Characterizing the hadronization of parton showers using the HOMER method

We update the HOMER method, a technique to solve a restricted version of the inverse problem of hadronization – extracting the Lund string fragmentation function f(z) f ( z ) from data using only observable information. Here, we demonstrate its utility by extracting f(z) f ( z ) from synthetic Pythia simulations using high-level observables constructed on an event-by-event basis, such as multiplicities and shape variables. Four cases of increasing complexity are considered, corresponding to e^+e^- e + e − collisions at a center-of-mass energy of 90≥v 90 ≥ v producing either a string stretched between a q q and q̄ q ‾ containing no gluons; the same string containing one gluon g g with fixed kinematics; the same but the gluon has varying kinematics; and the most realistic case, strings with an unrestricted number of gluons that is the end-result of a parton shower. We demonstrate the extraction of f(z) f ( z ) in each case, with the result of only a relatively modest degradation in performance of the HOMER method with the increased complexity of the string system.