Photo- and electroproduction of $K^{+}\mathrm{\Lambda }$ with a unitarity-restored isobar model

Exploiting the isobar model, kaon photo- and electroproduction on the proton in the resonance region comes under scrutiny. An upgrade of our previous model, comprising higher-spin nucleon and hyperon exchanges in the consistent formalism, was accomplished by implementing energy-dependent widths of nucleon resonances, which leads to a different choice of hadron form factor with much softer values of cutoff parameter for the resonant part. For a reliable description of electroproduction, the necessity of including longitudinal couplings of nucleon resonances to virtual photons was revealed. We present a new model whose free parameters were adjusted to photo- and electroproduction data and which provides a reliable overall description of experimental data in all kinematic regions. The majority of nucleon resonances chosen in this analysis coincide with those selected in our previous analysis and also in the Bayesian analysis with the Regge-plus-resonance model as the states contributing to this process with the highest probability.

Figure 1

Total cross section as predicted by the BS3 model (solid curve) in comparison with CLAS 2005 data [20]. The other curves illustrate the behavior of the BS3 model without particular resonance.

Figure 2

Cross-section predictions of BS1 (dashed curve), BS3 (solid curve), Saclay-Lyon (dash-dotted curve), and Kaon-MAID (dotted curve) models are shown for four kaon center-of-mass angles. The data are from CLAS 2005 [20], CLAS 2010 [22], MAMI [35], and LEPS [23] collaborations and from Ref. [18].

Figure 3

Angular dependence of the cross section is shown for three values of the c.m. energy. The data are from CLAS 2005 [20], CLAS 2010 [22], and MAMI [35] collaborations. Notation of the curves is the same as in the Fig. 2.

Figure 4

Total-cross-section prediction of the BS3 model (solid curve) compared to CLAS 2005 data [20]. Predictions of sole Born terms (dotted curve), background terms (dash-dotted curve), and nucleon resonances (dashed curve) are shown.

Figure 5

Results for the differential cross section for $p(\gamma ,K^{+})\mathrm{\Lambda }$ at ${\theta }_K^{c.m.}=6^{\circ }$ are shown for several models. Data points of Brown [25] and E94-107 [36] are for electroproduction with a very small value of the virtual-photon mass $|k^2|$; the only photoproduction datum available in this region stems from Bleckmann et al. [19]. Notation of the curves is the same as in the Fig. 2.

Figure 6

Results for the hyperon polarization $P$ are shown for several kaon c.m. angles. Data stem from CLAS collaboration, Refs. [22] and [37]. Notation of the curves is the same as in the Fig. 2.

Figure 7

Predictions of hyperon polarization $P$ are shown for several values of energy $E_{\gamma }^{lab}$. Data stem from GRAAL collaboration, Ref. [38]. Notation of the curves is the same as in the Fig. 2.

Figure 8

Predictions for the double-polarization observables $C_x$ and $C_z$ are shown for various kaon c.m. angles. Notation of the curves is the same as in the Fig. 2 and the data stem from the CLAS analysis [21].

Figure 9

Double-polarization observables $O_x$ and $O_z$ are shown for various kaon c.m. angles. Notation of the curves is the same as in the Fig. 2. The data are from the GRAAL collaboration [39]. The errors are quadratic sums of statistical and systematic uncertainties.

Figure 10

Overall description of the resonance region of the $p(\gamma ,K^{+})\mathrm{\Lambda }$ process by the BS1 model for all kaon c.m. angles and for energy from the threshold up to 2.5 GeV.

Figure 11

The same as Fig. 10 but with BS3 model.

Figure 12

Energy dependence of transverse, ${\sigma }_T$, and longitudinal, ${\sigma }_L$, cross sections for $Q^2=1.90{(\text{GeV}/c)}^2$ and $Q^2=2.35{(\text{GeV}/c)}^2$ and for zero kaon angle is shown. The result of the BS3 model and predictions of BS1, Saclay-Lyon, and Kaon-MAID models are compared with JLab data [30]. Notation of the curves is the same as in the Fig. 2.

Figure 13

Transverse, ${\sigma }_T$, and longitudinal, ${\sigma }_L$, cross sections for kaon electroproduction at $W=1.84\text{GeV}$ and for zero kaon angle as function of $Q^2$ are shown. The result of the BS3 model and predictions of BS1, Saclay-Lyon, and Kaon-MAID models are compared with JLab [11, 30] and Bleckmann et al. [19] ($Q^2=0$ for ${\sigma }_T$) data. Notation of the curves is the same as in the Fig. 2.

Figure 14

Energy dependence of transverse cross section ${\sigma }_T$ at $Q^2=1.0{(\text{GeV}/c)}^2$ is shown for several kaon angles. We compare the result of the BS3 model and predictions of BS1, Saclay-Lyon, and Kaon-MAID models with CLAS data [31]. Notation of the curves is the same as in the Fig. 2.

Figure 15

Differential cross section of kaon electroproduction in two kinematic regions is shown. The result of the BS3 model and predictions of BS1, Saclay-Lyon, and Kaon-MAID models are compared with MAMI data [12]. Notation of the curves is the same as in the Fig. 2.