  We present our results on open beauty production in proton-nucleus collisions
for the recent LHC $p$Pb run at $\sqrt{s_{NN}}$=5 TeV. We have analysed the
effect of the modification of the gluon PDFs in nucleus at the level of the
nuclear modification factor. Because of the absence of measurement in $pp$
collisions at the same energy, we also propose the study of the
forward-to-backward yield ratio in which the unknown proton-proton yield
cancel. Our results are compared with the data obtained by LHCb collaboration
and show a good agreement.
