  We determine the initial condition for the small-$x$ evolution equation (BK)
from the HERA deep inelastic scattering data using a new parametrization that
also keeps the unintegrated gluon distribution positive. The obtained dipole
amplitude and its uncertainty estimate can be used to compute single inclusive
particle production in proton-proton and proton-nucleus collisions. We argue
that one has to use consistently the proton transverse area measured in DIS and
the total inelastic cross section when calculating the single inclusive cross
section. This leads to a midrapidity nuclear modification factor $R_{pA}$ that
approaches unity at large transverse momentum, independently of the
center-of-mass energy.
