Refining new-physics searches in B→Dτν with lattice QCD

Jon A. Bailey, A. Bazavov, C. Bernard, C. M. Bouchard, C. Detar, Daping Du, A. X. El-Khadra, J. Foley, E. D. Freeland, E. Gámiz, Steven Gottlieb, U. M. Heller, Jongjeong Kim, A. S. Kronfeld, J. Laiho, L. Levkova, P. B. MacKenzie, Y. Meurice, E. T. Neil, M. B. OktaySi Wei Qiu, J. N. Simone, R. Sugar, D. Toussaint, R. S. Van De Water, Ran Zhou

Research output: Contribution to journalArticlepeer-review

94 Scopus citations


The semileptonic decay channel B→Dτν is sensitive to the presence of a scalar current, such as that mediated by a charged-Higgs boson. Recently, the BABAR experiment reported the first observation of the exclusive semileptonic decay B→Dτ -ν̄, finding an approximately 2σ disagreement with the standard-model prediction for the ratio R(D)=BR(B→Dτν)/BR(B→ν), where =e,μ. We compute this ratio of branching fractions using hadronic form factors computed in unquenched lattice QCD and obtain R(D)=0.316(12)(7), where the errors are statistical and total systematic, respectively. This result is the first standard-model calculation of R(D) from ab initio full QCD. Its error is smaller than that of previous estimates, primarily due to the reduced uncertainty in the scalar form factor f 0(q2). Our determination of R(D) is approximately 1σ higher than previous estimates and, thus, reduces the tension with experiment. We also compute R(D) in models with electrically charged scalar exchange, such as the type-II two-Higgs-doublet model. Once again, our result is consistent with, but approximately 1σ higher than, previous estimates for phenomenologically relevant values of the scalar coupling in the type-II model. As a by-product of our calculation, we also present the standard-model prediction for the longitudinal-polarization ratio P L(D)=0.325(4)(3).

Original languageEnglish (US)
Article number071802
JournalPhysical Review Letters
Issue number7
StatePublished - Aug 16 2012
Externally publishedYes

ASJC Scopus subject areas

  • General Physics and Astronomy


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