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Register a new userMeasurements of the photon induced production of $Lambda$ in the $^2$H$({gamma},{Lambda})$X process at threshold energies
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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.
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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.
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.
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.
Rare information on photodisintegration reactions of nuclei with mass numbers $A approx 160$ at astrophysical conditions impedes our understanding of the origin of $p$-nuclei. Experimental determination of the key ($p,gamma$) cross sections has been playing an important role to verify nuclear reaction models and to provide rates of relevant ($gamma,p$) reactions in $gamma$-process. In this paper we report the first cross section measurements of $^{160}$Dy($p,gamma$)$^{161}$Ho and $^{161}$Dy($p,n$)$^{161}$Ho in the beam energy range of 3.4 - 7.0 MeV, partially covering the Gamow window. Such determinations are possible by using two targets with various isotopic fractions. The cross section data can put a strong constraint on the nuclear level densities and gamma strength functions for $A approx$ 160 in the Hauser-Feshbach statistical model. Furthermore, we find the best parameters for TALYS that reproduce the A $thicksim$ 160 data available, $^{160}$Dy($p,gamma$)$^{161}$Ho and $^{162}$Er($p,gamma$)$^{163}$Tm, and recommend the constrained $^{161}$Ho($gamma,p$)$^{160}$Dy reaction rates over a wide temperature range for $gamma$-process network calculations. Although the determined $^{161}$Ho($gamma$, p) stellar reaction rates at the temperature of 1 to 2 GK can differ by up to one order of magnitude from the NON-SMOKER predictions, it has a minor effect on the yields of $^{160}$Dy and accordingly the $p$-nuclei, $^{156,158}$Dy. A sensitivity study confirms that the cross section of $^{160}$Dy($p$, $gamma$)$^{161}$Ho is measured precisely enough to predict yields of $p$-nuclei in the $gamma$-process.
Threshold measurements of the associated strangeness production reactions pp --> p K(+) Lambda and pp --> p K(+) Sigma(0) are presented. Although slight differences in the shapes of the excitation functions are observed, the most remarkable feature of the data is that at the same excess energy the total cross section for the Sigma(0) production appears to be about a factor of 28 smaller than the one for the Lambda particle. It is concluded that strong Sigma(0)-p final state interactions, and in particular the Sigma-N --> Lambda-p conversion reaction, are the likely cause of the depletion for the yield in the Sigma signal. This hypothesis is in line with other experimental evidence in the literature.
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