Papers by Stephen Cotanch
Physics Letters B, 1992
A new type of high resolution pair spectrometer for medium energy photons has been used for studi... more A new type of high resolution pair spectrometer for medium energy photons has been used for studies of the exclusive (p, ~/) reaction on ~ ~B at 98 MeV. Angular distributions of the differential cross section for transitions to the ground state and first excited state in J2C are presented. The distributions show good agreement with predictions from a microscopic continuum shell model calculation which uses a realistic finite-range effective interaction with tensor components.
Few-Body Systems, 1995
Using a relativistic quark model approach that successfully described flavored meson systems, ele... more Using a relativistic quark model approach that successfully described flavored meson systems, electromagnetic form factors and structure functions are calculated for the low mass baryons. The observed proton, neutron and lambda moments, rms radii and form factors are all reproduced and predictions are made for other baryon observables which will be measured at CEBAF. Most significantly, by properly including the quark potential energy the long standing neutron to proton structure function ratio anomaly for x ~ 1 has been resolved.
Nuclear Physics A, 1993
A new type of high resolution pair spectrometer for medium energy photons has been used for studi... more A new type of high resolution pair spectrometer for medium energy photons has been used for studies of the exclusive (P,7) and (p,e"e-) reactions on light nuclei in the energy region 100 to 200 MeV. From the current experiments we present angular distributions of the differential cross section for transitions to the ground state and first three excited states in 12C. The distributions from the ground state and first excited state are compared with predictions from a microscopic continuum shell model calculation which uses a realistic finite-range effective interaction with tensor components. Based on preliminary data, the salient features of the (P, 7) reaction on 12C and the (p,e÷e-) reaction on lib are also discussed.
Physics Letters B, 2013
The spectrum of tetraquark states with hidden charm is studied within an effective Coulomb gauge ... more The spectrum of tetraquark states with hidden charm is studied within an effective Coulomb gauge Hamiltonian approach. Of the four independent color schemes, two are investigated, the (qc) 1 (cq) 1 singlet-singlet (molecule) and the (qc) 3 (qc) 3 triplettriplet (diquark), for selected J P C states using a variational method. The predicted masses of triplet-triplet tetraquarks are roughly a GeV heavier than the singletsinglet states. There is also an interesting flavor dependence with (qq) 1 (cc 1) states about half a GeV lighter than (qc) 1 (qc) 1. The lightest 1 ++ and 1 −− predictions are in agreement with the observed X(3872) and Y (4008) masses suggesting they are molecules with ωJ/ψ and ηh c , rather than D * D * and DD, type structure, respectively. Similarly, the lightest isovector 1 ++ molecule , having a ρJ/ψ flavor composition, has mass near the recently observed charged Z c (3900) value. These flavor configurations are consistent with observed X, Y and Z c decays to ππJ/ψ.
Nuclear Physics, Mar 1, 1986
The formation of A hypernuclear systems through kaon photo and electroproduction is theoretically... more The formation of A hypernuclear systems through kaon photo and electroproduction is theoretically investigated. Utilizing the single virtual photon exchange approximation and density matrix formalism, general relations between the production cross section and hadronic current are developed. The curren~ is expressed in terms of elementary virtual photoproductlon (y,p~K A) amplitudes that are explicltly evaluated from diagrams representing the exchange of s and u channel baryons (p,A,r °) and t channel mesons (K,K*). Using coupling constants from a phenomenological photoproduction analysis and kaon form factors governed by the ~ meson ~vector dominance model), a reasonable description of the limited p(e,e'K)A data is obtained. Relativistic, covariant calculations for deuteron electrodisintegration, d(e,e'K)An, are also reported which document the cross section sensitivity to the kaon form factor and drip vertex function (deuteron wavefunction). The sensitivity to the An final state interaction is also examined and the utility of this reaction for investigating controversial strange dibaryon resonances ~s discussed. The excitation spectrum for hypernuclear formation from ~He and "~C targets is calculated and optimum kinematics for extracting the longitudinal hypernuclear structure function are determined. Finally, count rates supporting the feasibility of selected experiments are provided for existing low duty cycle and proposed high duty cycle facilities.
