Soft QCD Physics at the LHC: Highlights and Opportunities

The Large Hadron Collider (LHC) at CERN became operational in 2009 and has since then produced a plethora of physics results from proton–proton ( pp ) collisions. This short review covers results that relate to soft quantum chromodynamics (QCD) with a focus on nondiffractive physics at midrapidity. Most of the presented results are based on transverse momentum spectra and related derived observables, including multiplicity, the average transverse momentum, and various particle ratios. Additionally, the phenomenon of the observed ridge and its potential connection to the formation of a quark–gluon plasma in pp collisions are discussed. The goals of the review are to introduce the topics and provide references for scientists joining the LHC program and to highlight what we consider to be the most interesting results and open questions, to inspire novel measurements.