Cross Sections For Various Processes Research Articles

Algebraic model studies of the structure and reactions of 12C and 16O

The role of algebraic models and geometric cluster models of alpha clusters in the structure of ground and first excited 0+ and second excited 2+ states in 12C are evaluated with the aim of establishing if the rotational bands are compatible with rigid structures or if they are instead overlaps of different configurations. A rigid equilateral triangle shape is assumed in Ref.[2, 3]: the energy spectrum, electromagnetic observables are calculated and the transition densities are compared with elastic and inelastic cross-sections for various processes. In a different approach [4, 5], we solve the three-body quantum problem for 3 alphas using the orthogonality condition and the stochastic variational method with correlated Gaussian basis functions. The two-body density distributions indicate that the main configurations of both the second 0+ and 2+ states are acute iscosceles triangle shapes with a 8Be(0+)+α configuration. We also find clues that the second 2+ state is probably not a member of the rigid rotational band built on the Hoyle state.

ATOM Program System and Computational Experiment

The article is devoted to a brief description of the ATOM computer program system, designed to study the structure, transition probabilities and cross sections of various processes in multielectron atoms. The theoretical study was based on the concept of a computational experiment, the main provisions of which are discussed in the article. The main approximate methods used in the system of programs for taking many-electron correlations into account and determining their role in photoionization processes, elastic and inelastic electron scattering, the decay of vacancies, and many others are presented. The most significant results obtained with this software are listed.

Theoretical Progress at the Frontiers of Small-xPhysics

In recent years, the theoretical foundations of small-x physics have made significant advances in two frontiers: higher-order (NLO) corrections and power-suppressed (sub-eikonal) corrections. Among the former are the NLO calculations of the linear (BFKL) and nonlinear (BK-JIMWLK) evolution equations, as well as cross sections for various processes. Among the latter are corrections to the whole framework of high-energy QCD, including new contributions from quarks and spin asymmetries. One common element to both of these frontiers is the appearance of collinear logarithms beyond the leading-order framework. The proper treatment of these logarithms is a major challenge in obtaining physical cross sections at NLO, and they lead to a new double-logarithmic resummation parameter which governs spin at small x. In this paper, I will focus on the role of these collinear logarithms in both frontiers of small-x physics, as well as give a brief sample of other recent advances in its theoretical foundations.The authors acknowledge support from the US-DOE Nuclear Science Grant No. DE-SC0019175, and the Alfred P. Sloan Foundation, and the Zuckerman STEM Leadership Program.

Standard Model: Electroweak Physics with CMS and ATLAS at 13 TeV

This paper presents cross section measurements for inclusive W/Z boson production, and W/Z boson production in association with jets and diboson production, performed by the CMS [1] and ATLAS [2] collaborations using proton-proton (pp) collisions data at a centre-of-mass energy of at LHC. Differential and total production cross sections for various processes, are computed and compared to higher order predictions of the standard model (SM). Recent results on effective leptonic weak mixing angle are also presented.

Angular differential cross section calculations for ion-helium collisions

We have calculated projectile angular-differential cross sections for various processes in ion-helium collisions. Key ingredients of our approach are the independent electron model, the two-center basis generator method for orbital propagation, and the eikonal approximation for the extraction of angular-differential scattering amplitudes. In general, we find good agreement with measurements; in some cases even for two-electron processes, although correlation effects are not taken into account.

Deuteron structure and diffractive deuteron-nucleus interaction

A nonrelativistic deuteron wave function involving the D-wave state and having a correct asymptotic behavior is constructed on the basis of the experimentally measured deuteron charge form factor GC(q) and deuteron structure function A(q). The differential cross section for elastic deuteron-nucleus scattering is calculated by using this wave function and is found to agree with experimental data at an energy of 110 MeV. Integrated cross sections for various processes involving deuteron-nucleus interactions are also calculated. The distribution in the emission angle of the center of mass of the neutron-proton system produced in the diffractive dissociation of 110-MeV deuterons in the field of 208Pb nuclei is obtained.

