Diffractive beauty photoproduction as a short distance probe of QCD pomeron

Abstract

High-energy open beauty photoproduction probes the vacuum exchange at distances $\sim 1/m_b$ and detects significant corrections to the BFKL asymptotics coming from the subleading vacuum poles. We show that the interplay of leading and subleading vacuum exchanges gives rise to the cross section $\sigma^{b\bar b}(W)$ growing much faster than it is prescribed by the exchange of the leading pomeron trajectory with intercept $\alpha_{\Pom}(0)-1=\Delta_{\Pom}=0.4$. Our calculations within the color dipole BFKL model are in agreement with the recent determination of $\sigma^{b\bar b}(W)$ by the H1 collaboration. The comparative analysis of diffractive photoproduction of beauty, charm and light quarks exhibits the hierarchy of pre-asymptotic pomeron intercepts which follows the hierarchy of corresponding hardness scales. We comment on the phenomenon of decoupling of soft and subleading BFKL singularities at the scale of elastic $\Upsilon(1S)$-photoproduction which results in precocious color dipole BFKL asymptotics of the process $\gamma p \to \Upsilon p$.