STAT-TMDs: A statistical approach to TMD studies

ongoing

The description of the proton properties and its internal structure is still a challenging issue within Quantum Chromodynamics (QCD), the theory of strong interaction. The standard one-dimensional picture, encoded in collinear parton distribution functions (PDFs), is not able to explain the proton spin budget in terms of quark and gluon spin. A new class of parton distributions, including intrinsic transverse momentum effects, has then been introduced: the Transverse Momentum Dependent PDFs (TMDs). By encoding the correlation between the proton/parton spin and the parton intrinsic transverse momentum, they can provide a much richer and detailed picture: a 3D image of the proton. TMDs are now of great interest in hadron and spin physics, being able to describe several experimental observables at moderate and high energy. At the same time, they represent a perfect ground for testing fundamental properties of QCD, such as universality and factorisation. STAT-TMDs aims at building an improved statistical framework for studies of TMDs, applying for the first time modern statistical techniques to TMD analyses. Through a bottom-up approach, I will provide new and more robust phenomenological extractions of (un)polarised quark and gluon TMDs, carefully assessing the uncertainties in the data and extrapolation regions. This will eventually allow, thanks to global Bayesian reweighting techniques, for a quantitative estimate of factorisation breaking effects in inclusive polarised hadronic reactions. The project represents a timely effort, as it has the ambition to determine a new standard for the hadron physics community, and to set the ground for the future precision era of TMD studies, when data from the future US Electron-Ion Collider and fixed-target programs at the LHC will come.