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Bayesian inference of the resonance content of p(gamma,K+)Lambda

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 نشر من قبل Pieter Vancraeyveld
 تاريخ النشر 2012
  مجال البحث
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A Bayesian analysis of the worlds p(gamma,K+)Lambda data is presented. We adopt a Regge-plus-resonance framework featuring consistent couplings for nucleon resonances up to spin J=5/2, and evaluate 2048 model variants considering all possible combinations of 11 candidate resonances. The best model, labeled RPR-2011, is discussed with special emphasis on nucleon resonances in the 1900-MeV mass region.



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A Bayesian analysis of the worlds p(gamma,K^+)Lambda data is presented. From the proposed selection of 11 resonances, we find that the following nucleon resonances have the highest probability of contributing to the reaction: S11(1535), S11(1650), F1 5(1680), P13(1720), D13(1900), P13(1900), P11(1900), and F15(2000). We adopt a Regge-plus-resonance framework featuring consistent couplings for nucleon resonances up to spin J=5/2. We evaluate all possible combinations of 11 candidate resonances. The best model is selected from the 2048 model variants by calculating the Bayesian evidence values against the worlds p(gamma,K^+)Lambda data.
A Bayesian analysis of the worlds $p(gamma,K^+)Lambda$ data is presented. We adopt a Regge-plus-resonance framework featuring consistent interactions for nucleon resonances up to spin $J = 5/2$. The power of the momentum dependence of the consistent interaction structure rises with the spin of the resonance. This leads to unphysical structures in the energy dependence of the computed cross sections when the short-distance physics is cut off with standard hadronic form factors. A plausible, spin-dependent modification of the hadronic form factor is proposed which suppresses the unphysical artifacts. Next, we evaluate all possible combinations of 11 candidate resonances. The best model is selected from the 2048 model variants by calculating the Bayesian evidence values against the worlds $p(gamma,K^+)Lambda$ data. From the proposed selection of 11 resonances, we find that the following nucleon resonances have the highest probability of contributing to the reaction: $S_{11}(1535)$, $S_{11}(1650)$, $F_{15}(1680)$, $P_{13}(1720)$, $D_{13}(1900)$, $P_{13}(1900)$, $P_{11}(1900)$, and $F_{15}(2000)$.
Background: In $pi^+n$ and $pi^-p$ electroproduction, conventional models cannot satisfactory explain the data above the resonance region, in particular the transverse cross section. Although no high-energy L-T-separated cross-section data is availab le to date, a similar scenario can be inferred for $K^+Lambda$ electroproduction. Purpose: Develop a phenomenological model for the $p(gamma^*,K^+)Lambda$ reaction at forward angles and high-energies. Propose a universal framework for interpreting charged-kaon and charged-pion electroproduction above the resonance region. Method: Guided by the recent model for charged-pion electroproduction, developed by the authors, a framework for $K^+Lambda$ electroproduction at high energies and forward angles is constructed. To this end, a Reggeized background model for $K^+Lambda$ photoproduction is first developed. This model is used as a starting base to set up an electroproduction framework. Results: The few available data of the unseparated $p(gamma^*,K^+)Lambda$ cross section are well explained by the model. Predictions for the L-T-separation experiment planned with the 12 GeV upgrade at Jefferson Lab are given. The newly-proposed framework predicts an increased magnitude for the transverse structure function, similar to the situation in charged-pion electroproduction. Conclusions: Within a hadronic framework featuring Reggeized background amplitudes, $s$-channel resonance-parton effects can explain the observed magnitude of the unseparated $p(gamma^*,K^+)Lambda$ cross section at high energies and forward angles. Thereby, no hardening of the kaon electromagnetic form factor is required.
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