We have searched for the production of a neutral gauge boson (Z′) with mass above 100 Gev/${\mathrm{c}}^2$ in p¯p collisions with the Collider Detector at Fermilab. We present a 95% confidence level (C.L.) limit on the Z′→${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{\mathrm{-}}$ production cross section. We combine the Z′ limit with that from our previous dielectron search; the combined result sets a limit of ${\mathrm{M}}_{\mathrm{Z}\prime }$>412 GeV/${\mathrm{c}}^2$ (95% C.L.), assuming standard-model coupling strengths. In addition, the absence of any evidence for an effective muon-quark contact interaction is used to set a lower limit of 1.6 TeV (95% C.L.) on an associated muon-quark compositeness scale.

Fermilab experiment E-760 studies the resonant formation of charmonium states in proton-antiproton interactions using a hydrogen gas-jet target in the Antiproton Accumulator ring at Fermilab. Precision measurements of the mass and width of the charmonium states ${\mathrm{\chi }}_{\mathit{c}1}$,${\mathrm{\chi }}_{\mathit{c}2}$, a direct measurement of the ψ’ width, and a new precision measurement of the J/ψ mass are presented.

New limits are obtained, several orders of magnitude lower than previously reported, for coupling constant versus mass for the exchange of hypothetical light bosons coupling to baryons in the range 20 MeV>${\mathit{m}}_{\mathit{B}}$${\mathit{c}}^2$>20 μeV (interaction range 10 fm<${\mathit{R}}_{\mathrm{int}}$<1 cm). These limits are obtained from neutron-nucleus scattering below 10 keV and from neutron optics data. This closes the gap between high-energy physics and the macroscopic fifth-force experiments in the searches for new interactions. Constraints for the mass of a Higgs boson are extracted.

I propose to use the transverse momentum distribution of lepton pairs in the ${\mathrm{\rho }}^{0\mathrm{-}}$ω peak to measure the QCD transition temperature in ultrarelativistic nuclear collisions. The signal-to-background ratio is approximately unity, and the transition temperature can be determined with roughly 15% accuracy.

The sensitivity of moderate ${\mathit{p}}_{\mathit{T}}$≲8 GeV/c singles inclusive spectra in nuclear collisions to gluon shadowing and jet quenching is estimated using the higing Monte Carlo model. We show how the systematic study of the nuclear dependence of those spectra in p+A can be used to determine the magnitude of gluon shadowing and how the enhanced suppression in A+A would provide information on the energy-loss mechanisms in dense partonic matter.

The influence of trinuclear one-Δ and ΔΔ components on the triton binding energy is studied nonperturbatively using the Hannover and Argonne force models. This is the first such study of ΔΔ effects, and these are found to be appreciable. In the Hannover model, repulsive Δ dispersive effects and attractive Δ three-body-force effects cancel almost exactly, yielding little net Δ effect. A similar result obtains for the Argonne model, yielding a net Δ repulsive effect of only ∼380 keV. Implications for current approaches which make simplifying assumptions about Δ effects are indicated.

A computational formalism is presented to obtain total electron-ion recombination cross sections and rate coefficients employing the close-coupling approximation for photoionization and scattering and the Bell and Seaton theory of dielectronic recombination. The results differ significantly from separate treatments of the two processes, radiative and dielectronic recombination. The R-matrix method, as developed for the Opacity Project, is used and results are presented for recombination collision strengths and rate coefficients for boronlike ${\mathrm{O}}^{2+}$ and ${\mathrm{Ne}}^{4+}$

We have observed the effect of microscopic radiation pressure vortices on atomic motion in two crossed, near-resonant, optical standing waves. When the two standing waves oscillate synchronously the resulting light field and the corresponding light forces possess a 90° rotation symmetry. However, when one of the standing waves’ oscillations is delayed with respect to those of the other, a vortical radiation pressure force arises which can be identified by the breaking of this symmetry. Radiation pressure vortices should play a significant role for the atomic kinematics in optical molasses and magneto-optical traps.

Starting with Ba atoms in one Rydberg state we have observed the population of adjacent Rydberg states when the atom is exposed to an intense 1.5-ps laser pulse. The initial Rydberg state population is redistributed by a Raman-like two-photon process, rather than simply being photoionized. This population trapping, which is associated with stabilization against ionization, is described in terms of Rydberg antiwave packets.

We simulate a method to teach a laser pulse sequences to excite specified molecular states. We use a learning procedure to direct the production of pulses based on ‘‘fitness’’ information provided by a laboratory measurement device. Over a series of pulses the algorithm learns an optimal sequence. The experimental apparatus, which consists of a laser, a sample of molecules and a measurement device, acts as an analog computer that solves Schrödinger’s equation n/Iexactly, in real time. We simulate an apparatus that learns to excite specified rotational states in a diatomic molecule.

A large, broad peak has been found in the electron energy spectrum from 30 to 100-keV ${\mathrm{H}}^{+}$+H collisions. The peak, which is centered at 31 eV, appears only in the backward directions. It is suggested that while the peak is unlikely to come from collisions with atoms in the ground or metastable states, it could arise from collisions with atoms in highly excited states or from autoionizing states of the residual ${\mathrm{H}}_2$ in the target.

