Interpreting LHCb's ${\Lambda }_b\to {\Lambda }_c\tau \bar{\nu }$ measurement and puzzles in semileptonic ${\Lambda }_b$ decays

Abstract

Normalizing the recent LHCb measurement of ${\Lambda }_b\to {\Lambda }_c\tau \bar{\nu }$ to the standard model (SM) prediction for the ${\Lambda }_b\to {\Lambda }_c\mu \bar{\nu }$ rate, instead of a LEP measurement, provides a more consistent comparison with the SM prediction for the lepton flavor universality ratio $R({\Lambda }_c)$. This modestly increases $R({\Lambda }_c)$ compared to the quoted LHCb result, such that it no longer hints at a suppression compared to the SM, which would be hard to accommodate in new physics scenarios that enhance $R(D^{(\ast )})$. We point out that the fraction of excited states in inclusive semileptonic ${\Lambda }_b$ decay may be significantly greater than the corresponding fraction in $B$ decays. Possible implications are speculated upon.

arXiv comment3 pages

References in corpus (18)

• Inclusive Semileptonic B and Polarized Lambda_b Decays from QCD
• Averages of $b$-hadron, $c$-hadron, and $\tau$-lepton properties as of 2018
• ${\Lambda }_b\to p{\ell }^{-}{\bar{\nu }}_{\ell }$ and ${\Lambda }_b\to {\Lambda }_c{\ell }^{-}{\bar{\nu }}_{\ell }$ form factors from lattice QCD with relativistic heavy quarks
• Three loop calculations and inclusive $V_{cb}$
• Second Order Power Corrections in the Heavy Quark Effective Theory II. Baryon Form Factors
• Observation of the decay ${\Lambda }_b^0\to {\Lambda }_c^{+}{\tau }^{-}{\overline{\nu }}_{\tau }$
• Predictions for nonleptonic Lambda_b and Theta_b decays
• Precise predictions for ${\Lambda }_b\to {\Lambda }_c$ semileptonic decays
• New predictions for ${\Lambda }_b\to {\Lambda }_c$ semileptonic decays and tests of heavy quark symmetry
• Measurements of the properties of Lambda_c(2595), Lambda_c(2625), Sigma_c(2455), and Sigma_c(2520) baryons
• Measurement of the shape of the ${\Lambda }_b^0\to {\Lambda }_c^{+}{\mu }^{-}\overline{\nu }$ differential decay rate
• Semileptonic ${\Lambda }_b\to {\Lambda }_c\ell {\bar{\nu }}_{\ell }$ Transition in Full QCD
• Das ist der HAMMER: Consistent new physics interpretations of semileptonic decays
• Precise predictions for B -> Xc tau nu decay distributions
• Measurement of the Lambda_b^0 Decay Form Factor
• First Measurement of the Ratio of Branching Fractions B(Lambda_b to Lambda_c mu nu)/B(Lambda_b to Lambda_c pi)
• On the nature of the lowest-lying odd parity charmed baryon ${\Lambda }_c(2595)$ and ${\Lambda }_c(2625)$ resonances
• Form Factor Counting and HQET Matching for New Physics in ${\Lambda }_b\to {\Lambda }_c^{\ast }l\nu$

Cited by in corpus (5)

• Impact of ${\Lambda }_b\to {\Lambda }_c\tau \nu$ measurement on New Physics in $b\to cl\nu$ transitions
• Global fit to $b\to c\tau \nu$ anomalies as of Spring 2024
• Review of Semileptonic $B$ Anomalies
• Prospects for $B_c^{+}$ and $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ at FCC-ee
• Hint of a new scalar interaction in LHCb data?