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J. Chen

Publications and source records attributed to J. Chen.

At least 199 records · Page 11Linked to original sources
arXiv2020

Determination of strong-phase parameters in $D\rightarrow K^0_{S,L}π^+π^-$

We report the most precise measurements to date of the strong-phase parameters between $D^0$ and $\bar{D}^0$ decays to $K^0_{S,L}π^+π^-$ using a sample of 2.93 fb$^{-1}$ of $e^+e^-$ annihilation data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider. Our results provide the key inputs for a binned model-independent determination of the Cabibbo-Kobayashi-Maskawa angle $γ/ϕ_3$ with $B$ decays. Using our results, the decay model sensitivity to the $γ/ϕ_3$ measurement is expected to be between 0.7$^{\circ}$ and 1.2$^{\circ}$, approximately a factor of three smaller than that achievable with previous measurements. The improved precision of this work ensures that measurements of $γ/ϕ_3$ will not be limited by knowledge of strong phases for the next decade. Furthermore, our results provide critical input for other flavor-physics investigations, including charm mixing, other measurements of $CP$ violation, and the measurement of strong-phase parameters for other $D$-decay modes.

hep-ex↗
arXiv2020

Analysis of the decay $D^0\rightarrow K_{S}^{0} K^{+} K^{-}$

Using a data sample of $2.93~fb^{-1}$ of $e^+e^-$ collisions collected at $\sqrt{s}=3.773 GeV$ in the BESIII experiment, we perform an analysis of the decay $D^0\rightarrow K_{S}^{0} K^{+} K^{-}$. The Dalitz plot is analyzed using $1856\pm 45$ flavor-tagged signal decays. We find that the Dalitz plot is well described by a set of six resonances: $a_0(980)^0$, $a_0(980)^+$, $ϕ(1020)$, $a_2(1320)^+$, $a_2(1320)^-$ and $a_0(1450)^-$. Their magnitudes, phases and fit fractions are determined as well as the coupling of $a_0(980)$ to $K\bar{K}$, $g_{K\bar{K}}=3.77\pm 0.24\text{(stat.)}\pm0.35\text{(sys.)} GeV$. The branching fraction of the decay $D^0\rightarrow K_{S}^{0} K^{+} K^{-}$ is measured using $11660\pm 118$ untagged signal decays to be $(4.51\pm 0.05\text{(stat.)}\pm 0.16\text{(sys.)})10^{-3}$. Both measurements are limited by their systematic uncertainties.

hep-ex↗
arXiv2020

Non-Majorana states yield nearly quantized conductance in superconductor-semiconductor nanowire devices

Conductance at zero source-drain voltage bias in InSb nanowire/NbTiN superconductor devices exhibits peaks that are close to a quantized value of $2e^2/h$. The nearly quantized resonances evolve in the tunnel barrier strength, magnetic field and magnetic field orientation in a way consistent with Majorana zero modes. Our devices feature two tunnel probes on both ends of the nanowire separated by a 400 nm nanowire segment covered by the superconductor. We only find nearly quantized zero bias peaks localized to one end of the nanowire, while conductance dips are observed for the same parameters on the other end. This undermines the Majorana explanation as Majorana modes must come in pairs. We do identify states delocalized from end to end near zero magnetic field and at higher electron density, which is not in the basic Majorana regime. We lay out procedures for assessing the nonlocality of subgap wavefunctions and provide a classification of nanowire bound states based on their localization.

cond-mat.mes-hall↗
arXiv2020

Determination of the cluster-decay branching ratio from a near-threshold molecular state in $^{10}$Be

A puzzle has long existed for the $α$-cluster content in the near-threshold 7.54 MeV state of $^{10}$Be. A new measurement was conducted to measure the cluster-decay partial width of this state, using the reaction $\rm{^9Be}(\rm{^9Be}, \rm{^{10}Be}^{*} \rightarrow α+ \rm{^6He})\rm{^8Be}$ at 45 MeV beam energy. Special measures were taken to reduce the strong near-threshold background. The neutron-decay strength was also obtained based on the three-fold coincident measurement. A cluster-decay branching ratio of $(4.04 \pm 1.26)\times 10^{-4}$ is obtained, resulting in a reasonably large $α$-cluster spectroscopic factor. The present work confirms the formation of the $σ$-bond molecular rotational band headed by the 6.18 MeV state in $^{10}$Be.

