Hyperons Analogous to the Λ(1405)

The low mass of the Λ(1405) hyperon with j ^P =  1/2^?, which is higher than the ground state Λ(1116) mass by 290 MeV, is difficult to understand in quark models. We analyze the hyperon spectrum in the bound state approach of the Skyrme model that successfully describes both the Λ(1116) and the Λ(1405). This model predicts that several hyperon resonances of the same spin but with opposite parity form parity doublets that have a mass difference of around 300 MeV, which is indeed realized in the observed hyperon spectrum. Furthermore, the existence of the ${\Xi(1620)}$ and the ${\Xi(1690)}$ of j ^P  = 1/2^? is predicted by this model. Comments on the Ω baryons and heavy quark baryons are made as well.     

Isolating the Λ(1405) in lattice QCD

The odd-parity ground state of the Λ baryon lies surprisingly low in mass. At 1405 MeV, it lies lower than the odd-parity ground-state nucleon, even though it has a valence strange quark. Using the PACS-CS (2+1)-flavor full-QCD ensembles, we employ a variational analysis using source and sink smearing to isolate this elusive state. For the first time we reproduce the correct level ordering with respect to nearby scattering thresholds. With a partially quenched strange quark to produce the appropriate kaon mass, we find a low-lying, odd-parity mass trend consistent with the experimental value.     

Absorption of Λ(1520) hyperons in photon-nucleus collisions

In the framework of the nuclear spectral function approach for incoherent primary photon-nucleon and secondary pion-nucleon production processes we study the inclusive ??(1520)-hyperon production in the interaction of 2-GeV photons with nuclei. In particular, the A and momentum dependences of the absolute and relative ??(1520)-hyperon yields are investigated in two scenarios for its in-medium width. Our model calculations show that the pion-nucleon production channel contributes appreciably to the ??(1520) creation at intermediate momenta both in light and heavy nuclei in the chosen kinematics and, hence, has to be taken into consideration on close examination of the dependences of the ??(1520)-hyperon yields on the target mass number with the aim to get information on its width in the medium. They also demonstrate that the A and momentum dependences of the absolute and relative ??(1520)-hyperon production cross sections at incident energy of interest are markedly sensitive to the ??(1520) in-medium width, which means that these observables may be an important tool to determine the above width.     

Λ(Λ)production in p(p) collisions

We describe the production of (AA) in p(p) collisions using a constituent quark model which has been successfully applied to the N(N)system.     

Nonmesonic decay of the Λ-hyperon in hypernuclei produced by p + Au collisions

The β-delayed proton precursor ¹⁴⁹Yb was synthesized in the reaction ¹¹²Sn(⁴⁰Ca, 3n) and identified by using a proton-gamma coincidence measurements in combination with a helium-jet fast tape transport system. Its β-delayed proton spectrum was observed. The half-life of ¹⁴⁹Yb was determined to be 0.7±0.2 s. The 253, 101, and 365 keV γ transitions in ¹⁴⁷Dy, following β-delayed proton emission of ¹⁴⁸Ho decay, were reported for the first time. Received: 14 March 2001 / Accepted: 26 September 2001     

The Λ(1405) state in a chiral unitary approach with off-shell corrections to dimensional regularized loop functions

The Bethe-Salpeter equation is solved in the framework of the unitary coupled-channel approximation by using the pseudoscalar meson-baryon octet interaction. The loop function of the intermediate meson and baryon is deduced in a dimensional regularization scheme, where the relativistic kinetic effect and off-shell corrections are taken into account. Based on the experimental data at the K~-p threshold, the subtraction constants in the loop function are determined. The squared amplitude is suppressed strongly and only one Λ(1405) state is generated dynamically in the strangeness S =-1 and isospin I =0 sector.     

Can the Λ(1405) resonance Be seen in neutron spectra from the K − + d reaction?

Neutron spectra from the low-energy reaction K ^? + d → π +Σ+n were calculated using coupled-channel Faddeev equations. The possibility of tracing the signature of the Λ(1405) resonance in the spectra was investigated for four different phenomenological models describing K? N-πΣ interactions. We found, that while in the direct spectra kinematic effects mask completely the peak corresponding to the resonance, the deviation spectrum method [J. Esmaili et al., Phys. Rev. C 83, 055207 (2011)] is able to eliminate kinematics and differentiate between different models of Λ(1405).     

Production of Λ-hypernuclei in A(p,K~ )ΛB reactions

The production of Λ-hypernuclei in the A(p,K )ΛB reaction is investigated in the framework of the distorted wave impulse approximation(DWIA). The total cross sections and differential cross sections for various nuclear targets are calculated with an elementary process pN→NKΛ where the additional contributions from the N*(1535) resonance and the final state interaction between p and Λ are included. The dependence of the production cross sections of Λ-hypernuclei on the phenomenological nuclear density and the nucleon number in the target, as well as the distortion effect of the incident proton and outgoing kaon, are also explored. It is shown that the distortion effect tends to decrease the cross sections by a factor of about 3—10. The production cross sections are sensitive to the adopted nuclear density.     

