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T. -S. H. Lee

Publications and source records attributed to T. -S. H. Lee.

At least 37 records · Page 2Linked to original sources
arXiv2016

From Extraction of Nucleon Resonances to LQCD

The intrinsic difficulties in extracting the hadron resonances from reaction data are illustrated by using several exactly soluble $ππ$ scattering models. The finite-volume Hamiltonian method is applied to predict spectra using two meson-exchange Hamiltonians of $πN$ reactions. Within a three-channel model with $πN$, $πΔ$ and $σN$ channels, we show the advantage of the finite-volume Hamiltonian method over the approach using the Lüscher formula to test Lattice QCD calculations aimed at predicting nucleon resonances. We discuss the necessary steps for using the ANL-Osaka eight-channel Hamiltonian to predict the spectra for testing the LQCD calculations for determining the excited nucleon states up to invariant mass $W= 2 $ GeV.

nucl-th↗
arXiv2016

Neutrino-Deuteron Reactions in the $Δ$(1232) Region

The results from an investigation of the incoherent single pion electroweak production on the deuteron in the $Δ$(1232) region are reported. The importance of including the nucleon-nucleon final state interactions in extracting the neutrino-nucleon cross sections from the data obtained from the experiments on the deuteron target is demonstrated.

nucl-th↗
arXiv2015

Dynamical coupled-channels model of $K^- p$ reactions (II): Extraction of $Λ^*$ and $Σ^*$ hyperon resonances

Resonance parameters (pole masses and residues) associated with the excited states of hyperons, Lambda^* and Sigma^*, are extracted within a dynamical coupled-channels model developed recently by us [Phys. Rev. C 90, 065204 (2014)] through a comprehensive partial-wave analysis of the K^- p --> barK N, pi Sigma, pi Lambda, eta Lambda, K Xi data up to invariant mass W = 2.1 GeV. We confirm the existence of resonances corresponding to most, if not all, of the four-star resonances rated by the Particle Data Group. We also find several new resonances, and in particular propose a possible existence of a new narrow J^P=3/2^+ Lambda resonance that couples strongly to the eta Lambda channel. The J^P=1/2^- Lambda resonances located below the barK N threshold are also discussed. Comparing our extracted pole masses with the ones from a recent analysis by the Kent State University group, some significant differences in the extracted resonance parameters are found, suggesting the need of more extensive and accurate data of K^- p reactions including polarization observables to eliminate such an analysis dependence of the resonance parameters. In addition, the determined large branching ratios of the decays of high-mass resonances to the pi Sigma^* and barK^* N channels also suggest the importance of the data of 2 --> 3 reactions such as K^- p --> pi pi Lambda and K^- p --> pi barK N. Experiments on measuring cross sections and polarization observables of these fundamental reactions are highly desirable at hadron beam facilities such as J-PARC for establishing the Lambda^* and Sigma^* spectrum.

nucl-th↗
arXiv2015

Incoherent Pion Production in Neutrino - Deuteron Reactions

Within the multiple scattering formulation, the incoherent pion production in neutrino-deuteron reactions at energies near the $Δ(1232)$ resonance is investigated. The calculations include an impulse term and one-loop contributions from nucleon-nucleon ($NN$) and pion-nucleon ($πN$) final state interactions. The input amplitudes of $πN$ scattering and electroweak pion production reaction on nucleon are generated from a dynamical model which describes very extensive data of $πN$ scattering and both the electromagnetic and the weak pion production reactions on the nucleon. The $NN$ scattering amplitudes are generated from the Bonn potential. The validity of the calculational procedures is established by giving a reasonably good description of the data of pion photo-production on the deuteron. The constructed model is then applied to predict the cross sections of $ν+ d \rightarrow μ^- + π^+ + n+ p$ and $ν+d \rightarrow μ^-+π^0+p+p$ reactions. The importance of including the $NN$ final state interactions to understand the experimental data of these neutrino-deuteron reactions is demonstrated. Our results strongly suggest that the spectator approximation used in the previous analyses to extract the pion production cross sections on the nucleon from the data on the deuteron is not valid for the $ν+ d \rightarrow μ^-+ π^+ +n+p$, but is a good approximation for $ν+ d \rightarrow μ^-+ π^0 + p+p$.

