Four-body Reaction Research Articles

Charge exchange three- and four-body reactions in the presence of a laser field

SynopsisCross-sections computation of the formation of antihydrogen’ atoms or ions resulting from two consecutive collisions between positronium atoms and antiprotons is a central issue of GBAR’s experiment. In [2] cross-section calculations using a perturbative approach, have been undertaken, for the charge exchange three- and four-body reactions (1) and (2). In the present study, we investigate the influence of a laser field on these two reactions. We show that under special irradiation conditions, antihydrogen’ atom or ion formation cross-sections may be increased by the presence of the laser field.

Borromean Feshbach resonance in $^{11}$Li studied via $^{11}$Li($p$,$p'$)

Abstract A dipole resonance of $^{11}$Li is found by a $^9$Li + $n$ + $n$ three-body model analysis with the complex-scaling method. The resonance can be interpreted as a bound state in the $^{10}$Li + $n$ system, i.e., a Feshbach resonance in the $^9$Li + $n$ + $n$ system. As a characteristic feature of the Feshbach resonance of $^{11}$Li, the $^{10}$Li + $n$ threshold is open above the $^{9}$Li + $n$ + $n$ one, which reflects a distinctive property of the Borromean system. A microscopic four-body reaction calculation for the $^{11}$Li($p$,$p'$) reaction at 6 MeV/nucleon is performed by taking into account the resonant and nonresonant continuum states of the three-body system. The calculation of angular distributions of the elastic and inelastic scattering as well as the energy spectrum reproduced a recent experimental result. Furthermore, the $E1$ strength distribution from a Coulomb dissociation experiment was also reproduced in this framework. This means that the existence of the Borromean Feshbach resonance may consistently answer a long-standing open question of an excited state of $^{11}$Li.

First measurement of the 2.4 MeV and 2.9 MeV 6He three-cluster resonant states via the 3H(4He, pα)2n four-body reaction

Two new low-lying 6 He levels at excitation energies of about 2.4 MeV and 2.9 MeV were observed in the experimental investigation of the p-α coincidence spectra obtained by the 3 H (4 He , p α)2 n four-body reaction at E4 He beam energy of 27.2 MeV. The relevant E* peak energy and Γ energy width spectroscopic parameters for such 6 He * excited states decaying into the α+ n+n channel were obtained by analyzing the bidimensional (E p , Eα) energy spectra. The present new result of two low-lying 6 He * excited states above the 4 He +2 n threshold energy of 0.974 MeV is important for the investigation of the nuclear structure of neutron-rich light nuclei and also as a basic test for theoretical models in the study of the three-cluster resonance feature of 6 He .

Production of 6He and 9Be by radiative capture and four-body recombination

In this work we estimate the production rates for the three-body radiative capture processes α + n + n → 6He + γ and α + α + n → 9Be + γ, as well as the four-body recombination reactions α + α + n + n → 6He + α, α + n + n + n → 6He + n, α + α + n + n → 9Be + n and α + α + α + n → BeBe + α. These processes compete as a source of 6He and 9Be. The hyperspherical adiabatic expansion method is used. With this method no assumption is made about the capture mechanism. Both sequential and direct capture are included. The production rates for the radiative and the four-body recombination processes are found to be comparable for a mass density of about 107g/cm3 ( ∼ 1030 neutrons/cm3) and temperatures of a few GK.

Three-body-model calculations for 22C

There are now several well-studied instances where very neutron-rich light nuclei at or near the neutron drip-line, such as 6He, 11Li and 14Be, have been found to have a Borromean three-body structure. Such systems are modelled effectively as a well-bound core nucleus plus two weakly-bound valence neutrons, where none of the two-body subsystems forms a bound state. It is now known that the heaviest particle-bound carbon isotope, 22C, shares these properties. We discuss a development of four-body reaction model calculations, using the fast adiabatic approximation, that is particularly well-suited for a quantitative analysis of reactions of such neutron-rich nuclei with a target nucleus at beam energies of order 100-300 MeV per nucleon; energies available at new and future radioactive ion beam (RIB) facilities. The 22C projectile wave function is calculated using the 20C core plus two-valence neutron three-body description.

