Soft-QCD physics at the LHC

The hadronic interactions are accurately described when the perturbative QCD approach is used. This is true for hard processes with large momentum transfer compared to the QCD scale. However, perturbative QCD fails to describe hadronic interactions when the effective strong coupling constant is large, i.e. for processes at low transverse momentum called soft.

Multiple Parton Interactions (MPI) are composed of semi-hard parton interactions. Their contribution becomes more relevant at high centre-of-mass energy of the colliding hadrons. However, the non-perturbative component of MPI cannot be trivially separated from products of initial and final state soft radiation and beam remnants from the proton break up. Therefore, experimentally, one attempts to topologically separate the partons produced in the hardest scattering from the softer part, called the Underlying Event.

In this seminar, some of the newest results about soft QCD at LHC will be discussed. The focus will be on the characterisation of the event based on topological constraints and on how these techniques can bring minimum-bias and identified-particles studies to the precision era.