## Abstract

We discuss *B*_{c} → *η*_{c} and *B*_{c} → *J/ψ* semileptonic decays within the Standard Model (SM) and beyond. The relevant transition form factors, being the main source of theoretical uncertainties, are calculated in the sum rule approach and are provided in a full *q*^{2} range. We calculate the semileptonic branching fractions and find for the ratios, \( \left.{R}_{\eta_c}\right|\mathrm{S}\mathrm{M}=0.32\pm 0.02 \), *R*_{J/ψ} |SM = 0*.*23 ± 0*.*01. Both predictions are in agreement with other existing calculations and support the current tension in *R*_{J/ψ} at 2*σ* level with the experiment. To extend the potential of testing the SM in the semileptonic *B*_{c} decays, we consider the forward-backward asymmetry and polarization observables. We also study the 4-fold differential distributions of \( {B}_c\to J/\psi \left(J/\psi \to {\tilde{\ell}}^{-}{\tilde{\ell}}^{+}\right){\ell}^{-}{\overline{\nu}}_{\ell } \), where \( \tilde{\ell} = e,\mu \), in the presence of different new physics scenarios and find that the new physics effects can significantly modify the angular observables and can also produce effects which do not exist in the SM. Using the constraints on the new physics couplings from the recent combined analysis of BaBar, Belle and LHCb data on semileptonic *B* → *D*^{(∗)} decays, where the effects of new physics could be visible, we find that these different new physics scenarios are not able to simultaneously explain the current experimental value of *R*_{J/ψ}.

## References

- [1]
LHCb collaboration,

*Measurement of the ratio of branching fractions*ℬ(*B*^{+}_{ c}→*J*/*ψτ*^{+}*ν*_{τ})/ℬ(*B*^{+}_{ c}→*J*/*ψμ*^{+}*ν*_{μ}),*Phys. Rev. Lett.***120**(2018) 121801 [arXiv:1711.05623] [INSPIRE]. - [2]
W.-F. Wang, Y.-Y. Fan and Z.-J. Xiao,

*Semileptonic decays B*_{c}→ (*η*_{c}*, J/*Ψ)*lν in the perturbative QCD approach*,*Chin. Phys.***C 37**(2013) 093102 [arXiv:1212.5903] [INSPIRE]. - [3]
V.V. Kiselev,

*Exclusive decays and lifetime of B*_{c}*meson in QCD sum rules*, hep-ph/0211021 [INSPIRE]. - [4]
D. Bečirević, D. Leljak, B. Melić and O. Sumensari, work in preparation.

- [5]
D. Leljak,

*B*_{c}→*J/ψ form factors and lepton flavor universality violation in R*(*J/ψ*), talk at*Getting in Grips with QCD*, U. Paris, France, 4-6 April 2018, https://indico.cern.ch/event/685400/contributions/2947713/attachments/1627828/2592987/QCDgrips2018.pdf. - [6]
D. Bečirević,

*Hadronic uncertainties*, talk at*Getting in Grips with QCD*—*Summer Edition*, Primošten, Croatia, 18 September 2018, https://indico.cern.ch/event/736768/contributions/3141246/attachments/1720605/2793118/becirevic-Primosten2018.pdf. - [7]
T. Huang and F. Zuo,

*Semileptonic B*_{c}*decays and charmonium distribution amplitude*,*Eur. Phys. J.***C 51**(2007) 833 [hep-ph/0702147] [INSPIRE]. - [8]
D. Scora and N. Isgur,

*Semileptonic meson decays in the quark model: An update*,*Phys. Rev.***D 52**(1995) 2783 [hep-ph/9503486] [INSPIRE]. - [9]
A. Abd El-Hady, J.H. Muñoz and J.P. Vary,

*Semileptonic and nonleptonic B*_{c}*decays*,*Phys. Rev.***D 62**(2000) 014019 [hep-ph/9909406] [INSPIRE]. - [10]
M.A. Nobes and R.M. Woloshyn,

*Decays of the B*_{c}*meson in a relativistic quark meson model*,*J. Phys.***G 26**(2000) 1079 [hep-ph/0005056] [INSPIRE]. - [11]
D. Ebert, R.N. Faustov and V.O. Galkin,

