PoS - Proceedings of Science
Volume 308 - QCD Evolution 2017 (QCDEV2017) - Tuesday, May 23, 2017- Morning 1
Gluon Helicity Distribution at Small x
Y. Kovchegov*, D. Pitonyak and M. Sievert
Full text: pdf
Published on: March 23, 2018
We determine the small-$x$ asymptotics of the gluon
helicity distribution in a proton at leading order in
perturbative QCD at large $N_c$. To achieve this, we begin by
evaluating the dipole gluon helicity TMD at small $x$. We then
construct and solve novel small-$x$ large-$N_c$ evolution
equations for the operator related to the dipole gluon
helicity TMD. Our main result is the small-$x$ asymptotics
for the gluon helicity distribution:
\Delta G \sim \left(
\frac{1}{x} \right)^{\alpha_h^G} \ \ \ \mbox{with} \ \ \ \alpha_h^G =
\frac{13}{4 \sqrt{3}} \, \sqrt{\frac{\as \, N_c}{2 \pi}}
\approx 1.88 \, \sqrt{\frac{\as \, N_c}{2 \pi}}.
We note that the power $\alpha_h^G$ is approximately 20$\%$ lower than
the corresponding power $\alpha_h^q$ for the small-$x$ asymptotics of
the quark helicity distribution defined by
\Delta q \sim \left(
\frac{1}{x} \right)^{\alpha_h^q} \ \ \ \mbox{with} \ \ \ \alpha_h^q =
\frac{4}{\sqrt{3}} \, \sqrt{\frac{\as \, N_c}{2 \pi}} \approx 2.31 \,
\sqrt{\frac{\as \, N_c}{2 \pi}}
found in our earlier work.
DOI: https://doi.org/10.22323/1.308.0018
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