arXiv subjects

Xuan Luo

Publications and source records attributed to Xuan Luo.

At least 91 records · Page 5Linked to original sources

arXiv2023

$X$ and $Z_{cs}$ in $B^+\to J/ψϕK^+$ as $s$-wave threshold cusps and alternative spin-parity assignments to $X(4274)$ and $X(4500)$

Recent LHCb's amplitude analysis on $B^+\to J/ψϕK^+$ suggests the existence of exotic $X$ and $Z_{cs}$ hadrons, based on an assumption that Breit-Wigner resonances describe all the peak structures. However, all the peaks and also dips in the spectra are located at relevant meson-meson thresholds where threshold kinematical cusps might cause such structures. This points to the importance of an independent amplitude analysis with due consideration of the kinematical effects, and this is what we do in this work. Our model fits well $J/ψϕ$, $J/ψK^+$, and $K^+ϕ$ invariant mass distributions simultaneously, demonstrating that all the $X$, $Z_{cs}$, and dip structures can be well described with the ordinary $s$-wave threshold cusps. Spin-parity of the $X(4274)$ and $X(4500)$ structures are respectively $0^-$ and $1^-$ from our model, as opposed to $1^+$ and $0^+$ from the LHCb's. With all relevant threshold cusps considered, the number of fitting parameters seems to be significantly reduced. The LHCb data requires $D_s^{(*)}\bar{D}^{*}$ scattering lengths in our model to be consistent with zero, disfavoring $D_s^{(*)}\bar{D}^{*}$ molecule interpretations of $Z_{cs}(4000)$ and $Z_{cs}(4220)$ and, via the SU(3) relation, being consistent with previous lattice QCD results.

hep-ph↗

arXiv2022

Triangle mechanism in the decay process $B_0 \to J/ψK^0 f_0(980)(a_0(980))$

The role of the triangle mechanism in the decay process $B_0\to J/ψK^0f_0 \to J/ψK^0π^+π^-$ and $B_0\to JψK^0a_0\to J/ψK^0 π^0η$ is probed. In these process, the triangle singularity appears from the decay of $B^0$ into $J/ψϕK^0$ then $ϕ$ decays into $K^0\bar{K^0}$ and $K^0\bar{K^0}$ merged into $f_0$ or $a_0$ which finally decay into $π^+π^-$ and $π^0η$ respectively. We find that this mechanism leads to a triangle singularity around $M_{\rm inv}(K^0f_0(a_0))\approx1520\ {\rm MeV}$, and gives sizable branching fractions ${\rm{Br}}(B_0\to J/ψK^0f_0\to J/ψK^0π^+π^-)=1.38\times10^{-6}$ and $ {\rm{Br}}(B_0\to J/ψK^0a_0\to J/ψK^0π^0η)=2.56\times10^{-7}$. This potential investigation can help us obtain the information of the scalar meson $f_0(980)$ or $a_0(980)$.

hep-ph↗

arXiv2022

Explanation of Y(4630) as hadronic resonant state

After Y(4630) is discovered, theorists have given various explanations. We find that if Y(4630) is interpreted as the D-wave resonant state of $Λ_c \bar Λ_c$ system, the particle mass, decay width and all quantum numbers are consistent with experimental observations. We use the Bonn approximation to get the interaction potential of one boson exchange model, then extend the complex scaling method (CSM) to calculate the bound and resonant states. The results indicate that the $Λ_c \barΛ_c$ system can form not only the bound state of S wave, but also the resonant state of the high angular momentum, and the $^3D_1$ wave resonant state can explain the structure of Y(4630) very well.

