arXiv subjects

Chunjiang Shi

Publications and source records attributed to Chunjiang Shi.

11 recordsLinked to original sources

arXiv2025

Scalar and tensor structures in $J/\psi J/\psi$ scattering from lattice QCD

The $^1S_0$ and $^5S_2$ amplitudes of $J/\psi~J/\psi$ scattering are determined up to 6.6~GeV from $N_f=2$ lattice QCD simulations at $m_\pi \approx 420$~MeV and $250$~MeV. We observe an attractive interaction in the ${}^1S_0$ channel, which permits the existence of a near-threshold scalar structure. This structure may correspond to $X(6200)$, but the possible left-hand-cut effect prevents us from a precise pole determination. In the ${}^5S_2$ channel, while a near-threshold repulsive interaction is observed, a resonance appears at higher energies associated with a Castillejo-Dalitz-Dyson zero $\sqrt{s}_{\rm CDD}\approx 6.45~\rm{GeV}$ of the scattering amplitude. The tensor resonance has the parameters $(m_R,\Gamma_R)=(6.543(10), 0.548(34))~\rm{GeV}$ for $m_\pi\approx 420~\rm{MeV}$ and $(6.538(13),0.537(56))~\rm{GeV}$ for $m_\pi\approx 250~\rm{MeV}$, which are compatible with those of $X(6600)$ (or $X(6400)$) reported by ATLAS and CMS, and also support the $2^{++}$ assignment of the recent CMS study. The difference of the $^1S_0$ and $^5S_2$ $J/\psi J/\psi$ interaction is attributed to the dominance of the quark rearrangement effects. The systematic uncertainties owing to the unphysical pion mass, the finite lattice spacing, and the finite volume should be investigated by future lattice QCD studies with more sophisticated lattice setups.

hep-lat↗

arXiv2025

$\eta_c\eta_c$ and $J/\psi J/\psi$ scatterings from lattice QCD

We investigate the $S$-wave $\eta_c\eta_c$ and $J/\psi J/\psi$ scattering in the $J^{PC}=(0,2)^{++}$ channels up to a center-of-mass energy of 6.6~GeV. The calculations are carried out at two unphysical pion masses, $m_\pi\approx 420$~MeV and 250~MeV, in $N_f=2$ lattice QCD. For each $m_\pi$, we extract the finite-volume energy levels on two lattices with an identical lattice spacing ($a\simeq 0.136~\mathrm{fm}$) but different spatial volumes. Since the coupled-channel effects between the $\eta_c\eta_c$ and $J/\psi J/\psi$ channels are found to be negligible, we analyze the corresponding scattering properties using the single-channel L"{u}scher method. We find that the interactions in these dicharmonium systems are dominated by the quark rearrangement effect. In the $0^{++}$ channel, the near-threshold attraction in $J/\psi J/\psi$ and repulsion in $\eta_c\eta_c$ can be explained through the Fierz rearrangement. The attractive interaction in the ${}^1S_0$ $J/\psi J/\psi$ channel allows for the existence of a near-threshold scalar structure, which may correspond to the $X(6200)$. However, possible left-hand-cut effects due to light-hadron exchange prevent us from precisely determining the pole positions. In the $2^{++}$ channel, while the ${}^5S_2$ $J/\psi J/\psi$ system exhibits a repulsive interaction near threshold, the scattering amplitude has a Castillejo-Dalitz-Dyson zero at $\sqrt{s}=6.45~\mathrm{GeV}$ and a resonance pole at $\sqrt{s}=\big[6.543(10)-i,0.548(34)/2\big]~\mathrm{GeV}$ for $m_\pi\approx 420~\mathrm{MeV}$ and $\big[6.538(13)-i,0.537(56)/2\big]~\mathrm{GeV}$ for $m_\pi\approx 250~\mathrm{MeV}$, where the uncertainties are statistical. This resonance may correspond to the $X(6600)$ (or $X(6400)$) reported by the ATLAS and CMS Collaborations. Our result supports its $2^{++}$ assignment, in agreement with the latest spin-parity determination by CMS.

hep-lat↗

arXiv2025

Portraits of Charmoniumlike States

The charm quark density-density correlation is calculated for $1S$ and $1P$ conventional charmonia and $J^{PC}=1^{-+},0^{+-}$ charmoniumlike states from lattice QCD and are interpreted as spatial wave functions of these states with some approximations. The angular distributions of $c\bar{c}$ in conventional charmonia are found to be in accordance with the expectation of two-body systems, while that of the $1^{-+}$ state exhibits an $S$-wave feature. However, the $c\bar{c}$ radial distributions turn out to be strikingly different from the non-relativistic quark model and can be understood by the Dirac theory of two-body bound states. These results provide the first gauge invariant and model-independent three-dimensional portraits of charmonium(like) states.

