Initial State Radiation in Simulations of Vector Boson Production at Hadron Colliders

TL;DR

This work enhances vector-boson production simulations at hadron colliders by applying matrix-element corrections to initial-state radiation within the HERWIG shower. By mapping shower variables to exact matrix-element kinematics and implementing both hard and soft corrections, the authors achieve better high-q_T descriptions and improved agreement with Tevatron data, while maintaining compatibility with resummed calculations at low q_T. The study demonstrates substantial improvements in W/Z spectra and jet activity, and discusses detector effects, matching nuances with resummation approaches, and potential extensions to heavy-quark production. Overall, the approach provides a more reliable Monte Carlo framework for testing QCD and SM predictions at the Tevatron and LHC.

Abstract

The production of vector bosons at present and future hadron colliders will provide a crucial test for QCD and Standard Model physics. In this paper we improve parton shower simulations of Drell-Yan processes by implementing matrix-element corrections to the initial-state radiation. We apply our work to the HERWIG Monte Carlo event generator and compare our phenomenological results with the ones obtained using the previous version of HERWIG, with resummed calculations which we match to the exact first-order perturbative result, and with recent Tevatron data. We also make some predictions for jet events at the LHC.

Figures (12)

• Figure 1: The phase space for additional emission in Drell--Yan production with $s/m_V^2=6.25$, showing the kinematic limits (solid) and HERWIG's parton shower limits (dashed).
• Figure 2: The $W$$q_T$ distribution at the Tevatron, according to HERWIG without (dotted) and with (solid) matrix-element corrections. Also shown (dashed) is the '$W+$ jet' process with a cutoff of 10 GeV.
• Figure 3: The $W$$q_T$ distribution data from DØ, in comparison with HERWIG with matrix-element corrections but without detector corrections. The solid line has zero intrinsic transverse momentum while the dashed one has an r.m.s. $p_t$ of 1 GeV.
• Figure 4: As Fig. \ref{['fig:WqtD0']} but with the HERWIG results corrected for detector effects.
• Figure 5: The $W$$q_T$ distribution at the LHC, according to HERWIG without (dotted) and with (solid and dashed) matrix-element corrections, with zero intrinsic $p_t$ (solid) and an r.m.s. $p_t$ of 1 GeV (dashed).