Study of Parton Density Function Uncertainties with LHAPDF and PYTHIA at LHC

TL;DR

The paper develops an LHAPDF–PYTHIA interface to quantify parton-density-function uncertainties in hadron-collider predictions, enabling per-member PDF variation within a single framework. It validates the interface with consistency checks and applies it to Drell–Yan production at the Z pole and Higgs production via gluon fusion, finding percent-level PDF uncertainties at the Z pole and sub-4% uncertainties for Higgs across explored masses. It also analyzes the feasibility of a precision measurement of the electroweak mixing angle sin^2θ_eff^{lept}(M_Z^2) at the LHC, highlighting that PDF uncertainties could be a limiting systematic unless very large datasets and multi-channel analyses are employed. Overall, the work provides a practical workflow to propagate PDF uncertainties through collider predictions and informs experimental planning at the LHC.

Abstract

The experimental errors in current and future hadron colliders are expected to decrease to a level that will challenge the uncertainties in the theoretical calculations. One important component in the prediction uncertainties comes from the Parton Density Functions of the (anti)proton. In this work we develop an interface from the Les Houches Accord Parton Density Functions (LHAPDF) package to the very popular Monte Carlo generator {\tt PYTHIA} version 6.2. Then we proceed to estimate the PDF uncertainties for the production of Drell-Yan pairs from the Z pole to masses above 1 $\TeV$ and for Higgs bosons at LHC. The measurement of the electro-weak mixing angle at LHC as a particularly difficult case is studied.