Effect of intruder mass on collisions with hard binaries. II - Dependence on impact parameter and computations of the interaction cross sections

view Abstract Citations (47) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effects of Intruder Mass on Collisions With Hard Binaries. II. Dependence on Impact Parameter and Computations of the Interaction Cross Section Hills, J. G. Abstract Over 125,000 encounters between a hard binary with equal mass, components and orbital eccentricity of 0, and intruders with solar masses ranging from 0.01 to 10,000 are simulated. Each encounter was followed up to a maximum of 5 x 10 exp 6 integration steps to allow long-term 'resonances', temporary trinary systems, to break into a binary and a single star. These simulations were done over a range of impact parameters to find the cross sections for various processes occurring in these encounters. A critical impact parameter found in these simulations is the one beyond which no exchange collisions can occur. The energy exchange between the binary and a massive intruder decreases greatly in collisions with Rmin of not less than Rc. The semimajor axes and orbital eccentricity of the surviving binary also drops rapidly at Rc in encounters with massive intruders. The formation of temporary trinary systems is important for all intruder masses. Publication: The Astronomical Journal Pub Date: June 1992 DOI: 10.1086/116204 Bibcode: 1992AJ....103.1955H Keywords: Binary Stars; Stellar Evolution; Stellar Mass; Stellar Orbits; Stellar Systems; Triple Stars; Computational Astrophysics; Eccentric Orbits; Gravitational Effects; Astrophysics; BINARIES: CLOSE; BINARIES: GENERAL full text sources ADS |

Quantum electrodynamic theory of multiply charged ions

A Rayleigh-Schrodinger perturbation theory is constructed within quantum electrodynamics so as to calculate energy levels nad transition probabilities in multiply charged ions. The basic features of the suggested model are renormalization and its relative simplicity. Renormalization is guaranteed by the fact that all interesting quantities (energy levels, transition probabilities, and cross sections of various processes) are expressed in terms of many-electron Green's functions, whose renormalization is achieved by standard methods. To demonstrate the simplicity of the suggested method, expressions are obtained for corrections to the ground state energy of a two-electron multiply charged ion due to two-photon exchange diagrams, whose derivation by other methods is, in our opinion, quite more complicated.

?-? Physics with peripheral relativistic heavy ion collisions

The high flux of equivalent photons present in relativistic heavy ion collisions of two chargesZ 1 andZ 2 gives rise to the collision of two equivalent photons. The cross-sections for various processes are directly related to the correspondingγ- γ cross-sections. As compared toγ- γ physics being studied at e+ e− colliders, we find that high energy states will not be so easily accessible at the existing facilities, however, the enhancement factor (Z 1 Z 2)2 in the expression for the cross section will provide very large photon fluxes for lower energies.

Study of electron-detachment and inelastic processes in Cl--rare-gas collisions

Cl--rare-gas collisions are investigated in the laboratory energy range 80-2000 eV. The main processes are identified by the characteristic energy losses undergone by the scattered particles. Relative differential cross sections for various processes have been measured. Basic similarities with other closed-shell systems (rare-gas-rare-gas and alkali-ion-rare-gas collisions) are underlined, and this gives confidence in the application of the molecular-orbital description to the halide negative-ion-rare-gas collisions. In particular, the use of this model suggests a new type of mechanism for the simple detachment process as an alternative to direct coupling between the incident state and a continuum. The simple detachment proceeds via a two-step mechanism: population of a resonant singly excited quasi-molecular state occurs at small internuclear distance; on the way out, this state autodetaches in the continuum associated with the 2 Sigma + ground state.

