Interpreting LHCb's Λb→Λcτν̄ measurement and puzzles in semileptonic Λb decays

Creators: Bernlochner, Florian U.; Ligeti, Zoltan; Papucci, Michele¹; Robinson, Dean J.

1. California Institute of Technology

Abstract

Normalizing the recent LHCb measurement of Λ𝑏→Λ𝑐⁢𝜏⁢¯𝜈 to the standard model (SM) prediction for the Λ𝑏→Λ𝑐⁢𝜇⁢¯𝜈 rate, instead of a LEP measurement, provides a more consistent comparison with the SM prediction for the lepton flavor universality ratio 𝑅⁡(Λ𝑐). This modestly increases 𝑅⁡(Λ𝑐) 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(*)). We point out that the fraction of excited states in inclusive semileptonic Λ𝑏 decay may be significantly greater than the corresponding fraction in 𝐵 decays. Possible implications are speculated upon.

Copyright and License

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Acknowledgement

We thank Marina Artuso, Marcello Rotondo, Niels Tuning, Guy Wormser, and Wei-Ming Yao for helpful discussions. F. B. is supported by DFG EmmyNoether Grant No. BE 6075/1-1 and BMBF Grant No. 05H21PDKBA. F. B. thanks LBNL for its hospitality.
The work of Z. L. and D. J. R. is supported by the Office of High Energy Physics of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. M. P. is supported by the U.S. Department of Energy, Office of High Energy Physics, under Award No. DE-SC0011632 and by the Walter Burke Institute for Theoretical Physics.

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