REVIEW
Waiting for the Top Quark Mass, K^+ --> \pi^+ \nu \bar\nu, B_s^0-\bar{B}_s^0 Mixing and CP Asymmetries in B-Decays
High Energy Physics - Phenomenology · Submitted 29 Mar 1994 · 51 references
Pith's verdict: The durable contribution is the exact-unitarity (rho-bar, eta-bar) formulation and the analytic toolkit; the numerical predictions are conditional and the x_s number is the soft one.
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Referee report
The paper
The paper claims
With tighter inputs on the top mass, $|V_{cb}|$, $|V_{ub}/V_{cb}|$ and the hadronic parameters $B_K$ and $F_Bsqrt{B_B}$, the standard-model unitarity triangle becomes predictive for $sin(2beta)$, $|V_{td}|$, $x_s$ and $BR(K^+ to pi^+ nu bar
The reading
What carries the argument
The carrying object is the rescaled unitarity triangle in the $(bar rho, bar eta)$ plane, obtained by dividing the relation $V_{ud}V^{*}_{ub} + V_{cd}V^{*}_{cb} + V_{td}V^{*}_{tb} = 0$ by $V_{cd}V^{*}_{cb} = -A lambda^3$ so that one side has unit length and the apex sits at $(bar rho, bar eta)$ rather than $(rho, eta)$. Three experimental constraints cut this plane: $epsilon_K$ gives a hyperbola, $x_d$ gives a circle of radius $R_t$ fixed by $sqrt{x_d}$ and the (poorly known) $F_B sqrt{B_B}$, and $BR(K^+ to pi^+ nu bar u)$ gives an ellipse centred near $bar rho = 1$ whose axes are set by the next-to-leading QCD calculation of the decay. The ratio $x_d/x_s$ is the cleanest of these because the top mass and most hadronic uncertainties cancel, leaving $R_t$ in terms of $sqrt{x_d/x_s}$ and a small SU(3)-breaking factor $R_{ds}$. Two compact fits, $S(x_t) approx 0.784 x_t^{0.76}$ and $X(x_t) approx 0.65 x_t^{0.575}$, let the authors turn the numerical scan into analytic formulas accurate to a couple of percent.
Extended reading notes
Core claim
The central claim is conditional and quantitative. Using the standard model with the measured indirect CP violation in $K to pi pi$ ($epsilon_K$) and the measured $B^0_d$ mixing ($x_d$), together with the improved parameter ranges they anticipate, the authors find that the apex of the unitarity triangle is confined enough to predict $sin(2beta)$, $|V_{td}|$, the $B^0_s$ mixing parameter $x_s$ and the branching ratio for $K^+ to pi^+ nu bar u$ at the ten-to-twenty percent level, whereas $sin(2alpha)$ and $sin(2gamma)$ remain spread over nearly their full allowed ranges. They then show that adding a direct measurement of $sin(2alpha)$ or $sin(2gamma)$ to a measurement of $sin(2beta)$ collapses the allowed region dramatically, and that the combination of $BR(K^+ to pi^+ nu bar u)$, $sin(2beta)$, $|V_{cb}|$, $m_t$ and $x_d/x_s$ alone would give a respectable determination of $|V_{td}|$ provided each is measured to about ten percent. Along the way they extend the standard leading-order treatment of the triangle to next order in $lambda = |V_{us}|$, derive closed-form expressions for $sin(2phi_i)$ in terms of $(bar rho, bar eta)$, and give analytic bounds: a lower limit on $m_t$ from $epsilon_K$, a matching lower limit on $B_K$, an upper bound $(sin 2beta)_{max} = 2R_b sqrt{1 - R_b^2}$, and the curve $bar eta = (1 - bar rho)sqrt{bar rho/(2 - bar rho)}$ on which the standard model and superweak models would give indistinguishable $B$-decay asymmetries.
Load-bearing premise
The $x_s$ prediction and the extraction of $R_t$ from $x_d/x_s$ set the SU(3)-breaking ratio $R_{ds} = 1$, i.e. assume $F_{B_s}sqrt{B_{B_s}} = F_{B_d}sqrt{B_{B_d}}$ with equal lifetimes and masses; the paper states this explicitly in Section 5.1 and concedes in Section 5.3 that a ten percent $x_s$ determination requires $R_{ds}$ known to ten percent.
Editorial extensions
If this is right
- A measurement of $BR(K^+ to pi^+ nu bar u)$ at the ten percent level would either confirm the standard-model prediction of about $1.0 times 10^{-10}$ or expose a discrepancy with the triangle fixed by $epsilon_K$ and $x_d$.
