Inelastic collisions of medium energy atomic elements in solids

The stopping of medium atomic elements in solids has been calculated in the framework of classical approximation, taking into account elastic and inelastic collisions. The calculations are based on the 1) revised equations for the law of energy and impulse conservation, which were earlier used to describe inelastic collisions of atomic particles, 2) theory of quasi-small angle scattering, 3) power potential of LNS, and 4) limitation of the maximum distance of atoms approach determined by the interatomic distance in solids. Analytical equations have been obtained to calculate 1) a differential cross-section of elastic scattering in the presence of inelastic collisions, 2) energy transferred, 3) cross-sections of elastic and inelastic stopping, and penetration depth. Implantation into solids was found to be of threshold character.     

Rotational excitation of H2O by cold electrons

Experimental data are presented for the scattering of electrons by H2O between 17 and 250 meV impact energy. These results are used in conjunction with a generally applicable method, based on a quantum defect theory approach to electron-polar molecule collisions, to derive the first set of data for state-to-state rotationally inelastic scattering cross sections based on experimental values.     

Effects of Ps polarization potentials on Ps total cross-sections of the collisions of positrons with alkali metal atoms and alkaline-earth positive ions

Summary The previous form of the coupled-static approximation applied to the inelastic scattering of positrons by alkali metal atoms is improved by switching on the polarization potentials of the positroniums. The effect of these potentials on the total elastic and positronium formation cross-sections of three different scattering problems (namely the collisions of positrons with lithium, sodium and potassium atoms) is discussed in details. Particularly, we devote our interest to the comparison between the resultant positronium formation cross-sections and those of the inelastic collisions of positrons with berylium, magnesium and calcium positive ions.     

Study of the quenching of inelastic light scattering near an isolated resonance in I2 vapor

We have observed the variation in quenching behavior of inelastic light scattering near an isolated resonance in I₂ vapor. A quantitative fit of our measurements to a theory which takes into account the effects of both elastic and inelastic collisions is made.     

The four-jet structure of large transverse momentum events inpp interactions at the ISR

Deep inelastic proton-proton collisions have been recorded with the Split-Field-Magnet Detector (SFM) at the CERN Intersecting Storage Rings (ISR) by triggering on a single particle at high transverse momentum. Full reconstruction of the charged particles in these collisions was performed. In this paper we demonstrate the existence of a structure comprised of four jet-like clusters, two longitudinal and two transverse with respect to the beam, as would be expected from hard scattering of proton constituents.     

Electron scattering off simple atoms for large momentum transfer collisions

In a previous paper this author examined the Born expansion and isolated those parts of the expansion that contribute most significantly to the scattering amplitude for large momentum transfer collisions in inelastic collisions from the ground state of both hydrogen and helium. It turned out that certain terms where the scattering electron interacts once with the nucleus and once with the other electron dominate. The physical reason is that large momentum transfer collisions require the nucleus to take the bulk of the incident momentum but require an interaction with the one of the bound electrons to change the state of the atom. The arguments are quite general and this paper will extend this analysis by comparing the inelastic results obtained by this method for hydrogen and helium to a close coupling calculation with many intermediate states. Further, we will extend this analysis to the correction to the 1st Born result for elastic electron-hydrogen and electron-helium collisions and provide some results for scattering from the initial metastable states of hydrogen for large momentum transfer collisions. A comparison of the results of this analytic approach will be made to the numerical close coupling approach and experiments where available. The agreement is remarkable.     

Large effects of electric fields on atom-molecule collisions at millikelvin temperatures

Controlling interactions between cold molecules using external fields can elucidate the role of quantum mechanics in molecular collisions. We create a new experimental platform in which ultracold rubidium atoms and cold ammonia molecules are separately trapped by magnetic and electric fields and then combined to study collisions. We observe inelastic processes that are faster than expected from earlier field-free calculations. We use quantum scattering calculations to show that electric fields can have a major effect on collision outcomes, even in the absence of dipole-dipole interactions.     

