arXiv subjects

Xu Cao

Publications and source records attributed to Xu Cao.

At least 127 records · Page 7Linked to original sources

arXiv2019

UCT-ADP Progressive Bias Algorithm for Solving Gomoku

We combine Adaptive Dynamic Programming (ADP), a reinforcement learning method and UCB applied to trees (UCT) algorithm with a more powerful heuristic function based on Progressive Bias method and two pruning strategies for a traditional board game Gomoku. For the Adaptive Dynamic Programming part, we train a shallow forward neural network to give a quick evaluation of Gomoku board situations. UCT is a general approach in MCTS as a tree policy. Our framework use UCT to balance the exploration and exploitation of Gomoku game trees while we also apply powerful pruning strategies and heuristic function to re-select the available 2-adjacent grids of the state and use ADP instead of simulation to give estimated values of expanded nodes. Experiment result shows that this method can eliminate the search depth defect of the simulation process and converge to the correct value faster than single UCT. This approach can be applied to design new Gomoku AI and solve other Gomoku-like board game.

cs.AI↗

arXiv2019

Confronting pentaquark photoproduction with new LHCb observations

The newly measurement of production fractions of $P_c$ states by LHCb collaboration have put restriction on their branching ratios of $J/ψp$ decay, thus constraining their photoproduction in $γp\to J/ψp$ reaction. We show the tension between LHCb results and the current experiments in search of $P_c$ photoproduction. We also find that the present information of branching ratios of $P_c\to J/ψp$ has already confronted sharply with the models which study the nature of $P_c$.

hep-ph↗

arXiv2019

The spin parity of $Z_c^-$(4100), $Z_1^+$(4050) and $Z_2^+$(4250)

We conjecture that $Z_c^-$(4100) found by LHCb group from a Dalitz plot analysis of $B^0\to η_c K^+π^-$ decay is the charge conjugate of $Z_1^+$(4050) observed in $χ_{c1}π^+$ distribution from Belle collaboration. Some interesting conclusions are inferred from this assumption. The $Z_2$(4250) would be assigned to be a $J^P = 1^+$ or $1^-$ state because of its absence in $η_{c}π^-$ invariant mass distribution, while $Z_1^+$(4050)/$Z_c^-$(4100) could be a $0^+$ or $1^-$ state but $2^+$ is unfavored because it would be coupled to $η_{c}π$ in $D$-wave. The null observation of $Z_1 Z_2$, $Z_1 Z_1$ and $Z_2 Z_2$ production in $e^+ e^-$ annihilation and $Υ(1S,2S)$ decay by Belle collaboration would further allocate the spin parity combination of $Z_1^+$(4050)/$Z_c^-$(4100) and $Z_2$(4250). Our deductions can be used to exclude a set of proposed models and could be further tested by future experiment, e.g. in $γγ$ collisions.

hep-ph↗

arXiv2019

Neural Style Transfer for Point Clouds

How can we edit or transform the geometric or color property of a point cloud? In this study, we propose a neural style transfer method for point clouds which allows us to transfer the style of geometry or color from one point cloud either independently or simultaneously to another. This transfer is achieved by manipulating the content representations and Gram-based style representations extracted from a pre-trained PointNet-based classification network for colored point clouds. As Gram-based style representation is invariant to the number or the order of points, the same method can be extended to transfer the style extracted from an image to the color expression of a point cloud by merely treating the image as a set of pixels. Experimental results demonstrate the capability of the proposed method for transferring style from either an image or a point cloud to another point cloud of a single object or even an indoor scene.

cs.CV↗

arXiv2018

Vector mesons and electromagnetic form factor of the $Λ$ hyperon

The measured electromagnetic form factors of $Λ$ hyperon in the time-like region are significantly deviated from pQCD prediction. We attribute the non-vanishing cross section near threshold to be the contribution of below-threshold $ϕ$(2170) state, supporting its exotic structure. Above the threshold, we find significant role of a wide vector meson with the mass of around 2.34 GeV, which would be the same state present in $p\bar{p}$ annihilation reactions. As a result, we give a satisfactory description of the behavior of existing data without modifying pQCD expectation.

