arXiv subjects

Xu Cao

Publications and source records attributed to Xu Cao.

135 records · Page 8Linked to original sources

arXiv2014

Disentangle the nature of resonances in coupled-channel models

We present several possible hadronic states found in coupled-channel models within the on-shell approximation. The interaction potential is constructed as a sum of the tree-level Feynman diagrams calculated with the effective Lagrangians. Based on the recent empirical data, we illustrate the possible existence of several baryonic and mesonic states with definite quantum numbers in the model. We give their properties for the purpose of further study and discuss the potential of finding them in future experiments.

hep-ph↗

arXiv2014

Charmonium resonances and Fano line shapes

Anomalous line shapes of quarkonia are explained naturally as an interference effect of a $c\bar c$ confined closed channel with the surrounding continua, well established in other fields of physics as Fano-resonances. We discuss a quark model coupled-channel analysis describing quarkonium as a mixing of closed $Q\bar Q$ and molecular-like $D\bar D$ open channels. The asymmetric line shapes observed in $ψ(3770)$ production cross sections in $e^+e^-$ annihilation to $D^0\bar{D}^0$ and $D^+ D^-$, respectively, are described very well. The method allows to extract directly from the data the amount of $Q\bar Q \leftrightarrow D\bar D$ configuration mixing.

nucl-th↗

arXiv2013

Coupled-channel analysis of $KΣ$ production on the nucleon up to 2.0 GeV

A coupled-channel effective Lagrangian model respecting unitary and gauge invariance is applied to the combined analysis of the $(π,γ) N \to KΣ$ reactions for the center of mass energies up to 2 GeV. The recent photoproduction data obtained by the CLAS, CBELSA, LEPS, and GRAAL groups are included into our calculations with the aim to extract the resonance couplings to the $KΣ$ state. Both resonances and background contributions are found to be important to reproduce a correct shape of the angular distributions and polarization observables. Our description to the data is of good quality. The extracted properties of isospin $I = 3/2$ resonances are discussed in detail while the $I = 1/2$ resonances are largely determined by the non-strangeness channels.

nucl-th↗

arXiv2011

Phenomenological study on the $\bar p N\to \bar NNππ$ reactions

We extend our recent phenomenological study of $pN \to NNππ$ reactions to the $\bar{p}N \to \bar{N}Nππ$ reactions for anti-proton beam momenta up to 3.0 GeV within an effective Lagrangian approach. The contribution of $N^*(1440)$ with its $Nσ$ decay mode is found to be dominant at the energies close to threshold for $\bar NNπ^+π^-$ and $\bar NNπ^0π^0$ channels. At higher energies or for $p\bar nπ^-π^-$ and $\bar NNπ^\pmπ^0$ channels where $N^*(1440)\to Nσ$ mode cannot contribute, large contributions from double-$Δ$, $Δ(1600) \to N^*(1440)π$, $Δ(1600) \to Δπ$ and $Δ(1620) \to Δπ$ are found. In the near-threshold region, sizeable contributions from $Δ\to Δπ$, $Δ\to Nπ$, $N \to Δπ$ and nucleon pole are also indicated. Although these results are similar to those for $pN\to NNππ$ reactions, the antinucleon-nucleon collisions are shown to be complementary to the nucleon-nucleon collisions and may even have advantages in some aspects. The PANDA/FAIR experiment is suggested to be an excellent place for studying the properties of relevant $N^*$ and $Δ^*$ resonances.

nucl-th↗

arXiv2010

Double pion production in $NN$ and $\bar{N}N$ collisions

With an effective Lagrangian approach, we give a full analysis on the $NN \to NNππ$ and $\bar{N}N\to \bar{N}Nππ$ reactions by exploring the roles of various resonances with mass up to 1.72 GeV. We find large contributions from $Δ$, $N^*(1440)$, $Δ(1600)$ and $Δ(1620)$ resonances. Our calculations also indicate sizeable contributions from nucleon poles for the energies close to the threshold. A good description to the existing data of different isospin channels of $NN\to NNππ$ and $\bar{N}N\to \bar{N}Nππ$ for beam energies up to 2.2 GeV is reached. Our results provide important implications to the ABC effect and guildlines to the future experimental projects at COSY, HADES and HIRFL-CSR. We point out that the PANDA at FAIR could be an essential place for studying the properties of baryon resonances and the data with baryon and anti-baryon in final states are worth analyzing.