The prospects of sympathetic cooling of NH molecules with Li atoms

We calculate the quartet potential energy surface for Li+NH and use it to calculate elastic and spin-relaxation cross sections for collisions in magnetically trappable spin-stretched states. The potential is strongly anisotropic but spin-relaxation collisions are still suppressed by centrifugal barriers when both species are in spin-stretched states. In the ultracold regime, both the elastic and inelastic cross sections fluctuate dramatically as the potential is varied because of Feshbach resonances. The potential-dependence is considerably reduced at higher energies. The major effect of using an unconverged basis set in the scattering calculations is to shift the resonances without changing their general behaviour. We have calculated the ratio of elastic and spin-relaxation cross sections, as a function of collision energy and magnetic field, for a variety of potential energy surfaces. Most of the surfaces produce ratios that are favorable for sympathetic cooling, at temperatures below about 20 mK.     

Inclusive production of neutral strange particles in\bar pp interactions at 32 GeV/c

Multiplicities of charged particles produced in the forward and backward hemispheres are investigated for proton-nucleus and proton-nucleon collisions in the range from 20 to 400 GeV/c. Weak, but growing with incident beam momentum, forward-backward multiplicity correlations are observed which cannot be reduced to the inelastic diffraction. These correlations are more pronounced in proton-nucleus than proton-nucleon interactions. The experimental data are discussed in the frameworks of current cluster and multiple scattering models. It is shown that multiple scattering models describe well the forward-backward multiplicity correlations in nuclear production.     

Dynamics of adsorption,exchange reactions,and defect formation at solid surfaces

In real time computer simulations of reactive atoms incident on solid surfaces, several interesting fundamental processes have been observed. These include (1) a cascade of inelastic collisions between incident atom and substrate atoms that eventually results in equilibration and adsorption; (2) for sufficiently reactive atoms, and sufficiently high substrate temperatures, an exchange reaction in which the adsorbed atom replaces a substrate atom; and (3) the formation of defects as a result of adsorption or exchange events.     

Scattering of He atoms from rough surfaces

Three diverse rough surfaces have been studied using inelastic He scattering. The first is an ion bombarded Ag(110) surface where a broadened specular peak remains visible but scattering remains entirely elastic as viewed by the incoherent component. The second is a cleaved Te(10 ) surface composed of helical chains where the roughness originates from thermal oscillations and scattering is almost entirely inelastic. Thirdly, a glass (7740) disc is shown to be physically rough but the surface is sufficiently rigid to yield largely elastic incoherent scattering.     

A classical description of deep inelastic collisions

A classical friction model is applied to describe deep inelastic collisions between heavy ions. With only a very few parameters chosen once and for all, a quantitative fit to the existing fusion data as well as the different features of deep inelastic scattering are obtained.     

Closed-form quantal description of inelastic heavy ion scattering

The amplitude for inelastic heavy ion scattering, given by the distorted-wave theory for excitation of low-lying collective states, is evaluated in closed form. Use is made of the Austern-Blair relation and of other approximations appropriate for strongly absorptive interaction to express the inelastic partial-wave amplitude entirely in terms of the elastic S-matrix elements in the initial and final channels. The resulting formulae display explicitly the various contributions to the transition amplitude, whose superposition gives rise to the variety of interference patterns observable in the angular distributions and excitation functions of inelastic heavy ion scattering. It is shown that, as for elastic scattering, the dominant mechanism in inelastic heavy ion collisions near and above the Coulomb barrier is diffractive scattering of Fresnel type.     

