Fine structure of the diffraction cone: from ISR to the LHC

TL;DR

This paper investigates the low-$|t|$ structure in the elastic diffractive cone across a wide energy range, attributing it to threshold singularities from $t$-channel unitarity, and shows the recurrence of the 'break' phenomenon from ISR to LHC8.

Contribution

It demonstrates that the low-$|t|$ structure is due to a two-pion loop singularity in the Pomeron trajectory, using simple Regge-pole models across energies from ISR to LHC8.

Findings

Good fits to $pp$ elastic differential cross sections across energies

Recurrence of the low-$|t|$ 'break' phenomenon at LHC8

Attribution of the structure to two-pion loop singularity

Abstract

Following earlier findings, we argue that the low-$|t|$ structure in the elastic diffractive cone, recently reported by the TOTEM Collaboration at $8$ TeV, is a consequence of the threshold singularity required by $t-$channel unitarity, such as revealed earlier at the ISR. By using simple Regge-pole models, we analyze the available data on the $pp$ elastic differential cross section in a wide range of c.m. energies, namely those from ISR to LHC8, obtaining good fits of all datasets. This study hints at the fact that the non-exponential behaviour observed at LHC8 is a recurrence of the low-$|t|$ "break" phenomenon, observed in the seventies at ISR, being induced by the presence of a two-pion loop singularity in the Pomeron trajectory.