hep-ph↗

arXiv2022

Metal to Mott Insulator Transition in Two-dimensional 1T-TaSe$_2$

When electron-electron interaction dominates over other electronic energy scales, exotic, collective phenomena often emerge out of seemingly ordinary matter. The strongly correlated phenomena, such as quantum spin liquid and unconventional superconductivity, represent a major research frontier and a constant source of inspiration. Central to strongly correlated physics is the concept of Mott insulator, from which various other correlated phases derive. The advent of two-dimensional (2D) materials brings unprecedented opportunities to the study of strongly correlated physics in the 2D limit. In particular, the enhanced correlation and extreme tunability of 2D materials enables exploring strongly correlated systems across uncharted parameter space. Here, we discover an intriguing metal to Mott insulator transition in 1T-TaSe$_2$ as the material is thinned down to atomic thicknesses. Specifically, we discover, for the first time, that the bulk metallicity of 1T-TaSe$_2$ arises from a band crossing Fermi level. Reducing the dimensionality effectively quenches the kinetic energy of the initially itinerant electrons and drives the material into a Mott insulating state. The dimensionality-driven Metal to Mott insulator transition resolves the long-standing dichotomy between metallic bulk and insulating surface of 1T-TaSe$_2$. Our results additionally establish 1T-TaSe$_2$ as an ideal variable system for exploring various strongly correlated phenomena.

cond-mat.str-el↗

arXiv2022

Interplay of broken symmetry and delocalized excitations in the insulating state of 1$T$-TaS$_2$

Coexistence of localized and extended excitations is central to the macroscopic properties of correlated materials. For 5d transition metal compounds, electron correlations alone generally do not lead to a metal-insulator (Mott) transition, with insulating behavior usually resulting from their coupling with magnetic ordering and/or structural distortions. 1$T$-TaS$_2$ is a prototypical example of such correlated insulating behavior, with a high-symmetry metallic phase transforming into a distorted, charge density wave (CDW) insulating state at low temperatures. The relevance of the localized electron physics at play in 3d compounds to these 5d transition metal compounds remains an open question. We resolved this standing controversy in 1$T$-TaS$_2$ combining resonant inelastic X-ray spectroscopy and first-principles calculations. We observed five electronic excitations arising from the interband transitions of the Ta 5d orbitals and the S 3p ligand state, with none of the excitations on the order of the Mott gap. These excitations cannot be explained within the framework of standard multiplet calculations that assume a localized wavefunction, but instead, are captured by a band theory framework accounting for the low symmetry of the crystal field in the CDW state. Our findings suggest that the electronic property of 1$T$-TaS$_2$ is dominated by both plasmonic quasiparticles and inter-band transitions associated with a Drude-type response, with no resonance associated with a putative Mott transition. Our discovery provides new insights into the electron localization and the onset of insulating behavior in 5d transition metal materials.

cond-mat.mtrl-sci↗

arXiv2022

Investigation for $Z$-boson decay into $Ξ_{bc}$ and $Ξ_{bb}$ baryon with the NRQCD factorizations approach

The $Z$-boson decay provides good opportunities for the research on $Ξ_{bQ'}$ baryon due to large quantity of $Z$ events that can be collected at the high-energy colliders. We performed a completed investigation of the indirect production of the $Ξ_{bc}$ and $Ξ_{bb}$ baryon via $Z$-boson decay $Z\to Ξ_{bQ'}+\bar b +\bar Q'$ with $Q'= (c, b)$ quark according to NRQCD factorizations approach. After considering the contribution of the diquark states $\langle bc\rangle [^3S_1]_{\bar 3/6}$, $\langle bc\rangle [^1S_0]_{\bar 3/6}$, $\langle bb\rangle [^1S_0]_{6}$ and $\langle bb\rangle [^3S_1]_{\bar 3}$, the calculated branching ratio for $Z\toΞ_{bQ'}+X$ are ${\cal B}(Z\toΞ_{bc}+X) = 3.595\times 10^{-5}$ and ${\cal B}(Z\toΞ_{bc}+X) = 1.213\times 10^{-6}$. Moreover, the $Ξ_{bc}$ events produced are predicted to be of the $10^4(10^7)$ order at the LHC(CEPC), while the $Ξ_{bb}$ events produced are forecasted to be of the $10^3(10^6)$ order. Furthermore, we have estimated the production ratio ${\cal R}(Z_Q\toΞ^{+,0}_{bc})$ with four $Z$-boson decay channels. The ${\cal R}(Z_Q\toΞ^{+,0}_{bc})$ up to $10^{-6}$ for $Z\to c\bar c$ channel and $10^{-5}$ for $Z\to b\bar b$ channel, respectively. Finally, we present the differential decay widths of $Ξ_{bc}(Ξ_{bb})$ with respect to $s_{23}$ and $z$ distributions, and analysis the uncertainties.

hep-ph↗

arXiv2022

The strong coupling $g_{X J/ψϕ}$ of $X(4700) \to J/ψϕ$ in the light-cone sum rules

