XXVIII International Workshop on Deep Inelastic Scattering and Related Subjects

Helicity at Small x: Bringing Back the Quarks

24 Mar 2020, 15:06

18m

Brooklyn, NY

Contributed Talk Small-x, Diffraction and Vector Mesons Joint Session: WG2+WG5

Speaker

Yossathorn Tawabutr (The Ohio State University)

Description

We find the small-$x$ asymptotics of the quark helicity distribution in the large-$N_c$ & $N_f$ limit by numerically solving small-$x$ evolution equations derived in earlier works, where $N_c$ is the number of quark colors and $N_f$ is the number of quark flavors. Previously, those evolution equations were solved only in the large-$N_c$ limit. We find that $\mathrm{\Delta }q$ oscillates as a function of $\ln (1/x)$ at small $x$, with the oscillation frequency being dependent on the number of quark flavors, $N_f$. Our result may account for the apparent oscillation in the strange quark helicity distribution $\mathrm{\Delta }s$ as a function of Bjorken $x$. For $N_f=0$, these oscillations disappear; this is why they were not seen in the earlier large-$N_c$ studies. Our work presents the most precise theoretical determination of the small-$x$ asymptotics of the quark helicity distribution based on the Wilson line approach to small-$x$ evolution. When combined with the future EIC data, our approach should allow for a precise determination of the amount of the proton spin coming from small-$x$ partons, thus contributing to the resolution of the proton spin puzzle.