# Test of Lepton Flavour Universality using the B0 to D* tau nu decays at LHCb

Abstract : This thesis presents the measurement of the $\rdstar \equiv \frac{BR(B^0 \to D^{*-} \tau^+ \nu_\tau})}{BR(B^0 \to D^{*-} \mu^+ \nu_mu})}$ ratio with 2\invfb of $pp$ collisions collected at $\sqs=13\tev$ by \lhcb during 2015-2016 using 3-prong tau decays. The study comprises a test of the Lepton Flavour Universality in \btoclnu 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 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. The current relative statistical uncertainty on the $R(D^*)$ is 5.56\%.
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Theses

https://hal.archives-ouvertes.fr/tel-03100295
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Submitted on : Wednesday, January 6, 2021 - 3:33:04 PM
Last modification on : Monday, March 29, 2021 - 3:22:59 PM
Long-term archiving on: : Wednesday, April 7, 2021 - 8:32:32 PM

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• HAL Id : tel-03100295, version 1

### Citation

Dawid Gerstel. Test of Lepton Flavour Universality using the B0 to D* tau nu decays at LHCb. High Energy Physics - Experiment [hep-ex]. AMU - Aix Marseille Université, 2020. English. ⟨tel-03100295⟩

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