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Model-independent fits in the complex δ τ cb -(left) and τ cb -planes (right). The dark rings stem from R(D ( * ) ), the lighter discs from the shape information of the q 2 -distributions of B → D ( * ) τ ν, the dark green disc from the indirect bound on Br(B c → τ ν) (see text), and the dashed contour in the right plot encloses the allowed region from A λ (D * ). The yellow areas represent the global fit in each sector, while the dotted contour in the left plot encloses the allowed region from a fit to R(D ( * ) ) together with R(τ ) in scenario S2, see text. All coloured areas correspond to 95% CL regions, only the dashed contour to 68% CL. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) (right). For the B → Dτ ν data we find that the q 2 -distribution se-
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We perform a comprehensive analysis of scalar contributions in transitions including the latest measurements of , the differential distributions in , the τ polarization asymmetry for , and the bound derived from the total width of the meson. We find that scalar contributions with the simultaneous presence of both left- and right-handed couplings to...
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Context 1
... Fig. 2 4 We observe that our results are not affected in a significant manner by using instead the slightly stronger limit Br(B c → τ ν) 30% used in Ref. [27]. The overall χ 2 assuming real couplings does not increase compared to the general complex case, see Table 7, in agreement with Fig. 2, where these imaginary parts are seen to be well ...
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... Fig. 2 4 We observe that our results are not affected in a significant manner by using instead the slightly stronger limit Br(B c → τ ν) 30% used in Ref. [27]. The overall χ 2 assuming real couplings does not increase compared to the general complex case, see Table 7, in agreement with Fig. 2, where these imaginary parts are seen to be well compatible with zero. This is largely due to the fact that the imaginary part enters the considered observables only quadratically, while the real part enters linearly. Improved measurements of the included observables could nevertheless provide sensitivity on the imaginary part, since ...
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... can be observed from these fits, the distributions available so far allow for sizeable NP contributions, while at the same time being compatible with the SM predictions, in accordance with the Predicted q 2 distributions for R(D ( * ) ) from the model-independent fit to b → cτ ν data and within the SM. Fig. 2 and the analyses in Refs. [21,25]. On the other hand, the second NP distribution (green) is visibly different from the other two and in clear tension with the data (especially for B → Dτ ν). For large NP contributions relative to the SM ones, the distributions change due to kinematic effects. However, the region selected in B → Dτ ν is ...
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... taking into account all present data, the inclusion of R(τ ) worsens the minimal χ 2 significantly, χ 2 min ≈ 5. The reason is that, while R(D), R(D * ) and R(τ ) can be fitted simultaneously, R(τ ) selects a region in the parameter space that is in tension with the differential distribution of B → Dτ ν, as displayed in Fig. 2 6 For this statement to hold strictly the effect on the differential distributions has to be taken into account; however, the BaBar analysis [4,25] indicates that it holds even ...
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Citations
... The semileptonic B → D ( * ) ℓ −ν (ℓ = µ, e) decays are useful for the extraction of |V cb | [2][3][4][5][6][7][8][9][10]. In addition, the ratios of the decay rates which are defined as R(D ( * ) ) = Γ(B → D ( * ) τ −ν )/Γ(B → D ( * ) ℓ −ν ) are potentially sensitive to NP interactions [3,[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. In the SM, these ratios are lepton flavour universality conserving (LFU). ...
... The NP contribution is taken into account by the Wilson coefficients (WCs), C X (X = S L , S R ), normalized by the SM factor of 2 √ 2G F V cb . It has been well known that the B c lifetime constrains the scalar interpretation [27][28][29][30][31][32]. However, the recent result makes it possible to explain the deviations at the 1σ level using the scalar operators [25]. ...
A bstract
We discuss a model with a SU(2) L doublet vector leptoquark (LQ), motivated by the recent experimental results relating to the lepton universality of $$ \overline{B} $$ B ¯ → D (*) $$ \tau {\overline{\nu}}_{\tau } $$ τ ν ¯ τ . We find that scalar operators predicted by the LQ are favored to explain the deviations, taking into account the recent LHCb result. We investigate the extensive phenomenology of the model and conclude that B s → $$ \tau \overline{\tau} $$ τ τ ¯ , B → $$ K\tau \overline{\tau} $$ Kτ τ ¯ , B u → $$ \tau {\overline{\nu}}_{\tau } $$ τ ν ¯ τ and high- p T di- τ lepton signatures at the LHC will probe the interesting parameter region in the near future.
