Absorptive corrections to the electromagnetic form factor in high-energy elastic proton-proton scattering

Abstract

Recently, it was noted that absorptive corrections to the electromagnetic form factor in high-energy proton-proton scattering are important for the theoretical interpretation of the $p^\uparrow{p}$ and $p^\uparrow{A}$ analyzing power $A_\text{N}(t)$ measurements with the Hydrogen Jet Target polarimeter (HJET) at RHIC. Here, a concise expression for the absorptive correction was derived within the eikonal approach. The resulting analysis reveals a systematic bias, nearly independent of the beam energy, in the experimental determination of the real-to-imaginary ratio $\rho$ when absorption effects are overlooked in the data analysis. Quantification of this bias, as $\rho^\text{meas}=\rho + (0.036\pm0.016)_\text{bias}$, was achieved using a Regge fit applied to available proton-proton measurements of $\rho^\text{meas}(s)$ and $\sigma^\text{meas}_\text{tot}(s)$. Considering the potential impact of such an effect on the experimentally determined $A_\text{N}(t)$, one may enhance consistency between the HJET and STAR measurements of the hadronic spin-flip amplitude. While the sign of the bias in the value of $\rho$ aligns with the anticipated effective increase in the proton charge radius in $pp$ scattering due to absorption, it amplifies the observed discrepancy between $\sigma^\text{meas}_\text{tot}$ and $\rho^\text{meas}$ values at $\sqrt{s}=13\,\text{TeV}$ as measured in the TOTEM experiment. Evaluation (using published TOTEM data) of the measured proton-proton $d\sigma/dt$ dependence on the absorptive corrections indicated that possible soft photon corrections to the hadronic amplitude slope may be essential for such data analysis.