REVIEW
Decays of $B$ Mesons to Two Light Pseudoscalars
High Energy Physics - Phenomenology · Submitted 18 Apr 1994 · 28 references
Pith's verdict: A clean, honest SU(3) method paper: the new content is the Eq. (23) triangle and the rate-only γ extraction, and the authors are upfront that the whole thing rests on dropping E, A, PA.
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Referee report
The paper
The paper claims
The decays of B mesons into two light pseudoscalars obey triangle relations in flavour SU(3), and one of those triangles turns measured decay rates of charged B mesons into a determination of a CP-violating quark-mixing phase.
The reading
What carries the argument
The machinery is a graphical decomposition of $B to PP$ amplitudes that is equivalent to an SU(3) reduced-matrix-element expansion: five independent combinations of six diagrams, so that twelve amplitudes per strangeness sector satisfy seven linear relations. The relations come in three kinds — pure isospin triangles within $B to pi pi$ and within $B to pi K$, triangles that mix strange and non-strange final states, and cross-sector relations that use $T'/T = C'/C = E'/E = A'/A = r_u$ for tree-type graphs and $P'/P = PA'/PA = r_t$ for penguins. Neglecting $E$, $A$ and $PA$ translates into two simple statements about reduced matrix elements, ${8_1} = -sqrt{5}{1}/4$ and ${8_3} = {27}/4$, which is what converts the triangles into rate equalities such as $Gamma(B_s to pi^+ K^-) = Gamma(B^0 to pi^+ pi^-)$ and $Gamma(B^0 to pi^- K^+) = Gamma(B_s to K^- K^+)$.
Extended reading notes
Core claim
The central claim is that SU(3) flavour symmetry, organised graphically into a small set of topological amplitudes (tree $T$, colour-suppressed $C$, penguin $P$, exchange $E$, annihilation $A$, penguin annihilation $PA$, and their strangeness-changing primed partners), produces relations among $B to PP$ amplitudes that are simple enough to be used as measurement tools. The load-bearing relation is Eq. (23): $$sqrt{2},A(B^+ to $pi^{0}$ K^+) + A(B^+ to pi^+ $K^{0}$) = r_u, sqrt{2},A(B^+ to pi^+ $pi^{0}$),$$ which says that the combination of $B to pi K$ amplitudes carrying isospin $3/2$ is a pure 27-plet and is therefore proportional, with the known factor $r_u$, to the $B^+ to pi^+ pi^0$ amplitude. Because the $B^+ to pi^+ K^0$ amplitude is dominated by the penguin with weak phase $pi$ while the $pi^+ pi^0$ amplitude carries the tree phase $gamma$, the two triangles formed by this relation and its charge conjugate have a relative orientation that measures $gamma$ — provided the annihilation contribution $A'$ can be dropped, in which case the rates for $B^+ to pi^+ K^0$ and $B^- to pi^- bar K^0$ should be equal. The paper then shows that if the exchange, annihilation and penguin-annihilation graphs are neglected altogether, the surviving relations collapse into ten statements — six rate equalities, three triangles and one quadrangle — from which $gamma$, $alpha$, and the strong-phase differences $delta_P - delta_2$ and $delta_{P'} - delta_{3/2}$ can all be extracted from rates alone.
Load-bearing premise
The extraction of $gamma$, and the ten relations that follow, rest on treating the exchange, annihilation and penguin-annihilation diagrams (and their primed versions) as negligible, a suppression the authors justify by $f_B/m_B$ and helicity arguments but explicitly qualify as valid only if rescattering effects are unimportant.
Editorial extensions
If this is right
- Four measured rates — $B^+ to pi^0 K^+$, $B^- to pi^0 K^-$, $B^+ to pi^+ K^0$ and $B^+ to pi^+ pi^0$ — suffice to determine the weak phase $gamma$, with no time-dependent measurement and no tagging of the initial B flavour.
- A CP-violating rate difference between $B^+ to pi^0 K^+$ and $B^- to pi^0 K^-$ requires both two distinct weak subprocesses and a nonzero strong-phase difference between the $I = 1/2$ and $I = 3/2$ channels, so observing no asymmetry does not by itself rule out the mechanism.
