Monte Carlo simulations of Higgs-boson production at the LHC with the KrkNLO method

The European Physical Journal C, Mar 2017

We present numerical tests and predictions of the KrkNLO method for matching of NLO QCD corrections to hard processes with LO parton-shower Monte Carlo generators (NLO+PS). This method was described in detail in our previous publications, where it was also compared with other NLO+PS matching approaches (MC@NLO and POWHEG) as well as fixed-order NLO and NNLO calculations. Here we concentrate on presenting some numerical results (cross sections and distributions) for \(Z/\gamma ^*\) (Drell–Yan) and Higgs-boson production processes at the LHC. The Drell–Yan process is used mainly to validate the KrkNLO implementation in the Herwig 7 program with respect to the previous implementation in Sherpa. We also show predictions for this process with the new, complete, MC-scheme parton distribution functions and compare them with our previously published results. Then we present the first results of the KrkNLO method for Higgs production in gluon–gluon fusion at the LHC and compare them with MC@NLO and POWHEG predictions from Herwig 7, fixed-order results from HNNLO and a resummed calculation from HqT, as well as with experimental data from the ATLAS collaboration.

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Monte Carlo simulations of Higgs-boson production at the LHC with the KrkNLO method

Eur. Phys. J. C Monte Carlo simulations of Higgs-boson production at the LHC with the KrkNLO method S. Jadach 2 3 G. Nail 0 1 2 W. Płaczek 2 5 S. Sapeta 2 3 4 A. Siódmok 2 3 4 M. Skrzypek 2 3 0 Institute for Theoretical Physics, Karlsruhe Institute of Technology , Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe , Germany 1 Particle Physics Group, School of Physics and Astronomy, University of Manchester , Oxford Road, Manchester M13 9PL , UK 2 This work is partly supported by the Polish National Science Centre Grant UMO-2012/04/M/ST2/00240 3 Institute of Nuclear Physics, Polish Academy of Sciences , ul. Radzikowskiego 152, 31-342 Kraków , Poland 4 Theoretical Physics Department, CERN , Geneva 23 1211 , Switzerland 5 Marian Smoluchowski Institute of Physics, Jagiellonian University , ul. Łojasiewicza 11, 30-348 Kraków , Poland We present numerical tests and predictions of the KrkNLO method for matching of NLO QCD corrections to hard processes with LO parton-shower Monte Carlo generators (NLO+PS). This method was described in detail in our previous publications, where it was also compared with other NLO+PS matching approaches (MC@NLO and POWHEG) as well as fixed-order NLO and NNLO calculations. Here we concentrate on presenting some numerical results (cross sections and distributions) for Z /γ ∗ (DrellYan) and Higgs-boson production processes at the LHC. The Drell-Yan process is used mainly to validate the KrkNLO implementation in the Herwig 7 program with respect to the previous implementation in Sherpa. We also show predictions for this process with the new, complete, MC-scheme parton distribution functions and compare them with our previously published results. Then we present the first results of the KrkNLO method for Higgs production in gluon-gluon fusion at the LHC and compare them with MC@NLO and POWHEG predictions from Herwig 7, fixed-order results from HNNLO and a resummed calculation from HqT, as well as with experimental data from the ATLAS collaboration. The discovery of the Higgs boson, at the Large Hadron Collider (LHC) [1,2], opened a new era in the exploration of the electroweak sector of the standard model (SM). The measured value of the Higgs mass uniquely specifies all of the couplings and turns the SM into a fully predictive theory. - Hence, we are at a position to perform stringent tests of our current modelling of these fundamental interactions. This is only possible if we are in possession of precise theoretical predictions for the Higgs-production cross sections. Most of the Higgs-boson particles observed at hadron colliders are produced through the process of gluon fusion, a channel that is known to exhibit very slow convergence in perturbative quantum chromodynamics (QCD). At LHC energies, the next-to-leading order (NLO) corrections to the total cross section for the inclusive production of the Higgs boson through gluon fusion turn out to be as large as 70%, and the next-to-next-to-leading order (NNLO) corrections increase the cross section by another 30% [3–5]. The theoretical uncertainty of the NNLO result, arising from the missing higher orders and obtained by the standard renormalization and factorization scale variations, is estimated at around 10%, and is hence at the level of the experimental accuracy of the Run 1 LHC measurements. This large uncertainty at NNLO has motivated the efforts to further improve the precision by calculating the full next-to-next-to-next-to-leading order (N3LO) result for inclusive Higgs-boson production in gluon fusion [6]. Adding these contributions to the predictions for the cross section reduces their scale uncertainties down to the level of 3%. Apart from the inclusive Higgs cross section, which is the most fundamental quantity, as it enables one to predict the total number of Higgs particles produced at a given energy and luminosity, one is also equally interested in more differential observables. Therefore, a significant amount of work has also gone into obtaining predictions for differential cross sections for Higgs production in gluon fusion beyond NLO. In particular, differential observables have been predicted within frameworks of analytic resummation, like for example small-qT resummation performed in QCD in coordinate space up to the NNLL+NLO accuracy [7] and directly in momentum space up to NNLL+NNLO [8] as well as within SCET [9] up to NNLL+NLO. Differential cross sections for Higgs production in gluon fusion have also been widely studied with approaches in which fixed-order NLO results are matched to parton shower (NLO+PS) such as the MiNLO method [10, 11]. Recently, NNLO+PS matched results were computed with the UN2LOPS technique [12] as well as with an extended version of MiNLO [13–15] combined with the HNNLO program [5,16]. The current methods of performing NNLO+PS [11,14,15,17–21] represent clear progress in the matching of fixed-order NNLO QCD calculations with parton-shower Monte Carlos (PSMCs). The next challenge towards ev (...truncated)


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S. Jadach, G. Nail, W. Płaczek, S. Sapeta, A. Siódmok, M. Skrzypek. Monte Carlo simulations of Higgs-boson production at the LHC with the KrkNLO method, The European Physical Journal C, 2017, pp. 164, Volume 77, Issue 3, DOI: 10.1140/epjc/s10052-017-4733-9