Probing Light Dark Fermions in B → D(*)ℓ Xinv via Rate Distributions
Abstract
Experimental analyses of the semileptonic decays $ B \to D^{(*)} \ell \barν$ typically rely on the assumption that the missing energy originates from a massless neutrino, as predicted by the Standard Model. However, this assumption may not hold in scenarios where the invisible final-state particle is instead massive, such as a sterile neutrino or a dark-sector fermion. In this work, we explore how the presence of a massive dark sector fermion modifies the kinematic and angular distributions of these decays. Our analysis is carried out within the framework of a general weak effective theory, and we also discuss effective and simplified models in which these interactions may arise. In addition, we study the implications of these effects for the extraction of the CKM matrix element $ |V_{cb}|$. Overall, our results show that relaxing the standard assumption of a massless neutrino can lead to observable effects and provide a framework for systematically investigating their impact on semileptonic B- decay distributions.
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BibTeX
@misc{kolay2026probing,
title = {{Probing Light Dark Fermions in $B \to D^(*)\ell X_\rm inv$ via Rate Distributions}},
author = {Lipika Kolay and Soumitra Nandi and Shantanu Sahoo and Ria Sain},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2606.21642},
eprint = {2606.21642},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.21642},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Probing Light Dark Fermions in B → D^(*)ℓ X_inv via Rate Distributions
AU - Lipika Kolay
AU - Soumitra Nandi
AU - Shantanu Sahoo
AU - Ria Sain
PY - 2026
DA - 2026/09/30
PB - arXiv
DO - 10.48550/arxiv.2606.21642
UR - https://arxiv.org/abs/2606.21642
AB - Experimental analyses of the semileptonic decays $ B \to D^{(*)} \ell \barν$ typically rely on the assumption that the missing energy originates from a massless neutrino, as predicted by the Standard Model. However, this assumption may not hold in scenarios where the invisible final-state particle is instead massive, such as a sterile neutrino or a dark-sector fermion. In this work, we explore how the presence of a massive dark sector fermion modifies the kinematic and angular distributions of these decays. Our analysis is carried out within the framework of a general weak effective theory, and we also discuss effective and simplified models in which these interactions may arise. In addition, we study the implications of these effects for the extraction of the CKM matrix element $ |V_{cb}|$. Overall, our results show that relaxing the standard assumption of a massless neutrino can lead to observable effects and provide a framework for systematically investigating their impact on semileptonic B- decay distributions.
ER -