New detector system to measure (n,γ) reaction cross section precisely in China

Based on the urgent requirement of the (n,γ) reaction cross-section in the energy range of keV~MeV, 4π gamma total absorption facility (GTAF) is being constructed at China Institute of Atomic Energy (CIAE). In this paper, firstly the review of historic experimental facilities over the world is presented, and then measurement method of GTAF is described. Finally, the structure requirement for GTAF is presented. Neutron capture reactions are the key process of nucleosynthesis in astrophysics beyond iron element. The application of such facility will improve the experimental condition for the research of (n,γ) reaction.     

Forward-backward multiplicity correlations in σ+ p,K + p andpp collisions at 250 GeV/c

Forward-backward multiplicity correlations in σ⁺,K ⁺ p andpp collisions at 250 GeV/c ( \(\sqrt s \) =22 GeV) are given for all charges and for the different charge combinations. The correlations are found to be caused predominantly by centrally produced particles. It is demonstrated that this result is an agreement with observations at the ISR and the CERNp \(\bar p\) -Collider. The results are compared to expectations from LUND, DPM and FRITIOF Monte Carlo models and a geometrical picture relating correlations in hadron-hadron collisions toe ⁺ e ^? data in terms of impact parameters is tested.     

Line emission and alignment effects in state selective electron transfer in He2+-Li(2s, 2pΣ, 2pΠ) collisions

Classical Trajectory Monte-Carlo (CTMC) method has been used to investigate state selective electron capture by He²⁺ ions colliding with Li(2s) and Li(2p) in as well as alignments in the energy range 1-15 keV/amu. He⁺(4l) electron capture, line emission [He II(n = 4 3)] cross-sections and alignment parameters have been calculated and analyzed in the light of the available results. The undulatory structure of the capture and emission cross-sections have been explained qualitatively in terms of a quasi-molecular ion formation. Projectile impact energy and spatial overlap play crucial role in determining the alignment effects. Received 3 July 1998 and Received in final form 3 June 1999     

Production of Λ-hypernuclei in A(p,K+)ΛB reactions

The production of Λ-hypernuclei in the A(p, K⁺)_ΛB reaction is investigated in the framework of the distorted wave impulse approximation(DWIA). The total cross sections and differential cross sections for various nuclear targets are calculated with an elementary process pN→NKΛ where the additional contributions from the N^*(1535) resonance and the final state interaction between p and Λ are included. The dependence of the production cross sections of Λ-hypernuclei on the phenomenological nuclear density and the nucleon number in the target, as well as the distortion effect of the incident proton and outgoing kaon, are also explored. It is shown that the distortion effect tends to decrease the cross     

New localized excitations in a (2+1)-dimensional Broer—Kaup system

Starting with the extended homogeneous balance method and a variable separation approach, a general variable separation solution of the Broer—Kaup system is derived. In addition to the usual localized coherent soliton excitations like dromions, lumps, rings, breathers, instantons, oscillating soliton excitations, peakon and fractal localized solutions, some new types of localized excitations, such as compacton and folded excitations, are obtained by introducing appropriate lower-dimensional piecewise smooth functions and multiple-valued functions, and some interesting novel features of these structures are revealed.     

Jet production in hadronic collisions to0(α s 3 )

We present the full0(α _s ³ ) QCD corrections to jet production within a small opening angle δ at large transverse momenta for all partonic subprocesses. Results for CERN and Tevatron colliders are given with particular emphasis on the sensitivity to renormalization and factorization mass scales.     

Classical trajectory study of alignment effects in the capture process: He2+-Li1(2pΣ,2pΠ) collisions

A simulation method (CTMC) has been used to investigate the selectivity and alignment effects on the capture process in He²⁺-Li¹(2pΣ,2pΠ) collisions. The anomalous results of the experiment (∼ 50% error) as well as the AO calculation of Gieler et al. in case of capture into He II (n = 4) from the initial Li¹ (2pΣ) state are not found in the present work. Relative velocity and spatial overlap together mainly control the capture process in ion-atom collisions. The n-distribution of the final capture state is also presented.     

Comparison of π±, K± and p,p production in the central rapidity region in hadron-hadron collisions and in e+e− annihilation

We compare the p_T dependence of pion, kaon and proton production cross sections in the central rapidity region in e⁺e⁻ annihilation events and in proton-proton collisions at ISR energies. We find similarities both in the p_T dependence of cross sections and in the particle composition as a function of p_T, in agreement with the hypothesis of a universal mechanism of particle production.     

New localized excitations and cross-like fractal structures to the (2+1)-dimensional Broer–Kaup system

A broad general variable separation solution with two arbitrary lower-dimensional functions of the (2+1)-dimensional Broer–Kaup (BK) equations was derived by means of a projective equation method and a variable separation hypothesis. Based on the derived variable separation excitation, some new special types of localized solutions such as oscillating solitons, instanton-like and cross-like fractal structures are revealed by selecting appropriate functions of the general variable separation solution.