  The production of beauty and charm quarks in ep interactions has been studied
with the ZEUS detector at HERA for exchanged four-momentum squared 5 < Q^2 <
1000 GeV^2 using an integrated luminosity of 354 pb^{-1}. The beauty and charm
content in events with at least one jet have been extracted using the invariant
mass of charged tracks associated with secondary vertices and the decay-length
significance of these vertices. Differential cross sections as a function of
Q^2, Bjorken x, jet transverse energy and pseudorapidity were measured and
compared with next-to-leading-order QCD calculations. The beauty and charm
contributions to the proton structure functions were extracted from the
double-differential cross section as a function of x and Q^2. The running
beauty-quark mass, m_b at the scale m_b, was determined from a QCD fit at
next-to-leading order to HERA data for the first time and found to be 4.07 \pm
0.14 (fit} ^{+0.01}_{-0.07} (mod.) ^{+0.05}_{-0.00} (param.) ^{+0.08}_{-0.05}
(theo) GeV.
