Higher order corrections to parton showering from resummation calculations

TL;DR

The paper presents a hybrid approach that blends analytic soft-gluon resummation with parton shower Monte Carlo methods by introducing a modified parton distribution function (mPDF) and a Y-term for hard-emission corrections. This framework yields NLO-accurate total cross sections while maintaining realistic event kinematics and a smooth transition between showering and explicit hard emissions. Using a modified PYTHIA implementation, the authors demonstrate improved transverse-momentum distributions for W, Z, and Higgs bosons at the Tevatron and show that jet properties remain largely consistent with standard showering, with modest enhancements in radiation for certain processes. The work provides practical pathways to incorporate higher-order effects into showering and paves the way for extensions to more complex final states and higher-order corrections.

Abstract

The connection between analytic and Monte Carlo calculations of soft gluon emission is reanalyzed in light of recent, theoretical developments in resummation. An alternative Monte Carlo algorithm is suggested which incorporates (1) corrections beyond leading order to the showering and (2) smoothly merges with the higher order calculation of single, hard parton emission. In particular, it is possible to study jet properties in heavy boson production for all values of the boson transverse momentum with a total cross section of NLO accuracy. The specific cases of $W$, $Z$ and Higgs boson production at the Tevatron are addressed using a modified version of the Pythia Monte Carlo.

Figures (7)

• Figure 1: The prediction of the $W$ boson transverse momentum distribution in Run I at the Tevatron (solid line) compared to the DØ data (the upper and lower dashed lines represent the errors on the middle line). The prediction includes the effects of the modified parton distribution functions, the correction to the hard scattering process, and a tuned primordial $k_T$ of 3.6 GeV.
• Figure 2: Predicted $W$ boson transverse momentum distribution in Run II (solid line) showing the individual contributions from showering (long dashes), the corrected hard emission (short dashes) and the standard PYTHIA prediction using CTEQ4L structure functions (dot--dash).
• Figure 3: Same as Fig. 2, but for Higgs boson production ($m_H=100$ GeV).
• Figure 4: The ratio of Higgs boson transverse momentum distributions ($m_H=100$ GeV) from the modified showering algorithm and from the standard showering algorithm using the CTEQ4L PDF. The CTEQ4L result has been multiplied by a constant $K$--factor to reproduce the NLO rate.
• Figure 5: Jet multiplicity in $W$ boson events for different $Q_T$ binnings.