A framework for simultaneous fit of QCD and BSM parameters with xFitter

TL;DR

This paper extends the xFitter program to enable simultaneous fitting of QCD parameters, PDFs, and BSM physics parameters within SMEFT, demonstrated through a top quark analysis at the HL-LHC.

Contribution

It introduces a polynomial parameterization extension to xFitter for combined QCD and BSM parameter determination within SMEFT.

Findings

Simultaneous determination of PDFs, top quark mass, and SMEFT operator couplings is feasible.

Correlations among all parameters are crucial for accurate analysis.

The extended framework is validated with projections for HL-LHC top quark measurements.

Abstract

An extension of the xFitter open-source program for QCD analyses is presented, allowing for a polynomial parameterization of the dependence of physical observables on theoretical parameters. This extension enables simultaneous determination of parton distribution functions (PDFs) and new physics parameters within the framework of the Standard Model Effective Field Theory (SMEFT). The functionalities of the code are illustrated in a sensitivity study, where a simultaneous determination of the PDFs, top quark mass and the couplings of selected dimension-6 SMEFT operators is addressed using projections for measurements of top quark-antiquark pair production at the High-Luminosity LHC. The importance of considering all the correlations of the parton distributions, top quark mass and the EFT parameters in a simultaneous QCD+SMEFT analysis is demonstrated. This work serves as a new platform for simultaneous extraction of the PDFs and the SM/SMEFT parameters based on xFitter.