hep-ph↗

arXiv2018

Point Cloud Colorization Based on Densely Annotated 3D Shape Dataset

This paper introduces DensePoint, a densely sampled and annotated point cloud dataset containing over 10,000 single objects across 16 categories, by merging different kind of information from two existing datasets. Each point cloud in DensePoint contains 40,000 points, and each point is associated with two sorts of information: RGB value and part annotation. In addition, we propose a method for point cloud colorization by utilizing Generative Adversarial Networks (GANs). The network makes it possible to generate colours for point clouds of single objects by only giving the point cloud itself. Experiments on DensePoint show that there exist clear boundaries in point clouds between different parts of an object, suggesting that the proposed network is able to generate reasonably good colours. Our dataset is publicly available on the project page.

cs.CV↗

arXiv2018

Parton distributions and $\cos 2ϕ_h$ asymmetry induced by anomalous photon-quark coupling

In the spectator models of the nucleon with scalar and axial-vector diquarks, we show that the effect of Pauli coupling in photon-quark vertex to the parton distribution functions (PDFs) of nucleon and azimuthal asymmetry in the unpolarized semi-inclusive deep inelastic scattering (SIDIS). This anomalous coupling gives obvious contribution to unpolarized and polarized PDFs, and also leads to a $\cos 2ϕ_h$ azimuthal asymmetry proportional to the squared Pauli form factor, due to the helicity flip of the struck quark. After determining the model parameters by fitting PDFs to the global fits, this new distribution for $\cos 2ϕ_h$ asymmetry is given numerically. In the framework of transverse momentum dependence (TMD), we find that it is positive and of a few percent in the kinematical regime of HERMES and COMPASS collaborations, in the same order of magnitude with Cahn effect.

hep-ph↗

arXiv2017

Single-spin asymmetries in SIDIS induced by anomalous gluon-quark and photon-quark couplings

We calculate the contribution of the non-perturbative Pauli couplings in the quark-photon and quark-gluon vertices to the single-spin asymmetries (SSAs) in semi-inclusive deep inelastic scattering (SIDIS). We describe the nucleon using the spectator model with scalar and axial-vector diquarks. Both of the new couplings can cause the helicity flip of the struck quark. The helicity flip and the rescattering induced by the non-perturbative gluon exchange between the struck quark and diquark lead to the SSAs. Their azimuthal dependencies are the same as that usually ascribed to the Collins and Sivers effects. Our numerical results, based on the instanton model for the QCD vacuum, show that the non-perturbative quark-gluon and quark-photon interactions have a strong influence on these asymmetries.

hep-ph↗

arXiv2017

Compton scattering off proton in the third resonance region

Compton scattering off the proton in the third resonance region is analyzed for the first time, owing to the full combined analysis of pion- and photo-induced reactions in a coupled-channel effective Lagrangian model with K-matrix approximation. Two isospin $I=3/2$ resonances $D_{33}(1700)$ and $F_{35}(1930)$ are found to be essential in the range of 1.6 - 1.8 GeV. The recent beam asymmetry data of Compton scattering from the GRAAL facility are used to determine the helicity couplings of these resonances, and strong constraints are coming also from $πN$ and $KΣ$ photoproduction data. The possible spin and parity of new narrow resonances is discussed.

nucl-th↗

arXiv2017

L2GSCI: Local to Global Seam Cutting and Integrating for Accurate Face Contour Extraction

Current face alignment algorithms can robustly find a set of landmarks along face contour. However, the landmarks are sparse and lack curve details, especially in chin and cheek areas where a lot of concave-convex bending information exists. In this paper, we propose a local to global seam cutting and integrating algorithm (L2GSCI) to extract continuous and accurate face contour. Our method works in three steps with the help of a rough initial curve. First, we sample small and overlapped squares along the initial curve. Second, the seam cutting part of L2GSCI extracts a local seam in each square region. Finally, the seam integrating part of L2GSCI connects all the redundant seams together to form a continuous and complete face curve. Overall, the proposed method is much more straightforward than existing face alignment algorithms, but can achieve pixel-level continuous face curves rather than discrete and sparse landmarks. Moreover, experiments on two face benchmark datasets (i.e., LFPW and HELEN) show that our method can precisely reveal concave-convex bending details of face contours, which has significantly improved the performance when compared with the state-ofthe- art face alignment approaches.

cs.CV↗

arXiv2016

The role of $a_1(1260)$ in $π^- p \to a^-_1(1260) p$ and $π^- p \to π^- ρ^0 p$ reactions near threshold

