Dynamical approach to MPI in W+dijet and Z+dijet production within the PYTHIA event generator

B Blok,P Gunnellini

doi:10.1140/epjc/s10052-016-4035-7

Abstract

The new numerical approach that includes 1 to 2 mechanism is applied to double parton scattering (DPS) in W+dijet and Z+dijet final state production in proton-proton collisions at LHC. By using the underlying event (UE) simulation from a pythia 8 tune extracted in hadronic events, we show that, like in the case of a four-jet final state, the inclusion of 1 to 2 mechanism improves the description of experimental data measured at 7 TeV. In addition, predictions for proton-proton collisions at a center-of-mass energy of 14 TeV are shown for DPS- and UE-sensitive observables.

Highlights

A new approach based on perturbative Quantum Chromodynamics has been developed [22,23,24,25] for describing multiple parton interactions (MPI)
By using the underlying event (UE) simulation from a pythia 8.205 tune extracted in hadronic events, we show that, like in the case of a four-jet final state, the inclusion of 1 ⊗ 2 mechanisms improves the description of experimental data measured at 7 TeV
“UE Tune” [52]: predictions obtained without applying any reweighting of the simulation; this tune uses a constant value of σeff, following the standard Pythia approach, and its parameters have been extracted by fits to the UE measurement in hadronic final states;

Summary

Introduction

A new approach based on perturbative Quantum Chromodynamics (pQCD) has been developed [22,23,24,25] for describing MPI. Unlike a four-jet final state, it has been shown [44,45] that higher-order contributions from single parton scattering (SPS) are crucial for a consistent description of DPSsensitive observables in the Wjj channel These are not included in the matrix element simulated by the pythia event generator. Even though the hard scales are much higher than 5 GeV in inclusive W- and Z-boson events, our model-independent calculation of σeff in Wjj and Zjj final states shows values which are very similar to σeff obtained in the four-jet channel. This looks, like a pure numerical coincidence but motivates the choice of using the “UE Tune” for W- and Z-boson events. Theoretical dependence of σeff in Wjj and Zjj as a function of the dijet transverse scale is investigated in Appendix 1 for 7 and 13 TeV center-of-mass energies, while, in Appendix 2, results obtained with the madgraph MC event generator are considered

Theoretical tools

Monte Carlo implementation and definition of experimental observables

UE observables in inclusive W- and Z-boson events

Predictions of DPS-sensitive observables at 13 TeV

Findings

Conclusions