REVIEW
Lattice QCD calculation of $\bar{B}\to Dl\bar{\nu}$ decay form factors at zero recoil
High Energy Physics - Phenomenology · Submitted 15 Jun 1999 · 36 references
Pith's verdict: The double-ratio method is the real contribution and h+(1) holds up, but the headline F(1)−1 = 0.058 comes almost entirely from h−(1), which is exactly the piece with no computed one-loop matching.
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Referee report
The paper
The paper claims
The paper reports a lattice QCD determination of the zero-recoil $F_{B��to D}(1)=1.058^{+0.020}_{-0.017}$ from double ratios in which most statistical and matching uncertainties cancel.
The reading
What carries the argument
The machinery is the double ratio of three-point correlation functions, constructed so that the numerator and denominator share the same interpolating fields and current normalizations. Because the ratio is identically one in the degenerate-mass limit and in the static limit, the measured deviation from one carries the physical signal while most statistical and matching uncertainties cancel. Heavy-quark symmetry then restricts the expansion to even powers of $(1/m_c-1/m_b)$ for $h_+$ and to a leading linear term for $h_-$, so a few mass combinations suffice to interpolate to the physical $b$ and $c$ masses. The clover action with a tuned clover coefficient and a rotated current supplies the lattice realization of the heavy-quark expansion.
Extended reading notes
Core claim
The central claim is that the zero-recoil $��bar B��to D$ form factor can be obtained accurately from a ratio of lattice correlation functions in which the normalization of the heavy-heavy vector current cancels between numerator and denominator. For $h_+(1)$ the relevant ratio is $R^{B��to D}(t)=C^{DV_0B}C^{BV_0D}/(C^{DV_0D}C^{BV_0B})$, and in the asymptotic time-separation limit it tends to $|h_+(1)|^2$. For $h_-(1)$ a second double ratio involving spatial and temporal currents yields $1-h_-(1)/h_+(1)$ at small recoil. The authors then observe the heavy-quark mass dependence directly, fit it with constrained $1/m_Q$ expansions, and interpolate to physical masses, arriving at $F_{B��to D}(1)=1.058^{+0.020}_{-0.017}$. The paper presents this as filling the gap left by earlier lattice calculations, which could not control the current normalization and the heavy-quark mass dependence well enough to quote an absolute normalization.
Load-bearing premise
The load-bearing premise is that the omitted lattice-spacing and quenching errors scale with $F_{B��to D}(1)-1$ rather than with $F_{B��to D}(1)$ itself, so that a roughly 15 percent quenching estimate becomes a roughly 0.9 percent error on the quoted $1.058$; the paper does not compute that coefficient and imports the estimate from earlier $f_B$ work.
Editorial extensions
If this is right
- It supplies a lattice normalization for extracting $|V_{cb}|$ from $��bar B��to D��ell��bar��nu$, giving an independent cross-check on the $��bar B��to D^*��ell��bar��nu$ route.
- The fitted coefficients of the $1/m_Q$ expansion, such as $c_+^{(2)}=[0.20(4)\ \mathrm{GeV}]^2$, become targets for QCD sum rules and quark models.
- The same double-ratio construction can be adapted to other heavy-to-heavy matrix elements once the relevant current matching is known, including the axial-vector case of $��bar B��to D^*��ell��bar��nu$.
- If the lattice-spacing and quenching systematics are brought under control as the authors expect, the quoted $F_{B��to D}(1)$ precision is small enough to matter for the exclusive determination of $|V_{cb}|$.
Reading between the lines
- Beyond the paper, the double-ratio strategy looks like a general template: any matrix element with a symmetry-protected normalization condition can be turned into a ratio whose errors are proportional to the deviation from the symmetric limit.
- The most valuable next step is not more statistics but a direct nonperturbative estimate of the quenching and lattice-spacing coefficients, because the entire error budget rests on an uncomputed scaling assumption.
