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Register a new userComparative Regge analysis of $Lambda, Sigma^0, Lambda(1520)$ and $Theta^+$ production in $gamma p$, $pi p$ and $pp$ reactions
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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.
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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.
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)).
The $Lambda$-hypernucleus production by $A(p, pK^+)_{Lambda}B$ reactions is investigated within the framework of the distorted wave impulse approximation(DWIA). The amplitude for the elementary process is evaluated in a fully covariant two-nucleon model based on the effective Lagrangian. The reaction cross sections for $Lambda$-hypernucleus productions on $^6Li$, $^{12}C$ and $^{16}O$ targets are calculated. It is found that the distortion effects tend to reduce the cross sections by a factor of 3$sim$10. Various differential cross sections (DCS) and double differential cross sections (DDCS) are presented. It is shown that for the $s_{Lambda}-$wave hypernucleus production, the DCS is decreased with increasing nuclear mass, and the DCS for the $p_{Lambda}-$wave hypernucleus production is normally higher than that for the $s_{Lambda}-$wave hypernucleus production. As a reference, the DDCS with respect to the momenta of the outgoing proton and kaon is also demonstrated. Finally, the missing mass spectra of the inclusive reaction $p+Ato p+ K^+ + X$ for $^6Li$, $^{12}C$ and $^{16}O$ targets are presented, from which the masses of hypernuclei can accurately be extracted. Thus, we conclude that the missing mass spectrum method is an alternative to study hypernuclear physics. And the study of hypernuclear physics can be carried out in COSY and CSR by the $A(p,pK^+)_{Lambda}B$ reaction due to the $mu$b-order reaction cross sections.
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.
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