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B. S. Zou

Publications and source records attributed to B. S. Zou.

At least 73 records · Page 4Linked to original sources
arXiv2007

On the nature of the lowest $1/2^-$ baryon nonet and decuplet

From recent study of properties of the lowest spin-parity $1/2^-$ baryons, $N^*(1535)$ and $Δ^*(1620)$, new pictures for the internal structure of the lowest $1/2^-$ baryon octet and decuplet are proposed. While the lowest $1/2^-$ baryon octet may have large diquark-diquark-antiquark component, the lowest $1/2^-$ baryon decuplet is proposed to have large vector-meson-baryon components. Evidence for the "missing" members of the new pictures is pointed out and suggestions are made for detecting these predicted states from forthcoming experiments.

nucl-th↗
arXiv2007

The s-s(bar) asymmetry in nucleon and "NuTeV anomaly"

The $s$-$\bar{s}$ asymmetry in nucleon sea is an important observable for understanding nucleon structure and strong interaction. There have been many theoretical attempts on this subject and recently on its relation to the "NuTeV anomaly". Calculations with different theoretical frameworks lead to different conclusions. Here assuming a newly proposed penta-quark configuration for the $s$-$\bar{s}$ asymmetry in nucleon, we examine its contribution to the "NuTeV anomaly", with a result of about $10-20%$.

hep-ph↗
arXiv2007

The role of $N^*(1535)$ in $pp \to pp ϕ$ and $π^- p \to n ϕ$ reactions

The near threshold $ϕ$ meson production in proton-proton and $π^- p$ collisions is studied with the assumption that the production mechanism is due to the sub-$Nϕ$-threshold $N^*(1535)$ resonance. The $π^0$, $η$ and $ρ^0$-meson exchanges for proton-proton collisions are considered. It is shown that the contribution to the $pp \to pp ϕ$ reaction from the t-channel $π^0$ meson exchange is dominant. With a significant $N^*(1535)Nϕ$ coupling ($g^2_{N^*(1535)N ϕ}/4 π$ = 0.13), both $pp \to pp ϕ$ and $π^- p \to n ϕ$ data are very well reproduced. The significant coupling of the $N^*(1535)$ resonance to $N ϕ$ is compatible with previous indications of a large $s \bar{s}$ component in the quark wave function of the $N^*(1535)$ resonance and may be the real origin of the significant enhancement of the $ϕ$ production over the naive OZI-rule predictions.

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arXiv2007

Possibility of measuring a0(980)-f0(980) mixing from J/psi -> phi a0

The a0(980)-f0(980) mixing intensity has been predicted to be in the range of 0.01 to 0.1 by various theoretical models, but lacking firm experimental observation. We examine the possibility of extracting the a0(980)-f0(980) mixing from J/psi -> phi f0 -> phi a0 reaction at upgraded Beijing Electron Positron Collider with BESIII detector. While the branching ratio of this process through the a0(980)-f0(980) mixing is expected to be about $O(10^{-6})$ similar to the estimated total amount from two background reactions J/psi -> gamma* -> phi a0 and J/psi -> K* K + c.c. -> phi a0, the peak width from the a0(980)-f0(980) mixing is about 8 MeV, much smaller than that from other mechanisms. With $10^9$ $J/ψ$ events at BESIII, the a0(980)-f0(980) mixing intensity is expected to be unambiguously and precisely measured.

hep-ph↗
arXiv2007

The role of $Δ^{++*}(1620)$ resonances in $pp \to nK^+Σ^+$ reaction and its important implications

The $pp \to nK^+Σ^+$ reaction is a very good isospin 3/2 filter for studying $Δ^{++*}$ decaying to $K^+Σ^+$. With an effective Lagrangian approach, contributions from a previous ignored sub-$K^+Σ^+$-threshold resonance $Δ^{++*}(1620)1/2^-$ are fully included in addition to those already considered in previous calculations. It is found that the $Δ^{++*}(1620)1/2^-$ resonance gives an overwhelmingly dominant contribution for energies very close to threshold, with a very important contribution from the t-channel $ρ$ exchange. This solves the problem that all previous calculations seriously underestimate the near-threshold cross section by order(s) of magnitude. Many important implications of the results are discussed.

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arXiv2006

Strangeness in the proton and N*(1535)

The newest progress on the study of the strangeness in the proton and in the lowest negative parity nucleon excited state $N^*(1535)$ is reviewed. Implications on the internal quark structure of the proton, $N^*(1535)$ and other baryons are discussed. The diquark cluster picture for the 5-quark components in baryons gives a natural explanation not only to the empirical indications for a positive strangeness magnetic moment $μ_s$ and positive strangeness radius of the proton but also the longstanding mass-reverse problem of $N^*(1535)$, $N^*(1440)$ and $Λ^*(1405)$ resonances as well as the unusual decay pattern of the $N^*(1535)$ resonance. Evidence for possible existence of $N^*(1535)$'s ${1/2}^-$ SU(3) nonet partners in this picture is pointed out, and suggestion is made to search for these $1/2^-$ hyperon excited states under the well known $Σ^*(1385)$, $Λ^*(1520)$ and $Ξ^*(1530)$ peaks in various reactions.

