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Liuming Liu

Publications and source records attributed to Liuming Liu.

At least 37 records · Page 2Linked to original sources
arXiv2024

$ω$ meson from lattice QCD

Many excited states in the hadron spectrum have large branching ratios to three-hadron final states. Understanding such particles from first principles QCD requires input from lattice QCD with one-, two-, and three-meson interpolators as well as a reliable three-body formalism relating finite-volume spectra at unphysical pion mass values to the scattering amplitudes at the physical point. In this work, we provide the first-ever calculation of the resonance parameters of the $ω$ meson from lattice QCD, including an update of the formalism through matching to effective field theories. The main result of this pioneering study, the pole position of the $ω$ meson at $\sqrt{s_ω}= (778.0(11.2)-i\,3.0(5) )\,\mathrm{MeV}$, agrees reasonably well with experiment. In addition we provide an estimate of the $ω-ρ$ mass difference as $29(15)\,\mathrm{MeV}$.

hep-lat↗
arXiv2024

Pion mass dependence in $Dπ$ scattering and the $D_0^*(2300)$ resonance from lattice QCD

Lattice QCD results for isospin $I=\frac{1}{2}$ $Dπ$ scattering are presented. Utilizing a series of $N_{\text{f}}=2+1$ Wilson-Clover ensembles with pion masses of $m_π\approx 132, 208, 305$ and $317$ MeV, various two-particle operators are constructed and the corresponding finite-volume spectra are determined. The $S$ and $P$-wave scattering phase shifts are then extracted using the Lüscher approach. A clear trend for the motion of the $D_0^*(2300)$ pole is identified. With the physical pion mass configurations also included, this calculation constitutes the first lattice calculation in which the pion mass dependence of the $D_0^*(2300)$ pole is investigated and the scattering lengths are extrapolated/interpolated to the physical pion mass in $Dπ$ scattering.

hep-lat↗
arXiv2024

Quark masses and low energy constants in the continuum from the tadpole improved clover ensembles

We present the light-flavor quark masses and low energy constants using the 2+1 flavor full-QCD ensembles with stout smeared clover fermion action and Symanzik gauge actions. Both the fermion and gauge actions are tadpole improved self-consistently. The simulations are performed on 11 ensembles at 3 lattice spacings $a\in[0.05,0.11]$ fm, 4 spatial sizes $L\in[2.5, 5.1]$ fm, 7 pion masses $m_π\in[135,350]$ MeV, and several values of the strange quark mass. The quark mass is defined through the partially conserved axial current (PCAC) relation and renormalized to $\overline{\mathrm{MS}}$ 2 GeV through the intermediate regularization independent momentum subtraction (RI/MOM) scheme. The systematic uncertainty of using the symmetric momentum subtraction (SMOM) scheme is also included. Eventually, we predict $m_u=2.45(22)(20)$ MeV, $m_d=4.74(11)(09)$ MeV, and $m_s=98.8(2.9)(4.7)$ MeV with the systematic uncertainties from lattice spacing determination, continuum extrapolation and renormalization constant included. We also obtain the chiral condensate $Σ^{1/3}=268.6(3.6)(0.7)$ MeV and the pion decay constant $F=86.6(7)(1.4) $ MeV in the $N_f=2$ chiral limit, and the next-to-leading order low energy constants $\ell_3=2.43(54)(05)$ and $\ell_4=4.322(75)(96)$.

hep-lat↗
arXiv2023

Isospin-$\frac{1}{2}$ $Dπ$ scattering and the $D_0^*$ resonance

Preliminary lattice QCD results for $Dπ$ scattering in isospin $I=\frac{1}{2}$ channel are presented. Utilizing the $N_f=2+1$ Wilson-Clover configuration at two volumes ($L^3 \times T=32^3 \times 96$ and $48^3 \times 96$) with the same lattice spacing ($a=0.07746(18)$ fm) and pion mass ($m_π\approx 303$ MeV), various two-particle operators in both the COM and the moving frames are constructed and the corresponding finite-volume spectra are determined from their correlation functions. The $S$ and $P$-wave scattering phase shifts are then extracted using the Lüscher approach, assuming negligible contributions from higher partial waves. A virtual state associated with the $D_0^*$ is also identified.

