Very low <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>x</mml:mi></mml:math> gluon density determined by LHCb exclusive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>J</mml:mi><mml:mo stretchy="false">/</mml:mo><mml:mi>ψ</mml:mi></mml:math> data
Chris A. Flett, A. D. Martin, M. G. Ryskin, T. Teubner
Abstract
The low $x$ behavior of the gluon density $xg(x,{\ensuremath{\mu}}^{2})$ at scale ${\ensuremath{\mu}}^{2}=2.4\text{ }\text{ }{\mathrm{GeV}}^{2}$ is determined using exclusive $J/\ensuremath{\psi}$ production data from HERA and LHCb within the framework of collinear factorization at next-to-leading order (NLO). It is shown that in the interval $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}<x<{10}^{\ensuremath{-}3}$ the gluon distribution function grows as $xg(x,{\ensuremath{\mu}}^{2})\ensuremath{\propto}{x}^{\ensuremath{-}\ensuremath{\lambda}}$ with $\ensuremath{\lambda}=0.135\ifmmode\pm\else\textpm\fi{}0.006$. The impact this experimental data will have for the global parton distribution function (PDF) analyses in this low $x$ domain is quantified. No indication in favour of parton density saturation is observed.