Scattering amplitude of four non-relativistic particles

The exact integral equations for the non-relativistic four-particle scattering amplitudes are obtained, assuming only two-body forces. These equations can be solved when in the final state there are two pairs of particles with small relative energy of particles in the c.m. system of each pair. As an example, the reaction d+d→n+p+d is considered.     

Neutron-neutron final state interactions in the reaction H(d, pp)2n

The reaction ²H(d, pp)2n has been studied at a bombarding energy of 12 MeV, detecting the two protons in coincidence at angles of ±20° as well as +20° and −15°. In both cases, a narrow band was observed in a three-dimensional plot of the yield versus the energies of the two detected protons. E1 and E2, with most of the yield concentrated in the area where E1 ≈ E2. This suggests a two-step sequential process of the type d + d → (2p) + (2n) → p + p + n + n. In a missing mass plot for the third, undetected “particle” a pronounced, narrow peak appears at low relative energies in the (nn) system.     

The probability of non-radiative decay of the 3d level in muonic Np

The X-ray spectrum of muonic ²³⁷Np has been investigated with stopped muons in a NpO₂ target, containing about 10 g of ²³⁷Np. The probability of the radiationless muonic 3d→1s transition in ²³⁷Np, (9±4)%, was obtained by comparing the relative intensities of the main muonic X-ray transitions in singles and coincidence spectra. The coincidences were gated by the 2p→1s transitions.     

Suppression of the Coulomb interaction in the off-energy-shell p - p scattering from the p + d --> p + p + n reaction

Off-energy-shell effects in p - p scattering have been investigated at p - p relative energies from 600 down to 80 keV applying the Trojan horse method (THM) to the p + d --> p + p + n reaction at 5 MeV. In contrast with the on-energy-shell case, no Coulomb-nuclear interference minimum has been found in the extracted THM p - p cross section, due to the suppression of the Coulomb amplitude as predicted by the half-off-energy shell calculations. This hypothesis is strengthened by the agreement between THM p - p data and calculated on-energy-shell n + n, n + p and nuclear p + p cross sections.     

Suggestion for a dibaryon resonance in the pp system

The existence of a diproton resonance is indicated by the energy dependence of Legendre expansion coefficients of P dσ/dΩ for pp elastic scattering and the structure appearing in the data of Δσ_L = σ^Tot() − σ^Tot(→). The properties of such a resonance are described.     

Analyzing power in the reaction pp→dπ for beam momenta from 1.17 to 1.96 GeV/c

The analyzing power A_y0 in the reaction p↑p→dπ⁺ has been measured using the polarized proton beam at Argonne National Laboratory's zero gradient synchrotron. Data were taken at beam momenta of 1.17, 1.47, 1.70, and 1.96 GeV/c and for pion center of mass angles from 8° to 163°.     

The elastic and inelastic scattering of intermediate energy protons on deuterium at small momentum transfer

The differential cross sections for the elastic and inelastic scattering of protons on deuterium have been measured for scattering angles less than 14° at 198.5, 297.6 and 456.6 MeV. These quantities were determined relative to dσ / dΩ for pp elastic scattering with a precision of typically 2%. The range of excitation energies for the (p, p') reaction was chosen to emphasize the region near the np threshold dominated by the final-state interaction in the ¹S₀ channel. Particular attention was given to the dependence on excitation energy of the spectra at 198.5 MeV to examine the sensitivity to the ¹S₀ scattering length, a_np In this paper all data are compared with a new, detailed formulation of a simple model of the reaction mechanism based on the impulse approximation. The experimental results differ from the predictions by typically 10% and the differential cross sections exhibit a sensitivity to the intermediate-energy nucleon-nucleon amplitudes. If the impulse approximation is used to estimate a_np from the data at 198.5 MeV a value of − 24.7 ± 0.4 fm is obtained.     

Measurement of the analyzing power in p-->d-->(p p)n with a fast forward 1S0 proton pair

A measurement of the analyzing power A(y) of the p-->d--> (p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp) < 3 MeV. The S-wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at T(p) = 0.8 GeV the measured analyzing power almost vanishes, it rises to nearly unity at T(p) = 0.5 GeV for neutrons emitted at theta(c.m.)(n) = 167 degrees. The results are compared with a model taking into account one-nucleon exchange, single scattering, and Delta(1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier and the analyzing power at 0.8 GeV; it fails to reproduce A(y) at 0.5 GeV.     