*Weak decays of the B*_{c}*meson to charmonium and D mesons in the relativistic quark model*,*Phys. Rev.***D 68**(2003) 094020 [hep-ph/0306306] [INSPIRE]. - [12]
E. Hernandez, J. Nieves and J.M. Verde-Velasco,

*Study of exclusive semileptonic and non-leptonic decays of B*^{_}_{ c}*in a nonrelativistic quark model*,*Phys. Rev.***D 74**(2006) 074008 [hep-ph/0607150] [INSPIRE]. - [13]
C.-F. Qiao and R.-L. Zhu,

*Estimation of semileptonic decays of B*_{c}*meson to S-wave charmonia with nonrelativistic QCD*,*Phys. Rev.***D 87**(2013) 014009 [arXiv:1208.5916] [INSPIRE]. - [14]
W. Wang, Y.-L. Shen and C.-D. Lü,

*Covariant Light-Front Approach for B*_{c}*transition form factors*,*Phys. Rev.***D 79**(2009) 054012 [arXiv:0811.3748] [INSPIRE]. - [15]
A. Yu. Anisimov, I.M. Narodetsky, C. Semay and B. Silvestre-Brac,

*The B*_{c}*meson lifetime in the light front constituent quark model*,*Phys. Lett.***B 452**(1999) 129 [hep-ph/9812514] [INSPIRE]. - [16]
M.A. Ivanov, J.G. Körner and P. Santorelli,

*Exclusive semileptonic and nonleptonic decays of the B*_{c}*meson*,*Phys. Rev.***D 73**(2006) 054024 [hep-ph/0602050] [INSPIRE]. - [17]
BaBar collaboration,

*Measurement of an Excess of*\( \overline{B}\to {D}^{\left(\ast \right)}{\tau}^{-}{\overline{\nu}}_{\tau } \)*Decays and Implications for Charged Higgs Bosons*,*Phys. Rev.***D 88**(2013) 072012 [arXiv:1303.0571] [INSPIRE]. - [18]
Belle collaboration,

*Measurement of the branching ratio of*\( {\overline{B}}^0\to {D}^{\ast +}{\tau}^{-}{\overline{\nu}}_{\tau } \)*relative to*\( {\overline{B}}^0\to {D}^{\ast +}{\ell}^{-}{\overline{\nu}}_{\ell } \)*decays with a semileptonic tagging method*,*Phys. Rev.***D 94**(2016) 072007 [arXiv:1607.07923] [INSPIRE]. - [19]
LHCb collaboration,

*Measurement of the ratio of branching fractions*\( \mathrm{\mathcal{B}}\left({\overline{B}}^0\to {D}^{\ast +}{\tau}^{-}{\overline{\nu}}_{\tau}\right)/\mathrm{\mathcal{B}}\left({\overline{B}}^0\to {D}^{\ast +}{\mu}^{-}{\overline{\nu}}_{\mu}\right) \),*Phys. Rev. Lett.***115**(2015) 111803 [*Erratum ibid.***115**(2015) 159901] [arXiv:1506.08614] [INSPIRE]. - [20]
HFLAV collaboration,

*Averages of b-hadron, c-hadron, and τ -lepton properties as of summer 2016*,*Eur. Phys. J.***C 77**(2017) 895 [arXiv:1612.07233] [INSPIRE]. - [21]
LHCb collaboration,

*Test of lepton universality with B*^{0}→*K*^{∗0}*ℓ*^{+}*ℓ*^{−}*decays*,*JHEP***08**(2017) 055 [arXiv:1705.05802] [INSPIRE]. - [22]
R. Watanabe,

*New Physics effect on*\( {B}_c\to J/\psi \tau \overline{\nu} \)*in relation to the*\( {R}_{D^{\left(\ast \right)}} \)*anomaly*,*Phys. Lett.***B 776**(2018) 5 [arXiv:1709.08644] [INSPIRE]. - [23]
R. Dutta and A. Bhol,

*B*_{c}→ (*J/ψ, η*_{c})*τ ν semileptonic decays within the standard model and beyond*,*Phys. Rev.***D 96**(2017) 076001 [arXiv:1701.08598] [INSPIRE]. - [24]
T.D. Cohen, H. Lamm and R.F. Lebed,

*Model-independent bounds on R*(*J/ψ*),*JHEP***09**(2018) 168 [arXiv:1807.02730] [INSPIRE]. - [25]
A. Berns and H. Lamm,