hep-lat↗
arXiv2023

Hidden-charm Hexaquarks from Lattice QCD

We present a lattice QCD study of hidden-charm hexaquarks with quark content $usc\bar{d}\bar{s}\bar{c}$ based on four ensembles of gauge configurations generated by CLQCD Collaboration with pion mass in the range of 220-300MeV. Four operators with quantum numbers $0^{++}, 0^{-+}, 1^{++}$ and $1^{--}$ respectively are constructed to interpolate the hexaquarks. After validating the spectrum and the dispersion relation for ordinary hadrons, we calculate the masses of the hexaquarks and extrapolate the results to the physical pion mass and the continuum limit. We find that the masses of the four hexaquarks are all below the $Ξ_c \bar Ξ_c$ threshold, while the $0^{-+}$ hexaquark lies around the $η_c K^+K^-$ threshold. These results will be helpful for experimental searches in future and for a deep understanding of the nature of multiquark states.

hep-lat↗
arXiv2023

$Ξ_c-Ξ_c^{\prime}$ mixing From Lattice QCD

In heavy quark limit, the lowest-lying charmed baryons with two light quarks can form an SU(3) triplet and sextet. The $Ξ_c$ in the SU(3) triplet and $Ξ_c'$ in the sextet have the same $J^{PC}$ quantum number and can mix due to the finite charm quark mass and the fact the strange quark is heavier than the up/down quark. We explore the $Ξ_c$-$Ξ_c'$ mixing by calculating the two-point correlation functions of the $Ξ_c$ and $Ξ_c'$ baryons from lattice QCD. Based on the lattice data, we adopt two independent methods to determine the mixing angle between $Ξ_c$ and $Ξ_c'$. After making the chiral and continuum extrapolation, it is found that the mixing angle $θ$ is $1.2^{\circ}\pm0.1^{\circ}$, which seems insufficient to account for the large SU(3) symmetry breaking effects found in weak decays of charmed baryons.

hep-lat↗
arXiv2022

First observation of the hidden-charm pentaquarks on lattice

The s-wave scattering of $Σ_c \bar{D}$ and $Σ_c \bar{D}^*$ in the $I(J^P) = \frac{1}{2}(\frac{1}{2}^-)$ channel is calculated in lattice QCD using two ensembles with different volumes but the same lattice spacing $a\sim 0.08\mathrm{fm}$ and pion mass $M_π\sim 294\mathrm{MeV}$. The scattering amplitudes near threshold are obtained by Lüscher's finite volume method. We find bound state poles in both $Σ_c \bar{D}$ and $Σ_c \bar{D}^*$ channels, which are possibly related to the $P_c(4312)$ and $P_c(4440) / P_c(4457)$ pentaquarks observed in experiments. The binding energy is $6(2)(2)$MeV for $Σ_c \bar{D}$ and $7(3)(1)$MeV for $Σ_c \bar{D}^*$, where the first error is the statistical error and the second is the systematic error due to the lattice artifacts.

hep-lat↗
arXiv2021

Nucleon isovector scalar charge from overlap fermions

We calculate the nucleon isovector scalar charge in lattice QCD using overlap fermions on five ensembles of gauge configurations generated by the RBC/UKQCD collaboration using the domain-wall quark action with $2+1$ dynamical flavors. The five ensembles cover five pion masses, $m_π\approx$ 139, 171, 302, 337 and 371 MeV, and four lattice spacings, $a \approx $ 0.06, 0.08, 0.11 and 0.14 fm. Three to six valence quark masses are computed on each ensemble to investigate the pion mass dependence. The extrapolation to the physical pion mass, continuum and infinite volume limits is obtained by a global fit of all data to a formula originated from partially quenched chiral perturbation theory. The excited-states contamination is carefully analyzed with 3--5 sink-source separations and multi-state fits. Our final result, in the $\overline{\text{MS}}$ scheme at 2 GeV, is $g_{S}^{u-d}= 0.94 (10)_{stat}(8)_{sys}$, where the first error is the statistical error and the second is the systematic error.