- A measurement of $sin(2beta)$ near $0.6$ with an error of $pm 0.06$ would already be more informative than the $epsilon_K$ plus $x_d$ prediction, and adding $sin(2alpha)$ at $pm 0.10$ would shrink the allowed region for $delta$, $sin(2gamma)$, $|V_{td}|$, $x_s$ and the kaon branching ratio to a few percent.
- Because $sin(2alpha)$ and $sin(2gamma)$ cannot be predicted from $epsilon_K$, $x_d$, $|V_{cb}|$ and $|V_{ub}/V_{cb}|$ alone, measuring them is the only way to test whether the standard-model picture holds; a measured value outside the predicted band would be a signal of new physics.
- Comparing the measured $B^0 to psi K_S$ and $B^0 to pi^+ pi^-$ asymmetries against the curve where $sin(2alpha) = -sin(2beta)$ would let experiment rule out superweak models of CP violation.
- If $x_s$ is measured to about ten percent and the SU(3)-breaking ratio $R_{ds}$ is known to the same accuracy, $R_t$ and hence $|V_{td}|$ follow without any dependence on the top mass or on $|V_{cb}|$.
Reading between the lines
- The forecast is a snapshot of a moving target: several of the central values quoted here (notably $x_s$ near 13 and $BR(K^+ to pi^+ nu bar u)$ near $1.0 times 10^{-10}$) sit in a region that later data moved away from, so the durable content of the paper is less the numbers than the demonstration that a handful of theoretically clean observables over-determine the triangle.
- The same logic implies a sharp consistency test: any two of $sin(2beta)$, $BR(K^+ to pi^+ nu bar u)$ and $x_d/x_s$ fix the apex, so a third measurement that misses the intersection is a quantitative handle on new physics rather than a failure of the fit.
- The paper's insistence that $sin(2alpha)$ and $sin(2gamma)$ are the weak links suggests that the value of a future $B$-factory programme lies mostly in those two angles, since $sin(2beta)$ would already be predicted well by then.
- Treating the quoted $pm$ as scan half-widths rather than statistical errors means the forecasts are best read as honest ranges of ignorance about the inputs, not as confidence intervals; improving the hadronic inputs is therefore worth more than accumulating events.
Original abstract
Anticipating improved determinations of m_t, |V_ub/V_cb|, B_K and F_B \sqrt{B_B} in the next five years we make an excursion in the future in order to find a possible picture of the unitarity triangle, of quark mixing and of CP-violation around the year 2000. We then analyse what impact on this picture will have the measurements of four possibly cleanest quantities: BR(K^+ --> \pi^+ \nu \bar\nu), x_d/x_s, sin(2\alpha) and \sin(2\beta). Our analysis shows very clearly that there is an exciting time ahead of us. In the course of our investigations we extend the analysis of the unitarity triangle beyond the leading order in \lambda and we derive several useful analytic formulae for quantities of interest.
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
Anticipating improved determinations of m_t, |V_ub/V_cb|, B_K and F_B \sqrt{B_B} in the next five years we make an excursion in the future in order to find a possible picture of the unitarity triangle, of quark mixing and of CP-violation around the year 2000. We then analyse what impact on this picture will have the measurements of four possibly cleanest quantities: BR(K^+ --> \pi^+ \nu \bar\nu), x_d/x_s, sin(2\alpha) and \sin(2\beta). Our analysis shows very clearly that there is an exciting time ahead of us. In the course of our investigations we extend the analysis of the unitarity triangle beyond the leading order in \lambda and we derive several useful analytic formulae for quantities of interest.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Anticipating improved determinations of m_t, |V_ub/V_cb|, B_K and F_B \sqrt{B_B} in the next five years we make an excursion in the future in order to find a possible picture of the unitarity triangle, of quark mixing and of CP-violation around the year 2000. | contribution 0.51 | 0.38 | 0.06 | hedged possibility 0.38 |
| s1 | We then analyse what impact on this picture will have the measurements of four possibly cleanest quantities: BR(K^+ --> \pi^+ \nu \bar\nu), x_d/x_s, sin(2\alpha) and \sin(2\beta). | contribution 0.67 | 0.55 | 0.05 | asserted 0.46 |
| s2 | Our analysis shows very clearly that there is an exciting time ahead of us. | interpretation 0.97 | 0.68 | 0.50 | asserted 0.99 |
| s3 | In the course of our investigations we extend the analysis of the unitarity triangle beyond the leading order in \lambda and we derive several useful analytic formulae for quantities of interest. | contribution 0.84 | 0.95 | 0.06 | asserted 1.00 |
What was examined, and what was not
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Figures
Figures reproduced from arXiv:hep-ph/9403384 by the authors.
References
How later papers used it
58 later papers cite it
2 later papers by other authors are listed below: 2 used its method or tool.
