The K−d → πΣn reaction revisited

The appearance of some papers dealing with the K ^? d → πΣn reaction, with some discrepancies in the results and a proposal to measure the reaction at forward n angles at J-PARC justifies to retake the theoretical study of this reaction. We do this in the present paper showing results using the Watson approach and the truncated Faddeev approach. We argue that the Watson approach is more suitable to study the reaction because it takes into account the potential energy of the nucleons forming the deuteron, which is neglected in the truncated Faddeev approach. The paper shows the strength and limitations of both approaches and we perform calculations using four different approximations. Comparison of the results shows that the truncated Faddeev approach produces a strong asymmetry between the energy of the two nucleons of the deuteron, while in the Watson approach this energy is equally shared. From the experimental point of view the results are very valuable since they show that the different approximations share the feature that the peak of the πΣ mass distribution is drastically shifted in the presence of the Λ(1405). Additionally, we also show that in the angle-integrated cross section the threshold cusp effects are basically washed away and all approximations show a clear shape of the Λ(1405). In this sense, measurements of all these magnitudes in different K ^? energies are bound to bring new information that sheds new light on the properties and nature of the Λ(1405) resonance.     

Tensor analyzing capacity of the γd → Δp reaction

The relativistic momentum approximation has been used to calculate the tensor analyzing capacity F₂₀ of the d p reaction. At high proton moments (p50 MeV/sec), the dependence of F₂₀ of the parameters of the n vertex becomes substantial, which shows that experiments on F₂₀ can provide information on the electromagnetic form factor of the n transition.Research performed with financial support from the Russian Fundamental Research Fund (project code 93-02-3514).Nuclear Physics Research Institute, Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 35–38, October, 1994.     

The p + p → π+ + d reaction close to threshold at COSY

Differential and total cross sections of the p + p → π⁺ + d reaction close to threshold were measured employing a magnetic spectrograph with track reconstruction, a very thin liquid hydrogen target and an accelerated proton beam with high phase space density. The data resolve a previous discrepancy between the n + p → π⁰ + d and the π⁺ + d → 2p reaction close to threshold indicating that isospin symmetry may be broken in the s-wave part of the cross section.     

Study of Fermilab data for the reaction π− p→ηn

Fermilab data for the angular distribution measurements of the reaction ^– p n are investigated and it is shown that a good fit with experiment is obtained by using a simple Regge pole model with phenomenological residue functions. The energy dependence in this case is found to be different from that for the d/dt/ data obtained at Serpukhov.Work supported by the Pakistan Science Foundation under contract No. P-PU-PHY(11/1).     

Study of fermilab data for the reaction π−p → π0n

Fermilab data for the angular distribution measurements of the reaction ^–p ⁰n are investigated and it is shown that a good fit with experiment is obtained by using a simple Regge pole model with phenomenological residue functions. The energy dependence in this case is found to be different from that for the d/dt data obtained at Serpukhov.Work supported by the Pakistan Science Foundation under contract No. P-PU-PHY(11/1).     

On momentum dependence of the reaction π− p→ωn near threshold

We discuss the near–threshold behavior of the ω production amplitude in the reaction π⁻ p→ωn. In contrast to the results of earlier analyses we find that the averaged squared matrix element of the production amplitude must be a decreasing function of energy in order to describe the existing experimental data. Received: 11 August 1999     

Study of the reaction γp → pπ0η

The reaction γp → pπ⁰η has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction shows contributions from Δ⁺(1232)η , N(1535)⁺π⁰ and pa ₀(980) as intermediate states. A partial-wave analysis suggests that the reaction proceeds via formation of six Δ -resonances, Δ(1600)P ₃₃ , Δ(1920)P ₃₃ , Δ(1700)D ₃₃ , Δ(1940)D ₃₃ , Δ(1905)F ₃₅ , Δ(2360)D ₃₃ , and two nucleon resonances N(1880)P ₁₁ and N(2200)P ₁₃ , for which pole positions and decay branching ratios are given.     

