FEWZ

FEWZ
Name	FEWZ
Programming language	Fortran, C++
Operating system	Unix-like, Linux, macOS
Genre	Perturbative Quantum Chromodynamics, Monte Carlo integration

FEWZ

FEWZ is a precision computational program for calculating electroweak vector boson production cross sections in high-energy particle collisions. It provides next-to-next-to-leading order perturbative predictions for observables associated with Drell–Yan process, enabling comparisons with measurements from experiments such as ATLAS, CMS, LHCb, CDF, and DØ. The package is used alongside parton distribution functions from groups like CTEQ, MSTW, NNPDF, and HERAPDF and interfaces with software such as LHAPDF and ROOT.

Overview

FEWZ computes fiducial and differential cross sections for processes involving neutral-current and charged-current vector bosons, notably production of virtual photons, Z boson, and W boson. It incorporates radiative corrections at fixed order in perturbative Quantum Chromodynamics matched with electroweak parameters from collaborations like Particle Data Group. Users specify acceptance cuts inspired by analyses from ATLAS, CMS, LHCb, Tevatron, and other collider experiments to obtain theory predictions compatible with experimental fiducial definitions. The code is commonly run on computing resources managed by centers such as CERN, Fermilab, and national computing grids.

History and Development

The initial development of FEWZ originated from efforts within theoretical groups connected to institutions like Princeton University, University of Oxford, University of Cambridge, MIT, and University of Durham to provide precision predictions for Drell–Yan processes at hadron colliders. Early versions were motivated by analyses at the Tevatron experiments CDF and DØ and later extended for the Large Hadron Collider era to meet the precision needs of ATLAS and CMS. Subsequent releases drew on advances from collaborations including NNPDF, CTEQ-TEA, and MSTW for parton distribution inputs and incorporated methodological developments found in literature authored by researchers affiliated with Brookhaven National Laboratory, DESY, SLAC National Accelerator Laboratory, and INFN. The project evolved through contributions from groups participating in workshops such as the Les Houches meetings and the Snowmass Process.

Theoretical Framework and Features

FEWZ implements fixed-order perturbative calculations up to next-to-next-to-leading order for quark-initiated Drell–Yan channels, integrating matrix elements derived from analytic computations published by collaborations associated with CERN Theory Division, IHEP, and university groups. It handles leptonic final states including decay kinematics and accounts for finite-width effects of the Z boson and W boson. The program supports renormalization and factorization scale variations, PDF error propagation using eigenvector and replica sets from CTEQ, MSTW, NNPDF, and HERAPDF, and includes electroweak parameter choices consistent with recommendations from the Particle Data Group. Numerical integration relies on adaptive Monte Carlo algorithms similar to those in the VEGAS family and deterministic sector decomposition techniques developed by collaborations at Nikhef and Max Planck Institute for Physics.

Implementation and Usage

FEWZ is distributed as source code written in compiled languages and typically configured to link against LHAPDF for PDF access and CUBA or similar libraries for multi-dimensional integration. Users prepare configuration cards mirroring fiducial selections used by experiments such as ATLAS, CMS, LHCb, CDF, and DØ and run computations on local workstations or batch systems managed by HTCondor or cluster managers at institutions like CERN and Fermilab. Output formats are designed for post-processing with analysis frameworks including ROOT and plotting packages used in collaborations like ATLAS and CMS. Typical workflows incorporate simultaneous calculations for scale and PDF uncertainty envelopes for comparison with experimental covariance matrices provided by experimental collaborations.

Validation and Benchmarking

Validation of FEWZ predictions has been performed through comparisons with independent fixed-order codes and analytic results from groups at DESY, SLAC National Accelerator Laboratory, Brookhaven National Laboratory, and university groups. Benchmark studies compare inclusive and differential predictions against data from LEP measurements, Tevatron results from CDF and DØ, and high-statistics datasets from ATLAS and CMS. Cross-checks include matching of total cross sections to results from tools such as programs developed by authors affiliated with Max Planck Institute for Physics and validations against parton-shower–matched generators used by Herwig and Pythia teams.

Applications in Collider Physics

FEWZ predictions are used in determinations of electroweak parameters, precision measurements of the W boson mass, extractions of parton distribution constraints, and studies of rapidity and transverse momentum spectra relevant to searches reported by ATLAS, CMS, and LHCb. Results enter global PDF fits conducted by groups like CTEQ-TEA, MSTW, NNPDF, and HERAPDF and inform electroweak working groups convened at CERN and in national laboratories. The tool has supported phenomenological studies connected to beyond-Standard Model searches reported in proceedings of Les Houches workshops and conference series such as ICHEP and EPS-HEP.

Development and Community Contributions

FEWZ development has been sustained by collaborations among theorists and experimental analysts from institutions including Princeton University, University of Cambridge, MIT, DESY, INFN, and SLAC National Accelerator Laboratory. Community contributions often appear as patches, validation inputs, and analysis cards shared within working groups at CERN and via code repositories coordinated by university groups. Continued enhancements are driven by experimental requirements from ATLAS, CMS, and LHCb and by theoretical advances discussed at meetings such as Les Houches and the Snowmass Process.

Category:High energy physics software