*Model-Independent Prediction of R*(*η*_{c}),*JHEP***12**(2018) 114 [arXiv:1808.07360] [INSPIRE]. - [26]
C.W. Murphy and A. Soni,

*Model-Independent Determination of B*^{+}_{ c}→*η*_{c}*ℓ*^{+}*ν Form Factors*,*Phys. Rev.***D 98**(2018) 094026 [arXiv:1808.05932] [INSPIRE]. - [27]
C.-T. Tran, M.A. Ivanov, J.G. Körner and P. Santorelli,

*Implications of new physics in the decays B*_{c}→ (*J/ψ, η*_{c})*τ ν*,*Phys. Rev.***D 97**(2018) 054014 [arXiv:1801.06927] [INSPIRE]. - [28]
HPQCD collaboration,

*B*_{c}*decays from highly improved staggered quarks and NRQCD*,*PoS***LATTICE2016**(2016) 281 [arXiv:1611.01987] [INSPIRE]. - [29]
P. Ball and V.M. Braun,

*The ρ meson light cone distribution amplitudes of leading twist revisited*,*Phys. Rev.***D 54**(1996) 2182 [hep-ph/9602323] [INSPIRE]. - [30]
G. Duplančić and B. Melić,

*B, B*_{s}→*K form factors: An update of light-cone sum rule results*,*Phys. Rev.***D 78**(2008) 054015 [arXiv:0805.4170] [INSPIRE]. - [31]
P. Ball and R. Zwicky,

*B*_{d,s}→*ρ, ω, K*^{∗}*, ϕ decay form-factors from light-cone sum rules revisited*,*Phys. Rev.***D 71**(2005) 014029 [hep-ph/0412079] [INSPIRE]. - [32]
G. Duplančić, A. Khodjamirian, T. Mannel, B. Melić and N. Offen,

*Light-cone sum rules for B*→*π form factors revisited*,*JHEP***04**(2008) 014 [arXiv:0801.1796] [INSPIRE]. - [33]
G. Duplančić and B. Melić,

*Form factors of B, B*_{s}→*η*^{′}*and D, D*_{s}→*η*^{′}*transitions from QCD light-cone sum rules*,*JHEP***11**(2015) 138 [arXiv:1508.05287] [INSPIRE]. - [34]
A. Khodjamirian, C. Klein, T. Mannel and Y.M. Wang,

*Form Factors and Strong Couplings of Heavy Baryons from QCD Light-Cone Sum Rules*,*JHEP***09**(2011) 106 [arXiv:1108.2971] [INSPIRE]. - [35]
G. Bell, T. Feldmann, Y.-M. Wang and M.W.Y. Yip,

*Light-Cone Distribution Amplitudes for Heavy-Quark Hadrons*,*JHEP***11**(2013) 191 [arXiv:1308.6114] [INSPIRE]. - [36]
B. Chauhan and B. Kindra,

*Invoking Chiral Vector Leptoquark to explain LFU violation in B Decays*, arXiv:1709.09989 [INSPIRE]. - [37]
X.-G. He and G. Valencia,

*Lepton universality violation and right-handed currents in b*→*c*τν,*Phys. Lett.***B 779**(2018) 52 [arXiv:1711.09525] [INSPIRE]. - [38]
J. Zhu, B. Wei, J.-H. Sheng, R.-M. Wang, Y. Gao and G.-R. Lu,

*Probing the R-parity violating supersymmetric effects in*\( {B}_c\to J/\psi {\ell}^{-}{\overline{\nu}}_{\ell },{\eta}_c{\ell}^{-}{\overline{\nu}}_{\ell } \)*and*\( {\Lambda}_b\to\ {\Lambda}_c{\ell}^{-}{\overline{\nu}}_{\ell } \)*decays*,*Nucl. Phys.***B 934**(2018) 380 [arXiv:1801.00917] [INSPIRE]. - [39]
A. Biswas, D.K. Ghosh, S.K. Patra and A. Shaw,

*b*→*c*ℓν*anomalies in light of extended scalar sectors*, arXiv:1801.03375 [INSPIRE]. - [40]
R. Dutta,

*Exploring R*_{D}*,*\( {R}_{D^{*}} \)*and R*_{J/Ψ}*anomalies*, arXiv:1710.00351 [INSPIRE]. - [41]
Z.-R. Huang, Y. Li, C.-D. Lü, M.A. Paracha and C. Wang,

