arXiv subjects

Bijan Saghai

Publications and source records attributed to Bijan Saghai.

12 recordsLinked to original sources

arXiv2012

Intrinsic five-quark Fock states of baryons and meson-nucleon $σ$-terms

An extended chiral constituent quark approach, which embodies higher Fock five-quark components in the baryons wave-functions, is employed to study the sea quark content of the octet baryons. We report on the probabilities of $\bar{u}$, $\bar{d}$ and $\bar{s}$ in the nucleon, $Λ$, $Σ$ and $Ξ$ baryons, arising from the intrinsic five-quark states in the baryons wave functions. Based on those probabilities, results for meson-nucleon $σ$-terms; namely $σ_{πN}, σ_{K N}$ and $σ_{ηN}$, are presented.

hep-ph↗

arXiv2012

Sea flavor content of octet baryons and intrinsic five-quark Fock states

Sea quark contents of the octet baryons are investigated by employing an extended chiral constituent quark approach, which embodies higher Fock five-quark components in the baryons wave-functions. The well-known flavor asymmetry of the nucleon sea $\bar{d}-\bar{u}$, is used as input to predict the probabilities of $\bar{u}$, $\bar{d}$ and $\bar{s}$ in the nucleon, $Λ$, $Σ$ and $Ξ$ baryons, due to the intrinsic five-quark components in the baryons wave functions.

hep-ph↗

arXiv2011

Strong decay of low-lying $S_{11}$ and $D_{13}$ nucleon resonances to pseudoscalar mesons and octet baryons

Partial decay widths of the nucleon resonances $S_{11}(1535)$, $S_{11}(1650)$, $D_{13}(1520)$ and $D_{13}(1700)$ to the pseudoscalar mesons and octet baryons are studied within a chiral constituent quark model. The effects of the configurations mixing between the states $|N^{2}_{8}P_{M}>$ and $|N^{4}_{8}P_{M}>$ are considered, taking into account the breakdown of the $SU(6)\otimes O(3)$ symmetry. In addition, possible contributions of the strangeness components in the $S_{11}$ resonances are investigated. Experimental data for the partial decay widths of the $S_{11}$ and $D_{13}$ resonances are well reproduced. Predictions for coupling constants of the four nucleon resonances to pseudoscalar mesons and octet baryons, crucial issues in the photo- and hadron-induced meson production reactions, are reported.

nucl-th↗

arXiv2011

Coupling constants of the $S_{11}$ resonances to pseudoscalar mesons and octet baryons

Coupling constants of $S_{11}(1535)$ and $S_{11}(1650)$ resonances to meson-baryon ($πN$, $ηN$, $η^\prime N$, $KY$) are investigated in a chiral quark model, complemented by inclusion of five-quark components in those resonances. The known strong decay partial widths of both resonances are well reproduced, provided sizeable strangeness components in the relevant wave functions. %to excellent description for the strong decays of the above two resonances, which %cannot be reproduced very well in the traditional chiral quark model with or without %$SU(6)\otimes O(3)$ breaking. Finally, we find that $S_{11}(1535)$ and $S_{11}(1650)$ %couple strongly to the channels with strangeness.

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arXiv2010

Structure of $λ^$(1405) and the $λ^$-Meson-Baryon Coupling Constants

Within an extended chiral constituent quark model, three- and five-quark structure of the $S_{01}$ resonance $Λ(1405)$ is investigated with respect to the coupling constants $g^2_{Λ^* πΣ}$ and $g^2_{Λ^* \bar{K} N}$. Our findings corroborate with about 50% of five-quark admixture in the $Λ(1405)$ needed in reproducing the strong decay width, $Γ_{Λ(1405)\to (Σπ)^\circ}$.

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arXiv2007

Study of π^{-}p \to ηn at low energies in a chiral constituent quark model

A chiral quark model approach is extended to the study of the $πN$ scattering at low energies. The process of $π^{-}p \to ηn$ near threshold is investigated. The model is successful in describing the differential cross sections and total cross section near the $η$ production threshold. The roles of the resonances in $n\leq 2$ shells are clarified. Near threshold, the $S_{11}(1535)$ dominates the reactions, while the interferences from the $S_{11}(1650)$ turn out to be destructive around $W\lesssim 1.6$ GeV. The $D_{13}(1520)$ is crucial to give correct shapes of the differential cross sections. The nucleon pole term contributions are significant. The $P_{11}(1710)$ plays an important role around the c.m. energy $W=1.7$ GeV, it is crucial to produce an enhancement in the region of $W>1.6$ GeV as suggested by the data for total cross section. The $t$-channel is negligible in the reactions.

nucl-th↗

arXiv2007

Chiral constituent quark model study of the process $γp \to ηp$

A constituent quark model is developed for the reaction, allowing us to investigate all available data for differential cross sections as well as single polarization asymmetries (beam and target) by including {\it all} of the PDG, one to four star, nucleon resonances ($S_{11}$, $P_{11}$, $P_{13}$, $D_{13}$, $D_{15}$, $F_{15}$, $F_{17}$, $G_{17}$, $G_{19}$, $H_{19}$, $I_{1,11}$, and $K_{1,13}$). Issues related to the missing resonances are also briefly discussed by examining possible contributions from several new resonances ($S_{11}$, $P_{11}$, $P_{13}$, $D_{13}$, $ D_{15}$, and $H_{1,11}$).

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arXiv2007

$πN\to ηN$ process in a $χ$QM approach

A chiral quark model approach is used to investigate the $π^{-}p \to ηn$ process at low energies. The roles of the most relevant nucleon resonances in $n\leq 2$ shells are briefly discussed.

nucl-th↗

arXiv2003

Strangeness production via electromagnetic probes: 40 years later

A brief review of the associated strangeness electromagnetic production is presented. Very recent K+ Lambda photoproduction data on the proton from threshold up to E=2.6 GeV are interpreted within a chiral constituent quark formalism, which embodies all known nucleonic and hyperonic resonances. The preliminary results of this work are reported here.

nucl-th↗

arXiv1996

Pseudoscalar meson photoproduction: from known to undiscovered resonances

The role of dynamics in spin observables for pseudoscalar meson photoproduction is investigated using a density matrix approach in a multipole truncated framework. Extraction of novel rules for $γp \rightarrow π^+ n,~ K^+ Λ$ and $ηp$ reactions based on resonance dominance, and on other broad and reasonable dynamical assumptions, are discussed. Observables that are particularly sensitive to missing nucleonic resonances predicted by quark-based approaches, are singled out.

nucl-th↗

arXiv1995

Nodal trajectories of spin observables and kaon photoproduction dynamics

Spin observables for the reaction $γp \rightarrow K^+ Λ$ are examined using three recent dynamical models and are compared to the general features of such observables deduced earlier by Fasano, Tabakin and Saghai. These general features, such as the energy dependence of spin observables and the location of nodes in their angle dependence, are realized. Several instructive surprises, which occur in this comparison to the conjectures of Fasano et al., are then discussed. The sensitivity of spin observables to isobar and {\it t-}channel dynamics is analyzed and suggestions for selecting experiments which provide important dynamical information are presented.

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arXiv1995

Initial State Interactions for $K^-$-Proton Radiative Capture

The effects of the initial state interactions on the $K^--p$ radiative capture branching ratios are examined and found to be quite sizable. A general coupled-channel formalism for both strong and electromagnetic channels using a particle basis is presented, and applied to all the low energy $K^--p$ data with the exception of the {\it 1s} atomic level shift. Satisfactory fits are obtained using vertex coupling constants for the electromagnetic channels that are close to their expected SU(3) values.

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