Uses its method or tool 2 of 10 papers with this label
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Adopted this paper's definition of the Wolfenstein parameters to keep the CKM matrix unitary to all orders of lambda.
A Revisit to Top Quark Forward-Backward Asymmetry (2011) · 0.92 · paraphrased: the licence does not allow quoting
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Followed this paper to define its parameters, noting that V_ub is typically taken of order lambda^3 though numerically of order lambda^4.
How much space is left for a new family? (2009) · 0.89 · paraphrased: the licence does not allow quoting
How the literature uses it
49 arXiv papers cite this in 62 sentences
Papers citing it · 42 sentences without a confident label
Builds on it 1 paper
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The value of $sin2β$ from Table [ref] implies $β=(21.5±1.0)^∘$ or [equation] In terms of the improved Wolfenstein parameters $ρ̅$ and $η̅$ [ref] the unitarity triangle is then determined by [equation] [equation] These formulas have been derived in [ref] for $B→π^+π^-$, but they apply to the case of $B→ρ^+_Lρ^-_L$ as well.
B -> V_L V_L Decays at Next-to-Leading Order in QCD · Determination of $ρ̅$, $η̅$, $γ$ and $α$ · 0.87
Uses its method or tool 8 papers
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In finding the $$-independent correlations between various observables it is useful to use the so-called improved Wolfenstein parametrization [ref] of the CKM matrix that is much more precise than the original Wolfenstein parametrization [ref] .
Searching for New Physics in Rare $K$ and $B$ Decays without $|V_{cb}|$ and $|V_{ub}|$ Uncertainties · A Useful Parametrization of the UT · 0.88
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If we make use of the unitarity of the CKM matrix and apply the Wolfenstein parametrisation [ref] as generalised in Ref. [ref] , we can write ([ref]) as [equation] Here [equation] and [equation] are CP-conserving, “hadronic" parameters, where [equation] with $λ≡|V_us|=0.22521±0.00083$ are CKM parameters.
Extracting gamma and Penguin Topologies through CP Violation in B_s^0 -> J/psi K_S · The Basic Strategy · 0.80
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Given that $s_13≪s_23 ≪s_12 ≪1$, a perturbative expansion in powers of the sine of the Cabibbo angle $s_12$ can be performed [ref] , defining [equation] and imposing the unitarity constraint at the desired order [ref] .
Effective Theories for Quark Flavour Physics · The Cabibbo-Kobayashi-Maskawa mixing matrix · 0.89
Uses its data or values 2 papers
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Including the dominant corrections [ref] with the Wolfenstein parameters taken from global unitarity fits by CKMFitter [ref] (using values from the January 2022 update) gives [equation] using $=0.97367(32)$ from superallowed $0^+→0^+$ nuclear $β$ decays [ref] and $=0.22330(53)$ from $K_ℓ3$ decays [ref] .
D-meson semileptonic decays to pseudoscalars from four-flavor lattice QCD · Tests of CKM unitarity · 0.94
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Since it is better suited for our purpose, we adopt the Wolfenstein-like but exactly unitary parametrization of [ref] , for which we obtain up-to-date values for the parameters $λ=0.22481±0.00059$, $A=0.817±0.018$, $ρ=0.145±0.015$ and $η=0.366±0.012$ by performing our own fit to PDG data [ref] .
The Basis Invariant Flavor Puzzle · Quark sector flavor invariants · 0.87
Cites it as background 9 papers
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It was pointed out [ref] that as in any perturbative expansion, high order terms in $λ$ are not unique in the Wolfenstein parametrization, though the nonuniqueness of the high order terms does not change the physics.
Wolfenstein Parametrization at Higher Order: Seeming Discrepancies and Their Resolution · Introduction · 0.81
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The dominance of B physics constraints in the past decades has dictated the traditional presentation of consistency between observables, in the complex plane given by [ref] ,
Natural complex plane for kaon CKM data: framework, status and future · Introduction · 0.81
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In the Standard Model (SM), the complex phases $ϕ_d$ and $ϕ_s$ associated with the mixing between neutral $B_q^0$ and $B̅_q^0$ mesons, where $q∈{d,s}$, are parametrised as [equation] Their experimental determinations are powerful probes to search for evidence of physics beyond the Standard Model (BSM): The measurement of $ϕ_d$ constrains the angle $β$ of the Unitarity Triangle (UT), and the value of $ϕ_s$ can directly be compared with the SM prediction based on the Wolfenstein parametrisation [ref] of the Cabibbo–Kobayashi–Maskawa (CKM) quark-mixing matrix [ref] .
Taming Penguins: Towards High Precision Measurements in $\phi_d$ and $\phi_s$ · Introduction · 0.98
Discussion
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