Automatic spin-entangled decays of heavy resonances in Monte Carlo simulations

229

396

Run 2 LHC data show hints of a new resonance in the diphoton distribution at an invariant mass of 750 GeV. We analyse the data in terms of a new boson, extracting information on its properties and exploring theoretical interpretations. Scenarios covered include a narrow resonance and, as preliminary indications suggest, a wider resonance. If the width indications persist, the new particle is likely to belong to a strongly-interacting sector. We also show how compatibility between Run 1 and Run 2 data is improved by postulating the existence of an additional heavy particle, whose decays are possibly related to dark matter.

Section: A Benchmark Modelmentioning

confidence: 56%

What is the γγ resonance at 750 GeV?

Franceschini

Giudice

Kamenik

et al. 2016

229

396

“…[211], 39 and studied there for top and W decays in the SM, which has been fully automated and extended to generic models in ref. [213]; the corresponding module in the code has been dubbed MadSpin. 40 The method is based on the following identity:…”

Section: Jhep07(2014)079mentioning

confidence: 99%

“…that presented in ref. [213]. The most important of these is that the phasespace generation is now handled by the Fortran code (rather than by a Python routine).…”

Section: Jhep07(2014)079mentioning

confidence: 99%

The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations

Alwall

Frederix

Frixione

et al. 2014

6,050

5,572

We discuss the theoretical bases that underpin the automation of the computations of tree-level and next-to-leading order cross sections, of their matching to parton shower simulations, and of the merging of matched samples that differ by light-parton multiplicities. We present a computer program, MadGraph5 aMC@NLO, capable of handling all these computations -parton-level fixed order, shower-matched, merged -in a unified framework whose defining features are flexibility, high level of parallelisation, and human intervention limited to input physics quantities. We demonstrate the potential of the program by presenting selected phenomenological applications relevant to the LHC and to a 1-TeV e + e − collider. While next-to-leading order results are restricted to QCD corrections to SM processes in the first public version, we show that from the user viewpoint no changes have to be expected in the case of corrections due to any given renormalisable Lagrangian, and that the implementation of these are well under way.

“…For the parton shower we always use Pythia8 [76]. The fully inclusive phase-space is considered and the tops are kept stable, even though their decays can be considered in a fully automatic way via the MadSpin [77] package allowing further analysis of exclusive and realistic observables. Table 3.…”

Section: Resultsmentioning

confidence: 99%

Scalar production and decay to top quarks including interference effects at NLO in QCD in an EFT approach

Franzosi

Vryonidou

Zhang

2017

Scalar and pseudo-scalar resonances decaying to top quarks are common predictions in several scenarios beyond the standard model (SM) and are extensively searched for by LHC experiments. Challenges on the experimental side require optimising the strategy based on accurate predictions. Firstly, QCD corrections are known to be large both for the SM QCD background and for the pure signal scalar production. Secondly, leading order and approximate next-to-leading order (NLO) calculations indicate that the interference between signal and background is large and drastically changes the lineshape of the signal, from a simple peak to a peak-dip structure. Therefore, a robust prediction of this interference at NLO accuracy in QCD is necessary to ensure that higher-order corrections do not alter the lineshapes. We compute the exact NLO corrections, assuming a point-like coupling between the scalar and the gluons and consistently embedding the calculation in an effective field theory within an automated framework, and present results for a representative set of beyond the SM benchmarks. The results can be further matched to parton shower simulation, providing more realistic predictions. We find that NLO corrections are important and lead to a significant reduction of the uncertainties. We also discuss how our computation can be used to improve the predictions for physics scenarios where the gluon-scalar loop is resolved and the effective approach is less applicable.