*Footprints of New Physics in b*→*cτν Transitions*,*Phys. Rev.***D 98**(2018) 095018 [arXiv:1808.03565] [INSPIRE]. - [42]
Y. Li and C.-D. Lü,

*Recent Anomalies in B Physics*,*Sci. Bull.***63**(2018) 267 [arXiv:1808.02990] [INSPIRE]. - [43]
R. Alonso, A. Kobach and J. Martin Camalich,

*New physics in the kinematic distributions of*\( \overline{B}\to {D}^{\left(\ast \right)}\tau -\left(\to {\ell}^{-}{\overline{\nu}}_{\ell }{\nu}_{\tau}\right){\overline{\nu}}_{\tau } \) ,*Phys. Rev.***D 94**(2016) 094021 [arXiv:1602.07671] [INSPIRE]. - [44]
A. Greljo, J. Martin Camalich and J.D. Ruiz- Álvarez,

*The Mono-Tau Menace: From B Decays to High-p*_{T}*Tails*,*Phys. Rev. Lett.***122**(2019) 131803 [arXiv:1811.07920] [INSPIRE]. - [45]
M. Blanke et al.,

*Impact of polarization observables and B*_{c}→*τ ν on new physics explanations of the b*→*cτ ν anomaly*,*Phys. Rev.***D 99**(2019) 075006 [arXiv:1811.09603] [INSPIRE]. - [46]
F. Feruglio, P. Paradisi and O. Sumensari,

*Implications of scalar and tensor explanations of*\( {R}_{D^{\left(\ast \right)}} \),*JHEP***11**(2018) 191 [arXiv:1806.10155] [INSPIRE]. - [47]
A.K. Alok, D. Kumar, J. Kumar, S. Kumbhakar and S.U. Sankar,

*New physics solutions for R*_{D}*and*\( {R}_{D^{\ast }} \),*JHEP***09**(2018) 152 [arXiv:1710.04127] [INSPIRE]. - [48]
A.K. Alok, D. Kumar, S. Kumbhakar and S. Uma Sankar,

*Resolution of*\( {R}_D/{R}_{D^{\ast }} \)*puzzle*,*Phys. Lett.***B 784**(2018) 16 [arXiv:1804.08078] [INSPIRE]. - [49]
G.T. Bodwin, H.S. Chung, D. Kang, J. Lee and C. Yu,

*Improved determination of color-singlet nonrelativistic QCD matrix elements for S-wave charmonium*,*Phys. Rev.***D 77**(2008) 094017 [arXiv:0710.0994] [INSPIRE]. - [50]
A. Bharucha, D.M. Straub and R. Zwicky,

*B*→*V ℓ*^{+}*ℓ*^{−}*in the Standard Model from light-cone sum rules*,*JHEP***08**(2016) 098 [arXiv:1503.05534] [INSPIRE]. - [51]
V.M. Braun, A. Khodjamirian and M. Maul,

*Pion form-factor in QCD at intermediate momentum transfers*,*Phys. Rev.***D 61**(2000) 073004 [hep-ph/9907495] [INSPIRE]. - [52]
P. Ball and R. Zwicky,

*Improved analysis of B*→ π*eν from QCD sum rules on the light cone*,*JHEP***10**(2001) 019 [hep-ph/0110115] [INSPIRE]. - [53]
P. Ball and R. Zwicky,

*New results on B*→*π, K, η decay formfactors from light-cone sum rules*,*Phys. Rev.***D 71**(2005) 014015 [hep-ph/0406232] [INSPIRE]. - [54]
A. Khodjamirian, T. Mannel, N. Offen and Y.M. Wang,

*B*→*πℓν*_{l}*Width and*|*V*_{ub}|*from QCD Light-Cone Sum Rules*,*Phys. Rev.***D 83**(2011) 094031 [arXiv:1103.2655] [INSPIRE]. - [55]
P. Ball and V.M. Braun,

*Exclusive semileptonic and rare B meson decays in QCD*,*Phys. Rev.***D 58**(1998) 094016 [hep-ph/9805422] [INSPIRE]. - [56]
W. Altmannshofer, P. Ball, A. Bharucha, A.J. Buras, D.M. Straub and M. Wick,

