Ntuples for NLO events at hadron colliders

We present an event-file format for the dissemination of next-to-leading-order (NLO) predictions for QCD processes at hadron colliders. The files contain all information required to compute generic jet-based infrared-safe observables at fixed order (without showering or hadronization), and to recompute observables with different factorization and renormalization scales. The files also make it possible to evaluate cross sections and distributions with different parton distribution functions. This in turn makes it possible to estimate uncertainties in NLO predictions of a wide variety of observables without recomputing the short-distance matrix elements. The event files allow a user to choose among a wide range of commonly-used jet algorithms and jet-size parameters. We provide event files for a W or Z boson accompanied by up to four jets, and for pure-jet events with up to four jets. The files are for the Large Hadron Collider with a center of mass energy of 7 or 8 TeV. A C++ library along with a Python interface for handling these files is also provided and described in this article. The library allows a user to read the event files and recompute observables transparently for different pdf sets and factorization and renormalization scales. Program summary Program title: nTupleReader Catalogue identifier: AESC_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AESC_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 62761 No. of bytes in distributed program, including test data, etc.: 442886 Distribution format: tar.gz Programming language: C++ with Bython interface. Computer: Workstations. Operating system: Linux, MacOS. RAM: Varying bytes Classification: 11.1, 11.5. External routines: ROOT, LHAPDF Nature of problem: NLO QCD predictions for vector boson + jets and jet processes for generic observables. Solution method: Event files containing all information required to compute generic jet-based infrared-safe observables at fixed order and to recompute observables with different factorization and renormalization scales are provided. The library provides an interface to access the information in these files. Running time: The runtime scales linearly with the file size. (C) 2014 Elsevier B.V. All rights reserved.