Abstract
We study a few basic photon- and lepton-initiated processes at the LHC which can be computed using the recently developed photon and lepton parton densities. First, we consider the production of a massive scalar particle initiated by lepton-antilepton annihilation and photon-photon fusion as representative examples of searches of exotic particles. Then we study lepton-lepton scattering, since this Standard-Model process may be observable at the LHC. We examine these processes at leading and next-to-leading order and, using the POWHEG method, we match our calculations to parton shower programs that implement the required lepton or photon initial-states. We assess the typical size of cross-sections and their uncertainties and discuss the preferred choices for the factorization scale. These processes can also be computed starting directly from the lepto-production hadronic tensor, leading to a result where some collinear-enhanced QED corrections are missing, but all strong corrections are included. Thus, we are in the unique position to perform a comparison of results obtained via the factorization approach to a calculation that does not have strong corrections. This is particularly relevant in the case of lepton-scattering, that is more abundant at lower energies where it is affected by larger strong corrections. We thus compute this process also with the hadronic-tensor method, and compare the results with those obtained with POWHEG. Finally, for some lepton-lepton scattering processes, we compare the size of the signal to the main quark-induced background, which is double Drell-Yan production, and outline a preliminary search strategy to enhance the signal to background ratio.
Highlights
Is extended to next-to-leading order (NLO) and even to higher orders, depending upon the accuracy of the available PDF
In order to understand the relative impact of the NLO corrections and the remaining uncertainties associated to missing higher orders, we show in figures 1, th√e LO and NLO cross sections for the γ-initiated process in proton-proton collisions at s = 13 TeV, as a function of the scalar mass and for different choices of the central factorization scale, normalised to the NLO one computed at a fixed reference scale μF = Mφ
In this paper we have used the recently developed photon and lepton PDFs to study the impact of NLO corrections to a number of /γ-initiated processes and their matching to a parton shower
Summary
In figure 9 and 10, we show the transverse momentum of the scalar resonance and of the leading lepton, comparing the pure shower results with the NLO+PS ones using Herwig. In figure 9 and 10, we show the transverse momentum of the scalar resonance and of the leading lepton, comparing the pure shower results with the NLO+PS ones using Herwig7 In this case, we find a qualitatively good agreement among them. In the region of small values of the transverse momentum of the leading lepton, we observe a discontinuity in the NLO+PS prediction related to the minimum pT allowed in the POWHEG generation This is not a crucial problem in the simulation of the production of high-mass states. The probability to have a q → qγ splitting for the first and a γ → ll for the second are parametrically of the same order
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