... As it is a charged current process, the only possibilities are charged Higgses [135][136][137], W ′ bosons [138][139][140][141] (with or without right-handed neutrinos) or LQs [142][143][144][145]. While W ′ bosons have in general problems with LHC searches [138,139], despite bounds from the B c lifetime [93,[146][147][148] and LHC bounds [149], charged Higgses generating C S R can give a reasonably good fit to data. However, as LQs can generate C V L they are the best option for a full explanation, despite non-trivial constraints from B s −B s mixing, B → K * νν and LHC searches arise. ...
We review the current status and implications of the anomalies (i.e. deviations from the Standard Model predictions) in semi-leptonic $B$ meson decays, both in the charged and in the neutral current. In $b\to s\ell^+\ell^-$ transitions significant tensions between measurements and the Standard Model predictions exist. They are most pronounced in the branching ratios ${\cal B}_{B \to K\mu^+\mu^-}$ and ${\cal B}_{B_s\to\phi\mu^+\mu^-}$ (albeit quite dependent on the form factors used) as well as in angular observables in $B\to K^*\mu^+\mu^-$ (the $P_5^\prime$ anomaly). Because the measurements of ${\cal B}_{B_s\to \mu^+\mu^-}$ and of the ratios $R_K$ and $R_{K^*}$ agree reasonably well with the SM predictions, this points towards (dominantly) lepton flavour universal New Physics coupling vectorially to leptons, i.e. contributions to $C_9^{\rm U}$. In fact, global fits prefer this scenario over the SM hypothesis by $5.8\sigma$. Concerning $b\to c\tau\nu$ transitions, $R(D)$ and $R(D^*)$ suggest constructive New Physics at the level of $10\%$ (w.r.t. the Standard Model amplitude) with a significance above $3\sigma$. We discuss New Physics explanations of both anomalies separately as well as possible combined explanations. In particular, a left-handed vector current solution to $R(D^{(*)})$, either via the $U_1$ leptoquark or the combination of the scalar leptoquarks $S_1$ and $S_3$, leads to an effect in $C_9^{\rm U}$ via an off-shell penguin with the right sign and magnitude and a combined significance (including a tree-level effect resulting in $C_{9\mu}^\mathrm{V}=-C_{10\mu}^\mathrm{V}$ and $R(D^{(*)})$) of $6.3\sigma$. Such a scenario can be tested with $b \to s \tau^+\tau^-$ decays. Finally, we point out an interesting possible correlation of $R(D^{(*)})$ with non-leptonic $B$ anomalies.
... The contributions of these additional operators can be constrained using the measured B c lifetime. This leads to the upper limits BR(B − c → τ −ν τ ) ≤ 40% [23], BR(B − c → τ −ν τ ) ≤ 30% [24] and a much stronger bound BR(B − c → τ −ν τ ) ≤ 10% was obtained from the LEP data taken at the Z peak [25]. Later on, the bounds using the measured B c lifetime had been critically investigated and relaxed upper limit of ≤ 39% [26] and ≤ 60% [27,28] were obtained. ...
... The dependency of the scalar Wilson coefficients on the matrix elements of the quark mixing angle in the right sector turns to be important. We emphasized that the mixing element (V R C K M ) 23 should be complex in order to satisfy both R D and R D * . We have also shown the complex phase associated with this mixing element is essential to accommodate the experimental results of the ratios for charged Higgs masses of order 300 GeV while respecting the constraints from BR(B − c → τ −ν τ ), B s(d) −B s(d) mixing and other relevant constraints discussed above. ...
We investigate $$R_D$$ R D and $$R_{D^*}$$ R D ∗ anomalies in a low scale left–right symmetric model based on $$SU(3)_C\times SU(2)_L\times SU(2)_R\times U(1)_{B-L}$$ S U ( 3 ) C × S U ( 2 ) L × S U ( 2 ) R × U ( 1 ) B - L with a simplified Higgs sector consisting of only one bidoublet and one $$SU(2)_R$$ S U ( 2 ) R doublet. The Wilson coefficients relevant to the transition $$b\rightarrow c\tau \nu $$ b → c τ ν are derived by integrating out the charged Higgs $$H^\pm $$ H ± boson, which gives the dominant contributions. We emphasize that the charged Higgs effects, with the complex right-handed quark mixing matrix, can account for both $$R_D$$ R D and $$R_{D^*}$$ R D ∗ anomalies simultaneously, while adhering to a set of significant constraints including, for instance, $$\textrm{BR}(B^-_c \rightarrow \tau ^- \bar{\nu }_\tau ) $$ BR ( B c - → τ - ν ¯ τ ) and $$B_{s(d)}-\bar{B}_{s(d)}$$ B s ( d ) - B ¯ s ( d ) mixing. In relation to this, we show that the predicted values of the $$D^*$$ D ∗ , $$\tau $$ τ longitudinal polarizations and $$P_\tau (D)$$ P τ ( D ) can be affected for the set of the parameters of the model resolving the $$R_{D,D^*}$$ R D , D ∗ anomalies.