We assign the scalar tetraquark and the D-wave tetraquark state for $X(4700)$ and calculate the width of the decay $X(4700)$ $\to J/ψϕ$ within the framework of light-cone sum rules. The strong coupling $g_{X J/ψϕ}$ is obtained by considering the technique of soft-meson approximation. We also investigate the mass and the decay constant of $X(4700)$ in the framework of SVZ sum rules. Our prediction for the mass is in agreement with the experimental measurement, and that for the decay width of $X(4700)$ $\to J/ψϕ$ support the possibility that $X(4700)$ could be a scalar tetraquark state if $X(4700)$ $\to J/ψϕ$ is the predominant decay channel, or a D-wave tetraquark state if $X(4700)$ $\to J/ψϕ$ is not the predominant one and there exist other decays.

hep-ph↗

arXiv2022

Next-to-leading-order QCD correction to the exclusive double charmonium production via $Z$ decays

In this paper, we preformed a further research on the exclusive productions of double charmonium via $Z$-boson decay by using nonrelativistic QCD factorizations approach, where the single-photon fragmentation topologies of the QED diagrams, the interference terms between the QCD and full QED diagrams, the next-to-leading-order calculations of the interference terms are preformed. For the production of $J/ψ+J/ψ$ in $Z$-boson decay, the interference terms show a significantly phenomenological effect due to the addition of the newly calculated NLO QCD corrections. After adding together all contributions, the branching fraction $\mathcal{B}_{Z\to J/ψJ/ψ}$ still undershoots the CMS collaboration data obviously. In addition, we simultaneously complete the next-to-leading-order calculations for $Z\to J/ψ+η_c (χ_{cJ})$ with $J=(0,1,2)$. The calculated results show that the newly-calculated complete QED and cross terms will have obvious effective on the total decay widths.

hep-ph↗

arXiv2022

Impact of $Z \to η_{c,b}+g+g$ on the inclusive $η_{c,b}$ meson yield in $Z$-boson decay

In this paper, we carry out the next-to-leading-order QCD corrections to $Z \to η_Q+g+g~(Q=c,b)$ (labeled as $gg$) through the color-singlet (CS) state of $Q\bar{Q}[^1S_0^{[1]}]$, with the aim of assessing the impact of this process on $Z$ bosons decaying into inclusive $η_Q$. We find that the QCD corrections to the $gg$ process can notably enhance its leading-order results, especially for the $η_c$ case, which would then greatly increase the existing predictions of $Γ_{Z \to η_Q+X}$ given by the CS-dominant process $Z \to η_{Q}[^1S_0^{[1]}]+Q+\bar{Q}$. Moreover, with these significant QCD corrections, the $gg$ process would exert crucial influence on the CS-predicted $η_Q$ energy distributions. In conclusion, in the CS studies of $Z \to η_Q+X$, besides $Z \to η_{Q}[^1S_0^{[1]}]+Q+\bar{Q}$, $Z \to η_Q[^1S_0^{[1]}]+g+g$ can provide phenomenologically indispensable contributions as well.

hep-ph↗

arXiv2022

On Shapley Value in Data Assemblage Under Independent Utility

In many applications, an organization may want to acquire data from many data owners. Data marketplaces allow data owners to produce data assemblage needed by data buyers through coalition. To encourage coalitions to produce data, it is critical to allocate revenue to data owners in a fair manner according to their contributions. Although in literature Shapley fairness and alternatives have been well explored to facilitate revenue allocation in data assemblage, computing exact Shapley value for many data owners and large assembled data sets through coalition remains challenging due to the combinatoric nature of Shapley value. In this paper, we explore the decomposability of utility in data assemblage by formulating the independent utility assumption. We argue that independent utility enjoys many applications. Moreover, we identify interesting properties of independent utility and develop fast computation techniques for exact Shapley value under independent utility. Our experimental results on a series of benchmark data sets show that our new approach not only guarantees the exactness of Shapley value, but also achieves faster computation by orders of magnitudes.

