `red-and-dead' elliptical galaxies at $z \approx 3$.

astro-ph.GA↗
arXiv2017

A large enhancement of carrier mobility in phosphorene by introducing hexagonal boron nitride substrate

Carrier mobility is a crucial character for electronic devices since it domains power dissipation and switching speed. Materials with certain high carrier mobility, equally, unveil rich unusual physical phenomena elusive in their conventional counterparts. As a consequence, the methods to enhance the carrier mobility of materials receive immense research interests due to their potential applications in more effective electronic devices and enrichment of more unusual phenomena. For instance, introducing a flat hexagonal boron nitride (h-BN) substrate to enhance the carrier mobility has been achieved experimentally. However, the underlying mechanics is not well understood. In this study, we estimate the carrier mobility of phosphorene on h-BN substrate (P/h-BN) within the framework of the phonon-limited scattering model at first-principles level. %Our results are generic. Besides high-$κ$ dielectric property, h-BN also possesses excellent mechanical property of a high two-dimensional elastic modulus. The P/h-BN heterostructure inherits the high elastic modulus of h-BN, leading to an enhanced carrier mobility in phosphorene. Owing to the weak van der Waals interactions between the layers, the unique electronic properties of phosphorene are almost perfectly preserved near the Fermi level, guaranteeing the superior electronic transport in P/h-BN. Our findings offer a new perspective to improve the carrier mobility in phosphorene as well as other 2D materials based field effect transistors.

cond-mat.mtrl-sci↗
arXiv2016

The rhombohedral Sb2Se3 is also an intrinsic topological insulator

Topological insulators are new class of quantum materials, which have insulating energy gaps in bulk, but exhibit gapless edge states or surface states that are protected by time-reversal symmetry at boundary. It was theoretically predicted and experimentally confirmed that the binary tetradymites Bi2Te3, Bi2Se3, and Sb2Te3 are three-dimensional topological insulators. In this work, we demonstrate by first-principles approach that the ignored Sb2Se3, although with relatively smaller spin-orbital coupling strength, can also exhibit topologically protected surface states with a bulk gap of 0.19 eV, as long as the van der Waals interaction is explicitly included in the calculations. Detailed analysis of the band structures of Sb2Se3 thin films indicates that the non-trivial surface state appears at a critical thickness of six quintuple layers.

cond-mat.mes-hall↗
arXiv2015

Scattering strength of potassium on a carbon nanotube with known chirality

We have measured the scattering strength of charged impurities on a semiconducting single-walled carbon nanotube with known chirality. The resistivity of the nanotube is measured as a function of the density of adsorbed potassium atoms, enabling the determination of the resistance added by an individual potassium atom. Holes are scattered 37 times more efficiently than electrons by an adsorbed potassium atom. The determined scattering strength is used to reveal the spatial extent and depth of the scattering potential for potassium, a model Coulomb adsorbate. Our result represents an essential experimental input to understand adsorbate-induced scattering and provides a crucial step for paving the way to rational design of nanotube-based sensors.

cond-mat.mes-hall↗
arXiv2015

Understanding the structure of $d^*(2380)$ in chiral quark model

The structure and decay properties of $d^*$ have been detailedly investigated in both the chiral SU(3) quark model and the extended chiral SU(3) quark model that describe the energies of baryon ground states and the nucleon-nucleon (NN) scattering data satisfactorily. By performing a dynamical coupled-channels study of the system of $ΔΔ$ and hidden-color channel (CC) with quantum numbers $I(J^P)=0(3^+)$ in the framework of the resonating group method (RGM), we find that the $d^*$ has a mass of about $2.38-2.42$ GeV and a root-mean-square radius (RMS) of about $0.76-0.88$ fm. The channel wave function is extracted by a projection of the RGM wave function onto the physical basis, and the fraction of CC component in the $d^*$ is found to be about $66\%-68\%$, which indicates that the $d^*$ is a hexaquark-dominated exotic state. Based on this scenario the partial decay widths of $d^*\to d π^0 π^0$ and $d^*\to d π^+π^-$ are further explicitly evaluated and the total width is then obtained by use of the branching ratios extracted from the measured cross sections of other possible decay channels. Both the mass and the decay width of $d^*$ calculated in this work are compatible with the data ($M\approx 2380$ MeV, $Γ\approx 70$ MeV) reported by WASA-at-COSY Collaboration.

nucl-th↗
arXiv2015

Manifestation of unexpected semiconducting properties in few-layer orthorhombic arsenene

In this express, we demonstrate few-layer orthorhombic arsenene is an ideal semiconductor. Due to the layer stacking, multilayer arsenenes always behave as intrinsic direct bandgap semiconductors with gap values of around 1 eV. In addition, these bandgaps can be further tuned in its nanoribbons. Based on the so-called acoustic phonon limited approach, the carrier mobilities are predicted to approach as high as several thousand square centimeters per volt-second and simultaneously exhibit high directional anisotropy. All these make few-layer arsenene promising for device applications in semiconducting industry.

physics.comp-ph↗