Cross sections and Rosenbluth separations in ${}^1\mathrm{H}$($e,e^{\prime }{K}^{+}$)$\Lambda$ up to $Q^2=2.35$ GeV${}^2$

The kaon electroproduction reaction ${}^1\mathrm{H}$($e,e^{\prime }{K}^{+}$)$\Lambda$ was studied as a function of the virtual-photon four-momentum, $Q^2$, total energy, $W$, and momentum transfer, $t$, for different values of the virtual-photon polarization parameter. Data were taken at electron beam energies ranging from $3.40$ to $5.75$ GeV. The center of mass cross section was determined for twenty-one kinematics corresponding to $Q^2$ of $1.90$ and $2.35$ GeV${}^2,$ and the longitudinal, ${\sigma }_L$, and transverse, ${\sigma }_T$, cross sections were separated using the Rosenbluth technique at fixed $W$ and $t$. The separated cross sections reveal a flat energy dependence at forward kaon angles not satisfactorily described by existing electroproduction models. Influence of the kaon pole on the cross sections was investigated by adopting an off-shell form factor in the Regge model, which better describes the observed energy dependence of ${\sigma }_T$ and ${\sigma }_L$.

Figure 1

Electron-hadron coincidence time spectra with different aerogel-counter-based hadron selection. See the text for further explanation.

Figure 2

$\Lambda$ and $\Sigma$ missing mass spectra obtained at $Q^2=1.9$ GeV${}^2$. The region of integration is highlighted.

Figure 3

Separated cross sections from this experiment (full circle) and Ref. [4] (squares) as a function of $Q^2$ at $W=1.84$ GeV and zero kaon scattering angle in comparison with predictions of the models (see the text for discussion of the curves). The photoproduction point (full square) is from Ref. [16].

Figure 4

Energy dependence of separated cross sections from this experiment in comparison with predictions of models as in Fig. 3 for $Q^2=1.90$ GeV, (a) and (b), and 2.35 GeV, (c) and (d), and zero kaon angle.