MICROSCOPIC APPROACH TO SCATTERING OF UNSTABLE NUCLEI

This article is composed of three subjects. First, the relation between the method of continuum-discretized coupled channels (CDCC) and the Faddeev theory is clarified to show the validity of CDCC. Second, CDCC is applied to four-body reactions such as (6 He , nn 4 He ) as an example of recent progress in CDCC. Third, we propose a microscopic version of CDCC in which a localized form of the microscopic nucleon-nucleus optical potential is used as an input of CDCC calculation instead of the phenomenological optical potential commonly used. The validity of the Brieva-Rook localization is shown for the proton scattering in a wide incident-energy range.

Few-Body Reactions in Nuclear Astrophysics: application to6He and9Be production

In this work we obtain the astrophysical reaction and production rates for the two-particle radiative capture processes α + n + n → 6 He + γ and α + α + n → 9 Be + γ . The hyperspherical adiabatic expansion method is used. The four-body recombination reactions α + α + n + n → 6 He + α, α + n + n + n → 6 He + n, α + α + n + n → 9 Be + n and α + α + α + n → 9 Be + α are also investigated.

“Single-collision approximation for p 3-He elastic scattering at low energy”

A theoretical approach to studying four-body reactions of p3-He elastic scattering that takes consistently into account the single-collision mechanism is reported. The theoretical results obtained by this method were compared with experimental data, and the agreement is found to be quite satisfactory.

Single-collision approximation for p 3-He elastic scattering at low energy

A theoretical approach to studying four-body reactions of p 3-He elastic scattering that takes consistently into account the single-collision mechanism is reported. The theoretical results obtained by this method were compared with experimental data, and the agreement is found to be quite satisfactory.

Three- and Four-Body Scattering Calculations Including the Coulomb Force

The method of screening and renormalization for including the Coulomb interaction in the framework of momentum-space integral equations is applied to the three- and four-body nuclear reactions. The Coulomb effect on the observables and the ability of the present nuclear potential models to describe the experimental data is discussed.

Kaluza–Klein excitations of gauge bosons at the LHC

We consider the Randall–Sundrum extra-dimensional model with fields propagating in the bulk based on an extended electroweak gauge symmetry with specific fermion charges and localizations that allow to explain the LEP anomaly of the forward–backward asymmetry for b-quarks, A FB b . We study the manifestations of the strongly-interacting and electroweak gauge boson Kaluza–Klein excitations V KK at the LHC, with masses of the order of a few TeV, which dominantly decays into top and bottom quark pairs. We first analyze the two-body tree-level production processes p p → t t ¯ and b b ¯ in which the Kaluza–Klein (KK) excitations of gauge bosons are exchanged. We find that the additional channels can lead to a significant excess of events with respect to the Standard Model prediction; characteristic top quark polarization and angular asymmetries are quantitatively studied where the polarization is the probe the chiral structure of couplings to excited states. We then analyze higher order production processes for the gauge boson excitations which have too weak or no couplings to light quarks and, in particular, the loop induced process g g → V KK → t t ¯ and b b ¯ in which the anomalous g g V KK four-dimensional vertex has to be regulated. The RS effects in this process, as well as in the four-body reactions p p → t t ¯ b b ¯ , t t ¯ t t ¯ , b b ¯ b b ¯ and in the related three-body reactions g b → b t t ¯ , b b b ¯ , in which the V KK excitations are mainly radiated off the heavy quarks, are shown to be potentially difficult to test at LHC, due to small phase space and low parton density for M KK ≳ 3 TeV .

Ab initio potential energy surface for the H+OCS reaction

An ab initio MP4 study has been made of the potential energy surface of the H+OCS reaction. Minima and saddle points leading to formation of OH+CS or SH+CO were found. Stationary points were located using the 6–31G** basis set at the ROHF and UMP2 levels of theory, with energy refinements at the MP4(SDTQ) level. This theoretical study, in conjunction with the recent experimental results of Böhmer, Mikhaylichenko and Wittig, provides a mechanistic overview of the reactions of the H+OCS system. The results substantiate experimental hypotheses of the existence of stable, four-body reaction intermediates, as well as “tight” four-body transition states leading to products. Our calculations provide the first set of structural data that detail the reaction mechanisms for H+OCS going to SH+CO or OH+CS.

