Impact of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi mathvariant="normal">Λ</mml:mi><mml:mi>b</mml:mi></mml:msub><mml:mo stretchy="false">→</mml:mo><mml:msub><mml:mi mathvariant="normal">Λ</mml:mi><mml:mi>c</mml:mi></mml:msub><mml:mi>τ</mml:mi><mml:mi>ν</mml:mi></mml:math> measurement on new physics in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>b</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>c</mml:mi><mml:mi>l</mml:mi><mml:mi>ν</mml:mi></mml:math> transitions
Marco Fedele, Monika Blanke, Andreas Crivellin, Syuhei Iguro, Teppei Kitahara, Ulrich Nierste, Ryoutaro Watanabe
Abstract
Measurements of the branching ratios of $B\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\tau}\overline{\ensuremath{\nu}}/B\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\ell}\overline{\ensuremath{\nu}}$ and ${B}_{c}\ensuremath{\rightarrow}J/\ensuremath{\psi}\ensuremath{\tau}\overline{\ensuremath{\nu}}/{B}_{c}\ensuremath{\rightarrow}J/\ensuremath{\psi}\ensuremath{\ell}\overline{\ensuremath{\nu}}$ by the BABAR, Belle and LHCb collaborations consistently point towards an abundance of taus compared to channels with light leptons. However, the ratio ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}\ensuremath{\tau}\overline{\ensuremath{\nu}}/{\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}\ensuremath{\ell}\overline{\ensuremath{\nu}}$ shows a relative deficit in taus. In this paper, we critically address whether data still points towards a coherent pattern of deviations, in particular in light of the sum rule relating these decays in a model-independent way. We find that no common new physics explanation of all ratios is possible (within $2\ensuremath{\sigma}$ or $1.5\ensuremath{\sigma}$, depending on the $\mathcal{R}({\mathrm{\ensuremath{\Lambda}}}_{c})$ normalization to light lepton channels). While this inconsistency could be a statistical fluctuation, further measurements are required in order to converge to a coherent pattern of experimental results.