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arXiv2006

The $qqqq\bar q$ components and hidden flavor contributions to the baryon magnetic moments

The contributions from the $qqqq\bar q$ components to the magnetic moments of the octet as well as the $Δ^{++}$ and $Ω^-$ decuplet baryons are calculated for the configurations that are expected to have the lowest energy if the hyperfine interaction depends both on spin and flavor. The contributions from the $u\bar u$, $d\bar d$ and $s\bar s$ components are given separately. It is shown that addition of $qqqq\bar q$ admixtures to the ground state baryons can improve the overall description of the magnetic moments of the baryon octet and decuplet in the quark model without SU(3) flavor symmetry breaking, beyond that of the different constituent masses of the strange and light-flavor quarks. The explicit flavor (and spin) wave functions for all the possible configurations of the $qqqq\bar q$ components with light and strange $q\bar q$ pairs are given for the baryon and octet and decuplet. Admixtures of ~ 10% of the $qqqq\bar q$ configuration where the flavor-spin symmetry is $[4]_{FS}[22]_F[22]_S$, which is likely to have the lowest energy, in particular reduces the deviation from the empirical values of the magnetic moments of the $Σ^ -$ and the $Ξ^0$ compared with the quark model.

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arXiv2006

Subthreshold rho contribution in J/psi decay to omega pion pion and Kaon anti-Kaon pion

We carry out a theoretical and Monte Carlo study on the $J/ψ$ decays into $ωππ$ and $K\bar{K}π$ through intermediate subthreshold $ρ$ meson by using SU(3)-symmetric Lagrangian approach. It is found that the subthreshold $ρ$ contribution is not negligible and may have significant influence on partial wave analysis of resonances in these channels, especially near the $ωπ$ and $K \bar{K}$ thresholds.

hep-ph↗
arXiv2005

The strangeness form factors of the proton

The present empirical information on the strangeness form factors indicates that the corresponding $uuds\bar s$ component in the proton is such that the $uuds$ subsystem has the flavor spin symmetry $[4]_{FS}[22]_F[22]_S$ and mixed orbital symmetry $[31]_X$. This $uuds\bar s$ configuration leads to the empirical signs of all the form factors $G_E^s$, $G_M^s$ and $G_A^s$. An analysis with simple quark model wave functions for the preferred configuration shows that the qualitative features of the empirical strangeness form factors may be described with a $\sim$ 15% admixture of $uuds\bar s$ with a compact wave function in the proton. Transition matrix elements between the $uud$ and the $uuds\bar s$ components give significant contributions.

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arXiv2005

Strangeness spin, magnetic moment and strangeness configurations of the proton

The implications of the empirical signatures for the positivity of the strangeness magnetic moment $μ_s$, and the negativity of the strangeness contribution to the proton spin $Δ_s$, on the possible $uuds\bar s$ configurations of five quarks in the proton are analyzed. The empirical signs for the values of these two observables can only be obtained in configurations where the $uuds$ system is orbitally excited and the $\bar s$ quark is in the ground state. The configurations, in which the $\bar s$ is orbitally excited, which include the conventional $K^+Λ^0$ congfiguration, with the exception of that, in which the $uuds$ component has spin 2, yield negative values for $μ_s$. Here the strangeness spin $Δ_s$, the strangeness magnetic moment $μ_s$ and the axial coupling constant $G_A^s$ are calculated for all possible configurations of the $uuds\bar s$ component of the proton. In the configuration with $[4]_{FS}[22]_F[22]_S$ flavor-spin symmetry, which is likely to have the lowest energy, $μ_s$ is positive and $Δ_s\simeq G_A^s\simeq -1/3μ_s$.

hep-ph↗
arXiv2005

Multi-quark components in baryons

A brief review on some recent progresses in our understanding of multi-quark components in baryons is presented. The multi-quark components in baryons seem to be mainly in colored quark cluster configurations rather than in ``meson cloud'' configurations or in the form of a sea of quark-antiquark pairs. The colored quark cluster multi-quark picture gives a natural explanation of empirical indications for a positive strangeness magnetic moment $μ_s$ of the proton and the longstanding mass-reverse problem of S11(1535) and $P11(1440) N* resonances. A model-prediction for the $μ_s$ of the proton is given.

hep-ph↗
arXiv2005

The $s\bar s$ component of the proton and the strangeness magnetic moment

A complete analysis is given of the implications of the empirical indications for a positive strangeness magnetic moment $μ_s$ of the proton on the possible configurations of the $uuds\bar s$ component of the proton. A positive value for $μ_s$ is obtained in the $s\bar s$ configuration where the $uuds$ subsystem is in an orbitally excited state with $[4]_{[FS]}[22]_F[22]_S$ flavor-spin symmetry, which is likely to have the lowest energy. The configurations in which the $\bar s$ is orbitally excited, which include the conventional $K^+Λ^0$ configuration, with exception of that in which the $uuds$ component has spin 2, yield negative values for $μ_s$. The hidden strangeness analogues of recently proposed quark cluster models for the $θ^+$ pentaquark give differing signs for $μ_s$.