nucl-ex↗
arXiv2020

A Fractional Hawkes process

We modify ETAS models by replacing the Pareto-like kernel proposed by Ogata with a Mittag-Leffler type kernel. Provided that the kernel decays as a power law with exponent $β+ 1 \in (1,2]$, this replacement has the advantage that the Laplace transform of the Mittag-Leffler function is known explicitly, leading to simpler calculation of relevant quantities.

math.PR↗
arXiv2020

Linear magneto-electric phase in ultrathin MnPS$_{3}$ probed by optical second harmonic generation

The transition metal thiophosphates $M$PS$_3$ ($M$ = Mn, Fe, Ni) are a class of van der Waals stacked insulating antiferromagnets that can be exfoliated down to the ultrathin limit. MnPS$_3$ is particularly interesting because its N$\acute{\textrm{e}}$el ordered state breaks both spatial-inversion and time-reversal symmetries, allowing for a linear magneto-electric phase that is rare among van der Waals materials. However, it is unknown whether this unique magnetic structure of bulk MnPS$_3$ remains stable in the ultrathin limit. Using optical second harmonic generation rotational anisotropy, we show that long-range linear magneto-electric type N$\acute{\textrm{e}}$el order in MnPS$_3$ persists down to at least 5.3 nm thickness. However an unusual mirror symmetry breaking develops in ultrathin samples on SiO$_2$ substrates that is absent in bulk materials, which is likely related to substrate induced strain.

cond-mat.str-el↗
arXiv2020

Cross section measurement of $e^+e^- \rightarrow η'J/ψ$ from $\sqrt{s} = 4.178$ to $4.600$ GeV

The cross section of the process $e^+e^- \rightarrow η'J/ψ$ is measured at center-of-mass energies from $\sqrt{s} =$ 4.178 to 4.600 GeV using data samples corresponding to a total integrated luminosity of 11 fb$^{-1}$ collected with the BESIII detector operating at the BEPCII storage ring. The dependence of the cross section on $\sqrt{s}$ shows an enhancement around $4.2$ GeV. While the shape of the cross section cannot be fully explained with a single $ψ(4160)$ or $ψ(4260)$ state, a coherent sum of the two states does provide a reasonable description of the data.

hep-ex↗
arXiv2019

Measurement of the $e^+e^-\toπ^+π^-π^0$ cross section from 0.7 GeV to 3.0 GeV via initial-state radiation

The cross section of the process $e^+e^-\toπ^+π^-π^0$ is measured with a precision of 1.6% to 25% in the energy range between $0.7$ and 3.0 GeV using the Initial State Radiation method. A data set with an integrated luminosity of $2.93$fb$^{-1}$ taken at the center-of-mass energy of $\sqrt{s}=3.773$GeV with the BESIII detector at the BEPCII collider is used. The product branching fractions for $ω$, $ϕ$, $ω(1420)$, and $ω(1650)$ are measured to be $\mathcal{B}(ω\to e^+e^-) \times \mathcal{B}(ω\to π^+π^-π^0)=(6.94\pm0.08\pm0.16) \times 10^{-5}$, $\mathcal{B}(ϕ\to e^+e^-) \times \mathcal{B}(ϕ\toπ^+π^-π^0) = (4.20\pm0.08\pm0.19) \times 10^{-5}$, $\mathcal{B}(ω(1420)\to e^+e^-) \times \mathcal{B}(ω(1420) \to π^+π^-π^0) = (0.84\pm0.09\pm0.09) \times 10^{-6}$, and $\mathcal{B}(ω(1650) \to e^+e^) \times \mathcal{B}(ω(1650)\to π^+π^-π^0) = (1.14\pm0.15\pm0.15)\times10^{-6}$, respectively. The branching fraction $\mathcal{B}(J/ψ\to π^+π^-π^0)$ is measured to be $(2.188 \pm 0.024 \pm 0.024 \pm0.040 (Γ_{ee}^{J/ψ}))\%$, where $Γ_{ee}^{J/ψ}$ is the dileptonic width of $J/ψ$. The first errors are of statistical, the second and third ones of systematic nature.

hep-ex↗
arXiv2019

LEGaTO: Low-Energy, Secure, and Resilient Toolset for Heterogeneous Computing

The LEGaTO project leverages task-based programming models to provide a software ecosystem for Made in-Europe heterogeneous hardware composed of CPUs, GPUs, FPGAs and dataflow engines. The aim is to attain one order of magnitude energy savings from the edge to the converged cloud/HPC, balanced with the security and resilience challenges. LEGaTO is an ongoing three-year EU H2020 project started in December 2017.

