This thesis presents the measurements of the R(D*) = BF(B0->D*tau nu) / BF(B0->D*mu nu)
ratio with the 2015-2016 LHCb dataset using 3-prong tau decays.
The study comprises a test of the Lepton Flavour Universality in b->c l nu decays to help resolve the tension between the Standard Model R(D*)
estimation and the experimental results from the B-factories and LHCb.
The analysis builds upon a previous LHCb measurement ( 10.1103/PhysRevD.97.072013 and 10.1103/PhysRevLett.120.171802) with a new dataset and improved techniques.
Most importantly, a novel fast simulation technique, ReDecay, is used to generate large simulated samples and
Multivariate Analysis techniques are exploited in signal selection.
Since the analysis has yet to undergo an internal LHCb review, and several systematic uncertainties must be computed, the R(D*) value is blinded.
Nonetheless, nearly complete documentation of the analysis is presented in this thesis.