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arXiv2014

Dynamical coupled-channels model of $K^- p$ reactions (I): Determination of partial-wave amplitudes

We develop a dynamical coupled-channels model of K^- p reactions, aiming at extracting the parameters associated with hyperon resonances and providing the elementary antikaon-nucleon scattering amplitudes that can be used for investigating various phenomena in the strangeness sector such as the production of hypernuclei from kaon-nucleus reactions. The model consists of (a) meson-baryon (MB) potentials v_{M'B',MB} derived from the phenomenological SU(3) Lagrangian, and (b) vertex interactions Gamma_{MB,Y*} for describing the decays of the bare excited hyperon states (Y*) into MB states. The model is defined in a channel space spanned by the two-body barK N, pi Sigma, pi Lambda, eta Lambda, and K Xi states and also the three-body pi pi Lambda and pi barK N states that have the resonant pi Sigma* and barK* N components, respectively. The resulting coupled-channels scattering equations satisfy the multichannel unitarity conditions and account for the dynamical effects arising from the off-shell rescattering processes. The model parameters are determined by fitting the available data of the unpolarized and polarized observables of the K^- p --> barK N, pi Sigma, pi Lambda, eta Lambda, K Xi reactions in the energy region from the threshold to invariant mass W=2.1 GeV. Two models with equally good chi^2 fits to the data have been constructed. The partial-wave amplitudes obtained from the constructed models are compared with the results from a recent partial-wave analysis by the Kent State University group. We discuss the differences between these three analysis results. Our results at energies near the threshold suggest that the higher partial waves should be treated on the same footing as the S wave if one wants to understand the nature of Lambda(1405)1/2^- using the data below the barK N threshold, as will be provided by the J-PARC E31 experiment.

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arXiv2014

Finite-volume Hamiltonian method for coupled channel interactions in lattice QCD

Within a multi-channel formulation of $ππ$ scattering, we investigate the use of the finite-volume Hamiltonian approach to resolve scattering observables from lattice QCD spectra. The asymptotic matching of the well-known Lüscher formalism encodes a unique finite-volume spectrum. Nevertheless, in many practical situations, such as coupled-channel systems, it is advantageous to interpolate isolated lattice spectra in order to extract physical scattering parameters. Here we study the use of the Hamiltonian framework as a parameterisation that can be fit directly to lattice spectra. We find that with a modest amount of lattice data, the scattering parameters can be reproduced rather well, with only a minor degree of model dependence.

hep-lat↗
arXiv2013

Recent results on N* spectroscopy with ANL-Osaka dynamical coupled-channels approach

We report our recent effort on the extraction of N*- and Delta*-resonance parameters (pole masses, coupling constants, etc.) through the comprehensive analysis of pion- and photon-induced pi N, eta N, K Lambda, and K Sigma production reactions. The analysis was performed with the ANL-Osaka dynamical coupled-channels approach, which satisfies the multichannel unitarity of the S-matrix in the channel space spanned by pi N, eta N, K Lambda, K Sigma, and also three-body pi pi N that contains rho N, pi Delta, and sigma N resonant components. Ongoing projects and future plans are also discussed.

nucl-th↗
arXiv2013

Nucleon resonances within a dynamical coupled-channels model of pi N and gamma N reactions

The nucleon resonances are investigated within a dynamical coupled-channels model of pi N and gamma N reactions up to the invariant mass W = 2 GeV. The meson-baryon (MB) channels included in the calculations are MB = pi N, eta N, K Lambda, K Sigma, and pi pi N that has pi Delta, rho N, and sigma N resonant components. The meson-baryon amplitudes T_{M'B',MB}(W) are calculated from solving a set of coupled-channels integral equations defined by an interaction Hamiltonian consisting of (a) meson-exchange interactions v_{M'B',MB} derived from phenomenological Lagrangian, and (b) vertex interactions N* --> MB for describing the transition of a bare excited nucleon state N* to a channel MB. The parameters of v_{M'B',MB} are mainly constrained by the fit to the data of pi N --> pi N in the low energy region up to W =1.4 GeV. The bare masses of N* and the N* --> MB parameters are then determined in simultaneous fits to the data of pi N --> pi N up to W =2.3 GeV and those of pi N --> eta N, K Lambda, K Sigma and gamma N --> pi N, eta N, K Lambda, K Sigma up to W = 2.1 GeV. The pole positions and residues of nucleon resonances are extracted by analytically continuing the meson-baryon amplitudes T_{M'B',MB}(W) to the complex Riemann energy surface. From the extracted residues, we have determined the N* --> pi N, gamma N, eta N, K Lambda, K Sigma transition amplitudes at resonance poles. We compare the resonance pole positions from our analysis with those given by Particle Data Group and the recent coupled-channels analyses by the Juelich and Bonn-Gatchina groups. Four results agree well only for the first N* in each spin-parity-isospin (J^P,I) channel. For higher mass states, the number of states and their resonance positions from four results do not agree well. We discuss the possible sources of the discrepancies and the need of additional data from new hadron facilities such as J-PARC.