cs.DC↗
arXiv2019

Observation of the decays $χ_{cJ} \to ϕϕη$

Using a data sample of $(448.1\pm2.9)\times10^{6}$ $ψ(3686)$ decays collected by the BESIII detector at the Beijing Electron Positron Collider (BEPCII), we observe the decays $χ_{cJ}\to ϕϕη~(J=0,~1,~2)$, where the $χ_{cJ}$ are produced via the radiative processes $ψ(3686)\toγχ_{cJ}$. The branching fractions are measured to be $\mathcal B(χ_{c0}\toϕϕη)=(8.41\pm0.74\pm0.62)\times10^{-4}$, $\mathcal B(χ_{c1}\toϕϕη)=(2.96\pm0.43\pm0.22)\times 10^{-4}$, and $\mathcal B(χ_{c2} \to ϕϕη)=(5.33\pm0.52\pm0.39) \times 10^{-4}$, where the first uncertainties are statistical and the second are systematic. We also search for intermediate states in the $ϕϕ$ or $ηϕ$ combinations, but no significant structure is seen due to the limited statistics.

hep-ex↗
arXiv2019

A direct measurement of the 17O(a,g)21Ne reaction in inverse kinematics and its impact on heavy element production

During the slow neutron capture process in massive stars, reactions on light elements can both produce and absorb neutrons thereby influencing the final heavy element abundances. At low metallicities, the high neutron capture rate of 16-O can inhibit s-process nucleosynthesis unless the neutrons are recycled via the 17O(a,n)20Ne reaction. The efficiency of this neutron recycling is determined by competition between the 17O(a,n)20Ne and 17O(a,g)21Ne reactions. While some experimental data are available on the former reaction, no data exist for the radiative capture channel at the relevant astrophysical energies. The 17O(a,g)21Ne reaction has been studied directly using the DRAGON recoil separator at the TRIUMF Laboratory. The reaction cross section has been determined at energies between 0.6 and 1.6 MeV Ecm, reaching into the Gamow window for core helium burning for the first time. Resonance strengths for resonances at 0.63, 0.721, 0.81 and 1.122 MeV Ecm have been extracted. The experimentally based reaction rate calculated represents a lower limit, but suggests that significant s-process nucleosynthesis occurs in low metallicity massive stars.

nucl-ex↗
arXiv2019

First observation of the decay $χ_{cJ}\to Σ^{+}\bar{p}K_{S}^{0}+c.c. ~(J = 0, 1, 2)$

Using E1 radiative transitions $ψ(3686) \to γχ_{cJ}$ from a sample of $(448.1 \pm 2.9)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector, the decays $χ_{cJ}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.~(J = 0, 1, 2)$ are studied. The decay branching fractions are measured to be $\mathcal{B}(χ_{c0}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.) = (3.52 \pm 0.19\pm 0.21)\times10^{-4}$, $\mathcal{B}(χ_{c1}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.) = (1.53 \pm 0.10\pm 0.08)\times10^{-4}$, and $\mathcal{B}(χ_{c2}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.) = (8.25 \pm 0.83 \pm 0.49)\times10^{-5}$, where the first and second uncertainties are the statistical and systematic ones, respectively. No evident intermediate resonances are observed in the studied processes.

hep-ex↗
arXiv2019

Charge nonconservation of molecular devices in the presence of a nonlocal potential

In the presence of a nonlocal potential in molecular device systems, generally the charge conservation cannot be satisfied, and in literatures the modifications of the conventional definition of current were given to solve this problem. We demonstrate that, however, the nonconservation is not due to the invalidation of the conventional definition of current, but originates respectively from the improper approximations to electron-electron interactions and the inappropriate definition of current using pseudo wave functions in pseudopotential implementations. In this work, we propose a nonlocal-potential formulation of the interactions to fulfill the charge conservation and also give a discussion about the calculation of current when the pseudopotential is involved. As an example of application of our formulation, we further present the calculated results of a double-barrier model.