Existence and stability of propagating fronts for an autocatalytic reaction-diffusion system

We study a one-dimensional reaction-diffusion system which describes an isothermal autocatalytic chemical reaction involving both a quadratic (A + B → 2B) and a cubic (A + 2B → 3B) autocatalysis. The parameters of this system are in the ratio D = D_B/D_A of the diffusion constants of the reactant A and the autocatalyst B, and the relative activity k of the cubic reaction. First, for all values of D > 0 and k ≥ 0, we prove the existence of a family of propagating fronts (or travelling waves) describing the advance of the reaction. In particular, in the quadratic case k = 0, we recover the results of Billingham and Needham [Phil. Trans. R. Soc. London A 334 (1991) 1–24]. Then, if D is close to 1 and k is sufficiently small, we prove using energy functionals that these propagating fronts are stable against small perturbations in exponentially weighted Sobolev spaces. This extends part of the results that are known for the scalar equation to which our system reduces when D = 1.     

Quasi-α-particle mechanism of pion double charge exchange on light nuclei

A microscopic theory of π-meson double charge exchange (DCE) on light nuclei has been suggested and developed on the supposition that the corresponding elementary process proceeds by quasi-α-particle formation within the nucleus. Light nuclei consisting of both α-particles and α-particles and clusters of other kinds are considered. To describe the bound state of the quasi-α- particle and the continuum spectrum state of four identical nucleons, the four-body hyperspherical basis has been applied, while to obtain the wave functions of the centers of mass of the cluster relative motion we solve either the three-body Schrödinger equation (in the case of a three-body cluster configuration) or the two-body Schrödinger equation (in the case of a two-body cluster configuration). The reactions π^± + ¹²C → π + 4p(4n) + 2α, π⁻ + ⁷Li → π⁺ + 4n + ³H, π^± + ⁶Li → π + 4p(4n) + n + p, π^± + ⁶Li → π + 4p(4n) + d are investigated. It is shown that the effect of the final-state interaction between the four nucleons emitted by the nucleus in the process of π-meson DCE is rather important. The available experimental data on the ⁷Li nucleus can be explained quite satisfactorily on the supposition that this nucleus has a two-body cluster structure, and, hence, the π-meson DCE process occurs only on the α-particle.The differential and total cross sections of the reactions under investigation calculated as functions of the incident pion energy are essentially different for different nucleon-nucleon potentials. Experimental study of DCE on α-particle nuclei is shown to be a timely problem.     

On the B→Xs ll decays in general supersymmetric models

We analyze the inclusive semileptonic decays B→X_s l⁺l⁻ in the framework of the supersymmetric standard model with non-universal soft-breaking terms at GUT scale. We show that the general trend of universal and non-universal models is a decreasing of branching ratio (BR) and increasing of energy asymmetry (AS). However, only non-universal models can have chances to get very large enhancements in BR and AS, corresponding to large (negative) SUSY contributions to the b→sγ amplitude.     

Study of the nd-breakup reaction in the kinematical region of the nn final-state interaction

The neutron neutron (nn) final-state interaction has been studied in the n + d → p + n + n reaction at 40 ± 5 MeV. Data on the dependence of reaction yield on the relative energy of two neutrons emitted in a narrow cone of angles are obtained. The value of the nn-scattering length deduced from a comparison of the shape of FSI peak with simulation data is a _nn = −17.9 ± 1.0 fm, where the error indicates the statistical uncertainty. Original Russian Text ? S.V. Zuyev, E.S. Konobeevski, M.V. Mordovskoy, S.I. Potashev, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 6, pp. 843–845.     

U-spin symmetry in doubly Cabibbo-suppressed charmed meson decays

We prove a U-spin amplitude triangle relation among doubly Cabibbo-suppressed (DCS) charmed meson decays, D⁰→K⁺π⁻,D⁰→K⁰π⁰ and D⁺_s→K⁰K⁺, congruent to an isospin relation among corresponding Cabibbo-favored (CF) decays. U-spin breaking in relative phases between CF and DCS amplitudes affects time-dependent studies of D⁰– mixing. Comparison of final state phase patterns in DCS and CF amplitude triangles, which can shed some light on these phases, is carried out in a phenomenological framework incorporating resonance contributions.     

Single and double dissociation in πp collisions at 11 and 16 GeV/c

The reactions π⁻p → 2π⁻π⁺p, π⁻p → 2π⁻π⁺π^op and π⁻p → 2π⁻2π⁺n are analysed at 11 and 16 GeV/c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π⁻p → 2π⁻π⁺p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π⁻p → (2π⁻π⁺)p, and of the proton, π⁻p → π⁻(π⁻π⁺p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π⁻p → (2π)(πp) decrease with increasing energy.

