A posteriori inclusion of parton density functions in NLO QCD final-state calculations at hadron colliders: the APPLGRID project

By T. Carli, D. Clements, A. Cooper-Sarkar, C. Gwenlan, G. Salam, F. Siegert, P. Starovoitov, M. Sutton. 2009

306 citations recorded by the source corpus.

A method to facilitate the consistent inclusion of cross-section measurements based on complex final-states from HERA, TEVATRON and the LHC in proton parton density function (PDF) fits has been developed. This can be used to increase the sensitivity of LHC data to deviations from Standard Model predictions. The method stores perturbative coefficients of NLO QCD calculations of final-state observables measured in hadron colliders in look-up tables. This allows the a posteriori inclusion of parton density functions (PDFs), and of the strong coupling, as well as the a posteriori variation of the renormalisation and factorisation scales in cross-section calculations. The main novelties in comparison to original work on the subject are the use of higher-order interpolation of Lagrangian form, which substantially improves the trade-off between accuracy and memory use, and a CPU and computer memory optimised way to construct and store the look-up table using modern software tools. It is demonstrated that a sufficient accuracy on the cross-section calculation can be achieved with reasonably small look-up table size by using the examples of jet production and electro-weak boson (Z, W) production in proton-proton collisions at a center-of-mass energy of 14 TeV at the LHC. The use of this technique in PDF fitting is demonstrated in a PDF-fit to HERA data and simulated LHC jet cross-sections as well as in a study of the jet cross-section uncertainties at various centre-of-mass energies.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b70c5586dc4eb36500bedde3cf96b824d3f82962

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Citations in the corpus

Measurement of inclusive jet and dijet cross sections in proton-proton collisions at 7 TeV centre-of-mass energy with the ATLAS detector (2010, methodology): “To efficiently calculate all these uncertainties, the APPLGRID [52] program was used.”
Parton distribution benchmarking with LHC data (2012, methodology): “• For electroweak vector boson production, we have computed differential distributions at NLO with the MCFM code [61] interfaced to the APPLgrid software [62] that allows a fast computation of the observable when PDFs are varied, and cross checked against the DYNNLO code [63].”
The Structure of the Proton in the LHC Precision Era (2017, methodology): “27 we show a comparison of the timings per data point between the original APPLgrid computation of hadronic cross-sections, Eq.”
Les Houches 2015: Physics at TeV Colliders Standard Model Working Group Report (2016, methodology): “II.6: NLO predictions of dσ/dy(W+) in the process pp → W+c̄ at the LHC 13 TeV, computed with APPLgrid.”
Illuminating the photon content of the proton within a global PDF analysis (2017, methodology): “The results presented in this section have been obtained at leading order in both the QCD and QED couplings using MadGraph5 aMC@NLO interfaced to APPLgrid through aMCfast.”
The PDF4LHC report on PDFs and LHC data: Results from Run I and preparation for Run II (2015, methodology): “There are three projects most commonly used to exploit the described techniques: FastNLO [87, 88], APPLgrid [78,89] and aMCfast [58].”
A critical appraisal and evaluation of modern PDFs (2016, methodology): “4/30 NNLO APPLGrid [181], C-factors [183] (kinematic dependence with FEWZ3.”
Parton distributions from high-precision collider data (2017, methodology): “Theoretical predictions are obtained at NLO using APPLgrids constructed using MCFM, and at NNLO corrections have been computed [89] using FEWZ.”