nucl-th↗
arXiv2013

Studies of Nucleon Resonance Structure in Exclusive Meson Electroproduction

Studies of the structure of excited baryons are key to the N* program at Jefferson Lab. Within the first year of data taking with the Hall B CLAS12 detector following the 12 GeV upgrade, a dedicated experiment will aim to extract the N* electrocouplings at high photon virtualities Q2. This experiment will allow exploration of the structure of N* resonances at the highest photon virtualities ever yet achieved, with a kinematic reach up to Q2 = 12 GeV2. This high-Q2 reach will make it possible to probe the excited nucleon structures at distance scales ranging from where effective degrees of freedom, such as constituent quarks, are dominant through the transition to where nearly massless bare-quark degrees of freedom are relevant. In this document, we present a detailed description of the physics that can be addressed through N* structure studies in exclusive meson electroproduction. The discussion includes recent advances in reaction theory for extracting N* electrocouplings from meson electroproduction off protons, along with QCD-based approaches to the theoretical interpretation of these fundamental quantities. This program will afford access to the dynamics of the non-perturbative strong interaction responsible for resonance formation, and will be crucial in understanding the nature of confinement and dynamical chiral symmetry breaking in baryons, and how excited nucleons emerge from QCD.

nucl-th↗
arXiv2013

Production of $J/Ψ$ on the nucleon and deuteron targets

A coupled-channel model with $πN$, $ρN$ and $J/ΨN$ channels is developed to predict the $π+ N \rightarrow J/Ψ+ N $ cross sections. The $J/Ψ$-$N$ interaction is parameterized in a form related to what has been predicted by the effective field theory approach and Lattice QCD. The other interactions within the model are constrained by the decay width of $J/Ψ\rightarrow ρ+ π$ and the total cross section data of $πN$ reactions. The calculated meson-baryon amplitudes are then used to predict the cross sections of the $J/Ψ$ production on the deuteron target by including the contributions from the impulse term and the one-loop calculations of the final $NN$ and $J/ΨN$ re-scattering effects. Predictions of the dependence of the cross sections of $π^- + p \rightarrow J/Ψ+ n$, $γ+ d \rightarrow J/Ψ+ n + p$, and $π^+ d \rightarrow J/Ψ+p +p$ on the $J/Ψ$-$N$ potentials are presented for experimental determinations of the $J/Ψ$-$N$ interaction. Within the vector meson dominance model, we have also applied the constructed coupled-channel model to predict the $γ+ p\rightarrow J/Ψ+ p$ cross sections near the $J/Ψ$ production threshold.

nucl-th↗
arXiv2013

Neutrino-induced meson productions off nucleon at forward limit in nucleon resonance region

We study forward neutrino-induced meson production off the nucleon in the resonance region. Our calculation is based on a dynamical coupled-channels (DCC) model that reasonably describes pi (gamma) N -> pi N, eta N, K Lambda, K Sigma data in the resonance region. We apply the PCAC hypothesis to the DCC model to relate the pi N reaction amplitude to the forward neutrino reaction amplitude. In this way, we give a prediction for nu N -> pi N, pi pi N, eta N, K Lambda, K Sigma reaction cross sections. The predicted nu N -> pi pi N, eta N, K Lambda, K Sigma cross sections are, for the first time, based on a model extensively tested by data. We compare our results with those from the Rein-Sehgal model that has been very often used in the existing Monte Carlo simulators for neutrino experiments. We find a significant difference between them.

hep-ph↗
arXiv2012

Extraction of Meson Resonances from Three-pions Photo-production Reactions

We have investigated the model dependence of meson resonance properties extracted from the Dalitz-plot analysis of the three-pions photoproduction reactions on the nucleon. Within a unitary model developed in Phys. Rev. D 84, 114019 (2011), we generate Dalitz-plot distributions as data to perform an isobar model fit that is similar to most of the previous analyses of three-pion production reactions. It is found that the resonance positions from the two models agree well when both fit the data accurately, except for the resonance poles near branch points. The residues of the resonant amplitudes extracted from the two models and by the usual Breit-Wigner procedure agree well only for the isolated resonances with narrow widths. For overlapping resonances, most of the extracted residues could be drastically different. Our results suggest that even with high precision data, the resonance extraction should be based on models within which the amplitude parametrization is constrained by three-particle unitarity condition.