Measurement of PV asymmetry in +p→d+γ and ■+d→n+p

The measurement of parity-violating (PV) observables in few-nucleon system can shed light on our current understanding of the weak interaction between nucleons.Theoretical models describe the nucleonnucleon weak interaction at low energies use a series of undetermined parameters.Two parity violating measurements have been considered: the capture of polarized slow neutrons on hydrogen (n + p → d + γ) at Los Alamos National Laboratory for first phase and Oka Ridge National Laboratory for second phase and the helicity dependence of the deuteron photodisintegration cross section using circularly polarized photons (γ + d → n + p) at Shanghai Institute of Applied Physics.The goal of both experiments is to constraint the weak meson-nucleon couplings to a precision of 1 ×10-8 .The introduction of both experiments is presented.     

The π+ d → pp reaction at intermediate energies

Conclusion The joint efforts of the laboratories with intermediate energies accelerators at ANL, KEK, LANL, LNPI, Saclay, SIN and TRIUMF produced a rather definite picture of the ⁺pp reaction in the isobar region. However the problem of anomalies for the square-root branch point due to the production of isobar in the intermediate state have not been resolved so far. The poles obtained in different phenomenological analyses could be just the effective parametrization of these cuts (see e.g. [13]). Anyway, some singularities are definitely necessary to describe the data.The experimental data in regions s < 2·05 GeV and s < 2·25 GeV are clearly insufficient. Further accumulation of the data in these regions is necessary. Polarized deuteron data are badly needed in the whole kinematical range [13]. Besides as it was mentioned before it is necessary to measure accurately cross sections of other inelastic reactions which are important for the investigation (observation?) of dibaryonsNN N, NN andd N, NN [21]. It would be of interest also to measure cross sections of non quasi two-particle channels likeNN N, 2N andd N, 2N [22]. (In the case ofNN scattering quasi two-particle channels are known to dominate in a wide energy range.)Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.I am grateful to L. A. Kondratyuk, M. G. Ryskin and M. I. Strikman for valuable discussions of the considered problems.     

Investigation of the reaction π − p → η′π 0 n at the VES spectrometer

Results obtained by investigating the reaction π ^? p → η′π ⁰ n at the VES spectrometer (Institute for High Energy Physics, Protvino) are presented. The effective-mass spectrum and angular distributions of η′π ⁰ events are compared with their counterparts for ηπ ⁰ and η′π ^? events selected from the same data sample. The ratio R of the branching fractions for the decays of a ₂ ⁰ (1320) mesons into η′π and ηπ is measured. The result is R=0.047±0.018, which agrees with the value measured previously for a ₂ ^? . An investigation of P-wave production in the η′π ⁰ and ηπ ⁰ systems over the effective-mass interval 1.45–1.9 GeV/c2 leads to the conclusion that the coupling of the exotic object π ₁ (1600) to the ρπ channel is suppressed in relation to its coupling to the η′π or the b ₁(1235)π channel.     

Measurement of PV asymmetry in n＋p→d＋γ and γ＋d→n＋p

The measurement of parity-violating （PV） observables in few-nucleon system can shed light on our current understanding of the weak interaction between nucleons.Theoretical models describe the nucleonnucleon weak interaction at low energies use a series of undetermined parameters.Two parity violating measurements have been considered： the capture of polarized slow neutrons on hydrogen （n ＋ p → d ＋ γ） at Los Alamos National Laboratory for first phase and Oka Ridge National Laboratory for second phase and the helicity dependence of the deuteron photodisintegration cross section using circularly polarized photons （γ ＋ d → n ＋ p） at Shanghai Institute of Applied Physics.The goal of both experiments is to constraint the weak meson-nucleon couplings to a precision of 1 ×10^-8 .The introduction of both experiments is presented.     