Lower and upper bounds for time-smoothed total transition probabilities and their rates

A formalism of time-smoothed total transition probabilities and their rates is developed which employs Laplace averages of these quantities. Under conditions pertinent to scattering processes, the Laplace-average formalism is shown to yield results equivalent to those obtained from a stationary-state formalism. Rigorous lower and upper bounds are obtained for the Laplace-averaged quantities which reduce to equalities for two-level systems. The lower bounds appear to be potentially useful estimating lower bounds for total cross sections of various processes.

Annihilations of 3.0 and 3.6 GeV/c antiprotons into six or more pions

We report a study of the reactions\(\bar pp \to n\pi ^ + + n\pi ^ - + m\pi ^0 \) at 3.0 GeV/c and 3.6 GeV/c (Ec.m.s. is equal to 2.77 GeV and 2.96 GeV respectively) wheren=3, 4 or 5 andm≥0. The sample contains 1988 six-prong events at 3.0 GeV/c, 440 eight-prong events at 3.0 and 3.6 GeV/c and 10 ten-prong events at 3.0 and 3.6 GeV/c. The cross-sections for various processes observed are compared with the cross-sections obtained in other experiments at different incident antiproton momenta. A maximum in the 7π annihilation cross-section is seen at a c.m.s. energy of about 2.7 GeV. Appreciable production of ρ0 in the six-pion events and of\(\rho ^{\begin{array}{*{20}c} \pm \\ 0 \\ \end{array} } \) and ω0 mesons in the seven-pion events is observed. In the six-pion events the 2π+2π− mass distribution and the ρ0π+π− mass distribution show evidence of structure with peaks at (1704±10) MeV and (1834±10) MeV. In the seven-pion events selected to contain a π+π− and π+π−π0 mass combination in the ρ0 and ω0 regions respectively, the ρ0π± mass distribution shows peaks in the mass regions corresponding to the A1 and A2 mesons with masses of (1054±7) MeV and (1269±9) MeV respectively, the width of the peak in the region of the A2 being smaller, (38±19) Mev, than that usually observed in bubble chambers but is compatible with the lower-mass peak of the split A2 as observed by Levratet al. The ρ0ω0 mass distribution shows two peaks at masses of (1689±10) MeV and (1848±11) MeV. The angular distributions of pions are slightly collimated along the direction of the incident particles, this collimation being an increasing function of pion momentum in the c.m.s. The ρ0 and ω0 mesons also have anisotropic distributions in the c.m.s. A strong angular correlation is observed between pairs of pions of opposite charge. This correlation decreases with increasing energy of the c.m.s. or when the number of π0 produced in the annihilation increases.

Further consequences of the quark model in inelastic meson-baryon scattering

A model of inelastic meson-baryon scattering in terms of quark scattering is presented. Relations are found between cross-sections for various processes, and predictions are made for density matrix elements where particles of higher spin are produced. A number of predictions are made which do not depend on assumptions about quark dynamics other than those inherent in the quark scattering model. A comparison is made with experimental data available at the present time.

High energy theorems for total cross sections from a current algebra

Abstract An extended version of the Pomeranchuk theorem and certain relations between total off-mass-shell cross sections for various processes at high energies are derived from a subalgebra of SU(6). It is predicted that σ π + p - σ π − p = const./ v L , as v L → ∞ where const. > 0. reduce to the high energy Johnson-Treiman relations in the exact symmetry limit.

Regge poles and elastic scattering at high energies

Some consequences of an asymptote of the Regge type on high-energy elastic scattering are investigated. Relations between total cross-sections of various processes are obtained. It is shown that the imaginary part of the vacuum pole is a positive definite function. An approximate analytic expression is derived for the vacuum trajectory.

Complex Angular Momenta and the Relation Between the Cross Sections of Various Processes at High Energies

Relations for the functions f(t), corresponding to the reactions, are obtained by the unitarity conditions on complex j(t), the moving pole of a partial wave in the annihilation channel. Simple connections between total interaction cross sections for various particles at high energies are discussed. (L.N.N.)