Dissecting Soft Radiation with Factorization

Understand

An essential part of high-energy hadronic collisions is the soft hadronic activity that underlies the primary hard interaction.

• It includes soft radiation from the primary hard partons, secondary multiple parton interactions (MPI), and factorization-violating effects.
• The invariant mass spectrum of the leading jet in $Z$+jet and $H$+jet events is directly sensitive to these effects, and we use a QCD factorization theorem to predict its dependence on the jet radius $R$, jet $p_T$, jet rapidity, and partonic process for both the perturbative and nonperturbative components of primary soft radiation.
• We prove that the nonperturbative contributions involve only odd powers of $R$, and the linear $R$ term is universal for quark and gluon jets.