We report on a theoretical study of the $π^- p \to a^-_1(1260) p$ and $π^- p \to π^- ρ^0 p$ reactions near threshold within an effective Lagrangian approach. The production process is described by $t$-channel $ρ^0$ meson exchange. For the $π^- p \to π^- ρ^0 p$ reaction, the final $π^- ρ^0$ results from the decay of the $a_1(1260)$ resonance which is assumed as a dynamically generated state from the $K^* \bar K$ and $ρπ$ coupled channel interactions. We calculate the total cross section of the $π^- p \to a^-_1(1260) p$ reaction. It is shown that, with the coupling constant of the $a_1(1260)$ to $ρπ$ channel obtained from the chiral unitary theory and a cut off parameter $Λ_ρ\sim 1.5$ GeV in the form factors, the experimental measurement can be reproduced. Furthermore, the total and differential cross sections of $π^- p \to a^-_1(1260) p \to π^- ρ^0 p$ reaction are evaluated, and it is expected that our model calculations can be tested by future experiments. These reactions are important for the study of the $a_1(1260)$ resonance and would provide further clue for the nature of $a_1(1260)$ state.

nucl-th↗

arXiv2016

Production and Interactions of Hyperons and Hypernuclei

The production of strangeness on the nucleon and hyperon and hypernuclear production in heavy ion collisions at relativistic energies and in antiproton annihilation on nuclei is discussed. The reaction process is described by transport theory with focus on $S=-2$ channels and a comparison of different model interactions. The interactions of hyperons in nuclear matter is investigated in a novel SU(3) approach. An outlook to the $S=-3$ sector and $Ω^-$ physics is given.

nucl-th↗

arXiv2015

Neutral pion photoproduction on the nucleon in a chiral quark model

A chiral quark-model approach is adopted to study the $γp\rightarrow π^0p$ and $γn\rightarrow π^0 n$ reactions. Good descriptions of the total and differential cross sections and single-polarization observables are obtained from the pion production threshold up to the second resonance region. It is found that (i) the $n=0$ shell resonance $Δ(1232)P_{33}$, the $n=1$ shell resonances $N(1535)S_{11}$ and $N(1520)D_{13}$, and the $n=2$ shell resonance $N(1720)P_{13}$ play crucial roles in these two processes. They are responsible for the first, second and third bump structures in the cross sections, respectively. (ii) Furthermore, obvious evidences of $N(1650)S_{11}$ and $Δ(1620)S_{31}$ are also found in the reactions. They notably affect the cross sections and the polarization observables from the second resonance region to the third resonance region. (iii) The $u$-channel background plays a crucial role in the reactions. It has strong interferences with the $s$-channel resonances. (iv) The $t$-channel background seems to be needed in the reactions. Including the $t$-channel vector-meson exchange contribution, the descriptions in the energy region $E_γ= 600\sim 900$ MeV are improved significantly. The helicity amplitudes of the main resonances, $Δ(1232)P_{33}$, $N(1535)S_{11}$, $N(1520)D_{13}$, $N(1720)P_{13}$, $N(1650)S_{11}$ and $Δ(1620)S_{31}$, are extracted and compared with the results from other groups.

nucl-th↗

arXiv2015

Role of the $Λ^+_c(2940)$ in the $π^- p \to D^- D^0 p$ reaction close to threshold

We report on a theoretical study of the $π^- p \to D^- D^0 p$ reaction near threshold within an effective Lagrangian approach. The production process is described by $t$ channel $D^{*0}$ meson exchange, $s$-channel nucleon pole, and $u$ channel $Σ^{++}_{c}$ exchange. In our work, the final $D^0 p$ results from the ground $Λ^+_c(2286)$ state and also dominantly from the excited $Λ^+_c(2940)$ state which is assumed as a $D^{*0} p$ molecular state with spin parity $J^P = \frac{1}{2}^+$ or $\frac{1}{2}^-$. We calculate the total cross section of the $π^- p \to D^- D^0 p$ reaction. It is shown that the spin parity assignment of $\frac{1}{2}^-$ for $Λ^+_c(2940)$ gives a sizable enhancement for the total cross section in comparison with a choice of $J^p = \frac{1}{2}^+$. However, our theoretical result of the total cross section is sensitive to the value of the cutoff parameter involved in the form factor of the exchanged off-shell particles. Moreover, we also calculate the second order differential cross section and find it can be used to determine the parity of the $Λ^+_c(2940)$. It is expected that our model calculations can be tested by future experiments at J-PARC in Japan.

