NLO+NLL squark and gluino production cross sections with threshold-improved parton distributions

The European Physical Journal C, Jan 2016

We present updated predictions for the cross sections for pair production of squarks and gluinos at the LHC Run II. First of all, we update the calculations based on NLO+NLL partonic cross sections by using the NNPDF3.0NLO global analysis. This study includes a full characterization of theoretical uncertainties from higher orders, PDFs and the strong coupling. Then we explore the implications for this calculation of the recent NNPDF3.0 PDFs with NLO+NLL threshold resummation. We find that the shift in the results induced by the threshold-improved PDFs is within the total theory uncertainty band of the calculation based on NLO PDFs. However, we also observe that the central values of the NLO+NLL cross sections are modified both in a qualitative and a quantitative way, illustrating the relevance and impact of using threshold-improved PDFs together with resummed partonic cross sections. The updated NLO+NLL cross sections based on NNPDF3.0NLO are publicly available in the NLL-fast format, and should be an important ingredient for the interpretation of the searches for supersymmetric particles at Run II.

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NLO+NLL squark and gluino production cross sections with threshold-improved parton distributions

Eur. Phys. J. C NLO+NLL squark and gluino production cross sections with threshold-improved parton distributions Wim Beenakker 1 2 Christoph Borschensky 0 Michael Krämer 6 Anna Kulesza 0 Eric Laenen 3 4 5 Simone Marzani 8 Juan Rojo 7 0 Institute for Theoretical Physics, WWU Münster , 48149 Münster , Germany 1 Institute of Physics, University of Amsterdam , Amsterdam , The Netherlands 2 Theoretical High Energy Physics, IMAPP, Faculty of Science, Radboud University Nijmegen , Mailbox 79, P.O. Box 9010, 6500 GL Nijmegen , The Netherlands 3 Nikhef Theory Group , Science Park 105, 1098 XG Amsterdam , The Netherlands 4 ITF, Utrecht University , Leuvenlaan 4, 3584 CE Utrecht , The Netherlands 5 ITFA, University of Amsterdam , Science Park 904, 1018 XE Amsterdam , The Netherlands 6 Institute for Theoretical Particle Physics and Cosmology, RWTH Aachen University , 52056 Aachen , Germany 7 Rudolf Peierls Centre for Theoretical Physics, University of Oxford , 1 Keble Road, Oxford OX1 3NP , UK 8 Department of Physics, University at Buffalo, The State University of New York , Buffalo, NY 14260-1500 , USA We present updated predictions for the cross sections for pair production of squarks and gluinos at the LHC Run II. First of all, we update the calculations based on NLO+NLL partonic cross sections by using the NNPDF3.0NLO global analysis. This study includes a full characterization of theoretical uncertainties from higher orders, PDFs and the strong coupling. Then we explore the implications for this calculation of the recent NNPDF3.0 PDFs with NLO+NLL threshold resummation. We find that the shift in the results induced by the threshold-improved PDFs is within the total theory uncertainty band of the calculation based on NLO PDFs. However, we also observe that the central values of the NLO+NLL cross sections are modified both in a qualitative and a quantitative way, illustrating the relevance and impact of using threshold-improved PDFs together with resummed partonic cross sections. The updated NLO+NLL cross sections based on NNPDF3.0NLO are publicly available in the NLL-fast format, and should be an important ingredient for the interpretation of the searches for supersymmetric particles at Run II. 1 Introduction and motivation Supersymmetry (SUSY) [ 1–6 ] is one of the better motivated extensions of the Standard Model (SM). In addition to offering a natural solution to the hierarchy problem, it provides a number of dark-matter candidates and leads to the unification of gauge couplings at high scales. While so far searches for supersymmetry at the LHC 8 TeV have returned null results [ 7–9 ], the recently started Run II of the LHC, with its increase in center-of-mass energy and luminosity, opens a wide new region of the SUSY parameter space for scrutiny, extending in particular into the high-mass regime up to 2.5 TeV particles [10]. For this reason, it is crucial to provide precise theory predictions for the cross sections of supersymmetric particle pair production at 13 TeV with a robust estimate of the associated theory uncertainties. The next-to-leading order (NLO) QCD corrections to the total cross sections for squark and gluino pair production were first computed in [ 11–13 ]. Recently, a considerable effort has been made in automating these calculations [ 14– 16 ], including the decays [ 17 ] and matching the NLO corrections with a parton shower [ 18, 19 ]. Furthermore, NLO electroweak corrections have also been calculated [ 20–28 ]. A significant contribution to the QCD NLO corrections originates from soft-gluon emissions which dominate the region near the production threshold. In this region, the partonic center-of-mass energy sˆ is close to the kinematic restriction for the on-shell production of these particles, i.e. sˆ ≥ 4m2, with m being the average mass of the two produced particles. Soft-gluon corrections to squark and gluino pair production can be taken into account to all orders in perturbation theory either using threshold-resummation techniques in Mellin space [ 29–32 ] or in the framework of effective theories [ 33, 34 ]. Resummation of threshold corrections at the next-toleading logarithmic (NLL) accuracy has been performed for all processes contributing to squark and gluino production, resulting in matched NLO+NLL predictions [ 35–41 ]. Additionally, Coulomb corrections have been resummed simultaneously with soft-gluon corrections in [ 34,42 ]. The progress towards resummation at next-to-next-to-leading logarithmic (NNLL) accuracy and towards the corresponding LHC predictions has been reported in [ 43–52 ]. Finite width and bound state effects have been studied for squark and gluino production processes in [ 53–58 ]. Resummed calculations for sleptons and gauginos are also available at NLO+NLL accuracy [ 59–61 ]. A potential source of theory uncertainty in these calculations arises from the fact that they are based on parton distribution functions (PDFs) extrac (...truncated)


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Wim Beenakker, Christoph Borschensky, Michael Krämer. NLO+NLL squark and gluino production cross sections with threshold-improved parton distributions, The European Physical Journal C, 2016, pp. 53, Volume 76, Issue 2, DOI: 10.1140/epjc/s10052-016-3892-4