Searching for new physics inside jets with the Herwig 7 generalised parton shower

A

bstract

This study investigates parton shower evolution incorporating both Standard Model (SM) and beyond-the-Standard-Model (BSM) radiation, focusing on the phenomenology of a massive Z ^′ boson. While traditional approaches typically assume direct Z ^′ production in the hard process, the possibility of Z ^′ production within jets, enabled by subsequent emissions in the parton shower, offers a complementary opportunity to probe new physics through jet substructure and event topology. The newly developed Herwig 7 framework supporting BSM parton showers enables efficient simulation of Z ^′ production in the logarithmically enhanced regime. Using a simple BSM benchmark, the minimal U(1) _{B - L} extension of the SM, the interplay between the SM and BSM showers is evaluated to identify kinematic features that distinguish Z ^′ -induced jets from conventional signatures. BSM-radiation signatures are contrasted with SM backgrounds such as QCD, top-quark, and Drell-Yan production, identifying potential discriminants for experimental searches. Experimental sensitivity at the LHC and prospective future colliders is estimated via statistical-significance projections. We find that Z ^′ bosons produced through parton shower radiation populate non-isolated regions inside jets, providing an avenue for new-physics searches overlooked in traditional analyses.