| 1. |
- Broggio, Alessandro, et al.
(author)
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Top-quark pair hadroproduction in association with a heavy boson at NLO+NNLL including EW corrections
- 2019
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In: Journal of High Energy Physics. - 1029-8479. ; 2019:8
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Journal article (peer-reviewed)abstract
- This work studies the associated production of a top-quark pair with a W, Z, or Higgs boson at the LHC. Predictions for the total cross sections as well as for several differential distributions of the massive particles in the final state are provided. These predictions, valid for the LHC operating at 13 TeV, include without any approximation all the NLO electroweak and QCD contributions of O (αsαj+1) with i + j = 2, 3. In addition, the predictions presented here improve upon the NLO QCD results by adding the effects of soft gluon emission corrections resummed to next-to-next-to-leading logarithmic accuracy. The residual dependence of the predictions on scale and PDF choices is analyzed.
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| 2. |
- Broggio, Alessandro, et al.
(author)
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tt̄X Calculations and Modeling
- 2021
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In: The Ninth Annual Conference on Large Hadron Collider Physics : LHCP2021 - LHCP2021. - Trieste, Italy : Sissa Medialab. - 1824-8039. ; 397
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Conference paper (peer-reviewed)abstract
- In this talk, we review the status of calculations for the associated production of a top pair and a Higgs, W or Z boson at the Large Hadron Collider. In particular, we focus on the resummation of soft gluon emission effects and on their combination with the complete set of next-to-leading-order corrections of both QCD and electroweak origin, in calculations in which the final state top pair and massive boson are kept on shell. The impact of these corrections on the total cross section and several differential distributions is studied.
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| 3. |
- Butterworth, J., et al.
(author)
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Les Houches 2013: Physics at TeV Colliders: Standard Model Working Group Report
- 2014
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Conference paper (peer-reviewed)abstract
- This Report summarizes the proceedings of the 2013 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt primarily with (1) the techniques for calculating standard model multi-leg NLO and NNLO QCD and NLO EW cross sections and (2) the comparison of those cross sections with LHC data from Run 1, and projections for future measurements in Run 2.
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| 4. |
- Frederix, Rikkert, et al.
(author)
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A new way of reducing negative weights in MC@NLO
- 2023
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In: European Physical Journal C. - 1434-6044. ; 83:11
-
Journal article (peer-reviewed)abstract
- We introduce a new technique, that we dub Born spreading, aimed at reducing the number of negative-weight S events in the MC@NLO matching of NLO calculations with parton-shower simulations. We show that such a technique, based on a re-distribution of Born matrix elements in the radiative phase space, achieves a sizeable reduction of negative-weight events at little computational cost. The method does not induce any biases in physical distributions.
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| 5. |
- Frederix, Rikkert, et al.
(author)
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Electroweak corrections to the angular coefficients in finite- pT Z-boson production and dilepton decay
- 2020
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:10
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Journal article (peer-reviewed)abstract
- We present next-to-leading order (NLO) electroweak corrections to the dominant five angular coefficients parametrizing the Drell–Yan process in the Z-boson mass peak range for finite-pT vector boson production. The results are presented differentially in the vector boson transverse momentum. The Lam–Tung violating difference A- A2 is examined alongside the coefficients. A single lepton transverse momentum cut is needed in the case of electroweak corrections to avoid a double singularity in the photon induced diagrams, and the dependence on the value of this cut is examined. We compare the electroweak corrections to the angular coefficients to the NLO QCD corrections, including the single lepton cut. The size of the single lepton cut is found to affect the two coefficients A and A2 to largest extent. The relative size of the electroweak corrections to the coefficients is moderate for all single lepton cut values, and by extrapolation to the inclusive results, is moderate also for the full dilepton phase space case. However, for the Lam–Tung violation, there is a significant contribution from the electroweak corrections for low pT of the lepton pair.
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| 6. |
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| 7. |
- Frederix, Rikkert, et al.
(author)
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Matrix element corrections in top quark decays for the tt¯W± process
- 2024
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In: European Physical Journal C. - 1434-6044. ; 84:4
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Journal article (peer-reviewed)abstract
- We present a method that allows enabling matrix element corrections (MECs) in Pythia8 with MC@NLO matching, without incurring double counting. MECs are an interesting feature that may contribute to the accuracy of theoretical predictions, alongside matching and merging. We directly compare our method to a specific choice of settings in Pythia8, which can remove double-counting for MECs in certain processes. We show results by taking the tt¯W process as an example. This choice allows us to study the impact of decay MECs in the 2SSℓ and 3ℓ final states. We find that jet-related observables receive these corrections unevenly throughout the phase space. They can contribute up to ±6% in certain regions.
