F. Miyahara

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.

An event mixing technique for Bose-Einstein correlations of two pions in photoproduction around 1 GeV

We have developed an event mixing technique to observe Bose-Einstein correlations (BEC) between two identical neutral pions produced in photo-induced reactions in the non-perturbative QCD energy region. It is found that the missing-mass consistency cut and the pion-energy cut are essential for the event mixing method to effectively extract BEC observables. A Monte Carlo (MC) simulation is used to validate these constraints and confirms the efficiency of this method. Our work paves the way for similar BEC studies at lower energies where the multiplicity of emitted bosons is limited.

N* (1670) observed at LNS, Sendai

A resonance-like structure has been observed in the total cross section for the γd → ηnp reaction at E γ ∼ 1.02 GeV. The experiment was conducted at Laboratory of Nuclear Science, Tohoku University, by utilizing a tagged photon beam provided with an internal radiator in a 1.2 GeV electron synchrotron. A solid deuterium target was employed as well as a solid hydrogen target to extract information on the process γn → ηn. A clear bump has been observed in the total cross section for the γn’ → ηn reactio where n’ means a neutron in Fermi motion. A simple analysis gives the position of about 1670 MeV and the width of less than 40 MeV for the bump, respectively, taking into account the Fermi motion. There is no bump structure observed, in contrast, in the γp→ ηp process at the same energy region. The U-spin conservation may naturally account for this phenomenon, if the bump is an indication of a hidden-strangeness pentaquark baryon N 5(1670) in the anti-decuplet state.

DOUBLE PION PHOTOPRODUCTION EXPERIMENT AT LNS–TOHOKU

The total cross sections for the π+π− photoproduction on the deuteron were measured in an energy range of 0.8 to 1.1 GeV. The obtained total cross section for the quasi-free π+π− photoproduction on the deuteron was about 60 % of those on the free proton. The cross section for Δ++Δ− photoproduction was derived from the non-quasi-free π+π− photoproduction events. It was smaller than the previous data.

Narrow Resonance atEγ= 1020 MeV in theD(γ,η)pnReaction

Differential and total cross sections of the D(γ, η)pn reaction have been measured for photon energies between 600 and 1150 MeV. The data provide the information of the γn → ηn reaction above Eγ ≥ 800 MeV. The total cross section shows a narrow resonance structure peaked at Eγ = 1020 MeV. The angular distribution coefficients together with the total cross section are compared with the calculation of the isobar model by using the impulse approximation. Although the spin and parity of the resonance cannot be determined unambiguously, a negative parity assignment gives better fit to the data.