*Symmetries and Asymmetries of B*→*K*^{∗}*μ*^{+}*μ*^{−}*Decays in the Standard Model and Beyond*,*JHEP***01**(2009) 019 [arXiv:0811.1214] [INSPIRE]. - [57]
V.L. Chernyak and A.R. Zhitnitsky,

*Asymptotic Behavior of Exclusive Processes in QCD*,*Phys. Rept.***112**(1984) 173 [INSPIRE]. - [58]
C. McNeile, C.T.H. Davies, E. Follana, K. Hornbostel and G.P. Lepage,

*High-Precision c and b Masses, and QCD Coupling from Current-Current Correlators in Lattice and Continuum QCD*,*Phys. Rev.***D 82**(2010) 034512 [arXiv:1004.4285] [INSPIRE]. - [59]
C. McNeile, C.T.H. Davies, E. Follana, K. Hornbostel and G.P. Lepage,

*Heavy meson masses and decay constants from relativistic heavy quarks in full lattice QCD*,*Phys. Rev.***D 86**(2012) 074503 [arXiv:1207.0994] [INSPIRE]. - [60]
G.C. Donald et al.,

*Precision tests of the J/ψ from full lattice QCD: mass, leptonic width and radiative decay rate to η*_{c},*Phys. Rev.***D 86**(2012) 094501 [arXiv:1208.2855] [INSPIRE]. - [61]
C.T.H. Davies, C. McNeile, E. Follana, G.P. Lepage, H. Na and J. Shigemitsu,

*Update: Precision D*_{s}*decay constant from full lattice QCD using very fine lattices*,*Phys. Rev.***D 82**(2010) 114504 [arXiv:1008.4018] [INSPIRE]. - [62]
D. Bečirević, G. Duplančić, B. Klajn, B. Melić and F. Sanfilippo,

*Lattice QCD and QCD sum rule determination of the decay constants of η*_{c}*, J/ψ and h*_{c}*states*,*Nucl. Phys.***B 883**(2014) 306 [arXiv:1312.2858] [INSPIRE]. - [63]
G.T. Bodwin, E. Braaten and G.P. Lepage,

*Rigorous QCD analysis of inclusive annihilation and production of heavy quarkonium*,*Phys. Rev.***D 51**(1995) 1125 [*Erratum ibid.***D 55**(1997) 5853] [hep-ph/9407339] [INSPIRE]. - [64]
V.V. Braguta, A.K. Likhoded and A.V. Luchinsky,

*The study of leading twist light cone wave function of η*_{c}*meson*,*Phys. Lett.***B 646**(2007) 80 [hep-ph/0611021] [INSPIRE]. - [65]
V.V. Braguta,

*The study of leading twist light cone wave functions of J/ψ meson*,*Phys. Rev.***D 75**(2007) 094016 [hep-ph/0701234] [INSPIRE]. - [66]
Y. Grossman, M. König and M. Neubert,

*Exclusive Radiative Decays of W and Z Bosons in QCD Factorization*,*JHEP***04**(2015) 101 [arXiv:1501.06569] [INSPIRE]. - [67]
A. Czarnecki and K. Melnikov,

*Two loop QCD corrections to the heavy quark pair production cross-section in e*^{+}*e*^{−}*annihilation near the threshold*,*Phys. Rev. Lett.***80**(1998) 2531 [hep-ph/9712222] [INSPIRE]. - [68]
M. Beneke, A. Signer and V.A. Smirnov,

*Two loop correction to the leptonic decay of quarkonium*,*Phys. Rev. Lett.***80**(1998) 2535 [hep-ph/9712302] [INSPIRE]. - [69]
M. Beneke et al.,

*Leptonic decay of the ϒ*(1*S*)*meson at third order in QCD*,*Phys. Rev. Lett.***112**(2014) 151801 [arXiv:1401.3005] [INSPIRE]. - [70]
X.-P. Wang and D. Yang,

*The leading twist light-cone distribution amplitudes for the S-wave and P-wave quarkonia and their applications in single quarkonium exclusive productions*,*JHEP***06**(2014) 121 [arXiv:1401.0122] [INSPIRE]. - [71]
W. Wang, J. Xu, D. Yang and S. Zhao,

