  Using 7.3 pb-1 of ppbar collisions collected by the D0 detector at the
Fermilab Tevatron, we measure the distribution of the variable \phistar, which
probes the same physical effects as the Z/gamma* boson transverse momentum, but
is less susceptible to the effects of experimental resolution and efficiency. A
QCD prediction is found to describe the general features of the \phistar
distribution, but is unable to describe its detailed shape or dependence on
boson rapidity. A prediction that includes a broadening of transverse momentum
for small values of the parton momentum fraction is strongly disfavored.