- Rates for the full set of $pi pi$, $pi K$ and $K bar K$ charge states yield two CKM phases and several strong-phase differences, and the overlapping constructions provide independent cross-checks on SU(3) breaking.
- Several channels are predicted to be strongly suppressed or absent if the annihilation-type graphs are negligible: $B^0 to K^+ K^-$, $B_s to pi^+ pi^-$ and $B_s to pi^0 pi^0$ should all be near zero, making searches at the $10^{-7}$ level a direct test of the assumption.
- The same triangle logic applied to $B to pi bar D$ decays, where a single weak phase governs all channels, isolates final-state phase differences between $I = 1/2$ and $I = 3/2$ amplitudes; present data already bound the difference below about $35^circ$ at 90% confidence.
Reading between the lines
- The strategy is a template that outlives the specific SU(3) relations: whenever a symmetry forces one combination of amplitudes to be proportional to a single well-measured mode, that mode becomes a calibration leg for a triangle, and the phase information moves from interference in time to interference in the complex plane.
- Because the $gamma$ extraction is over-determined by the four rates, the residual of the triangle closure is itself a quantitative handle on SU(3) breaking — a use the paper notes only in passing when it suggests replacing $r_u$ by $(f_K/f_pi), r_u$ in Eq. (66).
- The rate equalities involving $B_s$ decays were not testable with the data available in 1994; they become sharp predictions for any experiment that can produce and identify $B_s$ mesons, and a measured $B_s to pi^+ pi^-$ rate above background would directly contradict the neglected-rescattering premise rather than merely strain it.
- The paper's insistence that strong-phase differences are needed for direct CP violation in charged-B decays suggests the natural follow-up is to ask whether the rescattering that would generate those phases can be computed, since that is what separates a rate-based phase extraction from a phase extraction that is robust to it.
Original abstract
The decays $B \to PP$, where $P$ denotes a pseudoscalar meson, are analyzed, with emphasis on charmless final states. Numerous triangle relations for amplitudes hold within SU(3) symmetry, relating (for example) the decays $B^+ \to \pi^+ \pi^0,~ \pi^0 K^+$, and $\pi^+ K^0$. Such relations can improve the possibilities for early detection of $CP$-violating asymmetries. Within the context of a graphical analysis of decays, relations are analyzed among SU(3) amplitudes which hold if some graphs are neglected. One application is that measurements of the rates for the above three $B^+$ decays and their charge-conjugates can be used to determine a weak CKM phase. With measurements of the remaining rates for $B$ decays to $\pi \pi,~\pi K$, and $K \bar K$, one can obtain two CKM phases and several differences of strong phase shifts.
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
The decays $B \to PP$, where $P$ denotes a pseudoscalar meson, are analyzed, with emphasis on charmless final states. Numerous triangle relations for amplitudes hold within SU(3) symmetry, relating (for example) the decays $B^+ \to \pi^+ \pi^0,~ \pi^0 K^+$, and $\pi^+ K^0$. Such relations can improve the possibilities for early detection of $CP$-violating asymmetries. Within the context of a graphical analysis of decays, relations are analyzed among SU(3) amplitudes which hold if some graphs are neglected. One application is that measurements of the rates for the above three $B^+$ decays and their charge-conjugates can be used to determine a weak CKM phase. With measurements of the remaining rates for $B$ decays to $\pi \pi,~\pi K$, and $K \bar K$, one can obtain two CKM phases and several differences of strong phase shifts.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The decays $B \to PP$, where $P$ denotes a pseudoscalar meson, are analyzed, with emphasis on charmless final states. | contribution 0.88 | 0.74 | 0.06 | asserted 0.92 |
| s1 | Numerous triangle relations for amplitudes hold within SU(3) symmetry, relating (for example) the decays $B^+ \to \pi^+ \pi^0,~ \pi^0 K^+$, and $\pi^+ K^0$. | result 0.58 | 0.33 | 0.13 | asserted 1.00 |
| s2 | Such relations can improve the possibilities for early detection of $CP$-violating asymmetries. | interpretation 0.99 | 0.11 | 0.14 | hedged possibility 0.96 |
| s3 | Within the context of a graphical analysis of decays, relations are analyzed among SU(3) amplitudes which hold if some graphs are neglected. | method 0.67 | 0.70 | 0.07 | asserted 0.86 |
| s4 | One application is that measurements of the rates for the above three $B^+$ decays and their charge-conjugates can be used to determine a weak CKM phase. | interpretation 0.63 | 0.32 | 0.20 | asserted 0.50 |
| s5 | With measurements of the remaining rates for $B$ decays to $\pi \pi,~\pi K$, and $K \bar K$, one can obtain two CKM phases and several differences of strong phase shifts. | result 0.40 | 0.23 | 0.26 | hedged possibility 0.75 |
What was examined, and what was not
- arXiv listing abstract v1
- 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
Showing 3 of the paper's 6 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-ph/9404283 by the authors.
