REVIEW
Measurements of branching fractions and $q^2$ distributions for $B \to \pi \ell \nu$ and $B \to \rho \ell \nu$ Decays with $B \to D^{(*)} \ell \nu$ Decay Tagging
High Energy Physics - Experiment · Submitted 12 Apr 2006 · 24 references
Pith's verdict: First tagging-based measurement of B->pi/rho l nu with B->D(*) l nu; clean and honest, with a genuine MC validation gap on the signal side.
T0 · AI review
Why Pith says this
Highlight any text to comment on it.
Referee report
The paper
The paper claims
Tagging the partner B decay measures B->pi/rho l nu rates and extracts |Vub|
The reading
What carries the argument
The central mechanism is the double-semileptonic cone constraint. With both B mesons decaying semileptonically, each neutrino's unknown momentum leaves the B direction on a cone around the visible system; the back-to-back condition in the Upsilon(4S) rest frame forces the B direction onto the intersection of two cones, encoded in the variable $xB^{2}$, which must lie between 0 and 1 for a correctly reconstructed double-semileptonic event. A binned maximum-likelihood fit to the ($xB^{2}$, MX) distribution, where MX is the hadronic mass (pion mass for pion modes, two-pion invariant mass for rho modes), separates the four signal modes from other B->Xu l nu and B Bbar backgrounds. The q2 variable is reconstructed from the beam energy and the visible hadronic system, with a resolution of 0.32-0.95 $GeV^{2}$/$c^{2}$, and an efficiency matrix epsilon(q2_rec, q2_true) unfolds migrations among the three q2 bins. The tagging side is validated with a B->D* l nu control sample whose ratio of observed to expected yield is consistent with unity.
Extended reading notes
Core claim
On its own terms, the paper establishes that the double-semileptonic tagging method works for charmless decays: with 2.75 x $10^{8}$ B Bbar events, it measures B(B0 -> pi- l+ nu) = (1.38 +/- 0.19 +/- 0.14 +/- 0.03) x $10^{-4}$, B(B0 -> rho- l+ nu) = (2.17 +/- 0.54 +/- 0.31 +/- 0.08) x $10^{-4}$, B(B+ -> pi0 l+ nu) = (0.77 +/- 0.14 +/- 0.08 +/- 0.00) x $10^{-4}$, and B(B+ -> rho0 l+ nu) = (1.33 +/- 0.23 +/- 0.17 +/- 0.05) x $10^{-4}$, where the three errors are statistical, experimental systematic, and form-factor systematic. It presents the partial branching fractions in three q2 bins and uses the q2 >= 16 $GeV^{2}$/$c^{2}$ bin with unquenched lattice QCD form factors to obtain |Vub| = (3.60 +/- 0.41 +/- 0.20 +0.62/-0.41) x $10^{-3}$ and (4.03 +/- 0.46 +/- 0.22 +0.59/-0.41) x $10^{-3}$ for the two lattice calculations. The charged and neutral pion modes are consistent with the isospin relation Gamma(B0 -> pi- l nu) = 2 Gamma(B+ -> pi0 l nu), and the measured q2 shapes disfavor one quark-model form-factor shape for B -> pi l nu.
Load-bearing premise
The measurement assumes the Monte Carlo simulation accurately predicts how often and in which q2 bin the charmless signal is detected, since only the tagging side is checked against data with a control sample.
Editorial extensions
If this is right
- With more integrated luminosity and smaller lattice QCD errors, the same method can push the |Vub| uncertainty below 10 percent.
- The measured q2 distributions, especially in the high-q2 bin where lattice QCD is reliable, provide a direct test of form-factor models; a quark-model prediction is disfavored for B -> pi l nu.
- The consistency of neutral and charged modes with isospin relations supports using isospin symmetry to combine B0 and B+ modes in future |Vub| determinations.
- The rho l nu branching fractions, measured with the smallest uncertainty among existing results, become a new benchmark for exclusive charmless semileptonic rates.
Reading between the lines
- The tagging method is not limited to pion and rho modes; the same double-semileptonic reconstruction could be applied to B->eta l nu, B->omega l nu, and other charmless final states with similar background suppression.
- Because the calibration sample only validates the tag side, a future analysis could use B->D(*) l nu events reconstructed on both sides to directly measure the signal-side efficiency matrix in data, reducing reliance on simulation.
