The high accuracy $ϕ$-meson photoproduction data from the CLAS experiment in Hall~B of Jefferson Laboratory allow us to determine the near-threshold total cross section of the $γp\toϕp$ reaction and use it for evaluating the $ϕp$ scattering length $α_{ϕp}$. These data result in an absolute value of $|α_{ϕp}| = (0.063\pm 0.010)$~fm, which is smaller than the typical hadron size. A comparative analysis of $α_{ϕp}$ with the previously determined scattering lengths for $ωp$ and $J/ψp$ from the A2 and GlueX experiments is performed.
The quality of the recent GlueX $J/ψ$ photoproduction data from Hall~D at Jefferson Laboratory, and the proximity of the data to the energy threshold, gives access to a variety of interesting physics aspects. As an example, an estimation of the $J/ψ$-nucleon scattering length $α_{J/ψp}$ is provided within the vector meson dominance model. It results in $|α_{J/ψp}| = (3.08\pm 0.55 ({\rm stat.}) \pm 0.45 ({\rm syst.}))$~mfm.
Among the light baryons, the $J^π= \frac{1}{2}^-$ $Λ(1405)$ hyperon is an important special case as it sits just below the $N\bar{K}$ threshold and decays almost exclusively to $Σπ$. Some long-standing hypotheses for $Λ(1405)$ are that it could be a $N\bar{K}$ bound state or a $Σπ$ continuum resonance. It may also be considered as a simple quark-model resonance, the $P$-wave companion of the $Λ(1520)$. In recent years chiral unitary models have suggested that there are two isospin zero poles present in this mass region, and that the "line shape" of the $Λ(1405)$ depends to what extent each of …
We briefly review and expand our recent analysis for all three invariant A,B,D gravitational form factors of the nucleon in holographic QCD. They compare well to the gluonic gravitational form factors recently measured using lattice QCD simulations. The holographic A-term is fixed by the tensor $T=2^{++}$ (graviton) Regge trajectory, and the D-term by the difference between the tensor $T=2^{++}$ (graviton) and scalar $S=0^{++}$ (dilaton) Regge trajectories. The B-term is null in the absence of a tensor coupling to a Dirac fermion in bulk. A first measurement of the tensor form factor A-term is…
Perturbative QCD is applied to investigate the near threshold heavy quarkonium photoproduction at large momentum transfer. We take into account the contributions from the leading three-quark Fock states of the nucleon. The dominant contribution comes from the three-quark Fock state with one unit quark orbital angular momentum (OAM) whereas that from zero quark OAM is suppressed at the threshold. From our analysis, we also show that there is no direct connection between the near threshold heavy quarkonium photoproduction and the gluonic gravitational form factors of the nucleon. Based on the co…
High-accuracy $Υ$-meson photoproduction data from EIC and EicC experiments will allow the measurement of the near-threshold total cross section of the reaction $γp\toΥp$, from which the absolute value of the $Υp$ scattering length, $|α_{Υp}|$, can be extracted using a Vector-Meson Dominance model. For this evaluation, we used $Υ$-meson photoproduction quasi-data from the QCD approach (the production amplitude can be factorized in terms of gluonic generalized parton distributions and the quarkonium distribution amplitude). A comparative analysis of $|α_{Υp}|$ with the recently determined scatte…
The diffractive photoproduction of $J/Ψ$ on a nucleon, is mostly due to gluonic exchanges at all $\sqrt{s}$. In holographic QCD (large number of colors and strong $^\prime$t Hooft coupling), these exchanges are captured by gravitons near threshold, and their Reggeized Pomeron form asymptotically. We revisit our holographic analysis of the A and D gravitational form factors in light of the new lattice data, and use them to refine our predictions for the photoproduction of $J/Ψ$ near threshold, and the comparison to the GlueX data. We use these results to estimate the scalar and mass radii of th…
The near threshold photo or electroproduction of heavy vector quarkonium off the proton is studied in quantum chromodynamics. Similar to the high-energy limit, the production amplitude can be factorized in terms of gluonic Generalized Parton Distributions and the quarkonium distribution amplitude. At the threshold, the threshold kinematics has a large skewness parameter $ξ$, leading to the dominance of the spin-2 contribution over higher-spin twist-2 operators. Thus threshold production data are useful to extract the gluonic gravitational form factors, allowing studying the gluonic contributio…
Near-threshold heavy quarkonium photoproduction in a light-front spectator model
Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学院大学核科学与技术学院）；CAS Key Laboratory of High Precision Nuclear Spectroscopy, Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所高精度核谱学重点实验室）；Department of Physics, Indian Institute of Technology Kanpur（坎普尔印度理工学院物理系）；University of Science and Technology of China（中国科学技术大学）
JLab and J-PARC for the J/{\ensuremathψ} Production at the Threshold
The George Washington University（乔治华盛顿大学）；Korea University（韩国大学）；NRC “Kurchatov Institute”, Petersburg Nuclear Physics Institute（俄罗斯核研究中心库尔恰托夫研究所，圣彼得堡核物理研究所）
Understanding the nature of the hidden charm pentaquark(like) signals in the LHCb data for $Λ_b^0\to J/ψp K^-$ is a central problem of hadron spectroscopy. We propose a scenario completely different from previous ones such as hadron molecules and compact pentaquarks. We identify relevant double triangle mechanisms with leading or lower-order singularities. The associated anomalous threshold cusps at the $Σ_c^{(*)}\bar{D}^{(*)}$ thresholds are significantly more singular than the ordinary ones. Then we demonstrate that the double triangle amplitudes reproduce the peak structures of $P_c(4312)^+…
The trace anomalous energy contribution to the proton mass is a very important topic in non-perturbative QCD and hadron physics. In experiments, it is under the hot discussions on how to measure the trace anomalous energy.The QCD interpretation of proton trace anomaly is still not clear.To connect the theory with the experiment,we extract the trace anomaly by analyzing the near-threshold photo-production data of $ϕ$ and J/$ψ$ vector mesons. Based on the vector-meson-dominance model and QCD Van der Waals representation, we find that the percentage of trace anomaly in the proton mass ranges from…
We present a holographic analysis of diffractive photoproducton of charmonium $J/ψ$ and upsilonium $Υ$ on a proton, considered as a bulk Dirac fermion, for all ranges of $\sqrt{s}$, i.e., from near threshold to very high energy. Using the bulk wave functions of the proton and vector mesons, within holographic QCD, and employing Witten diagrams in the bulk, we compute the diffractive photoproduction amplitude of $J/ψ$ and $Υ$. The holographic amplitude shows elements of the strictures of vector meson dominance (VMD). It is dominated by the exchange of a massive graviton or $2^{++}$ glueball res…