*Relativistic corrections to light-cone distribution amplitudes of S-wave B*_{c}*mesons and heavy quarkonia*,*JHEP***12**(2017) 012 [arXiv:1706.06241] [INSPIRE]. - [72]
H.S. Chung, J. Lee and C. Yu,

*NRQCD matrix elements for S-wave bottomonia and*Γ(*η*_{b}(*nS*) →*γγ*)*with relativistic corrections*,*Phys. Lett.***B 697**(2011) 48 [arXiv:1011.1554] [INSPIRE]. - [73]
G.T. Bodwin, H.S. Chung, J.-H. Ee, J. Lee and F. Petriello,

*Relativistic corrections to Higgs boson decays to quarkonia*,*Phys. Rev.***D 90**(2014) 113010 [arXiv:1407.6695] [INSPIRE]. - [74]
P. Ball, V.M. Braun and A. Lenz,

*Higher-twist distribution amplitudes of the K meson in QCD*,*JHEP***05**(2006) 004 [hep-ph/0603063] [INSPIRE]. - [75]
P. Ball, V.M. Braun, Y. Koike and K. Tanaka,

*Higher twist distribution amplitudes of vector mesons in QCD: Formalism and twist*—*three distributions*,*Nucl. Phys.***B 529**(1998) 323 [hep-ph/9802299] [INSPIRE]. - [76]
P. Ball and V.M. Braun,

*Handbook of higher twist distribution amplitudes of vector mesons in QCD*, in*Continuous advances in QCD. Proceedings, 3rd Workshop, QCD*’*98, Minneapolis, U.S.A., April 16-19, 1998*, pp. 125-141, 1998, hep-ph/9808229 [INSPIRE]. - [77]
M. Beneke and T. Feldmann,

*Symmetry breaking corrections to heavy to light B meson form-factors at large recoil*,*Nucl. Phys.***B 592**(2001) 3 [hep-ph/0008255] [INSPIRE]. - [78]
P. Ball, V.M. Braun and A. Lenz,

*Twist-4 distribution amplitudes of the K*^{∗}*and φ mesons in QCD*,*JHEP***08**(2007) 090 [arXiv:0707.1201] [INSPIRE]. - [79]
A. Issadykov, M.A. Ivanov and G. Nurbakova,

*Semileptonic decays of B*_{c}*mesons into charmonium states*,*EPJ Web Conf.***158**(2017) 03002 [INSPIRE]. - [80]
C. Bourrely, I. Caprini and L. Lellouch,

*Model-independent description of B*→*πlν decays and a determination of*|*V*_{ub}|,*Phys. Rev.***D 79**(2009) 013008 [*Erratum ibid.***D 82**(2010) 099902] [arXiv:0807.2722] [INSPIRE]. - [81]
A. Bharucha, T. Feldmann and M. Wick,

*Theoretical and Phenomenological Constraints on Form Factors for Radiative and Semi-Leptonic B-Meson Decays*,*JHEP***09**(2010) 090 [arXiv:1004.3249] [INSPIRE]. - [82]
ATLAS collaboration,

*Observation of an Excited B*^{±}_{ v}*Meson State with the ATLAS Detector*,*Phys. Rev. Lett.***113**(2014) 212004 [arXiv:1407.1032] [INSPIRE]. - [83]
LHCb collaboration,

*Observation of B*^{+}_{ c}→*J*/*ψD*^{(∗)}*K*^{(∗)}*decays*,*Phys. Rev.***D 95**(2017) 032005 [arXiv:1612.07421] [INSPIRE]. - [84]
E.J. Eichten and C. Quigg,

*Mesons with beauty and charm: Spectroscopy*,*Phys. Rev.***D 49**(1994) 5845 [hep-ph/9402210] [INSPIRE]. - [85]
S. Godfrey,

*Spectroscopy of B*_{c}*mesons in the relativized quark model*,*Phys. Rev.***D 70**(2004) 054017 [hep-ph/0406228] [INSPIRE]. - [86]
E.E. Jenkins, M.E. Luke, A.V. Manohar and M.J. Savage,

*Semileptonic B*_{c}*decay and heavy quark spin symmetry*,*Nucl. Phys.***B 390**(1993) 463 [hep-ph/9204238] [INSPIRE]. - [87]
V.V. Kiselev, A.K. Likhoded and A.I. Onishchenko,

