NNLOJET

NNLOJET
Name	NNLOJET
Developer	DESY, CERN, Uppsala University, Durham University, Nikhef
Released	2010s
Latest release	(ongoing)
Programming language	Fortran, C++, Python
Operating system	Linux, Unix
License	Scientific collaboration

NNLOJET

NNLOJET is a computational project for precision perturbative calculations in high‑energy particle physics. It provides next-to-next-to-leading order implementations for collider observables relevant to experiments such as Large Hadron Collider, HERA, and Tevatron. The project serves analysts working with collaborations like ATLAS, CMS, LHCb, and theory groups at institutions such as CERN and DESY by producing differential predictions for processes involving jets, electroweak bosons, and heavy flavours.

Overview

NNLOJET delivers fixed-order perturbative predictions through numerical Monte Carlo integration and analytic subtraction of infrared singularities. The code targets processes studied by collaborations including ATLAS, CMS, LHCb, HERA, and CDF to support precision tests of the Standard Model and determinations of parameters used by groups at CERN, DESY, and university theory groups such as Uppsala University and Durham University. Authors and contributors include researchers affiliated with institutions like Nikhef, MPI (Max Planck Institute), and national laboratories participating in experimental programmes such as the LHC Run 2 and LHC Run 3. NNLOJET outputs are frequently compared with predictions from Monte Carlo event generators and fixed-order programs developed at SLAC and FNAL.

Computational Framework

The framework combines Fortran and C++ components driven by Python steering scripts, relying on numerical integration techniques used in projects at CERN and numerical libraries common at DESY. Phase-space generation and mapping use algorithmic strategies similar to those in tools developed at MPI and university groups such as Oxford University and Cambridge University. The integration core interfaces to parton distribution sets provided by collaborations at CTEQ-TEA, NNPDF, and MMHT and supports electroweak parameter schemes consistent with conventions from PDG. Built for high-performance clusters operated at facilities like CERN and national computing centres used by GridPP and PRACE, NNLOJET leverages parallelization paradigms pioneered in large collaborations including ATLAS and CMS.

Perturbative Calculations and Implemented Processes

NNLOJET implements a suite of processes at next-to-next-to-leading order relevant to collider measurements: jet production in hadron collisions, deep-inelastic scattering observables measured at HERA, vector-boson plus jet production studied by ATLAS and CMS, and heavy-quark pair production channels probed at Tevatron experiments such as CDF and DØ. The project provides differential cross sections, scale uncertainties, and parton-level distributions that feed into global fits performed by groups such as CTEQ-TEA and NNPDF. Phenomenological applications include precision extractions of the strong coupling constant αs in analyses similar to those by Particle Data Group and determinations of parton distribution functions used by collaborations at CERN and national laboratories.

Subtraction Methods and Infrared Regularization

NNLOJET implements established subtraction schemes for handling infrared singularities at NNLO, building on theoretical formalisms developed in the literature by researchers associated with institutes like DESY, CERN, and Uppsala University. Techniques include antenna subtraction and sector-improved residue subtraction variants that mirror methods used in independent codes from groups at MPI and Durham University. The implementation handles double-real, real–virtual, and double-virtual contributions with analytic cancellations of soft and collinear divergences consistent with factorization theorems used in calculations cited by theorists at Harvard University and Princeton University.

Validation, Benchmarks, and Phenomenology

Validation of NNLOJET results has been performed through comparisons with independent NNLO calculations and experimental measurements from collaborations such as ATLAS, CMS, HERA, and CDF. Benchmarks include jet rates, transverse-momentum spectra, and shape observables used in precision tests by groups at CERN and in global PDF fits by NNPDF and CTEQ-TEA. Phenomenological studies using NNLOJET outputs contribute to analyses presented at conferences organized by EPS and ICHEP and to publications authored by researchers at university departments including Uppsala University and Durham University.

Software Architecture and Performance

The codebase is modular, separating matrix-element evaluation, phase-space generation, subtraction counterterms, and histogramming, following software engineering practices common at CERN and large collaborations like ATLAS and CMS. Performance tuning targets multi-core clusters and batch systems run at facilities such as CERN and national supercomputing centres coordinated by PRACE and GridPP, with parallel efficiency considerations similar to those in projects from DESY and Nikhef. Typical production runs involve substantial CPU time comparable to other NNLO programs developed at MPI and national laboratories.

Development History and Collaboration

NNLOJET evolved through collaborative efforts from research groups at DESY, CERN, Uppsala University, Durham University, and Nikhef, with methodological inputs from theory groups at institutions like MPI and university partners including Oxford University. The project has progressed alongside experimental campaigns at LHC Run 1 and LHC Run 2, and continues to interact with PDF fitting collaborations such as NNPDF and CTEQ-TEA and experimental working groups within ATLAS and CMS. Ongoing development remains community-driven, with contributions from researchers affiliated with national laboratories and universities active in precision collider phenomenology.

Category:Particle physics software