A general description is given to the unlimited acceleration of charged particles by a wave in the presence of a uniform magnetic field. The wave can have an arbitrary mixture of electrostatic and electromagnetic components and the propagation direction in the magnetic field is also arbitrary. Exact limits on parameters for trapping and acceleration are derived. The probability of trapping in a gyration period is also presented, and it is shown that a particle once trapped remains so and undergoes unlimited acceleration.

For pointlike singularities localized well away from the symmetry axis, axisymmetric flows with swirl are arbitrarily well approximated by two-dimensional Boussinesq convection. An adaptive mesh simulation of the latter equations was continued until the maximum three-dimensional vorticity showed a factor of ${10}^7$ increase, allowing a reasonable determination of exponents, and elucidation of the mechanism of blowup.

Turbulent Taylor vortex flow is studied in experiments for Reynolds numbers ${10}^3$<R<${10}^6$. Simple scaling of the torque with Reynolds number is m/Inot observed for any range of R, although the characteristic time scales and the transport of passive scalars are found to scale with the global torque measurements. Above a nonhysteretic transition observed at R=1.3×${10}^4$, the torque has a Reynolds number dependence similar to the drag observed in wall-bounded shear flows such as pipe flow and flow over a flat plate.

We present experimental and theoretical results on the shear thinning of electrorheological fluids. Rheological measurements on a model fluid consisting of monodisperse silica spheres immersed in a dielectric liquid show a power-law dependence μ∝γ${\mathrm{̇}}^{\mathrm{-}\mathrm{\Delta }}$ of the apparent viscosity μ on the strain rate γ̇, with Δ in the range Δ=0.68–0.93. We present a theoretical treatment of steady-state cluster formation in applied electric and shear fields, which correctly predicts the observed power-law shear thinning albeit with an exponent Δ=2/3. We observe no true yield stress in this material.

Heat transport in a stochastic magnetic-field configuration is investigated analytically and numerically with two complementary models: a Chirikov-Taylor map model and a Gaussian random-field model. Numerical solution of the Chirikov-Taylor model shows a short-time nonlocal regime, but at large time the Rechester-Rosenbluth effective diffusion regime is confirmed numerically. The Gaussian model, for which the associated nonlocal propagator is calculated, describes this short-time behavior.

A 0.5-TW, 120-fs Ti:sapphire laser, when focused to greater than ${10}^{18}$ W/${\mathrm{cm}}^2$ onto a solid target, creates a plasma which emits radiation that extends beyond 1 meV. The x-ray yield increases as the 3/2 power of the incident laser energy, reaching 0.3% energy conversion to radiation above 20 keV at 40 mJ of laser energy on target. An x-ray spectral distribution of 1/E fits the data for most of the radiation, falling faster at higher photon energies.

A nondisruptive β-limiting phenomenon in a large tokamak under a large bootstrap current fraction, up to ∼80% of the plasma current, is described; β=(plasma pressure)/(magnetic pressure). During long-pulse neutral-beam-heated discharges in the JT-60 tokamak, it occurs at ${\mathrm{\beta }}_{\mathit{p}}$∼3, leading to a limit of the normalized β lower than the Troyon limit. The MHD feature is characterized by a large-amplitude partial relaxation with a fast growth time. A hollow current profile evolution in the high-${\mathrm{\beta }}_{\mathit{p}}$ regime plays an essential role in the MHD stability, analysis of which shows that the ideal n=1 kink-ballooning modes can be unstable just before the collapse.

The absorption of subpicosecond, obliquely incident laser light is studied using a 11/2D particle-in-cell code. Density scale lengths from L/λ=0.01 to 2 and laser irradiances between I${\lambda }^2$=${10}^{14}$ and ${10}^{18}$ W ${\mathrm{cm}}^{\mathrm{-}2}$ μ${\mathrm{m}}^2$ are considered. ‘‘Vacuum heating’’ [F. Brunel, Phys. Rev. Lett. 59, 52 (1987)] dominates over resonance absorption for scale lengths L/λ<0.1, and is most efficient when ${\mathit{v}}_{\mathrm{osc}}$/c≃3.1(L/λ${)}^2$. Absorbed energy is carried mainly by a ‘‘superhot’’ electron population with ${\mathit{U}}_{\mathrm{hot}}$∼(I${\lambda }^2$${)}^{1/3–1/2}$.

The first high-resolution (spatial and temporal) 2D images of the density region close to the ablation surface of laser-irradiated targets are obtained using a novel x-ray imaging technique. These show that laser intensity nonuniformities imprint themselves onto the cold target surface, even if these exist only on short ≃10 ps time scales as is the case with a laser beam smoothed by induced spatial incoherence. This imprint phenomenon is interpreted in terms of the poor thermal smoothing under the conditions prevailing at the beginning of the pulse. It appears that the problem can be combatted by preforming a uniform plasma before interacting with the optical drive.