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arxiv: 1906.08596 · v1 · pith:67H27LYRnew · submitted 2019-06-20 · ✦ hep-ph

Global Bayesian Analysis of new physics in b to s μμ transitions after Moriond-2019

Dinesh Kumar , Kamila Kowalska , Enrico Maria Sessolo This is my paper

Pith reviewed 2026-05-25 19:46 UTC · model grok-4.3

classification ✦ hep-ph
keywords b to s mu mulepton flavor universalityBayesian global fitnew physicsR_K anomalyZ prime bosonleptoquarkseffective operators
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The pith

Bayesian global fit to b to s mu mu data after 2019 measurements updates credibility regions for new physics operators and compares models via Bayes factors.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper performs a global Bayesian analysis of new physics contributions to semileptonic b to s transitions, incorporating the latest LHCb R_K measurement along with new Belle results on R_K* and R_K*+. It scans multiple NP scenarios, extracts the 68% and 95.4% credibility intervals on the marginalized posteriors for each, and ranks the scenarios against one another by computing Bayes factors on the shared data set. The analysis also embeds a few concrete BSM models, including Z' exchange in setups with vector-like fermions and a scalar leptoquark model, to derive predictions for the required couplings and masses.

Core claim

A Bayesian global fit to all available b to s ll observables, including the post-Moriond-2019 R_K, R_K*, and R_K*+ measurements, yields updated 68% and 95.4% credibility regions for the Wilson coefficients in several new-physics scenarios; pairwise Bayes factors identify the relative support for each scenario, while two classes of ultraviolet models (heavy Z' and scalar leptoquarks) are shown to furnish viable high-scale completions with explicit predictions for their couplings and masses.

What carries the argument

Bayesian global fit of effective operators for b to s mu mu transitions, with marginalization over nuisance parameters to obtain posterior credibility regions and direct computation of Bayes factors between pairs of models.

If this is right

  • The 68% and 95.4% credibility regions for the new-physics Wilson coefficients are tightened by the inclusion of the 2019 data.
  • Pairwise Bayes factors rank the relative viability of different operator combinations on the common data set.
  • Explicit mass and coupling predictions are obtained for the Z' boson in vector-like fermion models.
  • Explicit mass and coupling predictions are obtained for scalar leptoquark models.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The preferred operator patterns could be tested by measuring additional angular observables in the same decays.
  • The derived mass ranges for the Z' or leptoquarks can be confronted with direct searches at the LHC.
  • If the current hierarchy of Bayes factors persists, it would favor flavor structures that suppress electron modes relative to muons.

Load-bearing premise

All relevant new physics effects are captured by the finite set of effective operators retained in the fit, with negligible contributions from any operators or scales omitted from the analysis.

What would settle it

A future high-precision measurement of any R_K-like ratio or angular observable that lies outside the 95.4% credibility region obtained for every scanned scenario would falsify the fit results.

Figures

Figures reproduced from arXiv: 1906.08596 by Dinesh Kumar, Enrico Maria Sessolo, Kamila Kowalska.

Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p002_3.png] view at source ↗
Figure 1
Figure 1. Figure 1: FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p002_4.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5 [PITH_FULL_IMAGE:figures/full_fig_p003_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6 [PITH_FULL_IMAGE:figures/full_fig_p003_6.png] view at source ↗
read the original abstract

The recent measurement of $R_K$ at LHCb continues to support the hint of violation of lepton flavor universality. We perform a global fit for new physics in semileptonic $b\to s$ transitions using all the relevant data with a Bayesian analysis technique. We include new measurements of $R_K$ at LHCb and new determinations of $R_{K^*}$ and $R_{K^{*+}}$ at Belle. We perform the scan for various NP scenarios and infer the 68\% and 95.4\% credibility regions of the marginalized posterior probability density for all scenarios. We also compare the models in pairs by calculating the Bayes factor given a common data set. A few well-known BSM models are analyzed that can provide a high energy framework for the EFT analysis. These include the exchange of a heavy $Z^{'}$ boson in models with heavy vector-like fermions and a scalar field, and a model with scalar leptoquarks. We provide predictions for the BSM couplings and expected mass values.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The paper performs a global Bayesian fit to new physics in b→sμμ transitions incorporating the post-Moriond-2019 LHCb R_K measurement and Belle R_K* and R_K*+ results. It scans multiple NP scenarios, extracts 68% and 95.4% credibility regions on the marginalized posteriors for the Wilson coefficients, computes pairwise Bayes factors on a common dataset, and matches a subset of scenarios to UV models (heavy Z' with vector-like fermions, scalar leptoquarks) to predict couplings and masses.