hep-ph↗

arXiv2024

Use QUDA for lattice QCD calculation with Python

We developed PyQUDA, a Python wrapper for QUDA written in Cython, designed to facilitate lattice QCD calculations using the Python programming language. PyQUDA leverages the optimized linear algebra capabilities of NumPy/CuPy/PyTorch, along with the highly optimized lattice QCD operations provided by QUDA to accelerate research. This integration simplifies the process of writing calculation codes, enabling researchers to build more complex Python packages like EasyDistillation for specific physics objectives. PyQUDA supports a range of lattice QCD operations, including hybrid Monte Carlo (HMC) with N-flavor clover/HISQ fermions and inversion for the Wilson/clover/HISQ fermion action with the multigrid solver. It also includes utility functions for reading lattice QCD data stored in Chroma, MILC, and $\chi$QCD formats. Type hints are supported by stub files and multi-GPU support is provided through mpi4py.

hep-lat↗

arXiv2024

Decay properties of light $1^{-+}$ hybrids

We explore the decay properties of the isovector and isoscalar $1^{-+}$ light hybrids, $\pi_1$ and $\eta_1$, in $N_f=2$ lattice QCD at a pion mass $m_\pi \approx 417~\mathrm{MeV}$. The McNeile and Michael method is adopted to extract the effective couplings for individual decay modes, which are used to estimate the partial decay widths of $\pi_1(1600)$ and $\eta_1(1855)$ by assuming SU(3) symmetry. The partial decay widths of $\pi_1(1600)$ are predicted to be $(\Gamma_{b_1\pi}, \Gamma_{f_1(1285)\pi}, \Gamma_{\rho\pi}, \Gamma_{K^*\bar{K}}) = (325 \pm 75, \mathcal{O}(10), 52 \pm 7, 8.6 \pm 1.3)~\mathrm{MeV}$, and the total width is estimated to be $396 \pm 90~\mathrm{MeV}$, considering only statistical errors. If $\eta_1(1855)$ and the $4.4\sigma$ signal observed by BESIII (labeled as $\eta_1(2200)$) are taken as the two mass eigenstates of the isoscalar $1^{-+}$ light hybrids in SU(3), then the dominant decay channel(s) of $\eta_1(1855)$ ($\eta_1(2200)$) is $K_1(1270)\bar{K}$ ($K_1(1270)\bar{K}$ and $K_1(1400)\bar{K}$) through the $1^{+(-)}0^{-(+)}$ mode. The vector-vector decay modes are also significant for the two $\eta_1$ states. Using the mixing angle $\alpha \approx 22.7^\circ$ obtained from lattice QCD for the two $\eta_1$ states, the total widths are estimated to be $\Gamma_{\eta_1(1855)}=282(85)~\mathrm{MeV}$ and $\Gamma_{\eta_1(2200)}=455(143)~\mathrm{MeV}$. The former is compatible with the experimental width of $\eta_1(1855)$. Although many systematic uncertainties are not well controlled, these results are qualitatively informative for the experimental search for light hybrids.

hep-lat↗

arXiv2024

Form factor for Dalitz decays from $J/\psi$ to light pseudoscalars

We calculate the form factor $M(q^2)$ for the Dalitz decay $J/\psi\to \gamma^*(q^2)\eta_{(N_f=1)}$ with $\eta_{(N_f)}$ being the SU($N_f$) flavor singlet pseudoscalar meson. The difference among the partial widths $\Gamma(J/\psi\to \gamma \eta_{(N_f)})$ at different $N_f$ can be attributed in part to the $\mathbf{U}_A(1)$ anomaly that induces a $N_f$ scaling. $M(q^2)$'s in $N_f=1,2$ are both well described by the single pole model $M(q^2)=M(0)/(1-q^2/\Lambda^2)$. Combined with the known experimental results of the Dalitz decays $J/\psi\to Pe^+e^-$, the pseudoscalar mass $m_P$ dependence of the pole parameter $\Lambda$ is approximated by $\Lambda(m_P^2)=\Lambda_1(1-m_P^2/\Lambda_2^2)$ with $\Lambda_1=2.64(4)~\mathrm{GeV}$ and $\Lambda_2=2.97(33)~\mathrm{GeV}$. These results provide inputs for future theoretical and experimental studies on the Dalitz decays $J/\psi\to Pe^+e^-$.

hep-lat↗

arXiv2024

$X(3872)$ Relevant $D\bar{D}^*$ Scattering in $N_f=2$ Lattice QCD

We study the $S$-wave $D\bar{D}^*(I=0)$ scattering at four different pion masses $m_\pi$ ranging from 250 MeV to 417 MeV from $N_f=2$ lattice QCD. Three energy levels $E_{2,3,4}$ are extracted at each $m_\pi$. The analysis of $E_{2,3}$ using the effective range expansion (ERE) comes out with a shallow bound state below the $D\bar{D}^*$ threshold, and the phase shifts at $E_{3,4}$ indicate the possible existence of a resonance near 4.0 GeV. We also perform a joint analysis to $E_{2,3,4}$ through the $K$-matrix parameterization of the scattering amplitude. In this way, we observe a $D\bar{D}^*$ bound state whose properties are almost the same as that from the ERE analysis. At each $m_\pi$, this joint analysis also results in a resonance pole with a mass slightly above 4.0 GeV and a width around 40-60 MeV, which are compatible with the properties of the newly observed $\chi_{c1}(4010)$ by LHCb. More scrutinized lattice QCD calculations are desired to check the existence of this resonance.