... In this context, various groups have proposed explanations in a model-independent approach [39][40][41][42][43][44][45][46][47] and also in different NP models. Some of the simplified NP models may include a new vector boson [48][49][50][51], a charged scalar [52][53][54][55][56][57][58][59] or a Leptoquark [60][61][62][63][64]. ...
A number of measurements in decays induced by the semileptonic $b\to s$ and $b\to c$ transitions hint towards a possible role of new physics in both sectors.
Motivated by these anomalies, we investigate the lepton flavor violating $B\to K^*_2 (1430)\mu^{\pm}\tau^{\mp}$ decays. We calculate the two-fold angular distribution of $B\to K^*_2\ell_1\ell_2$ decay in presence of vector, axial-vector, scalar and pseudo-scalar new physics interactions. We then compute the branching fraction and lepton forward-backward asymmetry in the framework of $U^{2/3}_1$ vector leptoquark which is a viable solution to the current $B$ anomalies. We find that the upper limits are $\mathcal{B}(B\to K^*_2\mu^-\tau^+)\leq 1.64\times 10^{-7}$ and $\mathcal{B}(B\to K^*_2\mu^+\tau^-)\leq 0.60\times 10^{-7}$ at $90\%$ C.L.
... The B + c → τ + ν τ decay is highly sensitive to new physics effects [10][11][12] but experimental accessibility to this mode is limited. Due to the large branching fraction of the B + c → B 0 s π + decay, its improved measurement contributes to a more stringent limit on the B + c → τ + ν τ decay via the B + c total decay width, depending on the theoretical model assumed [11,13,14]. In this paper, the ratio between the branching fractions of the B + c → B 0 s π + and B + c → J/ψπ + decays is measured, using proton-proton (pp) collision data collected with the LHCb experiment between 2016 and 2018 at a centre-of-mass energy of 13 TeV, corresponding 1 Inclusion of charge conjugate processes is implied throughout this paper. ...
A bstract
The ratio of branching fractions of $$ {B}_c^{+}\to {B}_s^0{\pi}^{+} $$ B c + → B s 0 π + and $$ {B}_c^{+}\to J/\psi {\pi}^{+} $$ B c + → J / ψ π + decays is measured with proton-proton collision data of a centre-of-mass energy of 13 TeV. The data were collected with the LHCb experiment during 2016–2018, corresponding to an integrated luminosity of 5 . 4 fb − 1 . The $$ {B}_s^0 $$ B s 0 mesons are reconstructed via the decays $$ {B}_s^0\to J/\psi \phi $$ B s 0 → J / ψϕ and $$ {B}_s^0\to {D}_s^{-}{\pi}^{+} $$ B s 0 → D s − π + . The ratio of branching fractions is measured to be $$ \mathcal{B}\left({B}_c^{+}\to {B}_s^0{\pi}^{+}\right)/\mathcal{B}\left({B}_c^{+}\to J/\psi {\pi}^{+}\right)=91\pm 10\pm 8\pm 3 $$ B B c + → B s 0 π + / B B c + → J / ψ π + = 91 ± 10 ± 8 ± 3 where the first uncertainty is statistical, the second is systematic and the third is due to the knowledge of the branching fractions of the intermediate state decays.
... The NP contribution is taken into account by the Wilson coefficients (WCs), C X (X = S L , S R ), normalized by the SM factor of 2 √ 2G F V cb . It has been well known that the B c lifetime constrains the scalar interpretation [27][28][29][30][31][32]. However, the recent result makes it possible to explain the deviations at the 1σ level using the scalar operators [25]. ...
We discuss a model with a SU$(2)_L$ doublet vector leptoquark (LQ), motivated by the recent experimental results relating to the lepton universality of $\overline{B} \to D^{(*)} \tau\overline{\nu}_\tau$. We find that scalar operators predicted by the LQ are favored to explain the deviations, taking into account the recent LHCb result. We investigate the extensive phenomenology of the model and conclude that $B_s\to\tau\overline\tau$, $B_u\to \tau\overline\nu_\tau$ and high-$p_T$ di-$\tau$ lepton signatures at the LHC will probe the interesting parameter region in the near future.
... This means that a sizable contribution from C V RL would indicate an effective field theory with non-linear realization of the SM gauge group SU(2) L × U(1) Y [92,93]. The scenarios with a single scalar operator O S LL or O S RL , like BP2, are already ruled out by the LEP data on the leptonic B − c → τ −ν τ decay rate [94][95][96][97]. However, as pointed JHEP05 (2023)173 out in refs. ...