On the general form of the double and triple angular correlation following the sequential decay of the heavy reaction products

The general form of the double and triple differential cross-sections for the sequential three-body reaction X(a,b) Y(c)Z and four-body reaction X(a,b)Y(c)Z(f)R, respectively, are derived in the one-level excitation hypothesis. The transition amplitudes for the sequential processes are related to the scattering matrixS. Moreover, theoretical expressions for the b-c angular correlation are given under the hypothesis that the excited and partly polarized nucleus Y is produced in heavy-ion deeply inelastic collisions.

A critical discussion of a prism plot analysis of the four-body reaction π−p → π−p π+π− at 3.93 GeV/c

A multidimensional analysis of the reaction π −p → π −p π + π − at 3.93 GeV/ c is presented. Its results are compared to those obtained with conventional methods and its limitations are discussed.

Triple-angular-correlation analysis in four-body reactions

The differential cross-section for a four-body reaction, in the sequential-decay assumption, X(a, b)Y*(c)Z*(f)R, is derived. The interesting case in which the b-particle is detected at 0° relative to the incident beam is investigated Some applications of the formalism to particular reactions are considered, in order to give some idea of what type of information is obtained from b-c-f triple-angular-correlation analyses

The four-body reaction6Li(p,pα)np as a probe of the cluster structure of6Li

The ground state of 6Li is examined through a comparison of the reactions 6Li(p,p alpha )d and 6Li(p,p alpha )np at a bombarding energy of 39.8 MeV. Evidence is presented for the existence of a cluster structure of alpha particle plus neutron-proton pair within the ground state of 6Li.

Meson-baryon four-body reaction amplitudes in exact SU(4)

Fully SU(4) symmetric meson-baryon four-body reaction amplitudes are presented in terms of SU(4) eigenamplitudes. The mesons and baryons considered belong to the SU(4) representations 15 and 20, respectively. Using there relations, the cross-sections for the production of two charmed particles can be predicted from known uncharmed reactions.

Production mechanism in the four-body reaction π+n → p π+π−π0 at 5.1 and 9 GeV/ c

The π +n → p π + π − π 0 reaction is studied in the longitudinal phase space (LPS). The cross sections, mass spectra and four-momentum transfer distributions are discussed in each LPS sector. The dominant processes seem to be the ΔQ = 0 and G parity positive exchange, and ΔQ = 0, 1 and G parity negative exchange. A low baryon diffraction dissociation is also present.

The K +π - elastic scattering cross section as observed in K +p→K +π-Δ++ from 3 to 13 GeV/ c

The four-body reaction K +p→K + π - Δ ++ is analysed in a sample of 77 300 bubble chamber events of K +p→K + π - π +p for beam momenta from 2.5 to 12.6 GeV/ c to study the K +π - elastic scattering cross section. The relative merits of several analytic continuations to the pion pole are discussed. Maximum likelihood method is used and, for each experiment fits are performed simultaneously over the whole range of the M(p π +), m(K + π -) and t variables. The K +π - cross section is parametrized in terms of the down solution for the s-wave, a p-wave resonating at the K ∗(890) and a d-wave resonating at the K ∗(1420). Fitted values are obtained for the four-body cross section, the s-wave contribution to the K +π - cross section, and the masses and widths of the K ∗(890) and K ∗(1420).

Longitudinal configurations of three- and four-body reactions containing strange particles produced in π−p collisions at 11.2 GeV/c

The reactions π−p→πKY, KKN, ππKY, πKKN at 11.2 GeV/c are analysed using longitudinal phase space (LPS) plots with some 800 events. In spite of the very limited statistics often available the LPS analysis proves to be useful in understanding the processes responsible for both strange-particle and resonance production. quasi-two-body processes are the main characteristics of three-particle final states, while the dominant mechanism in four-body reactions is the dissociation of the incident pion also in the case where strangeness exchange is necessary.