HEP Colloquia 2024

by Yossathorn Tawabutr

Friday 17 May 2024, 14:30 → 16:00 Europe/Rome

Sala Consiliare (Department of Physics)

 Small-$x$ Evolution of Polarized TMDs 

The proton spin puzzle is a longstanding in particle physics: how much spin of the proton comes from the orbital and spin angular momenta of quarks and gluons inside? Especially challenging to study are such contributions from the region of small Bjorken-$x$, where large center-of-mass energy would be required to directly obtain the experimental measurements. In our recent works, we developed the light-cone operator treatment (LCOT) method that allows one to study leading-twist quark transverse-momentum-dependent parton distribution functions (TMDs) at small $x$ via the amplitudes in the polarized version of the dipole model, in term of which the small-$x$ evolution equations for TMDs are derived. Subsequently, the evolution equations are solved in the large-$N_c$, linearized, double-logarithmic approximation (DLA), which eventually yield the small-$x$ asymptotics of all the polarized leading-twist, flavor-singlet quark TMDs. The effects of quark exchanges and the progress on global analysis will also be discussed for the case of helicity TMD.