arXiv subjects

B. S. Zou

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

At least 55 records · Page 3Linked to original sources

arXiv2009

Theory Support for the Excited Baryon Program at the Jlab 12 GeV Upgrade

This document outlines major directions in theoretical support for the measurement of nucleon resonance transition form factors at the JLab 12 GeV upgrade with the CLAS12 detector. Using single and double meson production, prominent resonances in the mass range up to 2 GeV will be studied in the range of photon virtuality $Q^2$ up to 12 GeV$^2$ where quark degrees of freedom are expected to dominate. High level theoretical analysis of these data will open up opportunities to understand how the interactions of dressed quarks create the ground and excited nucleon states and how these interactions emerge from QCD. The paper reviews the current status and the prospects of QCD based model approaches that relate phenomenological information on transition form factors to the non-perturbative strong interaction mechanisms, that are responsible for resonance formation.

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arXiv2009

Further evidence for the $Σ^{*}$ resonance with $J^P=1/2^-$ around 1380 MeV

The unquenched quark models predict the new particle $Σ^*$ with spin parity $J^P=1/2^-$ and its mass is around the well established $Σ^*(1385)$ with $J^P=3/2^+$. Here by using the effective Lagrangian approach we study \kp\ reaction at the range of $Λ^{*}(1520)$ peak, comparing the resulting total cross section, and $π^+π^-$, $Λπ^+$, $Λπ^-$ invariant squared mass distributions for various incident $K^-$ momenta, as well as the production angular distribution of the $Λ$ with the data from the Lawrence Berkeley Laboratory 25-inch hydrogen bubble chamber, we find that, apart from the existing resonance $Σ^{*}(1385)$ with $J^P=3/2^+$, there is a strong evidence for the existence of the new resonance $Σ^{*}$ with $J^P=1/2^-$ around 1380 MeV. Higher statistic data on relevant reactions are needed to clarify the situation.

hep-ph↗

arXiv2009

Complementary studies on $N^*$ from $e^+e^-$, $pp$ and $p\bar p$ collisions

Complementary to the conventional experimental studies on $N^*$ from $πN$ and $γ^{(*)}N$ reactions, the $e^+e^-$, $pp$ and $p\bar p$ collisions can give novel insights into these $N^*$ resonances. While the $e^+e^-$ collisions through production and decay of vector charmonium $ψ$ provide a nice isospin filter for a simultaneously study of $N^*$, $Δ^*$, $Λ^*$, $Σ^*$ and $Ξ^*$, the $pp$ collisions should be the best place for producing those $Δ^{*++}$ with large coupling to $ρ^+p$ though $pp\to nΔ^{*++}$ reaction, and the $p\bar p$ collisions should be the best place for looking for those $N^*$ with large coupling to $σN$.

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arXiv2009

Evidence for a new $Σ^{*}$ resonance with $J^P=1/2^-$ in the old data of $K^-p\toΛπ^+π^-$ reaction

Distinctive patterns are predicted by quenched quark models and unquenched quark models for the lowest SU(3) baryon nonet with spin parity $J^P=1/2^-$. While the quenched quark models predict the lowest $1/2^-$ $Σ^*$ resonance to be above 1600 MeV, the unquenched quark models predict it to be around $Σ^*(1385)$ energy. Here we re-examine some old data of the $\kp \to \la$ reaction and find that besides the well established $Σ^{*}(1385)$ with $J^P=3/2^+$, there is indeed some evidence for the possible existence of a new $Σ^{*}$ resonance with $J^P=1/2^-$ around the same mass but with broader decay width. Higher statistic data on relevant reactions are needed to clarify the situation.

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arXiv2009

Testing the predicted dynamically generated hidden charm $X$ scalar state through the $D\bar D$ invariant mass spectrum and the radiative decay of the $ψ(3770)$

In this work we present our model that dynamically generates resonances from charmed and light pseudoscalar and vector mesons. The model generates a rich spectrum of charmed and hidden charm scalar and axial resonances, most of them which can be associated with observed states. Other states are predicted, in particular a hidden charm scalar resonance with mass close to the $D\bar D$ threshold. For this resonance we present calculations which show that an observed enhancement in the $D\bar D$ mass spectrum measured by Belle in reactions producing $D\bar D J/ψ$ in the final state could be originated by this predicted state. We also present theoretical calculations on the radiative decay width of the $ψ(3770)$ into this state. The predicted branching fractions suggest that this predicted state could be observed by BES with statistics of one year run in the $ψ(3770)$ peak.

