Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTension in the inclusive versus exclusive determinations of $|V_{cb}|$: a possible role of new physics
92
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We reconsider the possibility that the tension in the $|V_{cb}|$ determinations from inclusive and exclusive $B$ decay modes is due to a new physics effect. We modify the Standard Model effective Hamiltonian for semileptonic $b to c$ transitions including a tensor operator with a lepton flavour dependent coupling $epsilon_T^ell$, and investigate separately the muon and electron modes. The interference term between SM and NP, proportional to the lepton mass, has different impact in the inclusive and exclusive $B$ modes to muon. Moreover, even when the lepton mass is small as for the electron, the NP effect is different in inclusive and exclusive $B$ channels. For both $mu$ and $e$ we find a region of $epsilon_T^{mu,,e}$ where the constraints from $B^- to D^{(*)0} ell^- {bar u}_ell$ and $B to X_c , ell , bar u_ell$ are satisfied for the same $|V_{cb}|$.
rate research
Read More
We perform the simultaneous $|V_{ub}|$ and $|V_{cb}|$ extractions with only the exclusive $Lambda_b$ decays of $Lambda_bto (p,Lambda_c^+)mubar u_mu$, $Lambda_bto ppi^-$ and $Lambda_bto Lambda_c^+ (pi^-, D^-)$. We obtain that $|V_{ub}|=(3.7pm 0.3)times 10^{-3}$ and $|V_{cb}|=(45.9pm 2.7)times 10^{-3}$. Our value of $|V_{ub}|$ is larger than that of $(3.27pm 0.15pm 0.16pm 0.06)times 10^{-3}$, previously extracted by the LHC Collaboration from the exclusive $Lambda_b$ decays also, but nearly identical to $(3.72pm 0.19)times 10^{-3}$ from the exclusive $B$ decays. On the other hand, our extracted result of $|V_{cb}|$ favors the value of $(42.2pm 0.8)times 10^{-3}$ from the inclusive $B$ decays.
We point out that the recently increased value of the angle $gamma$ in the Unitarity Triangle (UT), determined in tree-level decays to be $gamma=(74.0^{+5.0}_{-5.8})^circ$ by the LHCb collaboration, combined with the most recent value of $|V_{cb}|$ implies an enhancement of $Delta M_{d}$ over the data in the ballpark of $30%$. This is roughly by a factor of two larger than the enhancement of $Delta M_{s}$ that is independent of $gamma$. This disparity of enhancements is problematic for models with Constrained Minimal Flavour Violation (CMFV) and also for $U(2)^3$ models. In view of the prospects of measuring $gamma$ with the precision of $pm 1^circ$ by Belle II and LHCb in the coming years, we propose to use the angles $gamma$ and $beta$ together with $|V_{cb}|$ and $|V_{us}|$ as the fundamental parameters of the CKM matrix until $|V_{ub}|$ from tree-level decays will be known precisely. Displaying $Delta M_{s,d}$ as functions of $gamma$ clearly demonstrates the tension between the value of $gamma$ from tree-level decays, free from new physics (NP) contributions, and $Delta M_{s,d}$ calculated in CMFV and $U(2)^3$ models and thus exhibits the presence of NP contributions to $Delta M_{s,d}$ beyond these frameworks. We calculate the values of $|V_{ub}|$ and $|V_{td}|$ as functions of $gamma$ and $|V_{cb}|$ and discuss the implications of our results for $varepsilon_K$ and rare $K$ and $B$ decays. We also briefly discuss a future strategy in which $beta$, possibly affected by NP, is replaced by $|V_{ub}|$.
We discuss the impact of the recent $mathcal{O}(alpha_s^3)$ calculations of the semileptonic width of the $b$ quark and of the relation between pole and kinetic heavy quark masses by Fael et al. on the inclusive determination of $|V_{cb}|$. The most notable effects are a small increase in the value $|V_{cb}|$ and a reduction of the uncertainty. Our final result is $|V_{cb}|=42.16(50), 10^{-3}$.
We discuss the impact of the recent untagged analysis of ${B}^0rightarrow D^{*}lbar{ u}_l$ decays by the Belle Collaboration on the extraction of the CKM element $|V_{cb}|$ and provide updated SM predictions for the $bto ctau u$ observables $R(D^*)$, $P_tau$, and $F_L^{D^*}$. The value of $|V_{cb}|$ that we find is about $2sigma$ from the one from inclusive semileptonic $B$ decays, and is very sensitive to the slope of the form factor at zero recoil which should soon become available from lattice calculations.
We investigate the semi-leptonic decays of $bar B to D^{(*)} ellbar u$ in terms of the Heavy-Quark-Effective-Theory (HQET) parameterization for the form factors, which is described with the heavy quark expansion up to $mathcal O(1/m_c^2)$ beyond the simple approximation considered in the original CLN parameterization. An analysis with this setup was first given in the literature, and then we extend it to the comprehensive analyses including (i) simultaneous fit of $|V_{cb}|$ and the HQET parameters to available experimental full distribution data and theory constraints, and (ii) New Physics (NP) contributions of the $V_2$ and $T$ types to the decay distributions and rates. For this purpose, we perform Bayesian fit analyses by using Stan program, a state-of-the-art public platform for statistical computation. Then, we show that our $|V_{cb}|$ fit results for the SM scenarios are close to the PDG combined average from the exclusive mode, and indicate significance of the angular distribution data. In turn, for the $text{SM} + text{NP}$ scenarios, our fit analyses find that non-zero NP contribution is favored at the best fit point for both $text{SM} + V_2$ and $text{SM} + T$ depending on the HQET parameterization model. A key feature is then realized in the $bar B to D^{(*)} taubar u$ observables. Our fit result of the HQET parameters in the $text{SM} (+T)$ produces a consistent value for $R_D$ while smaller for $R_{D^*}$, compared with the previous SM prediction in the HFLAV report. On the other hand, $text{SM}+V_2$ points to smaller and larger values for $R_D$ and $R_{D^*}$ than the SM predictions. In particular, the $R_{D^*}$ deviation from the experimental measurement becomes smaller, which could be interesting for future improvement on measurements at the Belle II experiment.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
