Study of the strangeness photoproduction process in the γd→ΛX reaction at photon energies up to 1.08 GeV

Exploration of the photoinduced production of strangeness has been meticulously investigated on the proton and as of late the prominence is being veered to the neutron to ascertain a comprehensive description of the process for all isospin channels. Since a free neutron target is inaccessible, and in virtue of the low binding energy of deuteron, it serves as an effective target to provide a loosely bound neutron. Reactions on the deuteron can also be compared to results on a free proton to gain insight into the nuclear medium effect. Substantial effort was placed on advancing the investigation on the neutron and due to the favorable outcome of previous experiments with the Neutral Kaon Spectrometer (NKS) and NKS2 experiments [1, 2, 3] at the Research Center for Electron Photon Science (ELPH), Tohoku University in Sendai Japan, the spectrometer was upgraded by the replacement of the inner detectors in order to improve upon the acceptance. This thesis reports on the inclusive measurements of Λ in the γd→ΛX reaction at threshold energies. Exploratory data with the upgraded NKS2+ was taken at ELPH in 2010. The experiment was performed with tagged photon beams in the range of 0.8 ≤ Eγ ≤ 1.08 GeV that were directed to a liquid deuterium target positioned as the center of the spectrometer. The produced Λ (roughly 400 events) was detected in the pπ− decay channel with a corresponding width of 2.87 ± 0.19 MeV/c (σ). The focus of the work has been the determination of the energy dependence of Λ photoproduction, the momenta and angular distributions and also reports on the recoil polarization. The integrated cross sections of the γd→ΛX reaction in the angular integration regions of 0.9 ≤ cos θLAB Λ ≤ 1.0 and 0.75 ≤ cos θLAB Λ ≤ 1.0 were derived and compared with the experimental results of the NKS2 [4, 5]. In addition, the momentum spectra for two separate photon energy ranges, of 0.9 ≤ Eγ ≤ 1.0 and 1.0 ≤ Eγ ≤ 1.08 GeV was also procured. The differential cross section as a function of the Λ scattering angle in the laboratory was additionally deduced. The Λ recoil polarization was determined for three energy ranges, Eγ = 0.90−1.0, 0.95−1.05 and 1.00−1.08 GeV. Incorporating results of theoretical calculations, the total cross section of γd→ ΛX and γd → K0Λp were approximated and the latter compared with published findings. The results were compared to a handful of contemporary theoretical calculations, in particular, the Kaon-MAID (KM) [6] and Saclay-Lyon A (SLA) [7] isobar models, and the more recently introduced Regge-Plus-Resonance (RPR2007) model [8, 9]. Regarding the measured cross sections of the angle integrated Λ momentum dependent differential cross sections, the KM calculations replicate the general shape of the distributions in both energy bins and scattering angles. Nonetheless, it was deficient in converging with the magnitude at the most forward angles, in which it underscored the cross section by approximately 20-40% at Λ momenta between 0.65 ≤ PLAB Λ ≤ 0.90. GeV/c. On the other hand, the SLA model calculations had an admirable consensus with the shape and magnitude of the data with rK1Kγ = −1.4, where rK1Kγ is a free fitting parameter for the photo-coupling in the t-channel that arises from the ratio of the charged and neutral channels (rK1Kγ = gK0 1K0γ/gK+ 1 K+γ ). The RPR model produces an impressive description for the results of the integrated and total cross sections in both angular hemispheres, and exceptionally reproduces the shape of the angular distributions in all measured energy bins. The SLA model with a fitted coupling constant of rK1Kγ = −1.4, exhibit fairly good agreement with the data, describing well, the shape of the momentum and angular distributions, and most significantly the energy dependent integrated cross section. The KM calculations under predict the integrated and total cross sections by roughly 20%. The results reported in this dissertation are consistent across the board with the previous γd→ ΛX measurement and the estimated γd→ K0Λp cross section of the NKS2 collaboration [4], as well as with SLA predictions. The most significant conclusion that can be drawn is the relatively equivalent magnitude of the γd → K0Λp and γp → K+Λ processes, which are predicted to have strikingly dissimilar cross sections, here I conclude that they are in fact on par.