The reaction pp→pΛK + near threshold

We analyze the recent total cross section data for pp→pΛK ⁺ near threshold measured at COSY. Using an effective range approximation for the on-shell pΛ S-wave final state interaction we extract from these data the combination ?= (2|K _s|²+|K _t|²)^−1/2= 0.38 fm⁴ of the singlet (K _s) and triplet (K _t) threshold transition amplitudes. We present an exploratory calculation of various (tree-level) vector and pseudoscalar meson exchange diagrams. Pointlike ω-exchange alone and the combined (ρ⁰,ω,K^*+)-exchange can explain the experimental value of ?. The pseudoscalar meson exchanges based on a SU(3) chiral Lagrangian turn out to be too large. However, when adding π⁰-exchange in combination with the resonant πN→S ₁₁(1650) →KΛ transition and introducing monopole form factors with a cut-off Λ_c= 1.5 GeV one is again able to reproduce the experimental value of ?. More exclusive measurements are necessary to reveal the details of the pp→pΛK ⁺ production mechanism. Received: 28 October 1998 / Revised version: 12 January 1999     

A study of K−π+ scattering in the reaction K−p→K−π+n at 11 GeV/c

Results from a high statistics study of the reaction K⁻p→K⁻π⁺n are presented. These results are based on data obtained with an 11 GeV/c beam using the LASS spectrometer at SLAC. The mass dependence of the spherical harmonic moments provides clear evidence for the production of the complete leading orbitally excited K¹ series up through J^P = 5⁻. These moments are used to perform an energy independent partial wave analysis of the K⁻π⁺ system from threshold to 2.6 GeV/c² using a t-dependent parametrization of the production amplitudes. The amplitudes corroborate the leading K¹(892), K₂¹(1430), K₃¹(1780), K₄¹(2060), and K₅¹(2380) resonances observed directly in the moments, and also provide new evidence for underlying states. The 0⁺ amplitude contains the K₀¹(1350) and a second 0⁺K¹(1950) at higher mass. The 1⁻K¹(1790) seen earlier two and three-body analyses is confirmed, and evidence is provided for suppressed K⁻π⁺ decay mode of a second 1⁻ state, the K¹(1410), which has been seen in earlier three-body analyses.     

Spin structure of the “forward” charge-exchange reaction n + p → p + n and deuteron charge-exchange breakup d + p → (pp) + n

The spin structure of the nucleon charge-exchange process n + p → p + n is investigated. Analysis shows that the spin-dependent part of the differential cross section of the process n + p → p + n at zero angle, which is proportional to the differential cross section of the deuteron charge-exchange breakup d + p → (pp) + n in the “forward” direction, plays the predominant role in the wide range of neutron momenta.     

Energy and angular distributions of deuterons from the D + D → p + n + d reaction

The energy and angular distributions of deuterons from the D + D → p + n + d reaction are experimentally and theoretically studied. The experiment is conducted on the U-240 cyclotron at the Institute for Nuclear Research in an extracted beam of deuterons with energy E _D = 36.9 MeV. A theoretical analysis has been performed using the microscopic diffraction nuclear model, within which the final-state interaction is considered and simple expressions for internal wave functions and approximations that include quasibinary mechanisms are employed.     

Mechanism of K − p → ηΛ Reaction Near Threshold

Within an effective Lagrangian approach, we investigate the reaction mechanism of K ^? p → ηΛ near threshold. It is found that a new D ₀₃ resonance, with mass M = 1,668.5 ± 0.5 MeV and width Γ = 1.5 ± 0.5 MeV, is needed to interpret the experimental data reported by the Crystal Ball collaboration. To verify our results, remeasurements on the differential cross sections and Λ polarization in this reaction will be helpful. Furthermore, we also show that the reaction ${p\bar{p} \rightarrow \Lambda\bar{\Lambda}\eta}$ is a good place to look for this new resonance if it exists.     

Measurement of PV asymmetry in(→n)+p→d+γ and (→γ)+d→n+p

The measurement of parity-violating(PV)observables in few-nucleon system can shed light on our current understanding of the week interaction between nucleons.Theoretical models describe the nucleonnucleon weak interaction at low energies use a series of undetermined parameters.Two parity violating measurements have been considered: the capture of polarized slow neutrons on hydrogen((n)+p→d+γ)at Los Alamos National Laboratory for first phase and Oka Ridge National Laboratory for second phase and the helicity dependence of the deuteron photodisintegration cross section using circularly polarized photons((γ)+d→n+p*)at Shanghai Institute of Applied Physics.The goal of both experiments is to constraint the weak meson-nucleon couplings to a precision of 1 × 10-8.The introduction of both experiments is presented.