hep-lat↗
arXiv2021

Scattering of two and three physical pions at maximal isospin from lattice QCD

We present the first direct $N_f=2$ lattice QCD computation of two- and three-$π^+$ scattering quantities that includes an ensemble at the physical point. We study the quark mass dependence of the two-pion phase shift, and the three-particle interaction parameters. We also compare to phenomenology and chiral perturbation theory (ChPT). In the two-particle sector, we observe good agreement to the phenomenological fits in $s$- and $d$-wave, and obtain $M_πa_0 = -0.0481(86)$ at the physical point from a direct computation. In the three-particle sector, we observe reasonable agreement at threshold to the leading order chiral expansion, i.e.\@ a mildly attractive three-particle contact term. In contrast, we observe that the energy-dependent part of the three-particle quasilocal scattering quantity is not well described by leading order ChPT.

hep-lat↗
arXiv2021

Electron-Ion Collider in China

Lepton scattering is an established ideal tool for studying inner structure of small particles such as nucleons as well as nuclei. As a future high energy nuclear physics project, an Electron-ion collider in China (EicC) has been proposed. It will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy-ion Accelerator Facility (HIAF) which is currently under construction, together with a new electron ring. The proposed collider will provide highly polarized electrons (with a polarization of $\sim$80%) and protons (with a polarization of $\sim$70%) with variable center of mass energies from 15 to 20 GeV and the luminosity of (2-3) $\times$ 10$^{33}$ cm$^{-2}$ s$^{-1}$. Polarized deuterons and Helium-3, as well as unpolarized ion beams from Carbon to Uranium, will be also available at the EicC. The main foci of the EicC will be precision measurements of the structure of the nucleon in the sea quark region, including 3D tomography of nucleon; the partonic structure of nuclei and the parton interaction with the nuclear environment; the exotic states, especially those with heavy flavor quark contents. In addition, issues fundamental to understanding the origin of mass could be addressed by measurements of heavy quarkonia near-threshold production at the EicC. In order to achieve the above-mentioned physics goals, a hermetical detector system will be constructed with cutting-edge technologies. This document is the result of collective contributions and valuable inputs from experts across the globe. The EicC physics program complements the ongoing scientific programs at the Jefferson Laboratory and the future EIC project in the United States. The success of this project will also advance both nuclear and particle physics as well as accelerator and detector technology in China.

nucl-ex↗
arXiv2021

Meson-meson scattering lengths at maximum isospin from lattice QCD

We summarize our lattice QCD determinations of the pion-pion, pion-kaon and kaon-kaon s-wave scattering lengths at maximal isospin with a particular focus on the extrapolation to the physical point and the usage of next-to-leading order chiral perturbation theory to do so. We employ data at three values of the lattice spacing and pion masses ranging from around 230 MeV to around 450 MeV, applying Luescher's finite volume method to compute the scattering lengths. We find that leading order chiral perturbation theory is surprisingly close to our data even in the kaon-kaon case for our entire range of pion masses.

hep-lat↗
arXiv2020

Hadron-Hadron Interactions from $N_f=2+1+1$ Lattice QCD: The $ρ$-resonance

We present an investigation of the Rho-meson from Nf=2+1+1 flavour lattice QCD. The calculation is performed based on gauge configuration ensembles produced by the ETM collaboration with three lattice spacing values and pion masses ranging from 230 MeV to 500 MeV. Applying the Lüscher method phase shift curves are determined for all ensembles separately. Assuming a Breit-Wigner form, the Rho-meson mass and width are determined by a fit to these phase shift curves. Mass and width combined are then extrapolated to the chiral limit, while lattice artefacts are not detectable within our statistical uncertainties. For the Rho-meson mass extrapolated to the physical point we find good agreement with experiment. The corresponding decay width differs by about two standard deviations from the experimental value.