- The tension with sum-rule estimates of $c_-^{(1)}$ may be a useful diagnostic: if the missing one-loop matching for the spatial current moves $h_-(1)$ toward the sum-rule range, that would support the paper's error estimate; if it does not, the discrepancy points to a real gap between lattice and sum-rule treatments.
- If future $��bar B��to D$ and $��bar B��to D^*$ lattice normalizations both mature, a persistent difference in the extracted $|V_{cb}|$ would be a clean place to look for either underestimated lattice systematics or new physics in semileptonic decays.
Original abstract
A lattice QCD calculation of the $\bar{B}\to Dl\bar{\nu}$ decay form factors is presented. We obtain the value of the form factor $h_+(w)$ at the zero-recoil limit $w=1$ with high precision by considering a ratio of correlation functions in which the bulk of the uncertainties cancels. The other form factor $h_-(w)$ is calculated, for small recoil momenta, from a similar ratio. In both cases, the heavy quark mass dependence is observed through direct calculations with several combinations of initial and final heavy quark masses. Our results are $h_+(1) = 1.007(6)(2)(3)$ and $h_-(1)=-0.107(28)(04)(^{10}_{30})$. For both the first error is statistical, the second stems from the uncertainty in adjusting the heavy quark masses, and the last from omitted radiative corrections. Combining these results, we obtain a precise determination of the physical combination $F_{B\to D}(1)=1.058(^{20}_{17})$, where the mentioned systematic errors are added in quadrature. The dependence on lattice spacing and the effect of quenching are not yet included, but with our method they should be a fraction of $F_{B\to D}-1$.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
A lattice QCD calculation of the $\bar{B}\to Dl\bar{\nu}$ decay form factors is presented. We obtain the value of the form factor $h_+(w)$ at the zero-recoil limit $w=1$ with high precision by considering a ratio of correlation functions in which the bulk of the uncertainties cancels. The other form factor $h_-(w)$ is calculated, for small recoil momenta, from a similar ratio. In both cases, the heavy quark mass dependence is observed through direct calculations with several combinations of initial and final heavy quark masses. Our results are $h_+(1) = 1.007(6)(2)(3)$ and $h_-(1)=-0.107(28)(04)(^{10}_{30})$. For both the first error is statistical, the second stems from the uncertainty in adjusting the heavy quark masses, and the last from omitted radiative corrections. Combining these results, we obtain a precise determination of the physical combination $F_{B\to D}(1)=1.058(^{20}_{17})$, where the mentioned systematic errors are added in quadrature. The dependence on lattice spacing and the effect of quenching are not yet included, but with our method they should be a fraction of $F_{B\to D}-1$.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | A lattice QCD calculation of the $\bar{B}\to Dl\bar{\nu}$ decay form factors is presented. | contribution 1.00 | 0.94 | 0.06 | asserted 0.99 |
| s1 | We obtain the value of the form factor $h_+(w)$ at the zero-recoil limit $w=1$ with high precision by considering a ratio of correlation functions in which the bulk of the uncertainties cancels. | result 0.42 | 0.97 | 0.24 | asserted 1.00 |
| s2 | The other form factor $h_-(w)$ is calculated, for small recoil momenta, from a similar ratio. | method 0.88 | 0.96 | 0.03 | asserted 1.00 |
| s3 | In both cases, the heavy quark mass dependence is observed through direct calculations with several combinations of initial and final heavy quark masses. | method 0.91 | 0.95 | 0.03 | asserted 1.00 |
| s4 | Our results are $h_+(1) = 1.007(6)(2)(3)$ and $h_-(1)=-0.107(28)(04)(^{10}_{30})$. | result 1.00 | 0.97 | 0.48 | asserted 1.00 |
| s5 | For both the first error is statistical, the second stems from the uncertainty in adjusting the heavy quark masses, and the last from omitted radiative corrections. | interpretation 0.71 | 0.84 | 0.05 | asserted 1.00 |
| s6 | Combining these results, we obtain a precise determination of the physical combination $F_{B\to D}(1)=1.058(^{20}_{17})$, where the mentioned systematic errors are added in quadrature. | result 1.00 | 0.97 | 0.65 | asserted 1.00 |
| s7 | The dependence on lattice spacing and the effect of quenching are not yet included, but with our method they should be a fraction of $F_{B\to D}-1$. | limitation 1.00 | 0.33 | 0.04 | hedged possibility 0.85 |
What was examined, and what was not
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Figures
Figures reproduced from arXiv:hep-ph/9906376 by the authors.