hep-lat↗

arXiv2023

Radiative transition decay width of $\psi_2(3823)\rightarrow\gamma\chi_{c1}$ from lattice QCD

We present an exploratory $N_f=2$ lattice QCD study of $\psi_2(3823)\to \gamma \chi_{c1}$ at a pion mass $m_{\pi}\approx 350$~MeV. The related two-point and three-piont functions are calculated using the distillation method. The electromagnetic multipole form factor $\hat{V}(0)=2.083(11)$ for $J/\psi\to\gamma \eta_c$ is consistent with previous lattice results, the form factors $\hat{E}_1(0)$, $\hat{M}_2(0)$ and $\hat{E}_3(0)$ for $\Gamma(\chi_{c2}\to\gamma J/\psi)$ have the same hierarchy as that derived from experiments and the predicted decay width $\Gamma(\chi_{c2}\to\gamma J/\psi)=368(5)~\text{keV}$ is in excellent agreement with the PDG value $374(10)~\text{keV}$ and previous lattice QCD results in the quenched approximation. The same strategy is applied to the study of the process $\psi_2(3823)\to \gamma \chi_{c1}$ and the partial decay width is predicted to be $337(27)~\text{keV}$. According to the BESIII constraints on the $\psi_2(3823)$ decay channels and some phenomenological results, we estimate the total width $\Gamma(\psi_2(3823))=520(100)~\text{keV}$.

hep-lat↗

arXiv2023

Decays of $1^{-+}$ Charmoniumlike Hybrid

By extracting the transition amplitudes, we give the first lattice QCD prediction of the two-body decay partial widths of the $1^{-+}$ charmoniumlike hybrid $\eta_{c1}$. Given the calculated mass value $m_{\eta_{c1}}=4.329(36)$ GeV, the $\eta_{c1}$ decay is dominated by the open charm modes $D_1\bar{D}$, $D^*\bar{D}$ and $D^*\bar{D}^*$ with partial widths of $258(133)$ MeV, $88(18)$ MeV and $150(118)$ MeV, respectively. The coupling of $\eta_{c1}$ to $\chi_{c1}$ plus a flavor singlet pseudoscalar is not small, but $\chi_{c1}\eta$ decay is suppressed by the small $\eta-\eta'$ mixing angle. The partial width of $\eta_{c1}\to \eta_c\eta'$ is estimated to be around 1 MeV. We suggest experiments to search for $\eta_{c1}$ in the $P$-wave $D^*\bar{D}$ and $D^*\bar{D}^*$ systems. Especially, the polarization of $D^*\bar{D}^*$ can be used to distinguish the $1^{-+}$ product (total spin $S=1$) from $1^{--}$ products ($S=0$).

hep-lat↗

arXiv2022

$T_{cc}^{+}(3875)$ relevant $DD^*$ scattering from $N_f=2$ lattice QCD

The $S$-wave $DD^*$ scattering in the isospin $I=0,1$ channels is studied in $N_f=2$ lattice QCD at $m_π\approx 350$ MeV. It is observed that the $DD^*$ interaction is repulsive in the $I=1$ channel when the $DD^*$ energy is near the $DD^*$ threshold. In contrast, the $DD^*$ interaction in the $I=0$ channel is definitely attractive in a wide range of the $DD^*$ energy. This is consistent with the isospin assignment $I=0$ for $T_{cc}^+(3875)$. By analyzing the components of the $DD^*$ correlation functions, it turns out that the quark diagram responsible for the different properties of $I=0,1$ $DD^*$ interactions can be understood as the charged $ρ$ meson exchange effect. This observation provides direct information on the internal dynamics of $T_{cc}^+(3875)$.

hep-lat↗

arXiv2022

$1^{-+}$ Hybrid in $J/\psi$ Radiative Decays from Lattice QCD

We present the first theoretical prediction of the production rate of $1^{-+}$ light hybrid meson $\eta_1$ in $J/\psi$ radiative decays. In the $N_f=2$ lattice QCD formalism with the pion mass $m_\pi\approx 350$ MeV, the related electromagnetic multipole form factors are extracted from the three-point functions that involve necessarily quark annihilation diagrams, which are calculated through the distillation method. The partial width of $J/\psi\to \gamma \eta_1$ is determined to be $2.29(77)~\mathrm{eV}$ at the $\eta_1$ mass $m_{\eta_1}=2.23(4)$ GeV. If $\eta_1$ corresponds to the recently observed $\eta_1(1855)$ in the process $J/\psi\to \gamma\eta_1(1855)\to \gamma \eta\eta'$ by BESIII, then the branching fraction $\mathrm{Br}(J/\psi\to \gamma\eta_1(1855))$ is estimated to be $6.2(2.2)\times 10^{-5}$, which implies $\mathrm{Br}(\eta_1(1855)\to \eta\eta')\sim 4.3\%$.

hep-lat↗