The four-loop splitting functions determine the scale evolution of the parton distribution functions to N3LO in QCD and are required for precision physics at the LHC. I will introduce a theoretical framework to compute these quantities and discuss some recent results and phenomenological applications.
Wednesday, 20th December 2023, 14:30 — Sala Wataghin
I will discuss the calculation of the complete two-loop QCD corrections for the production of three photons at the LHC, including subleading colour contributions. The two-loop numerical unitarity approach used previously for the planar contributions is extended to handle five-point non-planar topologies. Analytic expressions for the two-loop remainders are reconstructed and simplified using spinor-helicity variables. The analytic results we obtain are found to be numerically stable and rarely require muti-precision recovery strategies. Finally, we explore the numerical size of the subleading-color contribution to the two-loop hard functions, and find them to be potentially relevant to achieve theoretical predictions at the 1% precision level.
Wednesday, 19th April 2023, 14:30 — Sala Wataghin
I present the first calculation of the next-to-next-to-leading order (NNLO) QCD radiative corrections to the production of a W boson in association with massive bottom quarks (Wbb) at the LHC. Retaining the dependence on the bottom quark mass is crucial to ensure the infrared safety of the perturbative calculation and avoids ambiguities associated with the correct flavour assignment in massless computations. This paves the way to a more realistic comparison with experimental data.
One of the main bottlenecks of the calculation is provided by the complexity of the corresponding two-to-three two-loop virtual amplitude with three massive legs, beyond the current state of art. Exploiting the hierarchy between the bottom quark mass and the characteristic energy scale of the process, a reliable expression has been obtained through a massification procedure applied to the available results for the massless case.
I present phenomenological results in proton–proton collisions at 13.6 TeV for inclusive Wbb production and within a fiducial region relevant for the associated production of a W boson and a Higgs boson decaying into a bottom-quark pair, for which Wbb production represents one of the most relevant backgrounds. NNLO corrections are substantial and their inclusion is mandatory to obtain reliable predictions.
Wednesday, 3rd May 2023, 14:30 — Sala Wataghin
In this talk we present the latest results of the MAP collaboration about the extraction of Transverse-Momentum-Dependent (TMD) distributions at the N3LL logarithmic accuracy. We discuss the extraction of unpolarized quark TMD Parton Distribution Functions (TMD PDFs) in the proton and in the pion, as well as TMD Fragmentation Functions (TMD FFs), from global fits of Drell-Yan and Semi-Inclusive Deep-Inelastic Scattering (SIDIS) data sets.
Wednesday, 17th May 2023, 14:30 — Sala Wataghin
I will give an introduction to the problem of exotic multiquark hadrons. Specifically, I will discuss their most exotic properties and the question regarding their internal structure. I will then give an overview of a handful of observable that can discriminate in a clear way between different possibilities. I will mostly focus on the most notable state: the X(3872). In particular, I will discuss what conclusions can be drawn from the measurement of its prompt production cross section, and from the study of its effective range, extracted from low energy DD* scattering.
Wednesday, 7th June 2023, 14:30 — Sala Wataghin
Precise theoretical predictions are a key ingredient in ongoing tests of the Standard Model and in searches for physics beyond it. Since its inception twenty years ago, Soft Collinear Effective Theory (SCET) has been successfully applied to improve the precision of many important observables in collider physics. It is now standard practice to use SCET to derive factorization theorems and apply renormalization group (RG) methods to achieve leading power resummation of large logarithms that appear in regions of phase space with disparate energy scales. In this talk, I will discuss the recent developments in taking the step beyond the leading term in the power expansion. Focusing on the threshold Drell-Yan process, I will explain how the general factorization formula can be derived and I will discuss new objects that emerge beyond leading power: collinear jet functions and generalized soft functions. I will also explain challenges in resummation at LL and beyond at next-to-leading power.
Wednesday, 14th June 2023, 14:30 — Sala Wataghin
Quarkonia are a perfect tool for testing QCD and hadronisation. Plenty of data from hadron-hadron and lepton-hadron colliders are available, but there is still a debate on the quarkonium production mechanism. Among different models for quarkonium production, the Colour Singlet Model (CSM), the Colour Evaporation Model (CEM), and the Non-Relativistic QCD (NRQCD) framework are the most used ones.
Within the NRQCD, a double expansion in $\alpha_s$ and in $v$, the heavy quark-antiquark pair relative velocity, is done, and the hadronisation of partons into a quarkonium is described in terms of Long-Distance Matrix Elements (LDMEs). Current LDME fits cannot describe at the same time the quarkonium production in different processes (as hadroproduction or photoproduction). To this extent, re-examining some of these processes in the CSM (that represents the leading-$v$ contribution of NRQCD) may be helpful for easing some of the issues currently faced in quarkonium physics.
In this talk, we present some recent studies on inclusive quarkonium photoproduction at lepton-hadron colliders at NLO in QCD in the CSM. First, we focus on transverse momentum differential cross sections for J/$\psi$ production. We show how, by properly accounting for some contributions as the feed-downs and the associated J/$\psi$+charm production, the photoproduction data from HERA can be described within the CSM. Then, we analyse the issue of negative integrated cross sections for inclusive quarkonium photoproduction at NLO in QCD. A solution to this problem is proposed, and predictions for future colliders such as the EIC and LHeC are given.
Wednesday, 28th June 2023, 14:30 — Sala Wataghin