Nuclear Physics, 1981
Angular distributions of the cross section for the (p, no) reaction on lsN and the (p, no), (p, n... more Angular distributions of the cross section for the (p, no) reaction on lsN and the (p, no), (p, n,) and (p, nz + n3) reactions on "C have been measured at energies from 9 to 17 MeV using neutron time-of-flight techniques. The (p, n,) results are extensively compared to previous measurements. A coupled-channels Lane model based on isospin-conserving potentials was used to describe the available (p, p), (p, n) and (n, n) data in this energy range. Although the behavior of the "N + nucleon system is reasonably well described, no satisfactory potential was found for the "C case.
Physical review, Jul 1, 1978
ABSTRACT
Nuclear Physics, Jul 1, 1973
The DWBA theory is examined under the assumption that both the form factors and distorted waves a... more The DWBA theory is examined under the assumption that both the form factors and distorted waves are functions of isospin. The formalism is developed and presented in both the coupled (isospin) and uncoupled (neutron-proton) representations. Applications are made in the areas of inelastic scattering and rearrangement phenomena. A model involving the t • T operator and the conservation of isospin for the strong interaction is introduced. The relation between this model and antisymmetry is discussed. A set of generalized Lane equations, the solutions of which describe both elastic and quasi-elastic scattering, are derived. This approach allows the charge exchange process to be explicitly incorporated into the transition amplitude. Numerical calculations are performed and partial success is attained in explaining certain spectroscopic anomalies deduced previously by conventional theory.
Bulletin of the American Physical Society, Dec 1, 1992
The electromagnetic properties of a relativistic constituent-quark model of light nonstrange and ... more The electromagnetic properties of a relativistic constituent-quark model of light nonstrange and strange mesons are investigated within the framework of light-front Hamiltonian dynamics. The authors demonstrate that the Poincare invariant quark model of the pion and kaon can give charge form factors in agreement with all available data. The relativistic features of the model are essential for the result. The radial confinement scale is much smaller than the charge radius due to the sizable effect from the spin-orbit coupling in the meson system.
Few-body systems, 1999
We continue our strangeness studies with new calculations for the nucleon time-like form factors ... more We continue our strangeness studies with new calculations for the nucleon time-like form factors and probing lepton pair production process N(π,e+e−)N. Using a recent value for the φN coupling constant obtained from our analysis of limited p(γ, φ))p data, we again document a several order of magnitude e + e − production resonant cross section structure. This dramatic φ peak follows from vector meson dominance and provides an interesting experimental signature for OZI violation and the strangeness content of the nucleon.
Utilizing conventional many-body techniques, an effective QCD Hamiltonian formulated in the Coulo... more Utilizing conventional many-body techniques, an effective QCD Hamiltonian formulated in the Coulomb gauge is approximately diagonalized. This approach preserves chiral symmetry yet generates constituents with dynamical mass confined through a linear potential with slope specified by lattice gauge theory. The experimental meson and lattice glueball spectra are reasonably described and exhibit Regge trajectories consistent with observation including the Pomeron. A fully relativistic, three quasiparticle calculation for hybrid mesons reinforces alternative theoretical models and predicts the lightest hybrid states are near but above 2 GeV. This strongly suggests the recently observed JPC = 1-+ exotics at 1.4 and 1.6 GeV are of a different, perhaps four quark, structure. Charmonium predictions now resolve the overpopulation of J/Psi states relative to observation. Extensions and preliminary results for low energy pipi scattering are also discussed.
