A $N_f=2+1+1$ "twisted" determination of the $b$-quark mass, $f_B$ and $f_{B_s}$

We present a lattice QCD determination of the $b$-quark mass and of the $f_{B_s}$ and $f_B$ decay constants performed with $N_f=2+1+1$ twisted mass Wilson fermions. We have used simulations at three values of the lattice spacing generated by ETMC with pion masses ranging from 210 to 440 MeV. To obtain physical quantities we performed a combined chiral and continuum limit and an extrapolation in the heavy quark mass from the charm to the $b$-quark region using suitable ratios calculated at nearby heavy-quark masses having an exactly known static limit. Our results are: $m_b(m_b)=4.29(13)$ GeV, $f_B = 196 (9)$MeV,$f_{B_s} = 235 (9)$MeV,$f_{B_s} / f_B = 1.201 (25)$,$(f_{B_s}/f_B)/(f_K/f_\pi) = 1.007 (16)$and$(f_{B_s}/f_B)/(f_{D_s}/f_D) = 1.008 (13)$.