nucl-th↗

arXiv2010

Phenomenological analysis of the double pion production in nucleon-nucleon collisions up to 2.2 GeV

With an effective Lagrangian approach, we analyze several NN \to NNππchannels by including various resonances with mass up to 1.72 GeV. For the channels with the pion pair of isospin zero, we confirm the dominance of N*(1440)\to Nσin the near threshold region. At higher energies and for channels with the final pion pair of isospin one, we find large contributions from N*(1440)\to Δπ, double-Delta, Δ(1600) \to N*(1440)π, Δ(1600) \to Δπand Δ(1620) \to Δπ. There are also sizeable contributions from Δ\to Δπ, Δ\to Nπ, N \to Δπand nucleon pole at energies close to the threshold. We well reproduce the total cross sections up to beam energies of 2.2 GeV except for the pp\to ppπ^0π^0 channel at energies around 1.1 GeV and our results agree with the existing data of differential cross sections of pp \to ppπ^+π^-, pp \to nnπ^+π^+ and pp \to ppπ^0π^0 which are measured at CELSIUS and COSY.

nucl-th↗

arXiv2009

Evidence of N*(1535) resonance contribution in the pn->dϕreaction

The N*(1535) resonance contributions to the pn->dϕreaction are evaluated in an effective Lagrangian model. The π-, η-, and ρ-meson exchange are considered. It is shown that the contributions from π- and ρ-meson exchange are dominant, while the contribution from η-meson exchange is negligibly small. Our theoretical results reproduce the experimental data of both total cross section and angular distribution well. This is another evidence that the N*(1535) resonance has large s\bar{s} component leading to a large coupling to Nϕ, which may be the real origin of the OZI rule violation in the \piN and pN reactions.

nucl-th↗

arXiv2008

Strangeness Production Process $pp \to nK^ + Σ^ +$ within Resonance Model

We explore production mechanism and final state interaction in the $pp \to nK^ + Σ^ +$ channel based on the inconsistent experimental data published respectively by COSY-11 and COSY-ANKE. The scattering parameter $a> 0$ for $nΣ^ +$ interaction is favored by large near-threshold cross section within a nonrelativistic parametrization investigation, and a strong $nΣ^ +$ interaction comparable to $pp$ interaction is also indicated. Based on this analysis we calculate the contribution from resonance $Δ^* (1920)$ through $π^ +$ exchange within resonance model, and the numerical result suggests a rather small near-threshold total cross section, which is consistent with the COSY-ANKE data. With an additional sub-threshold resonance $Δ^*(1620)$, the model gives a much better description to the rather large near-threshold total cross section published by COSY-11.

nucl-th↗

arXiv2008

The role of $N^{*}(1535)$ in $η'$ production

We study the near-threshold $η'$ production mechanism in nucleon-nucleon and $πN$ collisions under the assumption that sub-threshold resonance $N^{*}(1535)$ is predominant. In an effective Lagrangian approach which gives a reasonable description to the $pN \to pN η$ and $πp \to p η$ reactions, it is found that t-channel $π$ exchange make the dominate contribution to the $pN \to pN η'$ process, and a value of 6.5 for the ratio of $σ(pn \to pn η')$ to $σ(pp \to pp η')$ is predicted. A strong coupling strength of $N^{*}(1535)$ to $η' N$ ($g_{η' NN^*}^2 /4π= 1.1$) is extracted from a combined analysis to $pp \to pp η'$ and $πN \to N η'$, and the possible implication to the intrinsic component of $N^{*}(1535)$ is explored.

nucl-th↗