- The q2-bin unfolding relies on the efficiency matrix; a cross-check that compares reconstructed q2 in a control sample with known true q2 (for example, from B->D* l nu) would test the quoted q2 resolution assumption.
- The two lattice QCD normalizations give |Vub| values differing by about 11 percent, so an independent determination of the high-q2 form-factor normalization, or a measurement at intermediate q2 with light-cone sum rules, would decide which value is closer to the true one.
Original abstract
We report measurements of the charmless semileptonic decays $B^0 \to \pi^- / \rho^- \ell^{+} \nu$ and $B^+ \to \pi^0 / \rho^0 \ell^{+} \nu$, based on a sample of $2.75 \times 10^8$ $B \bar{B}$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ asymmetric collider. In this analysis, the accompanying $B$ meson is reconstructed in the semileptonic mode $B \to D^{(*)} \ell \nu$, enabling detection of the signal modes with high purity. We measure the branching fractions ${\mathcal B}(B^0 \to \pi^- \ell^+ \nu) = (1.38\pm 0.19\pm 0.14\pm 0.03) \times 10^{-4}$, ${\mathcal B}(B^0 \to \rho^- \ell^+ \nu) = (2.17\pm 0.54\pm 0.31\pm 0.08) \times 10^{-4}$, ${\mathcal B}(B^+ \to \pi^0 \ell^+ \nu) = (0.77\pm 0.14\pm 0.08\pm 0.00) \times 10^{-4}$ and ${\mathcal B}(B^+ \to \rho^0 \ell^+ \nu) = (1.33\pm 0.23\pm 0.17\pm 0.05) \times 10^{-4}$, where the errors are statistical, experimental systematic, and systematic due to form-factor uncertainties, respectively. For each mode we also present the partial branching fractions in three $q^2$ intervals: $q^2 < 8$, $8 \leq q^2 < 16$, and $q^2 \geq 16$ GeV$^2/c^2$. From our partial branching fractions for $B \to \pi \ell \nu$ and recent results for the form factor from unquenched Lattice QCD calculations, we obtain values of the CKM matrix element $|V_{ub}|$.
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
We report measurements of the charmless semileptonic decays $B^0 \to \pi^- / \rho^- \ell^{+} \nu$ and $B^+ \to \pi^0 / \rho^0 \ell^{+} \nu$, based on a sample of $2.75 \times 10^8$ $B \bar{B}$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ asymmetric collider. In this analysis, the accompanying $B$ meson is reconstructed in the semileptonic mode $B \to D^{(*)} \ell \nu$, enabling detection of the signal modes with high purity. We measure the branching fractions ${\mathcal B}(B^0 \to \pi^- \ell^+ \nu) = (1.38\pm 0.19\pm 0.14\pm 0.03) \times 10^{-4}$, ${\mathcal B}(B^0 \to \rho^- \ell^+ \nu) = (2.17\pm 0.54\pm 0.31\pm 0.08) \times 10^{-4}$, ${\mathcal B}(B^+ \to \pi^0 \ell^+ \nu) = (0.77\pm 0.14\pm 0.08\pm 0.00) \times 10^{-4}$ and ${\mathcal B}(B^+ \to \rho^0 \ell^+ \nu) = (1.33\pm 0.23\pm 0.17\pm 0.05) \times 10^{-4}$, where the errors are statistical, experimental systematic, and systematic due to form-factor uncertainties, respectively. For each mode we also present the partial branching fractions in three $q^2$ intervals: $q^2 < 8$, $8 \leq q^2 < 16$, and $q^2 \geq 16$ GeV$^2/c^2$. From our partial branching fractions for $B \to \pi \ell \nu$ and recent results for the form factor from unquenched Lattice QCD calculations, we obtain values of the CKM matrix element $|V_{ub}|$.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We report measurements of the charmless semileptonic decays $B^0 \to \pi^- / \rho^- \ell^{+} \nu$ and $B^+ \to \pi^0 / \rho^0 \ell^{+} \nu$, based on a sample of $2.75 \times 10^8$ $B \bar{B}$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ asymmetric collider. | contribution 0.84 | 0.92 | 0.05 | asserted 1.00 |
| s1 | In this analysis, the accompanying $B$ meson is reconstructed in the semileptonic mode $B \to D^{(*)} \ell \nu$, enabling detection of the signal modes with high purity. | method 1.00 | 0.82 | 0.03 | asserted 1.00 |