Stripping cross sections in collisions of light nuclei

By evaluating all the contributions of the intermediate states of the multiple scattering theory diagrams, we compute the integrated stripping cross sections of collisions among light nuclei. The resulting expressions have the simple form of a combination of total inelastic cross sections of nuclear reactions with projectile nuclei differing in the atomic mass number. We also check the accuracy of some widely used relations in heavy ion collisions. Received: 18 March 1998     

Theory of thermionic emission

A comprehensive theory of thermionic emission from clean metal surfaces is presented. The theory takes into account the energy band structure of the metal, inelastic scattering due to electron-electron collisions and the thermal vibration of the atoms. We applied the theory to thermionic emission from Cu(100). We calculated the thermally emitted current from this plane as a function of applied field. We find an almost periodic deviation from the Schottky line, similar in nature with that which is observed in emission from polycrystalline emitters [1]. We believe that accurate measurements of the amplitude and phase of these deviations from the Schottky line can, when analysed in the manner described here, provide valuable information on the surface optical potential. We have also calculated the total energy distribution of the emitted electrons for a typical value of the applied field. The dependence of the above measurable quantities on the parameters which enter the theory is analysed and demonstrated by explicit numerical calculations.     

Collisional properties of cold spin-polarized metastable neon atoms

We measure the rates of elastic and inelastic two-body collisions of cold spin-polarized neon atoms in the metastable 3P2 state for 20Ne and 22Ne in a magnetic trap. From particle loss, we determine the loss parameter of inelastic collisions beta=6.5(18) x 10(-12) cm(3) s(-1) for 20Ne and beta=1.2(3) x 10(-11) cm(3) s(-1) for 22Ne. These losses are caused by ionizing (i.e., Penning) collisions and occur less frequently than for unpolarized atoms. This proves the suppression of Penning ionization due to spin polarization. From cross-dimensional relaxation measurements, we obtain elastic scattering lengths of a=-180(40)a(0) for 20Ne and a = +150(+80)(-50)a(0) for 22Ne, where a(0)=0.0529 nm.     

Measurement of transverse single-spin asymmetries for Dijet production in proton-proton collisions at sqrt[s]=200 GeV

We report the first measurement of the opening angle distribution between pairs of jets produced in high-energy collisions of transversely polarized protons. The measurement probes (Sivers) correlations between the transverse spin orientation of a proton and the transverse momentum directions of its partons. With both beams polarized, the wide pseudorapidity (-1< or = eta < or = +2) coverage for jets permits separation of Sivers functions for the valence and sea regions. The resulting asymmetries are all consistent with zero and considerably smaller than Sivers effects observed in semi-inclusive deep inelastic scattering. We discuss theoretical attempts to reconcile the new results with the sizable transverse spin effects seen in semi-inclusive deep inelastic scattering and forward hadron production in pp collisions.     

Collisions of solitons and vortex rings in cylindrical Bose-Einstein condensates

Interactions of solitary waves in a cylindrically confined Bose-Einstein condensate are investigated by simulating their head-on collisions. Slow vortex rings and fast solitons are found to collide elastically contrary to the situation in the three-dimensional homogeneous Bose gas. Strongly inelastic collisions are absent for low density condensates but occur at higher densities for intermediate velocities. The scattering behavior is rationalized by use of dispersion diagrams. During inelastic collisions, spherical shell-like structures of low density are formed and they eventually decay into depletion droplets with solitary-wave features. The relation to similar shells observed in a recent experiment by Ginsberg et al. [Phys. Rev. Lett. 94, 040403 (2005)] is discussed.     

Quark Energy Loss and Shadowing in Nuclear Drell-Yan Process

The energy loss effect in nuclear matter is another nuclear effect apart from the nuclear effects on the parton distribution as in deep inelastic scattering process. The quark energy loss can be measured best by the nuclear dependence of the high energy nuclear Drell-Yan process. By means of three kinds of quark energy loss parameterizations given in literature and the nuclear parton distribution extracted only with lepton-nucleus deep inelastic scattering experimental data, measured Drell-Yan production cross sections are analyzed for 800 GeV proton incident on a variety of nuclear targets from FNAL E866. It is shown that our results with considering the energy loss effect are much different from those of the FNAL E866, who analyzes the experimental data with the nuclear parton distribution functions obtained by using the deep inelastic IA collisions and pA nuclear Drell-Yan data. Considering the existence of energy loss effect in Drell-Yan lepton pairs production, we suggest that the extraction of nuclear parton distribution functions should not include Drell-Yan experimental data.