Significance. If the results hold, the work supplies an updated, statistically coherent snapshot of the b→sℓℓ anomalies with quantitative model discrimination via Bayes factors and direct links to concrete BSM realizations. The inclusion of the newest R_K and R_K* data and the use of standard Bayesian outputs (credibility regions, Bayes factors) are clear strengths.

major comments (1)
  1. [EFT setup and fit definition] The central results (credibility regions and Bayes-factor rankings) rest on the assumption that NP contributions are exhausted by the specific set of effective operators retained in the fit. The manuscript does not quantify the effect of enlarging the operator basis (e.g., additional right-handed currents or four-fermion operators outside the baseline set), leaving open the possibility that the reported regions and model preferences would shift if such contributions are present.
minor comments (2)
  1. Clarify the exact list of observables and their correlations used in the likelihood; a table summarizing the data set would improve reproducibility.
  2. State the prior ranges and functional forms adopted for the Wilson coefficients explicitly, including any correlations imposed between real and imaginary parts.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive assessment of our work and for the detailed comment on the EFT setup. We respond to the point raised below.

read point-by-point responses

  1. Referee: [EFT setup and fit definition] The central results (credibility regions and Bayes-factor rankings) rest on the assumption that NP contributions are exhausted by the specific set of effective operators retained in the fit. The manuscript does not quantify the effect of enlarging the operator basis (e.g., additional right-handed currents or four-fermion operators outside the baseline set), leaving open the possibility that the reported regions and model preferences would shift if such contributions are present.

    Authors: Our analysis is performed within the standard basis of dimension-six operators relevant to b→sμμ transitions that is conventionally adopted in global fits to these anomalies. This basis is chosen because it captures the leading effects needed to accommodate the data while remaining consistent with existing constraints from other observables. The various NP scenarios we scan, as well as the matching to UV models (Z' and scalar leptoquarks), are defined within this framework. We agree that a larger operator set could in principle modify the posteriors and Bayes factors; however, such an extension would introduce additional free parameters whose effects cannot be robustly constrained by the current dataset alone and would require a substantially more involved analysis. The reported credibility regions and model rankings are therefore conditional on the adopted operator basis, which is the standard practice in the literature for this class of studies. revision: no

Circularity Check

0 steps flagged

No significant circularity; analysis is a direct Bayesian fit to external data

full rationale

The paper conducts a standard global Bayesian fit of effective operator coefficients to experimental observables in b→sμμ transitions, deriving posterior credibility regions and Bayes factors from the data likelihood. No quoted steps show self-definitional relations, fitted inputs relabeled as predictions, or load-bearing self-citations that reduce the central results to the inputs by construction. The BSM model matching and mass predictions follow from the EFT posteriors matched to UV completions, but remain externally constrained by the same data set. This is a self-contained statistical analysis against independent experimental inputs.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim rests on the effective field theory framework for b->sll transitions and the assumption that the selected operators suffice to describe any new physics.

free parameters (1)
  • Wilson coefficients
    NP Wilson coefficients for the relevant operators are fitted to the global dataset.
axioms (1)
  • domain assumption New physics effects are captured by dimension-6 operators in the b->sll effective Lagrangian
    Invoked when scanning NP scenarios and extracting credibility regions.

pith-pipeline@v0.9.0 · 5723 in / 1089 out tokens · 26418 ms · 2026-05-25T19:46:03.346413+00:00 · methodology

discussion (0)

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Reference graph

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