Abstract
Stringent relations between the B(∗) → D(∗) form factors exist in the heavy quark limit and the leading symmetry breaking corrections are known. We reconsider their uncertainty and role in the analysis of recent Belle data for B → D(∗)ℓν with model-independent parametrizations and in the related prediction of R(D(∗)). We find |Vcb| = 41.5(1.3) 10−3 and |Vcb| = 40.6(− 1.3+ 1.2) 10−3 using input from Light Cone Sum Rules, and R(D∗) = 0.260(8).
Highlights
D∗ is at rest in the B rest frame
They are grounded in the same foundations, the CLN parametrization makes use of Heavy Quark Effective Theory (HQET) relations between the B(∗) → D(∗) form factors in various ways in order to reduce the number of independent parameters
The main purpose of the present paper is to investigate to which extent the Heavy Quark Symmetry relations between the form factors affect the results of our previous analysis, once their uncertainty is properly accounted for
Summary
As explained in refs. [11, 13] the unitarity constraints on the parameters of the z-expansion can be made stronger by adding other hadronic channels which couple tocΓb currents. It is useful to recall that several of the form factors do not receive NLO power corrections at zero recoil because of Luke’s theorem [18]. ΣHQET is the total parametric relative uncertainty of the NLO HQET calculation, obtained combining in quadrature the uncertainty from the QCD sum rule parameters, mb, and αs Another condition that the replicas (Fj/Fi)α must comply with is that the coefficients a(nFj) of the form factor Fj, computed by expanding in powers of z the expression. The bounds in the (aV14, aV24) plane depend little on the exact value of aV04 in that range, besides being anyway much weaker than those on the coefficients of A1,5 In this case we obtain a two-dimensional allowed region, shown in figure 3. In the future, when new lattice information on the slopes of these form factors will become available, the bounds can be simplified; they will become one-dimensional bounds on aF2 i only
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