Publications

Order by: publication date number of citations

• Exclusive emissions of rho-mesons and the unintegrated gluon distribution

  Andrèe Dafne Bolognino, Francesco Giovanni Celiberto, Dmitry Yu. Ivanov, Alessandro Papa

  SciPost Phys. Proc. 8, 089 (2022) · published 13 July 2022 | Toggle abstract · pdf

  Exclusive emissions of vector mesons in forward directions of rapidity offer us a faultless chance to probe the proton structure at small-$x$. A high-energy factorization formula is established within BFKL, given as the convolution of an impact factor depicting the forward-meson emission and of an unintegrated gluon distribution (UGD) driving the gluon evolution at small-$x$. As a nonperturbative quantity, the UGD is not well known and several models for it exist. We present recent progresses on the study of the exclusive forward $\rho$-meson leptoproduction at HERA and EIC energies, showing how osbervables sensitive to different polarization states of the $\rho$-particle act as discriminators for the existing UGD models.

  6 citations

• A general-mass scheme for prompt charm production at hadron colliders

  Keping Xie, John M. Campbell, Pavel M. Nadolsky

  SciPost Phys. Proc. 8, 084 (2022) · published 12 July 2022 | Toggle abstract · pdf

  In these proceedings, we apply the recently developed S-ACOT-MPS factorization scheme at the next-to-leading order to prompt charm production at hadron colliders. It provides a good agreement with experimental data on charm meson production measured by LHCb at 7 and 13 TeV. The low-$p_T$ data are on the margins of the theoretical error bands, emphasizing the importance of including contributions beyond the next-to-leading order.

  2 citations

• A model for $F_L$ structure function at low values of $Q^2$ and $x$ - revisited

  Barbara Badelek, Anna Stasto

  SciPost Phys. Proc. 8, 082 (2022) · published 12 July 2022 | Toggle abstract · pdf

  A reanalysis of the model for the longitudinal structure function $F_L (x,Q^2)$ at low $x$ and low $Q^2$ was undertaken, in view of the advent of the EIC. The model includes the kinematic constraint $F_L\sim Q^4$ as $Q^2\rightarrow$ 0. It is based on the photon-gluon fusion mechanism suitably extrapolated to the region of low $Q^2$. Revised model was critically updated, extended to the EIC kinematic region, and e.g. contains new parameterisations of the parton distribution functions.

• PineAPPL: NLO EW corrections for PDF processes

  Christopher Schwan

  SciPost Phys. Proc. 8, 079 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Modern parton distribution function (PDF) determinations either neglect higher-order corrections in the electroweak (EW) coupling or implement them approximately for a subset of PDF processes. We present a new tool, PineAPPL, which supports perturbative correction in arbitrary powers of the EW and strong coupling constant, and stores theoretical predictions independently of the used PDFs in so-called interpolation grids. These are the foundation of any PDF determination, and will allow us to perform a PDF fit taking into account EW corrections for all processes consistently. Apart from PDF determinations PineAPPL can also be used in precision phenomenology to study the impact of different choices of PDF sets, without rerunning the time-consuming computation. As an application of this tool we show Drell-Yan (DY) lepton-pair production were larger effects of NLO EW corrections can be seen that will potentially influence the PDF fit and comment about which observables are particularly suited and NLO EW PDF fit and which are not.

• NLO collinear factorization of large mass diphoton photoproduction amplitude

  Oskar Grocholski, Bernard Pire, Paweł Sznajder, Lech Szymanowski, Jakub Wagner

  SciPost Phys. Proc. 8, 078 (2022) · published 12 July 2022 | Toggle abstract · pdf

  We calculate large mass diphoton exclusive photoproduction in the framework of collinear QCD factorization at next to leading order in {\alpha}s and at leading twist. Collinear divergences of the coefficient function are absorbed by the evolution of the generalized parton distributions (GPDs). This result enlarges the existing factorization proofs to 2 -> 3 processes, opening new reactions to a trustable extraction of GPDs.

• Can $\overline{MS}$ parton distributions be negative?