cs.DB↗

arXiv2022

Doubly-charmed baryon production in $Z$ boson decay

In this paper, we carry out a detailed study of doubly-charmed baryon production in $Z$ boson decay, on the basis of the nonrelativistic QCD factorization. With the inclusion of the di-quark states $(cc)[^3S_1]_{\bar{\textbf{3}}}$ and $(cc)[^1S_0]_{\textbf{6}}$, the branching ratio of $\mathcal{B}_{Z \to Ξ_{cc}+X}$ is predicted to be of the $10^{-5}$ order, indicating its experimental measurability. By comparing to the $Λ^{+}_{c}$ yield in $Z$ decay, we predict $\mathcal{R}_{Ξ_{cc}^{+}}(=\frac{Γ(Z \to Ξ^{+}_{cc}) \times \mathcal{B}(Ξ^{+}_{cc} \to Λ_c^{+}K^{-}π^{+})}{Γ(Z \to Λ_c^{+})})=(0.85^{+0.10}_{-0.07}) \times 10^{-4}$ and $\mathcal{R}_{Ξ_{cc}^{++}}(=\frac{Γ(Z \to Ξ^{++}_{cc}) \times \mathcal{B}(Ξ^{++}_{cc} \to Λ_c^{+}K^{-}π^{+}π^{+})}{Γ(Z \to Λ_c^{+})})=(1.70^{+0.20}_{-0.14}) \times 10^{-4}$, which are at clear variance with the SELEX measurements but comparable with the values given by the LHCb and Belle collaborations.

hep-ph↗

arXiv2022

Coexistence of Quasi-two-dimensional Superconductivity and Tunable Kondo Lattice in a van der Waals Superconductor

Realization of Kondo lattice in superconducting van der Waals materials not only provides a unique opportunity for tuning the Kondo lattice behavior by electrical gating or intercalation, but also is helpful for further understanding the heavy fermion superconductivity. Here we report a low-temperature and vector-magnetic-field scanning tunneling microscopy and spectroscopy study on a superconducting compound (4Hb-TaS2) with alternate stacking of 1T-TaS2 and 1H-TaS2 layers. We observe the quasi-two-dimensional superconductivity in the 1H-TaS2 layer with anisotropic response to the in-plane and out-of-plane magnetic fields. In the 1T-TaS2 layer, we detect the Kondo resonance peak that results from the Kondo screening of the unpaired electrons in the Star-of-David clusters. We also find the intensity of the Kondo resonance peak is sensitive to its relative position with the Fermi level, and it can be significantly enhanced when it's further shifted towards the Fermi level by evaporating Pb atoms onto the 1T-TaS2 surface. Our results are not only important for fully understanding the electronic properties of 4Hb-TaS2, but also pave the way for creating tunable Kondo lattice in the superconducting van der Waals materials.

cond-mat.supr-con↗

arXiv2022

Persistent photogenerated state attained by femtosecond laser irradiation of thin $T_d$-MoTe$_2$

Laser excitation has emerged as a means to expose hidden states of matter and promote phase transitions on demand. Such laser induced transformations are often rendered possible owing to the delivery of spatially and/or temporally manipulated light, carrying energy quanta well above the thermal background. Here, we report time-resolved broadband femtosecond (fs) transient absorption measurements on thin flakes of Weyl semimetal candidate $T_d$-MoTe$_2$ subjected to various levels and schemes of fs-photoexcitation. Our results reveal that impulsive fs-laser irradiation alters the interlayer behavior of the low temperature $T_d$ phase as evidenced by the persistent disappearance of its characteristic coherent $^1$A$_1$ $=$ 13 cm$^{-1}$ shear phonon mode. We found that this structural transformation withstands thermal annealing up to 500 K, although it can be reverted to the 1$T$\' phase by fs-laser treatment at room temperature. Our work opens the door to reversible optical control of topological properties.

cond-mat.mtrl-sci↗

arXiv2022

StyleSDF: High-Resolution 3D-Consistent Image and Geometry Generation

We introduce a high resolution, 3D-consistent image and shape generation technique which we call StyleSDF. Our method is trained on single-view RGB data only, and stands on the shoulders of StyleGAN2 for image generation, while solving two main challenges in 3D-aware GANs: 1) high-resolution, view-consistent generation of the RGB images, and 2) detailed 3D shape. We achieve this by merging a SDF-based 3D representation with a style-based 2D generator. Our 3D implicit network renders low-resolution feature maps, from which the style-based network generates view-consistent, 1024x1024 images. Notably, our SDF-based 3D modeling defines detailed 3D surfaces, leading to consistent volume rendering. Our method shows higher quality results compared to state of the art in terms of visual and geometric quality.