*Semileptonic B*_{c}*meson decays in sum rules of QCD and NRQCD*,*Nucl. Phys.***B 569**(2000) 473 [hep-ph/9905359] [INSPIRE]. - [88]
P. Colangelo and F. De Fazio,

*Using heavy quark spin symmetry in semileptonic B*_{c}*decays*,*Phys. Rev.***D 61**(2000) 034012 [hep-ph/9909423] [INSPIRE]. - [89]
Particle Data Group collaboration,

*Review of Particle Physics*,*Phys. Rev.***D 98**(2018) 030001 [INSPIRE]. - [90]
M. Beneke and G. Buchalla,

*The B*_{c}*Meson Lifetime*,*Phys. Rev.***D 53**(1996) 4991 [hep-ph/9601249] [INSPIRE]. - [91]
A. Angelescu, D. Bečirević, D.A. Faroughy and O. Sumensari,

*Closing the window on single leptoquark solutions to the B-physics anomalies*,*JHEP***10**(2018) 183 [arXiv:1808.08179] [INSPIRE]. - [92]
I. Doršner, S. Fajfer, A. Greljo, J.F. Kamenik and N. Košnik,

*Physics of leptoquarks in precision experiments and at particle colliders*,*Phys. Rept.***641**(2016) 1 [arXiv:1603.04993] [INSPIRE]. - [93]
D. Bečirević, S. Fajfer, N. Košnik and O. Sumensari,

*Leptoquark model to explain the B-physics anomalies, R*_{K}*and R*_{D},*Phys. Rev.***D 94**(2016) 115021 [arXiv:1608.08501] [INSPIRE]. - [94]
M. González-Alonso, J. Martin Camalich and K. Mimouni,

*Renormalization-group evolution of new physics contributions to (semi)leptonic meson decays*,*Phys. Lett.***B 772**(2017) 777 [arXiv:1706.00410] [INSPIRE]. - [95]
M.A. Ivanov, J.G. Körner and C.-T. Tran,

*Analyzing new physics in the decays*\( {\overline{B}}^0\to {D}^{\left(\ast \right)}\tau -{\overline{\nu}}_{\tau } \)*with form factors obtained from the covariant quark model*,*Phys. Rev.***D 94**(2016) 094028 [arXiv:1607.02932] [INSPIRE]. - [96]
T.D. Cohen, H. Lamm and R.F. Lebed,

*Tests of the standard model in B*→*Dlν*_{l}*, B*→*D*^{∗}*lν*_{l}*and B*_{c}→*J/ψlν*_{l},*Phys. Rev.***D 98**(2018) 034022 [arXiv:1807.00256] [INSPIRE]. - [97]
A. Faessler, T. Gutsche, M.A. Ivanov, J.G. Körner and V.E. Lyubovitskij,

*The exclusive rare decays*\( B\to K\left(K\ast \right)\ \overline{\ell}\ell \)*and*\( {B}_c\to D\left(D\ast \right)\ \overline{\ell}\ell \)*in a relativistic quark model*,*Eur. Phys. J. direct***4**(2002) 18 [hep-ph/0205287] [INSPIRE]. - [98]
T. Gutsche, M.A. Ivanov, J.G. Körner, V.E. Lyubovitskij and P. Santorelli,

*Polarization effects in the cascade decay*Λ_{b}→ Λ(→*p*π^{−}) +*J/ψ*(→*l*^{+}*l*^{−})*in the covariant confined quark model*,*Phys. Rev.***D 88**(2013) 114018 [arXiv:1309.7879] [INSPIRE]. - [99]
T. Gutsche, M.A. Ivanov, J.G. Körner, V.E. Lyubovitskij, P. Santorelli and N. Habyl,

*Semileptonic decay*Λ_{b}→ Λ_{c}+*τ*^{−}+*ν*¯_{τ}*in the covariant confined quark model*,*Phys. Rev.***91**(2015) 074001 [*Erratum ibid.***D 91**(2015) 119907] [arXiv:1502.04864] [INSPIRE].

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ArXiv ePrint: 1901.08368

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Leljak, D., Melić, B. & Patra, M. On lepton flavour universality in semileptonic *B*_{c} → *η*_{c}*, J/ψ* decays.
*J. High Energ. Phys.* **2019, **94 (2019). https://doi.org/10.1007/JHEP05(2019)094

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### Keywords

- Beyond Standard Model
- Heavy Quark Physics