Soft QCD in ATLAS: measurements and modelling of multi-parton interactions

Understand

Soft QCD contributes to all observables at the LHC, due to the presences of underlying event (UE) and pile-up in all events.

• Both these processes are dominated by multi-parton interactions (MPI), i.e.
• the result of proton collisions containing more than one partonic interaction due to collective and beam remnant effects.
• While there is undoubtedly interesting physics involved in MPI, the primary interest of LHC experiments is to characterise and model the behaviour of UE and pile-up sufficiently well that their influence may be cleanly subtracted in the process of searching for new physics signatures at 7 TeV and beyond.