Effect of future B_c → τν_τ measurements to constrain new physics in the b → cℓν_ℓ transition.

Sikkens, Mike (2025) Effect of future B_c → τν_τ measurements to constrain new physics in the b → cℓν_ℓ transition. Master's Thesis / Essay, Physics.

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Abstract

Anomalies in semileptonic B meson decays—particularly in the observables R(D) and R(D∗)—suggest possible violations of lepton flavour universality and point toward physics beyond the Standard Model (SM). In this thesis, I investigate the potential of the purely leptonic decay Bc → τν to further constrain New Physics (NP) contributions in the transition b → cℓν within the framework of Effective Field Theory (EFT). I build upon the framework created by R. Fleischer and others, using a complete basis of dimension-6 operators, and focus on scenarios involving pseudoscalar and left-handed vector operators, motivated by their direct contributions to the observables under study. A global fit is performed using the GammaCombo fitting framework which includes the latest measurements of R(D), R(D∗), Re/μ, and FL(D∗), along with the SM prediction and projected experimental uncertainty for a B(Bc → τν) measurement at LHCb. The inclusion of Bc → τν significantly improves constraints on the pseudoscalar Wilson coefficient C^{c,τ}_P , reducing the allowed parameter space by a factor of approximately 6.6. In multi-parameter scenarios, it provides a complementary constraint where other observables fail to do so. These results demonstrate the crucial role of leptonic decays in shaping modelindependent bounds on NP contributions and emphasize the importance of future experimental measurements of Bc → τν for resolving current tensions in flavour physics.

Item Type:	Thesis (Master's Thesis / Essay)
Supervisor name:	Bruyn, K.A.M. de
Degree programme:	Physics
Thesis type:	Master's Thesis / Essay
Language:	English
Date Deposited:	05 Aug 2025 08:23
Last Modified:	05 Aug 2025 08:23
URI:	https://fse.studenttheses.ub.rug.nl/id/eprint/36542

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