cs.CV↗

arXiv2022

High-Performance Mid-IR to Deep-UV van der Waals Photodetectors Capable of Local Spectroscopy at Room Temperature

The ability to perform broadband optical spectroscopy with sub-diffraction-limit resolution is highly sought-after for a wide range of critical applications. However, sophisticated tip-enhanced techniques are currently required to achieve this goal. We bypass this challenge by demonstrating an extremely broadband photodetector based on a two-dimensional (2D) van der Waals heterostructure that is sensitive to light across over a decade in energy from the mid-infrared (MIR) to deep-ultraviolet (DUV) at room temperature. The devices feature high detectivity (> 10^9 cm Hz^1/2 W^-1) together with high bandwidth (2.1 MHz). The active area can be further miniaturized to submicron dimensions, far below the diffraction limit for the longest detectable wavelength of 4.1 um, enabling such devices for facile measurements of local optical properties on atomic-layer-thickness samples placed in close proximity. This work can lead to the development of low-cost and high-throughput photosensors for hyperspectral imaging at the nanoscale.

physics.optics↗

arXiv2022

Inducing and tuning Kondo screening in a narrow-electronic-band system

Although the single-impurity Kondo physics has already been well understood, the understanding of the Kondo lattice problem where a dense array of local moments couples to the conduction electrons is still far from complete. The ability of creating and tuning the Kondo lattice in non-f-electron systems will be great helpful for further understanding the Kondo lattice behavior. Here we show that the Pb intercalation in the charge-density-wave-driven narrow-electronic-band system 1T-TaS2 induces a transition from the insulating gap to a sharp Kondo resonance in the scanning tunneling microscopy measurements. It results from the Kondo screening of the localized moment in the 13-site Star-of-David clusters of 1T-TaS2, and thus confirms the cluster Mott localization of the unpaired electrons and local moment formation in the 1T-TaS2 layer. As increasing the Pb concentration, the narrow electronic band derived from the localized electrons shifts away from the Fermi level and the Kondo resonance peak is gradually suppressed. Our results pave a way for creating and tuning many-body electronic states in layered narrow-electronic-band materials.

cond-mat.str-el↗

arXiv2022

Photoinduced Interlayer Dynamics in T$_d$-MoTe$_2$: A Broadband Pump-Probe Study

We report on time-resolved broadband transient reflectivity (tr-bb-TR) measurements performed on a bulk single crystal of T$_d$-MoTe$_2$ as a function of the incident pump fluence (F). Tr-bb-TR data unveil photoinduced electronic changes progressing on the sub-picosecond timescale as well as the dynamics of the coherent low-frequency $^1A_1$ interlayer shear phonon. Our results indicate a gradual evolution of both the TR and the $^1A_1$ Fourier intensity spectra as a function of F, ruling out the threshold-like change that has been associated with the ultrafast photoinduced $T_d \to 1T'$ phase transition. We also observe a large redshift of the $^1A_1$ Fourier spectral features, which suggests that large renormalization effects are taking place on interband transitions that are dielectrically susceptible to the $^1A_1$ interlayer phonon displacement.

cond-mat.mtrl-sci↗

arXiv2022

Effect of Stacking Order on the Electronic State of 1T-TaS$_2$

New theoretical proposals and experimental findings on transition metal dichalcogenide 1T-TaS$_2$ have revived interests in its possible Mott insulating state. We perform a comprehensive scanning tunneling microscopy and spectroscopy experiment on different single-step areas in pristine 1T-TaS$_2$. After accurately determining the relative displacement of Star-of-David super-lattices in two layers, we find different stacking orders can correspond to the similar large-gap spectrum on the upper terrace. When the measurement is performed away from the step edge, the large gap spectrum can always be maintained. The stacking order seems rarely disturb the large-gap spectrum in the ideal bulk material. We conclude that the large insulating gap is from the single-layer property, which is a correlation-induced Mott gap based on the single-band Hubbard model. Specific stacking orders can perturb the state and induce a small-gap or metallic spectrum for a limited area around the step edge, which we attribute to a surface and edge phenomenon. Our work provides more evidence about the surface electronic state and deepens our understanding of the Mott insulating state in 1T-TaS$_2$.

cond-mat.str-el↗