cond-mat.mes-hall↗
arXiv2019

Observation of the Kondo Screening Cloud of Micron Lengths

When a magnetic impurity exists in a metal, conduction electrons form a spin cloud that screens the impurity spin. This basic phenomenon is called the Kondo effect. Contrary to electric charge screening, the spin screening cloud occurs quantum coherently, forming spin-singlet entanglement with the impurity. Although the spins interact locally around the impurity, the cloud can spread out over micrometers. The Kondo cloud has never been detected to date, and its existence, a fundamental aspect of the Kondo effect, remains as a long-standing controversial issue. Here we present experimental evidence of a Kondo cloud extending over a length of micrometers comparable to the theoretical length $ξ_\mathrm{K}$. In our device, a Kondo impurity is formed in a quantum dot (QD), one-sided coupling to a quasi-one dimensional channel~\cite{Theory_Proposal_HS} that houses a Fabry-Perot (FP) interferometer of various gate-defined lengths $L > 1 \, μ$m. When we sweep a voltage on the interferometer end gate separated from the QD by the length $L$ to induce FP oscillations in conductance, we observe oscillations in measured Kondo temperature $T_\mathrm{K}$, a sign of the cloud at distance $L$. For $L \lesssim ξ_\mathrm{K}$ the $T_\mathrm{K}$ oscillation amplitude becomes larger for the smaller $L$, obeying a scaling function of a single parameter $L/ ξ_\mathrm{K}$, while for $L>ξ_\mathrm{K}$ the oscillation is much weaker. The result reveals that $ξ_\mathrm{K}$ is the only length parameter associated with the Kondo effect, and that the cloud lies mostly inside the length $ξ_\mathrm{K}$ which reaches microns. Our experimental method of using electron interferometers offers a way of detecting the spatial distribution of exotic non-Fermi liquids formed by multiple magnetic impurities or multiple screening channels and solving long-standing issues of spin-correlated systems.

cond-mat.mes-hall↗
arXiv2019

Erasing odd-parity states in semiconductor quantum dots coupled to superconductors

Quantum dots are gate-defined within InSb nanowires, in proximity to NbTiN superconducting contacts. As the coupling between the dot and the superconductor is increased, the odd-parity occupations become non-discernible (erased) both above and below the induced superconducting gap. Above the gap, conductance in the odd Coulomb valleys increases until the valleys are lifted. Below the gap, Andreev bound states undergo quantum phase transitions to singlet ground states at odd occupancy. We observe that the apparent erasure of odd-parity regimes coincides at low-bias and at high-bias. This observation is reproduced in numerical renormalization group simulations, and is explained qualitatively by a competition between Kondo temperature and the induced superconducting gap. In the erased odd-parity regime, the quantum dot exhibits transport features similar to a finite-size Majorana nanowire, drawing parallels between even-odd dot occupations and even-odd one-dimensional subband occupations.

cond-mat.mes-hall↗
arXiv2019

Earth wind as a possible source of lunar surface hydration

Understanding the sources of lunar water is crucial for studying the history of lunar evolution, and also the solar wind interaction with the Moon and other airless bodies. Recent observations revealed lunar hydration is very likely a surficial dynamic process driven by solar wind. Solar wind is shielded over a period of 3-5 days as the Moon passes through the Earth's magnetosphere, during which a significant loss of hydration is expected from previous works.Here we study lunar hydration inside the magnetosphere using orbital spectral data, which unexpectedly found that the polar surficial OH/H2O abundance remains at the same level when in the solar wind and in the magnetosphere. We suggest that particles from the magnetosphere (Earth wind, naturally different from solar wind) contribute to lunar hydration. From lunar orbital plasma observations, we find the existence of optimal energy ranges, other than 1 keV as previously thought, for surface hydration formation. These optimal energy ranges deduced from space observations may provide strong implications for laboratory experiments simulating lunar hydration processes.

astro-ph.EP↗
arXiv2018

Magnetization flip in Fe-Cr-Ga system

A systematic investigation about the structure and magnetism of Fe75-xCr25Gax (11<x<33) and Fe50Cr50-yGay (0<y<33) series has been carried out in this work. It shows that the parent Fe50Cr25Ga25 phase has higher tolerance for Ga replacing Cr than replacing Fe atoms. An abrupt flip of Curie temperature and magnetization in the Fe50Cr50-yGay (0<y<33) series was observed at the composition of Fe50Cr25Ga25. We proposed an explanation concerning anti-sites occupation and magnetic structure transition in this series. The induced structure is proved energetically favorable from first-principles calculations. This work can help us to understand the dependences between the crystal structure and magnetism in Fe-based Heusler compounds, and provides a method to deduce the atomic configurations based on the evolution of magnetism.

cond-mat.mtrl-sci↗