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Register a new userOn polarization of strange baryons in reactions p + p -> p + Lambda^0 + K^+ and p + p -> p + Sigma^0 + K^+ near thresholds
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Polarization properties of strange baryons produced in pp reactions, p + p -> p + Lambda^0 + K^+ and p + p -> p + Sigma^0 + K^$, near thresholds of the final states (p Lambda^0 K^+) and (p Sigma^0 K^+) are analysed relative to polarizations of colliding protons. The cross sections for pp reactions are calculated within the effective Lagrangian approach accounting for strong pp rescattering in the initial state of colliding protons with a dominant contribution of the one-pion exchange and strong final-state interaction of daughter hadrons (Eur. Phys. J. A 9, 425 (2000)).
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The cross sections for the reactions pp -> p Lambda^0K^+ and pn -> n Lambda^0K^+ are calculated near threshold of the final states. The theoretical ratio of the cross sections R = sigma(pn -> n Lambda^0K^+)/ sigma(pp ->pLambda^0K^+) = 3 shows the enhancement of the pn interaction with respect to the pp interaction near threshold of the strangeness production N Lambda^0K^+. Such an enhancement is caused by the contribution of the np interaction in the isospin-singlet state, which is stronger than the $pn$ interaction in the isospin-triplet state. For the confirmation of this result we calculate the cross sections for the reactions pp -> pp pi^0, pi^0 p -> Lambda^0 K^+ and pi^-p -> Lambda^0 K^0 near threshold of the final states. The theoretical cross sections agree well with the experimental data.
The $Lambda(1405)$ production in p+p collisions at 3.5 GeV and K$^-$-induced reactions is discussed. The shift of the measured spectral function of the $Lambda(1405)$ in p+p reactions does not match either theoretical calculations for p+p reactions or experimental observation in previous K$^-$-induced reactions. New experiments with stopped and in-flight $K^-$ are needed to study this initial state more in detail. The state of the art of the analysis is discussed.
We present calculations of the invariant mass spectra of the $Lambda$p system for the exclusive $p p to K^+ Lambda p$ reaction with the aim of studying the final state interaction between the $Lambda$-hyperon and the proton. The reaction is described within a meson exchange framework and the final state $Lambda p$ interaction is incorporated through an off-shell t-matrix for the $Lambda p to Lambda p$ scattering, constructed using the available hyperon-nucleon (YN) potentials. The cross sections are found to be sensitive to the type of YN potential used especially at the $Lambda$ and $Sigma$ production thresholds. Hence, data on this exclusive reaction, which can be used to constrain the YN potentials are desirable.
Using the Quark-Gluon Strings Model -- combined with Regge phenomenology -- we perform a comparative analysis of $Lambda$, $Sigma^0$, $Lambda(1520)$ and $Theta^+$ production in binary reactions induced by photon, pion and proton beams on the nucleon. We find that the existing experimental data on the $gamma p to K^+ Lambda$ differential and total cross sections can be described very well by the model for photon energies $1 - 16$ GeV and $-t < 2$ GeV$^2$ assuming a dominant contribution of the $K^*$ Regge trajectory. Moreover, using the same parameters we also reproduce the total $gamma p to K^+ Sigma^0$ and $gamma p to K^+ Lambda(1520)$ cross sections suggesting a universality of the Regge model. In order to check the consistency of the approach we evaluate the differential and total cross sections for the reaction $pi^- p to K^0 Lambda$ which is also found to be dominated by the $K^*$ Regge trajectory. Using the apparent universality of the Regge model we extend our scheme to the analysis of the binary reactions $gamma p to bar{K}^0 Theta^+$, $pi^- p to K^- Theta^+$ and $pp to Sigma^+ Theta^+$ as well as the exclusive and inclusive $Theta^+$ production in the reactions $pp to p bar{K}^0 Theta^+$ and $pp to Theta^+ X$. Our detailed studies demonstrate that $Theta^+$ production does not follow the universality principle thus suggesting an essentially different internal structure of the exotic baryon relative to conventional hyperons or hyperon resonances.
The determination of low-energy cross sections and branching ratios of the K$^-$ multi-nucleon absorption processes in $Lambda$p and $Sigma^0$p final states performed by the AMADEUS collaboration is presented. Low momentum K$^-$ ($p_mathrm{K} simeq$ 127 MeV/c) produced at the DA$Phi$NE collider are impinged on a Carbon target within the KLOE detector and the two and three nucleon absorption processes are disentangled by comparing the experimental data to phenomenological calculations. The $Lambda$p spectra are interpreted in terms of K$^-$ multi-nucleon absorption processes; the possible contribution of a K$^-$pp bound state is demonstrated to overlap with the two nucleon capture process, its absolute yield thus resulting indistinguishable.
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