A bstract
The semitauonic $$ {B}_c^{-}\to J/\psi {\tau}^{-}{\overline{\nu}}_{\tau } $$ B c − → J / ψ τ − ν ¯ τ decay provides an ideal and clean mode to scrutinize possible new physics effects in $$ b\to c{\tau}^{-}{\overline{\nu}}_{\tau } $$ b → c τ − ν ¯ τ transitions as indicated by the current data on R ( D (*) ) anomalies. In this work, we use the spin density matrix method to obtain the maximum information on the underlying physics of $$ {B}_c^{-}\to J/\psi {\tau}^{-}{\overline{\nu}}_{\tau } $$ B c − → J / ψ τ − ν ¯ τ decay with both polarized τ lepton and J/ψ meson. Their subsequent decays, with J/ψ → μ ⁺ μ − as well as τ − → π − ν τ , τ − → ρ − ν τ and $$ {\tau}^{-}\to {\ell}^{-}{\overline{\nu}}_{\ell }{\nu}_{\tau } $$ τ − → ℓ − ν ¯ ℓ ν τ , are exploited to extract the energy and angular distributions of the charged final-state particles in the processes. Starting with the most general effective Hamiltonian relevant for the $$ b\to c{\tau}^{-}{\overline{\nu}}_{\tau } $$ b → c τ − ν ¯ τ transitions, including all possible Lorentz structures of the dimension-six operators with both left- and right-handed neutrinos, we first derive the five-fold differential decay rate in terms of the visible final-state kinematics. From this distribution, we then construct in total 34 normalized observables, among which nine refer to the CP-violating triple product asymmetries that vanish within the Standard Model. We also construct five new observables based on the combinations of these normalized observables that can only be attributed to the right-handed neutrinos. On the other hand, considering the low statistics of the fully differential distribution, we introduce some integrated observables with only one kinematic variable left, which are more promising to be measured due to the largely increased statistics. The sensitivities of all these observables to the different new physics scenarios are investigated in detail. Finally, assuming an ideal circumstance, we give an estimate of the statistical uncertainties of the nine CP-conserving observables at LHCb and found that τ − → π − ν τ has the highest analyzing power among the three τ decay channels.
... 2 The possibility was originally pointed out in Ref. [37], and recently revisited in Ref. [38]. It is noted that thanks to the relaxed constraint from B c → τν [39][40][41][42] and the experimental shift, H þ can now explain R D ðÃÞ ¼ BRðB → D ðÃÞ τνÞ=BRðB → D ðÃÞ lνÞ within 1σ [43]. See also Refs. ...
We consider a general two Higgs doublet model which can simultaneously solve discrepancies in neutral B meson decay (b→sℓℓ¯ distribution) and charged B meson decay (b→cτν¯) with a charged Higgs. The model contains two additional neutral scalars at the same mass scale and predicts distinctive signals at the LHC. Based on the recent same-sign top search by the ATLAS collaboration, we found the constraint on the scalar mass spectrum. To probe the remaining mass window, we propose a novel cg→tττ¯ process at the LHC.
... Recent estimates [90,94] suggest that BRðB c → τνÞ as large as 60% to 63% is still possible. In our analysis we have not considered the constraint from the differential decay distributions of B → D ðÃÞ τν [3,6], which are known to be sensitive to scalar NP [95][96][97]. Compared to ratios R D ðÃÞ , the decay distributions are quite sensitive to hadronic form factors and parametric (e.g., V cb ) uncertainties. Furthermore, the corresponding experimental analyses [3,6] are model dependent and require the NP model's contributions to the background and the signal efficiency in order to obtain the data. ...
Current data on semileptonic charged- and neutral-current B decays show deviations from the predictions of the Standard Model. It is well known that a charged Higgs boson, belonging to the two-Higgs doublet model without Z2 symmetry, offers one of the simplest solution to the charged-current B decays. We show that this solution naturally induces a negative shift of O(1) in the Wilson coefficient (C9ℓ) of operator (s¯LγμbL)(ℓ¯γμℓ), potentially resolving the tension in neutral-current B decays as well. Interestingly, the lepton universality ratios in b→sℓ+ℓ− decays, in tune with the recent LHCb result, remain SM-like. Precision constraints from neutral B and K meson mixing, decays Bc→τν¯, B→Xsγ, and leptonic decays of τ and Z can be satisfied. Furthermore, a positive shift in W-boson mass, nicely in agreement with the CDF measurement, is also possible, requiring the neutral scalars to be heavier than the charged Higgs but within the sub-TeV region.