hep-ph↗
arXiv2012

Production of Bound States with Hidden Charm at J-PARC and JLab

The cross sections of the production of bound states with hidden charm in reactions induced by pions and photons are presented. To facilitate the experimental efforts to determine the $J/Ψ$-N interactions, we present results for $J/Ψ$ production on the deuteron.

nucl-th↗
arXiv2012

Photo-production of Bound States with Hidden Charms

The photo-production of $J/Ψ$-$^3He$ bound state ($[^3He]_{J/Ψ}$) on a $^4He$ target has been investigated using the impulse approximation. The calculations have been performed using several $γ+N \rightarrow J/Ψ+N$ models based on the Pomeron-exchange and accounting for the pion-exchange mechanism at low energies. The $J/Ψ$ wavefunctions in $[^3He]_{J/Ψ}$ are generated from various $J/Ψ$-nucleus potentials which are constructed by either using a procedure based on the Pomeron-quark coupling mechanism or folding a $J/Ψ$-N potential ($v_{J/Ψ,N}$) into the nuclear densities. We consider $v_{J/Ψ,N}$ derived from the effective field theory approach, Lattice QCD, and Pomeron-quark coupling mechanism. The upper bound of the predicted total cross sections is about $0.1 - 0.3$ pico-barn. We also consider the possibility of photo-production of a six quark-$J/Ψ$ bound state ($[q^6]_{J/Ψ})$ on the $^3He$ target. The Compound Bag Model of $NN$ scattering and the quark cluster model of nuclei are used to estimate the $[q^6]$-N wavefunction in $^3He$ by imposing the condition that the calculated $^3He$ charge form factor must be consistent with what is predicted by the conventional nuclear model. The upper bound of the predicted total cross sections of $γ+ ^3He \rightarrow [q^6]_{J/Ψ} +N$ is about 2 - 4 pico-barn, depending on the model of $γ+N \rightarrow J/Ψ+N$ used in the calculations. Our results call for the need of precise measurements of $γ+p \rightarrow J/Ψ+p$ and also the $γ+^2H\rightarrow J/Ψ+n + p $ reactions near the threshold.

nucl-th↗
arXiv2012

Pion-Exchange and Fermi-Motion Effects on the Proton-Deuteron Drell-Yan Process

Within a nuclear model that the deuteron has NN and πNN components, we derive convolution formula for investigating the Drell-Yan process in proton-deuteron (pd) reactions. The contribution from the πNN component is expressed in terms of a pion momentum distribution that depends sensitively on the πNN form factor. With a πNN form factor determined by fitting the πN scattering data up to invariant mass W = 1.3 GeV, we find that the pion-exchange and nucleon Fermi-motion effects can change significantly the ratios between the proton-deuteron and proton-proton Drell-Yan cross sections, R_{pd/pp} = σ^{pd}/(2σ^{pp}), in the region where the partons emitted from the target deuteron are in the Bjorken x_2 > 0.4 region. The calculated ratios R_{pd/pp} at 800 GeV agree with the available data. Predictions at 120 GeV for analyzing the forthcoming data from Fermilab are presented.

hep-ph↗
arXiv2012

Neutrino-induced forward meson-production reactions in nucleon resonance region

As a first step toward developing a reaction model that enables a comprehensive description of neutrino-nucleon reactions in the nucleon resonance region, we have applied for the first time a dynamical coupled-channels model, which successfully describes πN, γN --> πN, ηN, ππN, KΛ, KΣreactions up to W = 2 GeV, to predict the neutrino-induced meson-production reactions with ΔS = 0 at the forward angle limit. This has been achieved by relating the divergence of the axial-current matrix elements at Q^2 = 0 to the πN --> X reaction amplitudes through the PCAC hypothesis. We present the contributions from each of the πN, ηN, ππN, KΛ, KΣchannels to the F_2 structure function at Q^2 --> 0 limit up to W = 2 GeV.

nucl-th↗
arXiv2012

Nucleon Resonances with Hidden Charm in Coupled-Channel Models

The model dependence of the predictions of nucleon resonances with hidden charm is investigated. We consider several coupled-channel models which are derived from relativistic quantum field theory by using (1) a unitary transformation method, and (2) the three-dimensional reductions of Bethe-Salpeter Equation. With the same vector meson exchange mechanism, we find that all models give very narrow molecular-like nucleon resonances with hidden charm in the mass range of 4.3 GeV $ < M_R < $ 4.5 GeV, in consistent with the previous predictions.

nucl-th↗