M. Sotona

Photoproduction of neutral kaons on a liquid deuterium target in the threshold region

The photoproduction process of neutral kaons on a liquid deuterium target is investigated near the threshold region, E{sub {gamma}}=0.8-1.1 GeV. K{sup 0} events are reconstructed from positive and negative pions, and differential cross sections are derived. Experimental momentum spectra are compared with those calculated in the spectator model using a realistic deuteron wave function. Elementary amplitudes as given by recent isobar models and a simple phenomenological model are used to study the effect of the new data on the angular behavior of the elementary cross section. The data favor a backward-peaked angular distribution of the elementary n({gamma},K{sup 0}){lambda} process, which provides additional constraints on current models of kaon photoproduction. The present study demonstrates that the n({gamma},K{sup 0}){lambda} reaction can provide key information on the mechanism of the photoproduction of strangeness.

Spectroscopy of Electro- and Photo-Productions of Hypernuclei

Recently hypernuclear electroproduction experiments have been successfully carried out at the Thomas Jefferson Laboratory, providing high-resolution spectroscopic data. This article discusses several facets inherent to this reaction process: First, numerous theoretical attempts in describing the elementary kaon photoproduction are summarized so as to choose appropriate elementary amplitudes to be used for hypernuclear production estimates. The reaction process is characterized by both the sizable momentum transfer and the spin-flip dominace involved in the transition operator. The DWIA theoretical excitation spectra of producing p-shell hypernucli are discussed together with the experimental ones obtained recently. Encouraged with the successful theory-experiment comparison, the calculational framework has been applied beyond p-shell to typical medium-heavy hypernuclear production. The hypernuclear photo-production spectra predicted with the F, Si, and Ca targets suggest that the unique characters of the electroproduction are more clearly appeared in the medium-mass region, providing interesting opportunities of spectroscopic study beyond p-shell.

Strangeness Electromagnetic Production on Nucleons and Nuclei

Abstract Isobar models for the electromagnetic production of kaons are discussed with emphasis on the K + photoproduction at very small kaon angles and K 0 photoproduction on deuteron. Distorted-wave impuls approximation calculations of the cross sections for the electroproduction of hypernuclei are presented on the case of the 12 Λ B production.

Production of polarized hypernuclei: Photoproduction versus (π, K) and (K, π) reactions

Abstract On the basis of systematic calculations for p -shell targets, polarization phenomena in hypernuclear photoproduction, ( γ , K + ), are discussed in comparison with characteristics of the ( π + , K + ) reaction and the energetic ( K − , π − ) reaction at p K ≅ 1.1 and 1.5 GeV/c.

Hypernuclear and Λ-spin polarizations in the (π+, K+) and (K−, π−) reactions

Abstract For the ( π + , K + ) and ( K − , π − ) reactions, the hypernuclear polarizations and Λ-spin polarizations of Λ 12 C and Λ 13 C are calculated with use of the spin-nonflip ( f ) and spin-flip ( g ) elementary amplitudes. The depolarization effect is taken into account to obtain the final polarization of the hypernuclear ground state. The proton asymmetry from the non-mesonic decay of the polarized Λ 12 C and Λ 11 B states measured at KEK is discussed.

NEUTRAL KAON PHOTOPRODUCTION AT LNS, TOHOKU UNIVERSITY

The elementary photo-strangeness production process has been intensively studied based on the high-quality data of the charged kaon channel, γ + p → K+ + Λ(Σ0). However, there had been no reliable data for the neutral kaon channel γ + n → K0 + Λ(Σ0) and the theoretical investigations suffer seriously from the lack of the data. In order to have reliable data for the neutral kaon photo-production data, substantial effort has been made to measure the γ + n → K0 + Λ process in the π+π- decay channel, using a liquid deuterium target and a tagged photon beam (Eγ = 0.8-1.1 GeV) in the threshold region at the Laboratory of Nuclear Science (LNS), Tohoku University. We have taken exploratory data quite successfully with the use of Neutral Kaon Spectrometer (NKS) at LNS-Tohoku in 2003 and 2004. The data is compared to theoretical models and it indicates a hint that the K0 differential cross section has a backward peak in the energy region. The second generation of the experiment, NKS2, is designed to extend the NKS experiment by considerably upgrading the original neutral kaon spectrometer, fully replacing the spectrometer magnet, tracking detectors and all the trigger counters. The new spectrometer NKS2 has significantly larger acceptance for neutral kaons compared with NKS, particularly covering forward angles and much better invariant mass resolution. The estimated acceptance of NKS2 is three (ten) times larger for than that of NKS. The spectrometer is newly constructed and installed at the Laboratory of Nuclear Science, Tohoku University in 2005. The deuterium target data was taken with tagged photon beam in 2006-2007. We will report recent results of NKS2 in this paper. Additionally, a status of the upgrade project that gives us larger acceptance and capability of K0 + Λ coincidence measurement will be presented.

Hypernuclear production with a strong spin-flip

A kinematically correct treatment of the full transition amplitude for many-body hypernuclear production is presented. By an example of (π+, K+) reaction, effects of the spin-flip amplitude and its interference with the spin-non-flip amplitude are demonstrated and specified forΛ12C.

Spin-orbit splitting in σ-hypernuclei

AbstractThe shell model analysis of experimental 0+, 2+ spectra of

Spectroscopy of medium-mass hypernuclear production

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