hep-ph↗

arXiv2009

Comment on "Mass and K Lambda coupling of N*(1535)"

It is argued in [1] that when the strong coupling to the K Lambda channel is considered, Breit-Wigner mass of the lightest orbital excitation of the nucleon N(1535) shifts to a lower value. The new value turned out to be smaller than the mass of the lightest radial excitation N(1440), which effectively solved the long-standing problem of conventional constituent quark models. In this Comment we show that it is not the Breit-Wigner mass of N(1535) that is decreased, but its bare mass. [1] B. C. Liu and B. S. Zou, Phys. Rev. Lett. 96, 042002 (2006).

hep-ph↗

arXiv2009

Role of the $N^*$(1535) in the $J/ψ\to \bar{p}ηp$ and $J/ψ\to \bar{p}K^+Λ$ reactions

We study the $J/ψ\to \bar{p}ηp$ and $J/ψ\to \bar{p}K^+Λ$ reactions with a unitary chiral approach. We find that the unitary chiral approach, which generates the $N^*(1535)$ dynamically, can describe the data reasonably well, particularly the ratio of the integrated cross sections. This study provides further support for the unitary chiral description of the $N^*(1535)$. We also discuss some subtle differences between the coupling constants determined from the unitary chiral approach and those determined from phenomenological studies.

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arXiv2009

Theoretical study on pp --> p n pi+ reaction at medium energies

The $pp\to p n π^+$ reaction is a channel with the largest total cross section for pp collision in COSY/CSR energy region. In this work, we investigate individual contributions from various $N^*$ and $Δ^{*}$ resonances with mass up to about 2 GeV for the $pp\to p n π^+$ reaction. We extend a resonance model, which can reproduce the observed total cross section quite well, to give theoretical predictions of various differential cross sections for the present reaction at $T_p=2.88$ GeV. It could serve as a reference for identifying new physics in the future experiments at HIRFL-CSR.

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arXiv2009

The role of the $qqqq\bar{q}$ components in the electromagnetic transition $γ^N\to N^(1535)$

The helicity amplitudes $A^{p}_{1/2}$ and $S^{p}_{1/2}$ for the electromagnetic transition $γ^{*} N\to N^{*}(1535)$ are calculated in the quark model that is extended to include the lowest lying $qqqq\bar{q}$ components in addition to the $qqq$ component. It is found that with admixture of 5-quark components with a proportion of 20% in the nucleon and 25-65% in the $N^{*}(1535)$ resonance the calculated helicity amplitude $A^{p}_{1/2}$ decreases at the photon point, $Q^{2}=0$ to the empirical range. The $qqqq\bar{q}$ components contain $s\bar s$ pairs, which is consistent with the substantial width for $Nη$ decay of the $N^{*}(1535)$. The best description of the momentum dependence of the empirical helicity amplitudes is obtained by assuming that the $qqqq\bar{q}$ components are more compact than the $qqq$ component. However, this version of extended quark model still does not lead to a satisfactory simultaneous description of both $A^{p}_{1/2}$ and $S^{p}_{1/2}$ although with significant improvement.

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arXiv2008

Testing the nature of the $Λ$(1520) in the $J/ψ\to\barΛK^-p$ and $J/ψ\to\barΛπ^+π^-Λ$ reactions

We study the reactions $J/ψ\to\barΛK^-p$ and $J/ψ\to\barΛπ^+π^-Λ$ with a unitary chiral approach. We predict the ratio of the invariant mass distributions of these two reactions at the $Λ(1520)$ peak position, which is free of the unknown production mechanism and reflects only the properties of the $Λ(1520)$. An experimental measurement of this ratio will provide the couplings of the $Λ(1520)$ to its decay channels, allowing to test the predictions of the chiral unitary approach on this resonance, which appears as dynamically generated in that approach.

hep-ph↗

arXiv2008

Physics at BES-III

This physics book provides detailed discussions on important topics in $τ$-charm physics that will be explored during the next few years at \bes3 . Both theoretical and experimental issues are covered, including extensive reviews of recent theoretical developments and experimental techniques. Among the subjects covered are: innovations in Partial Wave Analysis (PWA), theoretical and experimental techniques for Dalitz-plot analyses, analysis tools to extract absolute branching fractions and measurements of decay constants, form factors, and CP-violation and \DzDzb-oscillation parameters. Programs of QCD studies and near-threshold tau-lepton physics measurements are also discussed.

