| 1. |
- Frederix, Rikkert, et al.
(författare)
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Electroweak corrections to the angular coefficients in finite- pT Z-boson production and dilepton decay
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:10
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Frederix, Rikkert, et al.
(författare)
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Probing the spin correlations of tt¯ production at NLO QCD+EW
- 2021
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:9
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Frederix, Rikkert, et al.
(författare)
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The colour matrix at next-to-leading-colour accuracy for tree-level multi-parton processes
- 2021
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2021:12
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Junker, Olov, et al.
(författare)
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Electromagnetic form factors of the transition from the spin-3/2 Σ to the Λ hyperon
- 2020
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Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society (APS). - 0556-2813 .- 1089-490X. ; 101:1
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Tidskriftsartikel (refereegranskat)abstract
- The three electromagnetic form factors for the transition from a spin-3/2 Σ* hyperon to the ground-state Λ hyperon are studied. At low energies, combinations of the transition form factors can be deduced from Dalitz decays of the Σ* hyperon to Λ plus an electron-positron pair. It is pointed out how more information can be obtained with the help of the self-analyzing weak decay of the Λ. In particular, it is shown that these transitionform factors are complex quantities already in this kinematical region. Such measurements are feasible at hyperon factories such as, for instance, the Facility for Antiproton and Ion Research (FAIR). At higher energies, the transition form factors can be measured in electron-positron collisions. The transition form factors are related to decay distributions and differential cross sections. Using dispersion theory, the low-energy electromagneticform factors for the Σ*-to-Λ transition are related to the pion vector form factor. The additionally required input, i.e., the two-pion–Σ*–Λ amplitudes, is determined from relativistic next-to-leading-order (NLO) baryon chiralperturbation theory, including the baryons from the octet and the decuplet. A poorly known NLO parameter is fixed to the experimental value of the Σ*→Λ γ decay width. Pion rescattering is taken into account by using dispersion theory and solving a Muskhelishvili-Omnès equation. Subtracted and unsubtracted dispersion relations are discussed. However, in view of the fact that the transition form factors are complex quantities, the current data situation does not allow for a full determination of the subtraction constants. To reduce the numberof free parameters, unsubtracted dispersion relations are used to make predictions for the transition form factors in the low-energy space- and timelike regions.
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| 5. |
- Pagani, Davide, et al.
(författare)
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Improving NLO QCD event generators with high-energy EW corrections
- 2024
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Ingår i: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 84:5
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Tidskriftsartikel (refereegranskat)abstract
- In this work we present a new method for the combination of electroweak (EW) corrections at high energies, the so-called EW Sudakov logarithms (EWSL), and next-to-leading-order QCD predictions matched to parton-shower simulations (NLO+PS). Our approach is based on a reweighting procedure of NLO+PS events. In particular, both events with and without an extra hard emission from matrix elements are consistently reweighted via the inclusion of the corresponding EWSL contribution. We describe the technical details and the implementation in the MadGraph5_aMC@NLO framework. Via a completely automated procedure, events at this level of accuracy can be obtained for a vast class of hadroproduction processes. As a byproduct we provide results for phenomenologically relevant physical distributions from top-quark pair and Higgs boson associated production (t¯tH) and from the associated production of three Z gauge bosons (ZZZ).
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| 6. |
- Pellen, Mathieu, et al.
(författare)
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Angular coefficients in W + j production at the LHC with high precision
- 2022
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 82:8
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Tidskriftsartikel (refereegranskat)abstract
- The extraction of the W-boson mass, a fundamental parameter of the Standard Model, from hadron-hadron collision requires precise theory predictions. In this regard, angular coefficients are crucial to model the dynamics of W-boson production. In this work, we provide, for the first time, angular coefficients at NNLO QCD + NLO EW accuracy for finite transverse momentum W-boson at the LHC. The corrections can reach up to 10 % in certain regions of phase space. They are accompanied by a significant reduction of the scale uncertainty. This work should, besides providing reference values for theory-data comparison, provide state-of-the-art theory input for W-boson mass measurements.
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| 7. |
- Vitos, Timea
(författare)
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Precision Standard Model Phenomenology for High Energy Processes
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present status of particle physics is that the Standard Model has been completed with the discovery of theHiggs boson in 2012, but there is a multitude of phenomena in nature which is not accounted for by this model.Researchers are investigating possibilities for detecting new physics at the current particle physics facilities, withthe Large Hadron Collider (LHC) at the frontier. As no significant sign of new physics has been observed as oftoday, precision phenomenology becomes increasingly important. This thesis and the four papers included in itcontribute to this field of precision predictions for various important processes at the LHC.In paper I and paper IV, the Drell-Yan process is investigated, and specifically, the decay coefficients whichparameterize the spherical distribution of the outgoing leptons in the process. In the first work, we investigatethe next-to-leading-order (NLO) electroweak corrections to the coefficients of the neutral-current process. In thesecond work, a similar study, but including also next-to-next-to-leading-order quantum chromodynamic (QCD)corrections, is performed for the decay coefficients of the charged-current Drell-Yan process. The latter processand the corresponding coefficients are of great importance for measuring the W boson mass at the LHC.In paper II, the top quark pair production and the spin correlations for the process are investigated. The spincorrelation information of the top quarks may reveal underlying new physics when probed at high precision.Therefore, this work computes approximate complete-NLO corrections, including electroweak corrections to thespin correlation coefficients and related leptonic distributions, contributing to the state-of-the-art high precisionStandard Model predictions for these observables.Finally, paper III is the theoretical base of a crucial improvement to matrix-element generators. We proposein this paper to utilize a next-to-leading-colour truncation of the colour matrix in the large-Nc limit, in order toreduce the complexity of the cross section computation when a large number of QCD patrons are involved in theprocess. The results suggest that such a truncation of the colour expansion will facilitate for efficient computationof multi-jet events, which are a dominant background for many important processes and new physics searches athadron colliders, such as the LHC.
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| 8. |
- Vitos, Timea
(författare)
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W-boson angular coefficients at LHC at high precision
- 2023
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Ingår i: Proceedings of the Tenth Annual Conference on Large Hadron Collider Physics. - Trieste, Italy : Sissa Medialab. - 1824-8039. ; 422
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Konferensbidrag (refereegranskat)abstract
- We present state-of-the-art high-precision theory predictions for the dominant angular coefficients parametrizing the spin-correlations in the production and decay of a W-boson produced at transverse momentum larger than 30 GeV. The computation at NNLO QCD and NLO EW accuracy are combined to obtain differential distributions in the W-boson transverse momentum and rapidity. The found results show up to 10 % corrections in certain regions of phase space, while the scale bands are significantly reduced as compared to NLO QCD.
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