Merging high energy with soft and collinear logarithms using HEJ and PYTHIA

Abstract

We present a method to combine the all-order treatment of the High Energy Jets exclusive partonic Monte Carlo (HEJ) with the parton shower of PYTHIA8, while retaining the logarithmic accuracy of both. This procedure enables the generation of fully realistic and hadronised events with HEJ. Furthermore, the combination of the two allorder treatments leads to improvements in the quality of the description of observables, in particular for regions with disparate transverse scales.

The Large Hadron–Electron Collider at the HL-LHC

“…Computational tools are being developed to address the structure of multijet final states by including low-x dynamic effects. These include CCFM MC tools [288,289], off-shell matrixelement parton-level generators [290,291], and BFKL MC generators [292][293][294]. Figure 44 gives an example of transverse momentum correlations in DIS at small Q 2 , where the electron is scattered in the backward region near the beam axis [288], compared with the measurements [295].…”

Aspects of High Energy Scattering

“…• The results above agree with quantum field theory, as they must do given that we are being fully general here. Equation (44) clearly matches the propagator of a scalar particle, if we identify the i required to ensure we are in the upper half plane of q 2 with the Feynman i prescription used to implement causality in QFT. However, the factorisation of an amplitude into smaller amplitudes, times a divergent propagatorlike function, also works if the exchanged state is described by a composite operator composed of many fields (e.g.…”

“…In collider physics, for example, present-day experiments such as the LHC (and to some extent the Tevatron and HERA beforehand) probe kinematic regions in which additional contributions arising from the Regge limit become relevant. This may affect the description of the quark and gluon distributions within the proton [54][55][56][57][58][59][60][61][62][63][64], for example, or the radiation profile of multiple jets [43][44][45][46][47][48][49][50][51][52][53][70][71][72][73].…”

Aspects of high energy scattering

“…In collider physics, for example, present-day experiments such as the LHC (and to some extent the Tevatron and HERA beforehand) probe kinematic regions in which additional contributions arising from the Regge limit become relevant. This may affect the description of the quark and gluon distributions within the proton [54][55][56][57][58][59][60][61][62][63][64], for example, or the radiation profile of multiple jets [43][44][45][46][47][48][49][50][51][52][53][71][72][73][74].…”