hep-ex↗

arXiv2008

Study a0(980)-f0(980) mixing from a0(980) -> f0(980) transition

Various processes have been proposed previously to study a0(980)-f0(980) mixing through f0(980)->a0(980) transition. Here we investigate in detail the difference between a0(980)->f0(980) and f0(980)->a0(980) transitions. It is found that the a0(980)->f0(980) transition can provide additional constrains to the parameters of a0(980) and f0(980) mesons. Proposal is made to study a0(980)-f0(980) mixing from chi_{c1}->pi^0 a0(980) -> pi^0 f0(980) reaction at the upgraded Beijing electron positron collider with the BESIII detector.

hep-ph↗

arXiv2008

Single spin asymmetry and five-quark components of the proton

We examine the single-spin asymmetry (SSA) caused by the five-quark components of the proton for semi-inclusive electroproduction of charged pions in deep-inelastic scattering on a transversely polarized hydrogen target. The large SSA is considered to have close relation with quark orbital motion in the proton and suggests that the quark orbital angular momentum is nonzero. For the five-quark $qqqq\bar{q}$ components of the proton, the lowest configurations with $qqqq$ system orbitally excited and the $\bar{q}$ in the ground state would give spin-orbit correlations naturally for the quarks in a polarized proton. We show that based on the basic reaction $γq \to πq'$, the orbital-spin coupling of the probed quarks in the five-quark configuration leads to the single-spin asymmetry consistent with recent experiment results.

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arXiv2008

The role of the N*(1535) resonance and the pi^- p --> KY amplitudes in the OZI forbidden pi N --> phi N reaction

We study the pi N --> phi N reaction close to the phi N threshold within the chiral unitary approach, by combining the pi^- p --> K^+ Sigma^-, pi^- p --> K^0 Sigma^0 and pi^- p --> K^0 Lambda amplitudes with the coupling of the phi to the K components of the final states of these reactions via quantum loops. We obtain a good agreement with experiment when the dominant pi^- p --> K^0 Lambda amplitude is constrained with its experimental cross section. We also evaluate the coupling of the N*(1535) to phi N and find a moderate coupling as a consequence of partial cancellation of the large KY components of the N*(1535). We also show that the N*(1535) pole approximation is too small to reproduce the measured cross section for the pi N --> phi N reaction.

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arXiv2008

The radiative decay of $ψ(3770)$ into the predicted scalar state X(3700)

We calculate the radiative decay width of the $ψ(3770)$ into the dynamically generated scalar resonance X(3700) which is predicted in a previous paper. The results show that it is possible that the upgraded BEPC-II facility will generate enough statistics in order to observe this decay and thus confirm the existence of the X(3700).

hep-ph↗

arXiv2008

$0^{++}$ Resonances Observed at BES

In last 10 years, $0^{++}$ resonances have been observed and studied at BES in many processes, such as $J/ψ\toγπ^+π^-π^+π^-$, $γπ^+π^-$, $γπ^0π^0$, $γK^+K^-$, $γK_SK_S$, $γωϕ$, $ωπ^+π^-$, $ωK^+K^-$, $ϕπ^+π^-$, $ϕK^+K^-$, $ψ(2S)\to J/ψπ^+π^-$, $χ_{c0}\toπ^+π^-K^+K^-$, $π^+π^-π^+π^-$ etc.. The results on $0^{++}$ resonances observed at BES are reviewed.

hep-ex↗

arXiv2008

On the role of meson loops in the $f_0(1710)$ decay into $Vγ$

We investigate the relevance of the meson loops in the $f_0(1710)$ scalar meson decay into one photon and one vector meson, ($ρ$, $ω$ and $ϕ$). In particular we estimate the size of the loops coming from the decay of the $f_0(1710)$ into two pseudoscalar mesons, containing three pseudoscalar mesons in the loop or two pseudoscalar and one vector meson. The results, despite having large uncertainties, manifest that the contribution of the meson loops to these radiative decays is quite relevant and should be taken into account by the theoretical calculations which use this observables as a test of the possible glueball nature of this resonance.

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arXiv2008

Baryon Resonances Observed at BES

The $ψ$ decays provide a novel way to explore baryon spectroscopy and baryon structure. The baryon resonances observed from $ψ$ decays at BES are reviewed. The implications and prospects at upgraded BESIII/BEPCII are discussed.

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