| s2 | We measure the branching fractions ${\mathcal B}(B^0 \to \pi^- \ell^+ \nu) = (1.38\pm 0.19\pm 0.14\pm 0.03) \times 10^{-4}$, ${\mathcal B}(B^0 \to \rho^- \ell^+ \nu) = (2.17\pm 0.54\pm 0.31\pm 0.08) \times 10^{-4}$, ${\mathcal B}(B^+ \to \pi^0 \ell^+ \nu) = (0.77\pm 0.14\pm 0.08\pm 0.00) \times 10^{-4}$ and ${\mathcal B}(B^+ \to \rho^0 \ell^+ \nu) = (1.33\pm 0.23\pm 0.17\pm 0.05) \times 10^{-4}$, where the errors are statistical, experimental systematic, and systematic due to form-factor uncertainties, respectively. | result 1.00 | 0.98 | 0.59 | asserted 1.00 |
| s3 | For each mode we also present the partial branching fractions in three $q^2$ intervals: $q^2 < 8$, $8 \leq q^2 < 16$, and $q^2 \geq 16$ GeV$^2/c^2$. | result 0.62 | 0.94 | 0.03 | asserted 0.99 |
| s4 | From our partial branching fractions for $B \to \pi \ell \nu$ and recent results for the form factor from unquenched Lattice QCD calculations, we obtain values of the CKM matrix element $|V_{ub}|$. | result 0.86 | 0.91 | 0.46 | asserted 1.00 |
What was examined, and what was not
- arXiv listing abstract v2
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Figures reproduced from arXiv:hep-ex/0604024 by the authors.
References
How the literature uses it
14 arXiv papers cite this in 18 sentences
Papers whose main result relates to this one's
States the same result 1 paper
-
Based on these results, the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element $V_{ub}$ is extracted.
Measurement of Exclusive $B \to X_u \ell \nu$ Decays with $D^{(*)} \ell \nu$ Decay Tagging · 0.93
Papers citing it · 9 sentences without a confident label
Uses its method or tool 1 paper
-
The detector simulation errors have been obtained following the procedure described in a Belle study of similar final states in reference [ref] .
Measurement of exclusive B to Xu l nu decays using full-reconstruction tagging at Belle · Systematic Uncertainties · 1.00
Uses its data or values 2 papers
-
In order to extrapolate the vector form factor $f_+(q^2)$ to the $B^*$ pole based on the various form-factor parametrizations, we first need to determine their shape parameters from the current experimental data on $B→πℓν$ decay reported by the BaBar [ref] and Belle [ref] collaborations.
Determination of the strong coupling $g_{B^* B\pi}$ from semi-leptonic $B\to \pi \ell \nu$ decay · The fitted $B→π$ form-factor shape parameters · 1.00
-
For the exclusive decays, we use the HFAG averages [ref] [equation] together with the theoretical estimates of the relevant normalized form factors to obtain $|V_ub|^excl=(33.3±2.7)×10^-4$.
An Improved Standard Model Prediction Of BR(B -> tau nu) And Its Implications For New Physics · Introduction · 0.92
Compares with it 1 paper
-
A similar discrepancy is also present in BELLE results [ref] .
Recent CKM and CP Results from BaBar · Measurement of $|V_ub|$ from Inclusive $X_u l$ Decays · 0.94
Cites it as background 5 papers
-
Although measurements of the decay distributions are available also from the same and other experiments [ref] and [ref] (with results collected in the corresponding sections in [ref] ), we restrict our analysis to this dataset only.
Hunting for new physics in $B$ meson $b \to u$ transitions: A fresh look with Belle II data · Data, analyses, results · 0.81
-
Measurements of branching fractions for exclusive decays, where $X_u$ denotes a light meson containing a $u$ quark, have been reported by the CLEO [ref] , BaBar [ref] and Belle [ref] collaborations.
Measurement of exclusive B to Xu l nu decays using full-reconstruction tagging at Belle · Introduction · 0.94
-
Measurements of branching fractions for exclusive decays, where $X_u$ denotes a light meson containing a $u$ quark and $ℓ$ an electron or muon, have been reported by the CLEO [ref] , [ref] and Belle [ref] collaborations.
Study of Exclusive B->X_u l nu Decays and Extraction of |V_{ub}| using Full Reconstruction Tagging at the Belle Experiment · Introduction · 0.90
Discussion
Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.