Unitarity constraints on meson electroproduction at backward angles

Abstract

At large virtuality Q 2 , the coupling to the ρ meson production channels provides us with a natural explanation of the surprisingly large cross section of the ω, as well as the π + , meson electroproduction recently measured at backward angles, without destroying the good agreement between the Regge pole model and the data at the real photon point. Together with elastic re-scattering of the outgoing meson it also provides us with a way to explain why the node, that appears at u ∼ −0.15 GeV 2 at the real photon point, disappears at moderate virtuality Q 2 . Predictions are given for the electroproduction of the π 0 meson.

Progress and Opportunities in Backward angle (u-channel) Physics

“…The green bands indicate correlated systematic uncertainties for σ T , the uncertainties for σ L have similar magnitudes. The JML18 model [16] reproduces σ L and σ T at Q 2 =2.45 GeV 2 , as shown by the black solid and dotted magenta curves, respectively. The full calculation includes σ LT and σ T T as presented in [16].…”

“…The JML18 model [16] reproduces σ L and σ T at Q 2 =2.45 GeV 2 , as shown by the black solid and dotted magenta curves, respectively. The full calculation includes σ LT and σ T T as presented in [16].…”

“…The red curves are the "Regge" predictions (by JML18) of [14,15] for solid: σ U , dashed curve: σ LT , dot-dashed: σ T T . An updated σ U calculation from JML18 model [16] are shown in red dotted curve. Regge calculations which consider parton contributions (described in Sec.…”

“…The first version (red curves) uses point like mesonbaryon vertices and canonical Regge propagators [14,15] (solid line for σ U , dashed line for σ LT and dotdashed for σ T T ), and includes the contribution of uchannel cuts [16] (dotted line for σ U ). We refer the reader to [16] for details. The second version (black curves) is presented in Sec.…”

“…Two Regge-based predictions are plotted in Fig. 4: JML04 [27] (prior to F π -2 data) and JML18 [16]. JML04 includes the near-forward Regge contribution at −t < 1 GeV 2 and N -exchange in the u-channel with a t-dependent cutoff mass, it significantly under predicts the backward-angle cross section.…”