hep-ph↗

arXiv2015

Reexamination of the role of the $Δ^{\ast}$ resonances in the $pp\rightarrow nK^{+}Σ^{+}$ reaction

In this work, the role of the $Δ^{\ast }$ resonances in the process of $pp\rightarrow nK^{+}Σ^{+}$ are systematically investigated with the effective Lagrangian approach and the isobar model. We find that a $P_{31}$ state, either $Δ^{\ast }(1750)$ or $Δ^{\ast }(1910)$, is favored by the data while the $P_{33}$ state, namely $Δ^{\ast }(1920)$, has small contribution. Besides, either sub-threshold $S_{31}$ $Δ^{\ast }(1620)$ resonance or strong $nΣ$ final state interaction or both have possible contribution at near threshold region, depending on the measured cross sections. We demonstrate the invariant mass distributions and the Dalitz Plots in order to investigate whether it is possible to distinguish the controversial $KΣ$ production mechanism in these observables.

nucl-th↗

arXiv2015

The nature and line shapes of charmonium in the $e^+e^- \to D\bar{D}$ reactions

We explore the nature of sharp resonances with asymmetric line shape observed in cross section data, a general physical phenomenon produced by the interference of continuum background and resonances. A Fano scheme and the coupled-channel T-matrix approach are employed to this aim and their close relationship is present. As a typical example, we point out that the $ψ(3770)$ state observed in the $e^+e^-$ reactions with an anomalous line shape can be explained naturally as a resonance embedded in the $D\bar{D}$ continuum. From a coupled-channels analysis the background of $ψ(3770)$ resonance is found to originate from a pole at $\sqrt{s}=3716.0 \pm$ 30.0~MeV. As a by-product, the broad structure $X(3900)/G(3900)$ seen in the Belle data, is found to be the tail of the $ψ(3770)$ state, distorted by the opening of the $D^*\bar{D} + c.c$ channel and the onset of the $ψ(4040)$ spectral distribution, thus making the assignment as a genuine charmonium state unlikely.

nucl-th↗

arXiv2014

The nucleon resonances in the $J/ψ\to p\bar{p}η'$ decay

We are aiming to study the $J/ψ\to p\bar{p}η'$ decay in an isobar model and the effective Lagrangian approach. After a careful exploration of the contributions of the $S_{11}(1535)$, $P_{11}(1710)$, $P_{13}(1900)$, $S_{11}(2090)$ and $P_{11}(2100)$ resonances, we conclude that either a subthreshold resonance or a broad $P$-wave state in the near threshold range seems to be indispensable to describe present data of the $πN \to η'N$. Furthermore, at least one broad resonance above $η'N$ threshold is preferred. With this detailed analysis, we could give the invariant mass spectrum and Dalitz plot of the $J/ψ\to p\bar{p}η'$ decay for the purpose of assisting the future detailed partial wave analysis. It is found that the $J/ψ\to p\bar{p}η'$ data are useful for disentangling the above or below threshold resonant contribution, though it still further needs the differential cross section data of $πN \to η'N$ to realize some of the resonant and the non-resonant contribution. Our results are enlightening for the $η'N$ production mechanism and the properties of the nucleon resonances with the mass around 2.0~GeV.

nucl-th↗

arXiv2014

The $R_{uds}$ value in the vicinity of $ψ(3770)$ state

The anomalous line shape of the $ψ(3770)$ state has resulted in some difficulty in the determination of the $R$ value for the continuum light hadron production in the resonance energy range. We parameterize the asymmetric line shape using a Fano-type formula and extract the $R_{uds}$ value to be $2.156\pm 0.022$ from the data of BESIII Collaboration in the energy region between 3.650 and 3.872 GeV. The small discrepancy between experiment and theory is removed. The cross sections of the $e^+e^- \rightarrow hadrons$ are given by subtracting the part of continuum light hadron production and are compared to the data of the $e^+e^- \rightarrow D\bar{D}$ reaction.

hep-ph↗