Beauty, charm and $F_L$ at HERA: new data vs. early predictions

TL;DR

This paper analyzes small-x charm and beauty structure functions at HERA using BFKL dynamics, comparing early theoretical predictions with recent experimental data, and discusses implications for the understanding of QCD vacuum exchanges.

Contribution

It extends previous BFKL-Regge phenomenology to new HERA data, highlighting the decoupling of subleading exchanges and providing updated predictions for structure functions.

Findings

Good agreement with 1999 predictions and 2006 H1 data for $F_2^c$ and $F_2^b$

Contradicts recent 2008 H1 results on $F_2^b$

Comparison of $F_L$ predictions with recent low-x data

Abstract

One of the well known effects of the asymptotic freedom is splitting of the leading-$\log$ BFKL pomeron into a series of isolated poles in complex angular momentum plane. Following our earlier works we explore the phenomenological consequences of the emerging BFKL-Regge factorized expansion for the small-$x$ charm ($F_2^c$) and beauty ($F_{2}^{b}$) structure functions of the proton. As we found earlier,the color dipole approach to the BFKL dynamics predicts uniquely decoupling of subleading hard BFKL exchanges from $F_2^c$ at moderately large $Q^{2}$. We predicted precocious BFKL asymptotics of $F_2^c(x,Q^2)$ with intercept of the rightmost BFKL pole $\alpha_{\Pom}(0)-1=\Delta_{\Pom}\approx 0.4$. High-energy open beauty photo- and electro-production probes the vacuum exchange at much smaller distances and detects significant corrections to the BFKL asymptotics coming from the subleading vacuum poles. In view of the accumulation of the experimental data on small-$x$ $F_{2}^{c}$ and $F_{2}^{b}$ we extended our early predictions to the kinematical domain covered by new HERA measurements.Our structure functions obtained in 1999 agree well with the determination of both $F_2^c$ and $F_2^b$ by the H1 published in 2006 but contradict to very recent (2008, preliminary) H1 results on $F_2^b$. We present also comparison of our early predictions for the longitudinal structure function $F_L$ with recent H1 data (2008) taken at very low Bjorken $x$. We comment on the electromagnetic corrections to the Okun-Pomeranchuk theorem.