hep-lat↗
arXiv2019

Towards the understanding of $Z_c(3900)$ from lattice QCD

Within the framework of three-channel Ross-Shaw effective range theory, we derive the constraints among different parameters of the theory in the case of a narrow resonance close to the threshold of the third channel, which is relevant for the resonance-like structure $Z_c(3900)$. The usage of these constraint relations, together with the multi-channel Lüscher formula in lattice QCD calculations are also discussed and the strategies are outlined.

hep-lat↗
arXiv2019

A coupled-channel lattice study on the resonance-like structure $Z_c(3900)$

In this exploratory study, near-threshold scattering of $D$ and $\bar{D}^*$ meson is investigated using lattice QCD with $N_f=2+1+1$ twisted mass fermion configurations. The calculation is performed within the coupled-channel Lüscher's finite-size formalism. The study focuses on the channel with $I^G(J^{PC})=1^+(1^{+-})$ where the resonance-like structure $Z_c(3900)$ was discovered. We first identify the most relevant two channels of the problem and the lattice study is performed within the two-channel scattering model. Combined with a two-channel Ross-Shaw theory, scattering parameters are extracted from the energy levels by solving the generalized eigenvalue problem. Our results on the scattering length parameters suggest that, at the particular lattice parameters that we studied, the best fitted parameters do not correspond to a peak behavior in the elastic scattering cross section near the threshold. Furthermore, within the zero-range Ross-Shaw theory, the scenario of a narrow resonance close to the threshold is disfavored beyond $3σ$ level.

hep-lat↗
arXiv2019

Topological susceptibility and $η'$ meson mass from $N_f=2$ lattice QCD at the physical point

In this paper we explore the computation of topological susceptibility and $η'$ meson mass in $N_f=2$ flavor QCD using lattice techniques with physical value of the pion mass as well as larger pion mass values. We observe that the physical point can be reached without a significant increase in the statistical noise. The mass of the $η'$ meson can be obtained from both fermionic two point functions and topological charge density correlation functions, giving compatible results. With the pion mass dependence of the $η'$ mass being flat we arrive at $M_{η'}= 772(18)\ \mathrm{MeV}$ without an explicit continuum limit. For the topological susceptibility we observe a linear dependence on $M_π^2$, however, with an additional constant stemming from lattice artifacts.

hep-lat↗
arXiv2018

Resonance properties from lattice energy levels using chiral effective field theory

We use the chiral effective field theory to study the lattice finite-volume energy levels from the meson-meson scattering. The hadron resonance properties and the scattering amplitudes at physical masses are determined from the lattice energy levels calculated at unphysically large pion masses. The results from the $πη, K\bar{K}$ and $πη'$ coupled-channel scattering and the $a_0(980)$ resonance are explicitly given as a concrete example.

hep-lat↗
arXiv2018

Towards a precise determination of the scattering amplitudes of the charmed and light-flavor pseudoscalar mesons

We study the scattering of the light-flavor pseudoscalar mesons ($π, K, η$) off the ground-state charmed mesons ($D,D_s$) within chiral effective field theory. The recent lattice simulation results on various scattering lengths and the finite-volume spectra both in the moving and center-of-mass frames, most of which are obtained at unphysical meson masses, are used to constrain the free parameters in our theory. Explicit formulas to include the $S$- and $P$-wave mixing to determine the finite-volume energy levels are provided. After a successful reproduction of the lattice data, we perform a chiral extrapolation to predict the quantities with physical meson masses, including phase shifts, inelasticities, resonance pole positions and the corresponding residues from the scattering of the light pseudoscalar and charmed mesons.

hep-ph↗