Near Threshold Neutral Pion Electroproduction at High Momentum Transfers and Generalized Form Factors

TL;DR

This study measures near-threshold neutral pion electroproduction cross sections at high momentum transfers, extracting structure functions and generalized form factors, and compares experimental results with theoretical predictions within the light-cone sum-rule framework.

Contribution

It provides new experimental data on pion electroproduction at high Q^2 and tests the validity of LCSR predictions for generalized form factors.

Findings

Good agreement of G_1^{c0} p(Q^2) with LCSR predictions.

Poor agreement of G_2^{c0} p(Q^2) with theoretical models.

Access to pion-nucleon s-wave multipoles near threshold.

Abstract

We report the measurement of near threshold neutral pion electroproduction cross sections and the extraction of the associated structure functions on the proton in the kinematic range $Q^2$ from 2 to 4.5 GeV$^2$ and $W$ from 1.08 to 1.16 GeV. These measurements allow us to access the dominant pion-nucleon s-wave multipoles $E_{0+}$ and $S_{0+}$ in the near-threshold region. In the light-cone sum-rule framework (LCSR), these multipoles are related to the generalized form factors $G_1^{\pi^0 p}(Q^2)$ and $G_2^{\pi^0 p}(Q^2)$. The data are compared to these generalized form factors and the results for $G_1^{\pi^0 p}(Q^2)$ are found to be in good agreement with the LCSR predictions, but the level of agreement with $G_2^{\pi^0 p}(Q^2)$ is poor.