Search Results (17 total)

Kaon electroproduction from light nuclei and hydrogen, using ¹H, ²H, ³He, ⁴He, and carbon targets has been measured at the Thomas Jefferson National Accelerator Facility. The quasifree angular distributions of Λ and Σ hyperons were determined at Q²=0.35 (GeV/c)² and W=1.91 GeV. Electroproduction on hydrogen was measured at the same kinematics for reference.

We derive completely integrated formulas for emittance growth times due to intrabeam scattering for charged particle beams in the high energy limit, including the effect of lattice parameters that vary around the accelerator ring. Using accelerator lattices for the prototype damping ring called the Accelerator Test Facility at KEK and those for two proposed International Linear Collider damping rings, we compare our results with other calculations.

The _Λ^3,4H and _Λ⁴H hypernuclear bound states have been observed for the first time in kaon electroproduction on ^3,4He targets. The production cross sections have been determined at Q²=0.35   GeV² and W=1.91   GeV. For either hypernucleus the nuclear form factor is determined by comparing the angular distribution of the ^3,4He(e,e^′K⁺)_Λ^3,4H processes to the elementary cross section ¹H(e,éK⁺)Λ on the free proton, measured during the same experiment.

Electroproduction of the ω meson was investigated in the ¹H(e,e^′p)ω reaction. The measurement was performed at a four-momentum transfer Q²≈0.5  GeV². Angular distributions of the virtual photon-proton center-of-momentum cross sections have been extracted over the full angular range. These distributions exhibit a strong enhancement over t-channel parity exchange processes in the backward direction. According to a newly developed electroproduction model, this enhancement provides significant evidence of resonance formation in the γ*p→ωp reaction channel.

We report measurements of cross sections for the reaction ¹H(e,e^′K⁺)Y, for both the Λ and Σ⁰ hyperon states, at an invariant mass of W=1.84 GeV and four-momentum transfers 0.5<Q²<2 (GeV/c)². Data were taken for three values of virtual photon polarization ε, allowing the decomposition of the cross sections into longitudinal and transverse components. The Λ data are a revised analysis of prior work, whereas the Σ⁰ results have not been previously reported.

Tensor polarization observables ( t₂₀, t₂₁, and t₂₂) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7 (GeV/c)². The experiment was performed at the Jefferson Laboratory in Hall C using the electron High Momentum Spectrometer, a specially designed deuteron magnetic channel and the recoil deuteron polarimeter POLDER. The new data determine to much larger Q² the deuteron charge form factors G_C and G_Q. They are in good agreement with relativistic calculations and disagree with perturbative QCD predictions.

The A(Q²) structure function in elastic electron-deuteron scattering was measured at six momentum transfers Q² between 0.66 and 1.80 (GeV/c)² in Hall C at Jefferson Laboratory. The scattered electrons and recoil deuterons were detected in coincidence, at a fixed deuteron angle of 60.5°. These new precise measurements resolve discrepancies between older sets of data. They put significant constraints on existing models of the deuteron electromagnetic structure, and on the strength of isoscalar meson exchange currents.

The ¹H(e,e^′K⁺)Λ reaction was studied as a function of the squared four-momentum transfer, Q², and the virtual photon polarization, ɛ. For each of four Q² settings, 0.52, 0.75, 1.00, and 2.00 (GeV/c)², the longitudinal and transverse virtual photon cross sections were extracted in measurements at three virtual photon polarizations. The Q² dependence of the σ_L/σ_T ratio differs significantly from current theoretical predictions. This, combined with the precision of the measurement, implies a need for revision of existing calculations.

The theory of the anisotropic ferrite wake-field accelerator is solved for the case of any general angular mode m. The ferrite is driven into saturation by a static magnetic field, resulting in the permeability tensor having off-diagonal elements. Expressions for the radial and angular transverse forces are obtained. Finally, we give numerical examples showing that the transverse forces in the anisotropic ferrite wake-field accelerator are reduced as the static saturated magnetization is increased.

The theory of the anisotropic ferrite wake-field accelerator is solved, wherein the ferrite is driven into saturation by a static magnetic field, resulting in a permeability tensor having off-diagonal elements. We show that it is possible to obtain a maximum accelerating gradient of 1.5 MV/[m (nC driver beam charge)] for a driver beam of 0.7-mm rms bunch length. This compares favorably with wake-field accelerators based upon other types of structures.

We derive formulas which describe the interaction of laser beams with electron beams. Specializing to the case of 1-TeV electron beams from the future generation of electron linear accelerators, we calculate the production rate of backscattered 1-TeV photons, and using these photons, we show that it is possible to organize the photoproduction of beauty particles so as to measure 10⁹ bb¯ pairs per year. This should be adequate to study rare decays and CP violation in B meson decay.

We reformulate the theory of the acceleration of charged particles in the recently proposed plasma-wake-field acceleration scheme. Our treatment makes manifest the transient effects. To illustrate, we consider a point-charge driving beam traversing a semi-infinite plasma. We show that it takes a few plasma wavelengths for transient effects to dissipate and give the wake-field solutions currently discussed in the literature. Thus our treatment provides needed justification for the existing theoretical discussions since they neglect transient effects.

We study the nucleon structure function F₂ for deep-inelastic scattering of leptons on an isoscalar target. The Owens-Reya parton distributions with charm added give good agreement with the data up to Q²∼100 GeV for the case of no color production. If color is produced, we describe in detail what effect this would have on F₂ to leading nontrivial order in Pati-Salam quantum chromodynamics with massive gluons.

Based upon the invariance of SU(2)⊗SU(2) and SU(3)⊗SU(3) for asymptotic momenta, we first derive constraints on certain strong and electromagnetic exclusive scattering processes, where all the hadrons are viewed as fundamental fields. Then we consider asymptotic SU(3)⊗SU(3) for meson-meson and baryon-baryon fixed-angle, elastic scattering in the Landshoff model, wherein the hadrons are viewed as bound states of quarks and antiquarks. We find that the part of the pseudoscalar-pseudoscalar scattering amplitude which is a function of the center-of-mass scattering angle only is just the average of the analogous functions of the scattering angle for the independent nonzero helicity amplitudes for vector-vector scattering. Finally, in the case of baryon-baryon scattering we find that total baryon helicity is conserved.

We discuss the decays of ψ into octet-baryon-antibaryon pairs using a model due to Okubo wherein ψ decays into uncharmed hadrons via its couplings to both hadronic and electromagnetic currents with appreciable interference effects. Relations are derived for the baryon form factors in terms of the nucleon electromagnetic form factors. As a model for the nucleon electromagnetic form factors we use a Veneziano-type dual current model subject to the Drell-Yan constraints and the Okubo-Zweig-Iizuka rule. Branching ratios are computed and comparisons are made to other form-factor models.

We discuss the conditions under which chiral symmetries become exact at asymptotic momenta, utilizing the homogeneous Callan-Symanzik equations so that momenta are not restricted to the deep Euclidean domain as others have done previously. In particular, we consider as our prototype the chiral SU(2) ⊗ SU(2) σ model of Gell-Mann and Levy without fermions, where we allow for both spontaneous symmetry breaking and explicit breaking of the symmetry via a term in the Lagrangian linear in the σ field. To check our general results, we calculate to two-loop order in perturbation theory the coefficients of the homogeneous Callan-Symanzik equations along with the interesting amplitudes of the theory and finally show that under suitable conditions the symmetry-broken theory and the symmetry-conserved theory both approach the same massless, symmetric theory as the momenta become asymptotic.