  Alessandro Candido, Stefano Forte, Felix Hekhorn

  SciPost Phys. Proc. 8, 077 (2022) · published 12 July 2022 | Toggle abstract · pdf

  We review our recent paper, where we proved Parton distributions functions (PDFs) to be positive at NLO in the $\overline{MS}$ factorization scheme. We present some additional material that was useful in completing the steps for the actual proof, but we won't attempt to report on the full proof, but referring the reader to the paper itself.

• The photon content of the proton in the CT18 global analysis

  Keping Xie, T. J. Hobbs, Tie-Jiun Hou, Carl Schmidt, Mengshi Yan, C. -P. Yuan

  SciPost Phys. Proc. 8, 074 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Recently, two photon PDF sets based on implementations of the LUX ansatz into the CT18 global analysis were released. In CT18lux, the photon PDF is calculated directly using the LUX master formula for all scales, $\mu$. In an alternative realization, CT18qed, the photon PDF is initialized at the starting scale, $\mu_0$, using the LUX formulation and evolved to higher scales $\mu(>\mu_0)$ with a combined QED+QCD kernel at $\mathcal{O}(\alpha),~\mathcal{O}(\alpha\alpha_s)$ and $\mathcal{O}(\alpha^2)$. In the small-$x$ region, the photon PDF uncertainty is mainly induced by the quark and gluon PDFs, through the perturbative DIS structure functions. In comparison, the large-$x$ photon uncertainty comes from various low-energy, nonperturbative contributions, including variations of the inelastic structure functions in the resonance and continuum regions, higher-twist and target-mass corrections, and elastic electromagnetic form factors of the proton. We take the production of doubly-charged Higgs pairs, $(H^{++}H^{--})$, as an example of scenarios beyond the Standard Model to illustrate the phenomenological implications of these photon PDFs at the LHC.

• Physics from Photons at the LHC

  Lucian Harland-Lang

  SciPost Phys. Proc. 8, 072 (2022) · published 12 July 2022 | Toggle abstract · pdf

  LHC collisions can act as a source of photons in the initial state. This mechanism plays an important role in the production of particles with electroweak couplings, and a precise account of photon-initiated (PI) production at the LHC is a key ingredient in the LHC precision physics programme. I will discuss the possibility of modelling PI processes directly via the structure function approach. This can provide percent level precision in the production cross sections, and is therefore well positioned to account for LHC precision requirements. This formalism in addition allows one to make use of another useful feature of photons, namely that they are colour-singlet and can often be emitted elastically (or quasi-elastically) from the proton. I will discuss recent work on applications of the structure function approach to precision calculations of PI production in the inclusive mode, and to `exclusive' processes with rapidity gaps, which can provide a unique probe of the Standard Model and physics beyond it.

• What do DVCS data tell us about TCS observables?

  O. Grocholski, H. Moutarde, B. Pire, P. Sznajder, J. Wagner

  SciPost Phys. Proc. 8, 070 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Deeply virtual Compton scattering (DVCS) and timelike Compton scattering (TCS) leading twist amplitudes are intimately related thanks to their analytic properties as a function of $Q^2$. We exploit this feature to use Compton form factors previously extracted from available DVCS data and derive data-driven predictions for TCS observables to be measured in near future experiments. Our results quantitatively illustrate the complementarity of DVCS and TCS experiments.

• Opportunities for inclusive diffraction at EIC

  Wojciech Slominski, Nestor Armesto, Paul R. Newman, Anna Stasto

  SciPost Phys. Proc. 8, 069 (2022) · published 12 July 2022 | Toggle abstract · pdf

  The possibilities for inclusive diffraction in the Electron Ion Collider, EIC, in the US, are analyzed. We find that thanks to the excellent forward proton tagging, the EIC will be able to access a wider kinematical range of longitudinal momentum fraction and momentum transfer of the leading proton than at HERA. This opens up the possibility to measure subleading diffractive exchanges. The extended $t$-range would allow the precise extraction of 4-dimensional reduced cross section in diffraction. In addition, the varying beam energy setups at the EIC would allow for precise measurements of the longitudinal diffractive structure function.