hep-ph↗
arXiv2004

Coupled channel effects in pion pion S-wave interaction

We study coupled channel effects upon isospin I=2 and I=0 $ππ$ S-wave interaction. With introduction of the $ππ\toρρ\toππ$ coupled channel box diagram contribution into $ππ$ amplitude in addition to $ρ$ and $f_2 (1270)$ exchange, we reproduce the $ππ$ I=2 S-wave and D-wave scattering phase shifts and inelasticities up to 2 GeV quite well in a K-matrix formalism. For I=0 case, the same $ππ\toρρ\toππ$ box diagram is found to give the largest contribution for the inelasticity among all possible coupled channels including $ππ\toωω\toππ$, $ππ\to K \bar{K}\toππ$. We also show why the broad $σ$ appears narrower in production processes than in $ππ$ scattering process.

hep-ph↗
arXiv2004

Mechanisms for $χ_{cJ}\to ϕϕ$ Decays

Exclusive decays of $χ_{cJ}(J=0,2)$ into $ϕϕ$ are investigated in the framework of perturbative quantum chromodynamics(pQCD) and $\tpz$ quark pair creation model. The results show that these two mechanisms exhibit a quite different behavior in evaluating the decay width for the $χ_{c0}$ and $χ_{c2}$. In pQCD method with nonrelativistic(NR) approximation, while the calculated $\cxpp{2}$ decay width is comparable with measured one, the result for the $\cxpp{0}$ decay width is suppressed and much smaller than experimental value. However, in $\tpz$ quark pair creation model, the situation is reversed: the decay width of $\cxpp{0}$ is greatly enhanced and can reproduce the large measured value, while the contribution to the $\cxpp{2}$ decay width is small. The results suggest that while the pQCD mechanism is the dominant mechanism for $\cxpp{2}$ decay, the $\tpz$ quark pair creation mechanism is the dominant one for $\cxpp{0}$ decay.

hep-ph↗
arXiv2004

A Study of the Roper Resonance as a Hybrid State from $J/ψ$ Decays

The structure of the Roper resonance as a hybrid baryon is investigated through studying the transitional amplitudes in J/psi-> p\barN*, N*\barN* decays. We begin with perturbative QCD to describe the dynamical process for the J/psi-> 3\bar q+3q decay to the lowest order of α_s, and by extending the modified quark creation model to the J/psi energy region to describe the J/psi-> 3\bar q+3q +g process. The non-perturbative effects are incorporated by a simple quark model of baryons to evaluate the angular distribution parameters and decay widths for the processes J/psi-> pbar N*,N*bar N*. From fitting the decay width of J/psi->gamma p pbar to the experimental data, we extract the quark-pair creation strength g_I=15.40 GeV. Our numerical results for J/psi->pbar N*,N* bar N* decays show that the branching ratios for these decays are quite different if the Roper resonance is assumed to be a common $3q$ state or a pure hybrid state. For testing its mixing properties, we present a scheme to construct the Roper wave function by mixing |qqqg> state with a normal |qqq,2s> state. Under this picture, the ratios of the decay widths to that of the J/psi->p pbar decay are re-evaluated versus the mixing parameter. A test of the hybrid nature of the Roper resonance in J/psi decays is discussed.

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arXiv2004

Understanding I=2 pi-pi Interaction

A correct understanding and description of the I=2 pi-pi S-wave interaction is important for the extraction of the I=0 pi-pi S-wave interaction from experimental data and for understanding the I=0 pi-pi S-wave interaction theoretically. With t-channel rho, f2(1270) exchange and the pi pi -> rho rho -> pi pi box diagram contribution, we reproduce the pi-pi isotensor S-wave and D-wave scattering phase shifts and inelasticities up to 2.2 GeV quite well in a K-matrix formalism.

hep-ph↗
arXiv2003

CP Test in J/Psi -> gamma phi phi Decay

We propose to test CP symmetry in the decay $\jp\to γϕϕ$, for which large data sample exists at BESII, and a data sample of $10^{10}$ $J/ψ$'s will be collected with BESIII and CLEO-C program. We suggest some CP asymmetries in this decay mode for CP test. Assuming that CP violation is introduced by the electric- and chromo-dipole moment of charm quark, these CP asymmetries can be predicted by using valence quark models. Our work shows a possible way to get information about the electric- and chromo-dipole moment of charm quark, which is little known. Our results show that with the current data sample of $J/ψ$, electric- and chromo-dipole moment can be probed at order of $10^{-14}e cm$. In the near future with a $10^{10}$ data sample, these moments can be probed at order of $10^{-16}e cm$.

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