Tomography of high-twist proton structure through $ep$ elastic scattering

Abstract

We present the first high-twist study of the proton form factors $F_{1,2}(Q^2)$ in $ep$ elastic scattering based on the perturbative QCD $k_T$ factorization, $Q^2$ being momentum transfer squared. It is motivated by unexpectedly large higher-power contributions from subleading-twist light-cone distribution amplitudes (LCDAs), which are attributed to the enhancement in endpoint regions of parton momentum fractions. We highlight that the endpoint enhancement, tamed by the $k_T$ resummation effect, is crucial for accommodating the approximate scaling behavior of the $Q^4F_1(Q^2)$ data at intermediate $Q^2\sim {\cal O}(10)$ GeV$^2$. The proton LCDAs up to twist 6 are then extracted, and verified by the charge-parity asymmetries observed in hadronic heavy baryon decays. Our work provides new insights into the proton three-dimensional structure and manifests the precision requirement for reliable perturbative analyses of baryonic exclusive processes.

Figures (2)

• Figure 1: Contributions of different twists $n = t + t^\prime$ to the Dirac FF $Q^4F_1(Q^2)$ with the QCDSR parameters Braun:2006hz.
• Figure 2: pQCD predictions for (a) the Dirac FF $Q^4F_1(Q^2)$, (b) $Q^4F_1(Q^2)$ from each twist combination $(t,t')$, and (c) $ep$ elastic scattering cross section, where "BLW 06" refers to the input of the QCDSR parameters Braun:2006hz.