References
How the literature uses it
36 arXiv papers cite this in 41 sentences
Papers citing it · 11 sentences without a confident label
Builds on it 1 paper
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Double ratio methods similar to what has been developed for lattice studies of $B →D l ν$ [ref] can be adapted to semileptonic $D$ meson decays [ref] .
Weak Charm Decays with Lattice QCD · Semileptonic $D$ Meson Form Factors · 0.88
Uses its method or tool 23 papers
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The semileptonic form factor $h_A_1(w)$ at zero recoil (i.e. $w=1$) can be obtained with the Hashimoto ratio [ref] :
Current progress on the semileptonic form factors for $\bar{B} \to D^{\ast} \ell \bar{\nu}$ decay using the Oktay-Kronfeld action · Preliminary result on $h_A_1(w=1)/ρ_A_1$: $B →D^∗ℓν$ form factor at zero recoil · 1.00
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The pioneering work of Hashimoto et al. [ref] introduced several double ratios to this end.
Update of $|V_{cb}|$ from the $\bar{B}\to D^*\ell\bar{\nu}$ form factor at zero recoil with three-flavor lattice QCD · Introduction · 0.80
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We use a mostly nonperturbative method [ref] to match the $b→q$ ($q=u,c$) vector and axial vector currents from the lattice scheme to the continuum $MS$ scheme.
$\Lambda_b \to p \ell^- \bar{\nu}_\ell$ and $\Lambda_b \to \Lambda_c \ell^- \bar{\nu}_\ell$ form factors from lattice QCD with relativistic heavy quarks · Lattice actions and currents · 1.00
Compares with it 2 papers
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Previous lattice calculations by the Fermilab collaboration [ref] quote the value of $G^B→D(w)$ only at zero recoil where it can be extracted with good statistical accuracy by using the so called "double ratio" technique.
Quenched lattice calculation of the B --> D l nu decay rate · Form factors and decay rate · 0.80
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This result is an interesting, and fully non-perturbative, analogue of the Fermilab [ref] partially-perturbative approach to currents that are conserved in the continuum.
The decay constants ${\mathbf{f_D}}$ and ${\mathbf{f_{D_{s}}}}$ in the continuum limit of ${\mathbf{N_f=2+1}}$ domain wall lattice QCD · RI/SMOM and the axial vertex function · 0.80
Cites it as background 3 papers
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Currently, there have been some studies on the semileptonic decays $B̅_s^0→D_s^+(1968,2317) l ν̅_l$ ranging from phenomenological model [ref] to QCD sum rules approach [ref] , PQCD approach [ref] and Lattice QCD [ref] .
Exclusive $B_s$ decays to the charmed mesons $D_s^+(1968,2317)$ in the standard model · Introduction · 0.98
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There have existed some phenomenological studies using different approaches, including the phenomenological model [ref] , the QCD sum rules approach [ref] , PQCD approach [ref] , Lattice QCD [ref] , as well as the light-cone sum rules (LCSR) [ref] .
Charmed Scalar Meson Production in $B$ Decays · Introduction · 0.96
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Theoretically, numerous effective approaches exist to make reasonable predictions for TFF of the $B→Dℓ^+ν_ℓ$ semileptonic decay process, such as the perturbative QCD (pQCD) [ref] , the QCD light-cone sum rule (LCSRs) [ref] , and the lattice QCD (LQCD) [ref] .
Footprint in fitting $B \to D$ vector form factor and determination for $D$-meson leading-twist LCDA · Introduction · 0.84
Discussion
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