34280769
Measurement of inclusive quasielastic scattering of polarized electrons from polarized 3He.
We report a measurement of the asymmetry in spin-dependent quasielastic scattering of longitudinally polarized electrons from a polarized 3He gas target. This measurement represents the first demonstration of a new method for studying electromagnetic nuclear structure: the scattering of polarized electrons from a polarized nuclear target. The measured asymmetry is in good agreement with a Faddeev calculation and supports the picture of spin-dependent quasielastic scattering from polarized 3He as predominantly scattering from a polarized neutron.
119473046
Adventures of the coupled Yang–Mills oscillators: I. Semiclassical expansion
We study the quantum mechanical motion in the x2y2 potentials with n = 2, 3, which arise in the spatially homogeneous limit of the Yang–Mills (YM) equations. These systems show strong stochasticity in the classical limit ( = 0) and exhibit a quantum mechanical confinement feature. We calculate the partition function Z(t) going beyond the Thomas–Fermi (TF) approximation by means of the semiclassical expansion using the Wigner–Kirkwood (WK) method. We derive a novel compact form of the differential equation for the WK function. After separating the motion in the channels of the equipotential surface from the motion in the central region, we show that the leading higher order corrections to the TF term vanish up to eighth order in , if we treat the quantum motion in the hyperbolic channels correctly by adiabatic separation of the degrees of freedom. Finally, we obtain an asymptotic expansion of the partition function in terms of the parameter g24t3.
121776811
Delta electrons as a probe of strong magnetic fields in heavy ion collisions
Abstract We propose that the spin polarization of delta electrons should be used as a measure of the strong magnetic fields ( B ∼10 17 G) induced by the nuclear motion in collisions of very heavy ions. The polarization is typically of the order of 10–20 percent in Pb-Pb and U-U collisions. We also discuss the bombarding energy dependence up to E 1ab = 200MeV/ u , where 500 keV level splitting between spin up and down states is obtained.
121675477
Stability of massive objects in a new scalar-tensor theory
The existence of black holes is closely related to the problem of singularities in space-time. In general relativity the formation of black holes i s the consequence of the collapse of massive objects with masses greater than several t imes the so lar mass. It was discussed in the l i terature whether in other theories of gravity, which a r e in accord with present gravitational experiments, the formation of event horizons o r the collapse of massive objects might not o c c ~ r . ' ~ Good candidates for theories with the lat ter feature may be scalartensor theories, where the gravitational constant G o r the particle res t mass i s variable (i.e., Bergmann-Wagoner theory ,'" Nordtvedt t h e ~ r y , ~ Brans-Dicke theory,*-l' and variable-mass theory,lZJ3 to mention just a few). In general, in scalartensor theories the metric i s generated by a sca lar gravitational field which ac ts together with nongravitational fields (matter). The sca lar gravitational field itself is generated by the nongravitational fields via a wave equation in curved space-time. In this paper we discuss a new kind of scalartensor theory of gravity, where the gravitational constant depends on a scalar field, which itself couples to the surrounding masses via the curvature scalar . The idea behind this model is that during the collapse of a s t a r which in general relativity would form a black hole, in our theory a strong sca lar field might be built up, which should reduce the gravitational constant until the collapse i s stopped and the whole system reaches a new s table configuration. In this paper we therefore look for stable, time-independent solutions of the field equations of our theory, representing such a final configuration with very large nucleon number, surrounded by a sca lar field.14 If there exist such solutions for any se t of parameters, a time-dependent treatment would be necessary to find out whether a given initial configuration can reach this state. If, however, i t turns out that there a r e no such stable end configurations if the nucleon number exceeds a definite finite boundary, this would already prove that gravitational collapse i s also possible in our theory, if the initial s t a r configuration has a mass large enough; no further time-dependent studies a r e then necessary. We shall show in this paper that the lat ter case i s true. Even when varying the coupling constant between sca lar and gravitational fields over the whole allowed range, the effective gravitational constant only varies within narrow bounds. It i s not reduced strongly enough by the sca lar field that stable solutions with arbitrary large masses a r e possible. Our paper is organized a s follows. In Sec. I1 we derive the field equations for the scalar field and the gravitational field from an action integral. In Sec. I11 we make a static, spherically symmetric Ansatz f o r the metric and derive the generalized Tolman-Oppenheimer-VolkofI equation. In Sec. IV we define a quantity which allows us to measure the stabilizing effect of the sca lar field. In Sec. V we make some estimates concerning the strong-coupling limit and the weak-field limit. Our numerical results a r e presented in Sec. VI.
121125499
Quark-gluon plasma cooling through pion emission in a chiral bag model
Abstract A hypothetical quark-gluon plasma is described as a large bag, filled with quarks, antiquarks, and gluons, of radius R ∼ 2–6 fm and temperature T ∼ 100–250 MeV. We consider the cooling of this plasma through pion emission at the bag surface in a chiral-model approach. Comparison is made between results for a large, spherical bag and a model in the limit in which the plasma fills half of space and pion emission is across a planar interface. We find a rather low initial cooling rate per unit surface area for this mechanism, of roughly (10–100) × 10 23 MeV/fm 2 .s. This rate per unit surface becomes independent of R for R ⩾ 3 fm, and, because of the nature of the coupling in the chiral bag model, varies with temperature as T 6 .
29765436
Role of Multistep Processes in Heavy-Ion Inner-Shell Excitations
This Letter discusses inner-shell excitation in collisions of very heavy ions (2, -2, 2 140) in the framework of the quasimolecular model. The importance of multistep excitations and of coupling between continuum states is demonstrated. The lso vacancy probabilities resulting from coupled-channels calculations exceed perturbation theory by a factor 3-5, thus giving good agreement with recent experimental results.
8932657
Diffractive leptoproduction of vector mesons in QCD.
We demonstrate that the distinctive features of the forward differential cross section of diffractive leptoproduction of a vector meson can be legitimately calculated in perturbative QCD in terms of the light-cone [ital q[bar q]] wave function of the vector meson and the gluon distribution of the target. In particular, we calculate the [ital Q][sup 2] and nuclear dependence of the diffractive leptoproduction of vector mesons and estimate the cross section. The production of longitudinally polarized vector mesons by longitudinally polarized virtual photons is predicted to be the dominant component, yielding a cross section behaving as [ital Q][sup [minus]6]. The nuclear dependence of the diffractive cross sections, which follows from a factorization theorem in perturbative QCD, provides important tests of color transparency as well as constraints on the shadowing of the gluon structure functions and the longitudinal structure functions of nuclei.