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Register a new userNear threshold angular distributions of the $^2$H$(gamma,Lambda)$X reaction
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A study of the $^2$H$({gamma},{Lambda})$X reaction was performed using a tagged photon beam at the Research Center for Electron Photon Science (ELPH), Tohoku University. The photoproduced $Lambda$ was measured in the $p{pi^{-}}$ decay channel by the upgraded Neutral Kaon Spectrometer (NKS2+). The momentum integrated differential cross section was determined as a function of the scatting angle of ${Lambda}$ in the laboratory frame for five energy bins. Our results indicated a peak in the cross section at angles smaller than cos$theta^{LAB}_{Lambda}$ = $0.96$. The experimentally obtained angular distributions were compared to isobar models, Kaon-Maid (KM) and Saclay-Lyon A (SLA), in addition to the composite Regge-plus-resonance (RPR) model. Both SLA(r$K_{1}K_{gamma}$ = $-1.4$) and RPR describe the data quite well in contrast to the KM model, which substantially under predicted the cross section at the most forward angles. With the anticipated finalized data on ${Lambda}$ integrated and momentum dependent differential cross sections of $^2$H$({gamma},{Lambda})$X~cite{Kaneta_Beckford}, we present our findings on the angular distributions in this report.
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An experiment was carried out with the NKS2+ in 2010 at the Research Center for Electron Photon Science (ELPH), in which tagged photon beams in the range of 0.8 $le$ $E_{gamma}$ $le$ 1.1 GeV were impinged on a liquid $^2$H target positioned at the center of the NKS2+. The produced $Lambda$ was subsequently detected by the $p{pi^{-}}$ decay channel. Integrated cross sections of the $^2$H$({gamma},{Lambda})$X in the angular region of 0.9 $le$ $cos{theta}_{Lambda}^{LAB}$ $le$ 1.0 was derived and compared with preceding experimental results of the NKS2 collaboration. In addition, the momentum spectra for two photon energy regions were also procured. The ${Lambda}$ angle dependent cross sections as a function of the scattering angle in the laboratory system was additionally deduced. We present the latest results on the excitation function of ${Lambda}$ photoproduction, the momentum distributions, angular distributions, and polarization.
The 3Lambda H and 4Lambda H hypernuclear bound states have been observed for the first time in kaon electroproduction on 3,4He targets. The production cross sections have been determined at Q**2= 0.35 GeV**2 and W= 1.91 GeV. For either hypernucleus the nuclear form factor is determined by comparing the angular distribution of the 3,4He(e,eK+)3,4Lambda H processes to the elementary cross section 1H(e,eK+) Lambda on the free proton, measured during the same experiment.
Differential cross sections and photon-beam asymmetries for the gamma p -> K+ Lambda(1520) reaction have been measured with linearly polarized photon beams at energies from the threshold to 2.4 GeV at 0.6<cos(theta)<1. A new bump structure was found at W=2.11 GeV in the cross sections. The bump is not well reproduced by theoretical calculations introducing a nucleon resonance with J<=3/2. This result suggests that the bump might be produced by a nucleon resonance possibly with J>=5/2 or by a new reaction process, for example an interference effect with the phi photoproduction having a similar bump structure in the cross sections.
The $phi$-$Lambda(1520)$ interference effect in the $gamma pto K^+K^-p$ reaction has been measured for the first time in the energy range from 1.673 to 2.173 GeV. The relative phases between $phi$ and $Lambda(1520)$ production amplitudes were obtained in the kinematic region where the two resonances overlap. The measurement results support strong constructive interference when $K^+K^-$ pairs are observed at forward angles, but destructive interference for proton emission at forward angles. Furthermore, the observed interference effect does not account for the $sqrt{s}=2.1$ GeV bump structure in forward differential cross sections for $phi$ photoproduction. This fact suggests possible exotic structures such as a hidden-strangeness pentaquark state, a new Pomeron exchange and rescattering processes via other hyperon states.
The production of neutron rich $Lambda$-hypernuclei via the ($K^-_stop$,$pi^+$) reaction has been studied using data collected with the FINUDA spectrometer at the DA$Phi$NE $phi$-factory (LNF). The analysis of the inclusive $pi^+$ momentum spectra is presented and an upper limit for the production of $^6_Lambda$H and $^7_Lambda$H from $^6$Li and $^7$Li, is assessed for the first time.
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