  Neutron diffraction and calorimetric measurements are used to study the
field-induced quantum phase transition in
piperazinium-Cu$_2$(Cl$_{1-x}$Br$_x$)$_6$ ($x=0$, x=3.5% and x=7.5%), a
prototypical quantum antiferromagnet with random bonds. The critical indexes
$\phi$ and $\beta$ are determined. The findings contradict some original
predictions for Bose Glass based on the assumption $z=d$, but are consistent
with recent theoretical results implying $z<d$. Inelastic neutron experiments
reveal that disorder has a profound effect on the lowest-energy magnetic gap
excitation in the system.
