arXiv subjects
Publications and source records attributed to K. Miyagawa.
We analyze the reaction gamma + d --> K^+ + Lambda (Sigma) + N using the Nijmegen soft core hyperon-nucleon interactions NSC97f and NSC89 and a recently updated production operator for the gamma + N --> K^+ + Lambda(Sigma) processes. Significant effects of the YN final state interaction are found near both the K^+ Lambda N and K^+ Sigma N thresholds.
We search $t$-matrix poles for $ΛN-ΣN$ coupling interactions using two soft core models of the Nijmegen group which bind the hypertriton at the correct binding energy, and hard core models which are still influential in hypernuclear physics. To treat the hard core potentials, a useful method for calculating the off-shell $t$-matrix is proposed. We find poles close to the $ΣN$ threshold in the second or third quadrant of the complex plane of the $ΣN$ relative momentum. The relation between the poles and the shape of the $ΛN$ elastic total cross section is discussed based on a so-called uniformization by which two-channel $t$-matrices become single-valued on a complex valuable. We also find poles near the $ΛN$ threshold. These are correlated to the $S$-wave $ΛN$ scattering lengths, the values of which have yet to be determined.
Inclusive $K^+$ and exclusive $K^+Y$ photoproduction on the deuteron are investigated theoretically. Modern hyperon-nucleon forces and a recently updated kaon photoproduction operator for the $γ+N\to K^++Y$ process are used. Sizable effects of the hyperon-nucleon final state interaction are found near the $K^+ΛN$ and $K^+ΣN$ thresholds in the inclusive reaction. Angular distributions for the exclusive process show clear $YN$ final state interaction effects in certain kinematic regions. Precise data especially for the inclusive process around the $K^+ΣN$ threshold would help to clarify the strength and property of the $ΛN-ΣN$ interaction.
Based on realistic calculations for the nonmesonic decay rate of Hypertriton we demonstrate, that in principle it is not possible to measure the total n- and p- induced decay rates and as a consequence $Γ_n /Γ_p$ for that lightest hypernucleus.For the nonmesonic decay process the calculations are performed with modern YN forces based on various meson exchanges and taking the final state interaction among the three nucleons fully into account. Our findings have consequences also for the interpretation of experimental $Γ_n/Γ_p$ ratios for heavier hypernuclei where severe discrepancies exist to theoretical $Γ_n/Γ_p$ ratios.
The pi-mesonic decay of the hypertriton is calculated based on a hypertriton wavefunction and 3N scattering states, which are rigorous solutions of 3-body Faddeev equations using realistic NN and hyperon-nucleon interactions. The total pi-mesonic decay rate is found to be 92% of the free Lambda decay rate, which is close to the experimental data. Together with the nonmesonic decay the total life time of 3Lambda H is predicted to be 2.78 x 10^-10 sec which is 6 % larger than for the free Lambda particle. The differential decay rate is evaluated as a function of the pion momentum. The decay into the N+d+pi channel is stronger than in the 3N+pi channel in contrast to the situation for the nonmesonic decay. The ratio for the decay rate into 3He + pi^- to the decay rate into all channels including pi^- is found to be 0.40, which is close to the experimental value. We visualise the decay into the dominant channel p+d+pi^- in a Dalitz plot. Finally we compare the polarisation of the outgoing proton in free unpolarised Lambda-decay to the polarisation of 3He in unpolarised 3_Lambda H-decay and we compare the closely related asymmetry of pi^- emitted parallel and antiparallel with respect to the spin-direction for a polarised Lambda to the corresponding asymmetry for a polarised 3_Lambda H.
The nonmesonic decay of the hypertriton is calculated based on a hypertriton wavefunction and 3N scattering states, which are rigorous solutions of 3-body Faddeev equations using realistic NN and hyperon-nucleon interactions. The pion-exchange together with heavier meson exchanges for the $ΛN \to N N $ transition is considered. The total nonmesonic decay rate is found to be 0.5% of the free $Λ$ decay rate. Integrated as well as differential decay rates are given. The p- and n- induced decays are discussed thoroughly and it is shown that the corresponding total rates cannot be measured individually.