References
How later papers used it
68 later papers cite it
1 later paper by other authors is listed below: 1 used its method or tool.
Uses its method or tool 1 of 12 papers with this label
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Decomposed the decay amplitudes of B to K* rho into linear combinations of the topological amplitudes in this paper's quark diagram approach.
Generalized analysis on $B\to K^* \rho$ within and beyond the Standard Model $-$ Can it help understand the $B \to K \pi$ puzzle? (2007) · 0.87 · paraphrased: the licence does not allow quoting
How the literature uses it
54 arXiv papers cite this in 91 sentences
Papers citing it · 62 sentences without a confident label
Uses its method or tool 10 papers
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[ref] , which made use of the well established topological amplitude formalism [ref] and asymptotic relations [ref] in the large $m_b$ limit.
Two-body Baryonic $B_{u,d,s}$ and $B_c$ to Charmless Final State Decays · Introduction · 0.98
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[ref] , which was used to study two-body baryonic $B$ decays, $B→'$, making use of the well established topological amplitude formalism [ref] .
Charmless Semileptonic Baryonic $B_{u,d,s}$ Decays · Introduction · 0.99
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Within the diagrammatic approach of Refs. [ref] , $B$-decay amplitudes are expressed in terms of six diagrams[The annihilation, exchange and penguin-annihilation diagrams are neglected, as they are expected to be very small in the SM.]: the color-favored and color-suppressed tree amplitudes $T'$ and $C'$, the gluonic penguin amplitudes $P'_tc$ and $P'_uc$, and the color-favored and color-suppressed electroweak penguin amplitudes $$ and $$ (the primes on the amplitudes indicate $$ transitions).
Uniting Low-energy Semileptonic and Hadronic Anomalies within SMEFT · $$ · 0.99
Compares with it 1 paper
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Importantly, our results are consistent with [ref] , but differ by a sign from those reported in [ref] .
A Phenomenological Model of Mesons for Charged Current Weak Decays · Consistency checks in hadronic decays via isospin sum rules · 0.94
Cites it as support 1 paper
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Yet, we expect an equivalence between the two approaches [ref] .
Flavor $SU(3)$ in Cabibbo-favored $D$-meson decays · Connections between flavor-flow and matrix elements in $SU(3)_F$ · 0.96
Cites it as background 16 papers
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In Ref. [ref] , Neubert and Rosner established a relation between the electroweak penguin (EWP) and tree topological diagrams of Ref. [ref] .
Comment on "QCD-factorization amplitudes from flavour symmetries: beyond the $SU(3)$ symmetric case'' · Introduction · 0.96
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The four amplitudes may be written in terms of penguin ($P_tc$ and $P_uc$), tree ($T$), color-suppressed ($C$), annihilation ($A$), color-favored electroweak penguin ($P_EW$), and color-suppressed electroweak penguin ($P_EW^C$) contributions [ref] :
Diagnostic for new physics in $B \to \pi K$ decays · Introduction · 0.80
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These decays involve several contributing amplitudes (diagrams) [ref] .
CP Violation in $B$ Decays (and the Search for New Physics) · Direct CP Violation · 0.87
Discussion
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