# First joint measurement of $R(D^*)$ and $R(D^0)$ at LHCb

- Institution: CERN
- Department: LHC Seminar
- Speaker: Gregory Max Ciezarek
- Year: 2022
- Language: English
- Source: [CERN](https://videos.cern.ch/record/3011067)
- Licence: [CERN](http://copyright.web.cern.ch)
- Who can watch: Teens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

Previous measurements of the ratio of semileptonic decays $R(D^{*})=B(B \to D^{*} \tau^+ \nu) / B(B \to D^{*} \mu^+ \nu)$ and $R(D^0)=B(B \to D^0 \tau^+ \nu) / B(B \to D^0 \mu^+ \nu)$ from Babar, Belle, and LHCb hint at a deviation from lepton universality. This seminar presents the first joint measurement of both $R(D^*)$ and $R(D^0)$ at LHCb, reconstructed with the $\tau^+ \to \mu^+ \nu \bar{\nu}$ decay mode in the $D^{*+} \mu$ and $D^0 \mu$ final states and assuming isospin symmetry. This pathfinder analysis is based on Run 1 data. This result supersedes the previous LHCb measurement of $R(D^{(*+)})$ alone with the muonic decay of the tau. .

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## Lectures

1. [First joint measurement of $R(D^*)$ and $R(D^0)$ at LHCb](https://invisiblenetwork.ai/learn/cern/3011067/4d2d7b1e836b), 1 h 11 min (CERN's player)