The space–time structure of hadronization in the Lund model

Abstract

The assumption of linear confinement leads to a proportionality of the energy–momentum and space–time pictures of fragmentation for a simple system in the Lund string model. The hadronization of more complicated systems is more difficult to describe, and in the past only the energy–momentum picture has been implemented. In this article also the space–time picture is worked out, for open and closed multiparton topologies, for junction systems, and for massive quarks. Some first results are presented, for toy systems but in particular for LHC events. The density of hadron production is quantified under different conditions. The (not unexpected) conclusion is that this density can become quite high, and thereby motivate the observed collective behaviour in high-multiplicity collisions. The new framework, made available as part of the Pythia event generator, offers a starting point for future model building in a number of respects, such as hadronic rescattering.

Spacetime colour reconnection in Herwig 7

“…One may also look to study the final state of the event in more detail using spacetime coordinates, an avenue started by [26]. One interesting idea is the interplay between Bose-Einstein correlations, and hadron position and extent [61].…”

“…spacetime evolution of the parton shower was introduced, for example, to study jets in hadronic e + e − events at LEP [34] and in deep-inelastic ep scattering [35]. Very recently in a publication on the space-time structure of hadronization in the Lund Model [26] the authors mention that a sensible spacetime picture of parton-shower evolution would introduce some spacetime offsets to their model. However, the authors assumed that the offsets are most likely small in their case and therefore neglected them in their studies.…”

“…As a result, pp-oriented event generators have also started to include more spacetime information, using these coordinates for various aspects of the simulation, such as collective hadronization effects [23,24], and a spacetime evolution of the parton shower [25]. Pythia recently introduced a framework for generating spacetime coordinates [26] for quantitative studies of Lund string fragmentation [27]. The effects of introducing spacetime coordinates have been recently studied in dipole evolution in γ * A collisions [28].…”

Soft modifications to jet fragmentation in high energy proton–proton collisions

“…With the discovery of small system collectivity, several approaches have been developed also for pp collisions (e.g. [32,33,34,35]), most (but not all) aiming for a description of flow effects. It is crucial for the future efforts that such space-time models attempt at describing both soft and hard observables at once, in order to avoid "over tuning" of sensitive parameters.…”

Hadronization from color interactions *

“…Thus some phenomenological models are often needed to describe the dynamical features of non-perturbative QCD, e.g. the Lund string fragmentation model [1][2][3][4][5] used in PYTHIA [6,7], the cluster model used in HERWIG [8,9], coalescence models [10][11][12][13] used in the Monte Carlo transport models such as AMPT [14] and PACIAE [15][16][17], etc. The Lund model is based on the assumption of linear confinement supported by lattice QCD.…”