Soft QCD Physics at the LHC: highlights and opportunities

TL;DR

This paper reviews soft QCD results from the LHC, focusing on non-diffractive physics in proton-proton collisions, discussing spectra, correlations, and the potential quark-gluon plasma, highlighting key findings and open questions.

Contribution

It provides a comprehensive overview of soft QCD phenomena at the LHC, emphasizing recent results and future research opportunities in non-diffractive pp collisions.

Findings

Observation of the ridge phenomenon in pp collisions

Measurements of transverse momentum spectra and ratios

Discussion of quark-gluon plasma signatures in small systems

Abstract

The Large Hadron Collider (LHC) at CERN in Switzerland became operational in 2009 and has since then produced a plethora of results for proton-proton (pp) collisions. This short review covers results that relates to soft QCD focusing on non-diffractive physics at mid-rapidity. Most of the presented results comes from transverse momentum ($p_{\rm T}$) spectra and related/derived observables such as multiplicity, $\langle p_{\rm T} \rangle$ and ratios, but also the observed ``ridge'' and the questions of quark-gluon plasma in pp collisions will be discussed. The goal of the review is on one hand to introduce the topics and provide references for scientists joining the LHC program while at the same time highlighting what we consider the most interesting results and open questions to inspire novel measurements.