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| 8. |
- Frederix, Rikkert, et al.
(author)
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On improving NLO merging for t t ¯ W production
- 2021
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In: Journal of High Energy Physics. - 1029-8479. ; 2021:11
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Journal article (peer-reviewed)abstract
- We introduce an improvement to the FxFx matrix element merging procedure for pp →tt¯ W production at NLO in QCD with one and/or two additional jets. The main modification is an improved treatment of jets that are not logarithmically enhanced in the low transverse-momentum regime. We provide predictions for the inclusive cross section and the tt¯ W differential distributions including parton-shower effects. Taking also the NLO EW corrections into account, this results in the most-accurate predictions for this process to date. We further proceed to include the on-shell LO decays of the tt¯ W including the tree-level spin correlations within the narrow-width approximation, focusing on the multi-lepton signatures studied at the LHC. We find a ∼30% increase over the NLO QCD prediction and large non-flat K-factors to differential distributions.
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| 9. |
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| 10. |
- Frederix, Rikkert, et al.
(author)
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Probing the spin correlations of tt¯ production at NLO QCD+EW
- 2021
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:9
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Journal article (peer-reviewed)abstract
- In this work we investigate the NLO QCD+EW corrections to the top quark pair production and their effects on the spin correlation coefficients and asymmetries at fixed-order top quark pair production and LO decay in the dilepton channel, within the narrow-width approximation. The spin correlations are implicitly measured through the lepton kinematics. Moreover we study the EW effects to the leptonic differential distributions. We find that the EW corrections to the tt¯ production are within the NLO QCD theoretical uncertainties for the spin correlation coefficients and the leptonic asymmetries. On the other hand, for the differential distributions we find that the EW corrections exceed the NLO QCD scale uncertainty band in the high rapidity regimes and are of the order of the NLO QCD scale uncertainty in the case of invariant mass and transverse momentum distributions.
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| 11. |
- Frederix, Rikkert, et al.
(author)
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Subleading EW corrections and spin-correlation effects in tt¯ W multi-lepton signatures
- 2020
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:9
-
Journal article (peer-reviewed)abstract
- Recently a slight tension between data and predictions has been reported in tt¯ W production by both the CMS and ATLAS collaborations. We revisit the theoretical predictions for this process, focussing on the following two effects. We disentangle various effects that lead to asymmetries among the leptonic decay products of the (anti-)top quarks and W bosons, for which we find that the spin correlations in the top-quark pair are the dominant source. We also discuss the impact of the large, formally subleading, electroweak corrections to tt¯ W production at the LHC. We find that this effect changes the tt¯ W cross section significantly in the signature phase-space regions, and should therefore be included differentially in the theory to data comparisons.
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| 12. |
- Frederix, Rikkert, et al.
(author)
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The colour matrix at next-to-leading-colour accuracy for tree-level multi-parton processes
- 2021
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In: Journal of High Energy Physics. - 1029-8479. ; 2021:12
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Journal article (peer-reviewed)abstract
- We investigate the next-to-leading-colour (NLC) contributions to the colour matrix in the fundamental and the colour-flow decompositions for tree-level processes with all gluons, one quark pair and two quark pairs. By analytical examination of the colour factors, we find the non-zero elements in the colour matrix at NLC. At this colour order, together with the symmetry of the phase-space, it is reduced from factorial to polynomial the scaling of the contributing dual amplitudes as the number of partons participating in the scattering process is increased. This opens a path to an accurate tree-level matrix element generator of which all factorial complexity is removed, without resulting to Monte Carlo sampling over colour.
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| 13. |
- Valassi, Andrea, et al.
(author)
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Challenges in Monte Carlo Event Generator Software for High-Luminosity LHC
- 2021
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In: Computing and Software for Big Science. - : Springer Science and Business Media LLC. - 2510-2044 .- 2510-2036. ; 5:1
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Journal article (peer-reviewed)abstract
- We review the main software and computing challenges for the Monte Carlo physics event generators used by the LHC experiments, in view of the High-Luminosity LHC (HL-LHC) physics programme. This paper has been prepared by the HEP Software Foundation (HSF) Physics Event Generator Working Group as an input to the LHCC review of HL-LHC computing, which has started in May 2020.
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