Photons in the proton: implications for the LHC

We present NNPDF4.0MC, a variant of the NNPDF4.0 set of parton distributions (PDFs) at LO, NLO and NNLO, with and without inclusion of the photon PDF, suitable for use with Monte Carlo (MC) event generators, which require PDFs to satisfy additional constraints in comparison to standard PDF sets. These requirements include PDF positivity down to a low scale Q ~ 1 GeV, smooth extrapolation in the very small and large x regions, and numerically stable results even in extreme regions of phase space for all PDFs. We compare the NNPDF4.0MC PDFs to their baseline NNPDF4.0 counterparts, and to the NNPDF2.3LO set entering the Monash tune of the Pythia8 event generator. We briefly assess the phenomenological impact of these PDFs on the cross-sections for hard and soft QCD processes at the LHC.

LO, NLO, and NNLO parton distributions for LHC event generators

Cruz-Martinez,

Forte,

Laurenti

et al. 2024

NLO corrections to triple vector-boson production in final states with three charged leptons and two jets

Denner,

Lombardi,

Lopez Portillo Chavez

et al. 2024

Tri-boson production together with vector-boson scattering is a privileged channel to study the electroweak structure of the Standard Model. Upcoming LHC running stages will allow to measure these processes at unprecedented accuracy and for all possible final states, which requires to push theory predictions to still unexplored frontiers. In this work we present the first calculation for the process pp → μ+μ−e+νejj at the LHC in a tri-boson phase space. We evaluate the three LO contributions, namely the $$ \mathcal{O} $$ O (α6), which contains the genuine tri-boson signature, along with the $$ \mathcal{O} $$ O (αsα5) and $$ \mathcal{O} $$ O ($$ {\alpha}_{\textrm{s}}^2 $$ α s 2 α4), and the two $$ \mathcal{O} $$ O (α7) and $$ \mathcal{O} $$ O (αsα6) NLO corrections. The calculation is based on full Standard-Model matrix elements, including all resonant and non-resonant terms, complete spin correlations and interference effects. Integrated and differential cross sections are presented for a fiducial region inspired by High Luminosity LHC prospect studies. We find electroweak corrections of −14% for the fiducial cross section, almost twice as large as for other tri-boson processes.

An FONLL prescription with coexisting flavor number PDFs

Barontini,

Candido,

Hekhorn

et al. 2024

We present a new prescription to account for heavy quark mass effects in the determination of parton distribution functions (PDFs) based on the FONLL scheme. Our prescription makes explicit use of the freedom to choose the number of active flavors at a given scale and, thus, use coexisting PDFs with different active flavor number. This new prescription is perturbatively equivalent to the former but improves the implementation in two ways. First, it can be naturally generalized to account simultaneously for multiple heavy quark effects, such as charm and bottom effects, which can both be relevant at the same scale due to the small mass difference. Second, it can be trivially generalized to use at any fixed-order or collinear resummed accuracy, while previous prescriptions required ad-hoc expansions of the DGLAP evolution kernels for each coefficient. We supplement the paper with codes for the computation of deep inelastic scattering observables in this new prescription.