Measurement of beauty production in DIS and F_2^bbbar extraction at ZEUS

TL;DR

The paper measures beauty-quark production in DIS via the $ep\to e b\bar{b}X\to e\,\mathrm{jet}\,\mu\,X'$ channel using ZEUS data from HERA, employing the $p_T^{\mathrm{rel}}$ distribution to separate $b$-quark decays and extracting both cross sections and the $F_2^{b\bar{b}}$ structure function. It compares measurements to LO+PS MC and NLO QCD predictions in the FFNS (Hvqdis) and assesses extrapolations to full phase space with hadronization corrections; systematic studies address muon detection, background shapes, fragmentation, energy scales, and luminosity. The results show reasonably good agreement in shape between data and predictions, with normalisation differences mainly in the low-$Q^2$, low-$x$ region, and provide extended measurements of $F_2^{b\bar{b}}$ down to $Q^2\approx3$ GeV$^2$ and $x\approx1.3\times10^{-4}$, aiding precision tests of perturbative QCD in DIS. Overall, the analysis reinforces the validity of perturbative approaches to heavy-flavor production in DIS while highlighting areas where theory underestimates data at the lowest kinematic scales.

Abstract

Beauty production in deep inelastic scattering with events in which a muon and a jet are observed in the final state has been measured with the ZEUS detector at HERA using an integrated luminosity of 114 pb^-1. The fraction of events with beauty quarks in the data was determined using the distribution of the transverse momentum of the muon relative to the jet. The cross section for beauty production was measured in the kinematic range of photon virtuality, Q^2 > 2 Gev^2, and inelasticity, 0.05 < y < 0.7, with the requirement of a muon and a jet. Total and differential cross sections are presented and compared to QCD predictions. The beauty contribution to the structure function F_2 was extracted and is compared to theoretical predictions.

Figures (5)

• Figure 1: Data (dots) compared to MC predictions (histograms) using the $p_T^{\mathrm{rel}}$-fit after final cuts, for which beauty (dashed), charm (dotted) and light flavours are combined (continous) as described in Section \ref{['sect:fit']} . The distributions of (a) $p_T^\mu$, (b) $\eta^\mu$, (c) $E_T^{\rm jet}$ and (d) $\eta^{\rm jet}$ are shown. Only statistical uncertainties are given.
• Figure 2: Measured $p_T^{\mathrm{rel}}$-distribution and fit from MC. Details as in Fig. \ref{['fig-contr']}.
• Figure 3: Differential beauty cross section as a function of the photon virtuality, $Q^2$, for events with at least one jet and one muon, compared to the Rapgap LO+PS MC normalised to the data, and compared to the Hvqdis NLO QCD calculations. The errors on the data points correspond to the statistical uncertainty (inner error bars) and to the statistical and systematic uncertainty added in quadrature (outer error bars). The shaded bands show the uncertainty of the theoretical prediction originating from the variation of the renormalisation and factorisation scales and the $b$-quark mass.
• Figure 4: Differential beauty cross section as a function of (a) $p_T^\mu$, (b) $\eta^\mu$, (c) $p_T^{\rm jet}$ and (d) $\eta^{\rm jet}$ compared to the Hvqdis NLO QCD calculations and to the scaled Rapgap MC. Other details as in Fig. \ref{['fig-crq2']}.
• Figure 5: $F_2^{b\bar{b}}$ as a function of $Q^2$. The errors on the data points (filled circles) correspond to the statistical uncertainty (inner error bars) and to the statistical and systematical uncertainty added in quadrature (outer error bars). The horizontal lines indicate the zero-line for each series of measurements. Results from previous measurements (open symbols) and from different QCD predictions (lines and band) are also shown. See Section 5 and Table 1 for details.