In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/c a maximum for single dissociation of the proton into 3πp, namely π⁻p → π⁻(π⁻π⁺π^op); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π⁻p → π⁻(π⁻2π⁺)n. Another strong maximum corresponds to the pion dissociation π⁻p → (2π⁻π⁺π^o)p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π⁻p → (2π⁻2π⁺)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π⁻p → (2π⁻π⁺)(π^op) and π⁻p → (2π⁻π⁺)(π⁺n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed.

An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy.     

Resonance states of superheavy hydrogen nuclei obtained in transfer reactions with exotic beams

A resonance state situated at 1.8±0.1 and, most likely, another state positioned at 2.7±0.1 MeV above the t+n+n decay threshold were observed in the missing mass energy spectrum of the ⁵H nucleus produced in the reaction ³H(t,p)⁵H. The peak located close to $E_{^5 H} = 1.8$ MeV also was seen in the ⁵H spectrum obtained from the energy distributions of ³H nuclei emitted in the reaction ²H(⁶He,⁵H)³He. The width (Γ_obs ≤ 0.5 MeV) obtained for the two ⁵H resonance states is surprisingly small. A state of ⁴H with E _res = 3.3 MeV and γ² = 2.3 MeV was obtained in the reaction ²H(t,p)⁴H from the proton spectrum.     

Mathematical simulation of few-nucleon experiments with three or more particles in the final state

A computer program for the kinematic simulation of nuclear reactions with three or more particles in the final state is described. Simulation results for the d + ²H → (nn)^S + (pp)^S → p + p + n + n reaction, which proceeds through the formation of a singlet dineutron and diproton in the intermediate state, are presented as an example. It is shown that the kinematic parameters of breakup particles depend on the parameters of the intermediate state. The results from simulating secondary neutron spectra are compared to an experimental neutron time-of-flight spectrum obtained in a kinematically complete experiment at a deuteron energy of 15 MeV. As a result of the comparison, the energy of the quasi-bound singlet ¹S₀ state of the ²n-system is determined.     

Experimental study of the time-dependent rate of K → πππ

The time-dependence of the decay rate of initially pure K⁰ into the final state (π⁺π⁻π⁰) has been studied in search for the decay k_S⁰→π⁺π⁻π⁰. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K_S⁰ amplitude and the K_L⁰ amplitude is η₊₋₀ = (0.13_−0.20^+0.17) + i(0.17_−0.26^+0.27); the ratio of the CP-conserving K_S⁰ amplitude and the K_L⁰ amplitude is < 0.4. The energy dependence of the K⁰→π⁺π⁻π⁰ matrix element is found to be a₊₋₀ = −0.31 ± 0.03.     

DETERMINATION OF THE AVERAGE NEUTRON ENERGY USING CROSS SECTION RATIO OF 58Ni(n,p)58m+gCo and 58Ni(n,2n)57Ni REACTIONS

The method of determination for average neutron energy from D-T reaction by using two silicon semiconductor detectors and the cross section ratios of ⁵⁸Ni(n,p)^58m+gCo and ⁵⁸Ni(n,2n)⁵⁷Ni reactions is described.The plot of the cross section ratio against the neutron energy has been obtained.The results have been compared with existing data.     

A microscopic approximation for sequential decay processes in light nuclear systems

An approximative treatment for sequential decay processes is presented which uses the cluster model reaction formalism. In the case of a dominating sequential decay mechanism, the break-up amplitude is decomposed in two factors which can be obtained from two-particle reaction calculations. This factorization is essentially based on the same idea as the Watson-Migdal formalism. The method is applied to the α + d →⁵He + p → α + n + p break-up. The results are in good agreement with recent experimental data.     

The Cross Section Measurement for the Reactions of 48,46Ti(n,p) 48,46Sc 50Ti(n,α) 47Ca and 58Ni (n,2n) 57Ni 58Ni(n,p)58m+gCo

The cross sections for the ⁵⁰Ti(n,α)⁴⁷Ca,⁴⁶Ti(n,p)⁴⁶Sc、⁴⁸Ti(n,p)⁴⁸Sc and ⁵⁸Ni(n,2n)⁵⁷Ni ⁵⁸Ni(n,p)^58m+gCo reactions have been measured by using the activation method relative to the cross sections of the ²⁷Al(n,α)²⁴Na reaction in the neutron energy range of 13.50—14.81MeV.The neutron energies were determined by the cross section ratios of the ⁹⁰Zr(n,2N) ^89m+gZr and ⁹³Nb (n,2n) ^92mNb reactions.The results obtained are compared with the published and to be published data of several authors.