Precise simulation of the initial-state QCD activity associated with $Z$-boson production in hadron collisions

TL;DR

This paper demonstrates that a leading-order event generator can accurately simulate the initial-state QCD activity in Z-boson production at the LHC, achieving 1% agreement with experimental data by tuning energy scales.

Contribution

It shows that precise simulation of initial-state QCD effects in Z-boson production is possible using a leading-order generator with scale adjustments, without higher-order calculations.

Findings

Default simulation agrees within 5% of ATLAS data.

Adjusting energy scales reduces deviation to 1%.

Accurate modeling over a wide range without modifying the parton shower.

Abstract

The $\phi_{\eta}^{*}$ distribution of the $Z/\gamma^{*} \rightarrow \ell^{+}\ell^{-}$ production in hadron collisions is simulated using a leading-order event generator, GR@PPA. The initial-state parton shower, which simulates the multiple QCD-radiation effects in the initial state, plays the dominant role in this simulation. The simulation in the default setting agrees with the high-statistics measurement by ATLAS at LHC with the precision at the level of 5%. The observed systematic deviation, which can be attributed to the effects of ignored higher-order contributions, can be reduced by adjusting the arbitrary energy scales in the simulation. The agreement at the level of 1% can be achieved over a very wide range without introducing any modification in the implemented naive leading-logarithmic parton shower.