Exclusive production of two and four pions in proton-proton scattering

TL;DR

This paper models exclusive two- and four-pion production in high-energy proton-proton collisions using a tensor pomeron framework, analyzing resonance contributions, interference effects, and comparing with experimental data.

Contribution

It introduces a tensor pomeron model for exclusive pion production, including resonance and continuum effects, and provides detailed predictions for experimental comparisons.

Findings

Resonance contributions depend on proton transverse momentum cuts.

Interference effects significantly influence pion production spectra.

Theoretical results align with existing experimental data and guide future experiments.

Abstract

We consider exclusive $pp \to pp \pi^{+} \pi^{-}$ and $pp \to pp \pi^{+} \pi^{-}\pi^{+} \pi^{-}$ reactions at high energies. The calculation is based on a tensor pomeron model and the amplitudes for the processes are formulated in an effective field-theoretic approach. In the case of $pp \to pp \pi^{+} \pi^{-}$ process we consider both diffractive and photoproduction mechanisms and we include the non-resonant $\pi^{+}\pi^{-}$ continuum and the resonance $f_{0}(500)$, $f_{0}(980)$, $f_{2}(1270)$, $\rho(770)$ contributions. We discuss how two pomerons couple to tensor meson $f_{2}(1270)$ and the interference effects of resonance and dipion continuum. We find that the relative contribution of resonances $\rho(770)$, $f_2(1270)$ and dipion continuum strongly depends on the cut on proton transverse momenta. In the case of exclusive central $4 \pi$ production we include the contribution via the intermediate $\sigma\sigma$ and $\rho\rho$ states. For both processes the theoretical results have been compared with the experimental data and predictions for planned or being carried out experiments (e.g. STAR, ATLAS-ALFA) are presented.