Progress in Particle and Nuclear Physics, 2003
ABSTRACT A unified quark and gluon description of mesons, glueballs and exotic hybrids is present... more ABSTRACT A unified quark and gluon description of mesons, glueballs and exotic hybrids is presented for a relativistic field theoretical Hamiltonian in the Coulomb gauge. The effective QCD Hamiltonian entails a linear confining interaction with slope predetermined by lattice theory and is approximately diagonalized using different many-body techniques: BCS for the vacuum ground state; TDA and RPA for the excited hadron spectrum. Chiral symmetry rigorously emerges and is spontaneously broken by the model BCS vacuum which contains dynamically generated constituent quark and gluon condensates described by respective gap equations. The observed low energy meson spectrum and the quenched lattice glueball measurements are reproduced along with a Regge trajectory consistent with the Pomeron. Using generalized vector meson dominance, glueball decays are predicted and a glueball photoproduction experimental signature is predicted. Finally, a variational relativistic three quasiparticle calculation for hybrid mesons is reported which concurs with alternative model predictions that the lightest hybrid states are near but above 2 GeV. This strongly indicates that the recently observed JPC = 1 −+ exotics at 1.4 and 1.6 GeV are more likely four quark states.
Physical review, Nov 9, 2004
Double vector meson photoproduction, p(γ, G → V V)p, mediated by a scalar glueball G is investiga... more Double vector meson photoproduction, p(γ, G → V V)p, mediated by a scalar glueball G is investigated. Using vector meson dominance (VMD) and Regge/pomeron phenomenology, a measureable glueball enhancement is predicted in the invariant V V = ρρ and ωω mass spectra. The scalar glueball is assumed to be the lightest physical state on the daughter pomeron trajectory governing diffractive vector meson photoproduction. In addition to cross sections, calculations for hadronic and electromagnetic glueball decays, G → V V ′ (V, V ′ = ρ, ω, φ, γ), and γvV → G transition form factors are presented based upon flavor universality, VMD and phenomenological couplings from φ photoproduction analyses. The predicted glueball decay widths are similar to an independent theoretical study. A novel signature for glueball detection is also discussed.
Physical Review Letters, Aug 20, 1973
Discrepancies between observed ratios of d, 3 He and d f t yields populating analog states in 18 ... more Discrepancies between observed ratios of d, 3 He and d f t yields populating analog states in 18 0 and 18 F and ratios calculated by standard distorted-wave theory, which were thought to provide evidence for a charge-dependent nuclear interaction, are resolved by extending the conventional theory to include both an explicit charge-exchange channel in the continuum and form factors generated from a microscopic analysis.
Physics Letters B, May 1, 1978
The two-step charge exchange contribution from the process 160(7, p)lSN(p, n)lSo is calculated fo... more The two-step charge exchange contribution from the process 160(7, p)lSN(p, n)lSo is calculated for the photonuclear reaction 160(% n) 150. The total cross section, computed as a function of energy, is compared to the conventional, onestep direct cross section for Both E1 and E2 transitions. For each transition the two-step correction to the cross section is found to be sizable, approximately 50% of the one-step cross section.
We review theoretical calculations for the pseudoscalar-vector meson hyperfine splitting with no ... more We review theoretical calculations for the pseudoscalar-vector meson hyperfine splitting with no open flavor and also report a many body field theoretical effort to assess the impact of chiral symmetry in the choice of effective potentials for relativistic quark models. Our calculations predict the missing η b meson to have mass near 9400 MeV .
Bulletin of the American Physical Society, Dec 1, 1992
Using their previously developed crossing and duality constrained model for kaon photo/electropro... more Using their previously developed crossing and duality constrained model for kaon photo/electroproduction and radiative capture, the authors make predictions for the reactions p(K{sup {minus}}, e{sup +}e{sup {minus}})Y for Y = {Lambda}, {Sigma}{sup o}, and {Lambda}(1405). The K{sup {minus}} induced pair production reactions offer an opportunity to study kaon and nucleon form factors in the time-like region. Very large resonance effects are observed when the time-like 4-momentum transfer of the photon (q{sup 2} > O) approaches a vector meson pole. Due to the nearly equal total mass energy in the final and initial states, the {rho}, {omega}, and {phi} dominance regions are all kinematically accessible, in contrast to annihilation processes (eg. p{bar p} {leftrightarrow} e{sup +}e{sup {minus}}, K{sup +}K{sup {minus}} {leftrightarrow} e{sup +}e{sup {minus}}).
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Papers by Stephen Cotanch