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Register a new user$K^+Lambda$ electroproduction above the resonance region
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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 available 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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[Background] Above the nucleon resonance region, the $N(e,epi^pm)N$ data cannot be explained by conventional hadronic models. For example, the observed magnitude of the transverse cross section is significantly underestimated in a framework with Reggeized background amplitudes. [Purpose] Develop a phenomenological framework for the $N(e,epi^pm)N$ reaction at high invariant mass $W$ and deep photon virtuality $Q^2$. [Method] Building on the work of Kaskulov and Mosel, a gauged pion-exchange current is introduced with a running cutoff energy for the proton electromagnetic transition form factor. A new transition form factor is proposed. It respects the correct on-shell limit, has a simple physical interpretation and reduces the number of free parameters by one. [Results] A study of the $W$ dependence of the $N(e,epi^pm)N$ lends support for the newly proposed transition form factor. In addition, an improved description of the separated and unseparated cross sections at $-t lesssim 0.5 ;text{GeV}^2$ is obtained. The predictions overshoot the measured unseparated cross sections for $-t > 0.5 ;text{GeV}^2$. Introducing a strong hadronic form factor in the Reggeized background amplitudes brings the calculations considerably closer to the high $-t$ data. [Conclusions] Hadronic models corrected for resonance/parton duality describe the separated pion electroproduction cross sections above the resonance region reasonably well at low $-t$. In order to validate the applicability of these models at high $-t$, separated cross sections are needed. These are expected to provide a more profound insight into the relevant reaction mechanisms.
A model based on the hadronic fluctuations of the real photon is developed to describe the total photonucleon and photonuclear cross sections in the energy region above the nucleon resonances. The hadronic spectral function of the photon is derived including the finite width of vector-meson resonances and the quark-antiquark continuum. The shadowing effect is evaluated considering the effective interaction of the hadronic component with the bound nucleons within a Glauber-Gribov multiple scattering theory. The low energy onset of the shadowing effect is interpreted as a possible signature of a modification of the hadronic spectral function in the nuclear medium. A decrease of the $rho$-meson mass in nuclei is suggested for a better explanation of the experimental data.
High-resolution spectrometer measurements of the reaction H(e,e K+)X at small Q2 are used to extract the mass and width of the Lambda(1520). We investigate dependence of the resonance parameters on different parametrizations of the background and the resonance peak itself. Our final values for the Breit-Wigner parameters are M=1520.4+-0.6(stat)+-1.5(syst) MeV and Gamma=18.6+-1.9(stat)+-1(syst) MeV. The width appears to be more sensitive to the assumptions than the mass. We also estimate, for the first time, the pole position for this resonance and find that both the pole mass and width seem to be smaller than their Breit-Wigner values.
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.
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), F15(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.
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