Catalog · Beauty · B006

B006 $\mathcal{B}(B^0\to\mu^+\mu^-)$

Rare leptonic decay B0 $ \to \mu^+ \mu^-$

Status REVIEWED VERIFIED Medium Code: NO Priority Medium

PDG / equivalent values

Observable	Value	Year	Experiment / source	Provenance
BR(B0 $ \to \mu^+ \mu^-$)	? branching fraction	-	PDG2026:BdMuMu
BR(B0 $ \to \mu^+ \mu^-$) / $BR(B_s0 \to \mu^+ \mu^-$)	? dimensionless ratio	-	HFLAV2023:BdOverBsMuMu	source ↑
SM $BR(B_d \to \mu^+ \mu^-$)	1.06e-10 branching fraction	-	Bobeth et al. 2013	source ↑

Why this constrains the RS scan

This mode is a clean $\Delta B=1$ leptonic rare decay. In warped/anarchic flavor models, flavor-changing $Z$, KK electroweak gauge, Higgs, radion, or other scalar exchanges can contribute to axial-vector, scalar, and pseudoscalar $b\to d\mu\mu$ Wilson coefficients. Scalar and pseudoscalar terms are especially diagnostic because they can compete with the helicity-suppressed Standard Model amplitude.

What's changed since the original paper

Since the arXiv:0804.1954 RS-flavor baseline (CsakiFalkowskiWeiler2008:CompositeFlavor), this channel moved from pre-LHC upper limits to a mature LHC rare-decay search. ATLAS combined Run 1 and 2015--2016 data to set $2.1\times10^{-10}$ at $95\%$ CL (ATLAS2019:BdMuMu). LHCb later set $2.6\times10^{-10}$ at $95\%$ CL and constrained the $B^0/B_s^0$ dimuon branching-ratio ratio (LHCb2022:BdMuMu). CMS Run 2, with $140\,{\rm fb}^{-1}$ at $\sqrt{s}=13~{\rm TeV}$, now supplies the PDG canonical $90\%$-CL limit (CMS2023:BdMuMu; PDG2026:BdMuMu). On the theory side, $B_{s,d}\to\ell^+\ell^-$ Standard Model predictions now include reduced perturbative electroweak and QCD uncertainties (BobethEtAl2013:BdMuMuSM).

Validity and model dependence

The experimental object is robust as an upper limit on a short-distance branching fraction, but the catalog interpretation is model-dependent. A live constraint needs a consistent $\Delta B=1$ Hamiltonian, CKM convention, normalization to $f_{B_d}$, and treatment of scalar/pseudoscalar operators. Unlike angular $b\to d\ell\ell$ modes it does not require a multi-bin form-factor likelihood.

Code coverage in this repo

NO. The required catalog greps over quarkConstraints/, qcd/, flavorConstraints/, neutrinos/, yukawa/, warpConfig/, solvers/, scanParams/, and tests/ found no $B^0\to\mu^+\mu^-$ or $b\to d\mu\mu$ observable implementation. Nearby hits such as quarkConstraints/deltaf2.py:225 and quarkConstraints/deltaf2.py:903 are $B_d$ $\Delta F=2$ mixing entries, not this rare leptonic $\Delta B=1$ decay.

Linked evidence (opens GitHub blob at flavor-catalog-website/2026q2):

Implementation difficulty

MEDIUM. This requires a new $\Delta B=1$ leptonic rare-decay observable and Wilson normalization for $C_{10}^{(\prime)}$, $C_S^{(\prime)}$, and $C_P^{(\prime)}$. It should not need new lattice matrix-element machinery beyond decay-constant inputs, RG for a full angular analysis, or exclusive semileptonic form factors.

Key references

Process-local raw reference keys before bibliography consolidation: PDG2026:BdMuMu, HFLAV2023:BdOverBsMuMu, CMS2023:BdMuMu, LHCb2022:BdMuMu, ATLAS2019:BdMuMu, BobethEtAl2013:BdMuMuSM, and CsakiFalkowskiWeiler2008:CompositeFlavor.

fallback_value_uncertainty BR(B0 -> mu+ mu-) < 1.5e-10 90% CL

AMBIGUOUS

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L4: HTML summary URL: https://pdglive.lbl.gov/view/S042.7
L5: Access date: 2026-05-16
L6: Edition: 2026
L7: Local snapshot purpose: canonical current PDG value for B0 -> mu+ mu-.
L8: 
L9: Relevant PDG API metadata:
L10: request_timestamp: 2026-05-16 10:12:21 PST

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L9: Relevant PDG API metadata:
L10: request_timestamp: 2026-05-16 10:12:21 PST
L11: pdgid: S042.7
L12: description: B0 --> mu+ mu-
L13: parent_pdgid: S042
L14: parent_description: B0
L15: related_data pdgid: S042R7

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L11: pdgid: S042.7
L12: description: B0 --> mu+ mu-
L13: parent_pdgid: S042
L14: parent_description: B0
L15: related_data pdgid: S042R7
L16: related_data description: G(B0 --> mu+ mu-)/G(total)
L17: note: Test for DeltaB=1 weak neutral current. Allowed by higher-order electroweak interactions.

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L13: parent_pdgid: S042
L14: parent_description: B0
L15: related_data pdgid: S042R7
L16: related_data description: G(B0 --> mu+ mu-)/G(total)
L17: note: Test for DeltaB=1 weak neutral current. Allowed by higher-order electroweak interactions.
L18: 
L19: Canonical summary row:

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L17: note: Test for DeltaB=1 weak neutral current. Allowed by higher-order electroweak interactions.
L18: 
L19: Canonical summary row:
L20: Mode: B0 -> mu+ mu-
L21: Fraction Gamma_i/Gamma: < 1.5 E-10
L22: Confidence level: 90%
L23: PDG summary display value: <1.5 x 10^-10

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L18: 
L19: Canonical summary row:
L20: Mode: B0 -> mu+ mu-
L21: Fraction Gamma_i/Gamma: < 1.5 E-10
L22: Confidence level: 90%
L23: PDG summary display value: <1.5 x 10^-10
L24:

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L20: Mode: B0 -> mu+ mu-
L21: Fraction Gamma_i/Gamma: < 1.5 E-10
L22: Confidence level: 90%
L23: PDG summary display value: <1.5 x 10^-10
L24: 
L25: Input measurement used in PDG average/fit:
L26: document_id: TUMASYAN 2023A

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L29: doi: 10.1016/j.physletb.2023.137955
L30: inspire_id: 2616304
L31: technique: CMS
L32: title: Measurement of the B0_s -> mu+ mu- decay properties and search for the B0 -> mu+ mu- decay in proton-proton collisions at sqrt(s) = 13 TeV
L33: measurement value: < 1.5 E-10
L34: confidence_level: 90.0
L35: footnote: Corresponds to a 95% CL upper limit of <1.9E-10.

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L30: inspire_id: 2616304
L31: technique: CMS
L32: title: Measurement of the B0_s -> mu+ mu- decay properties and search for the B0 -> mu+ mu- decay in proton-proton collisions at sqrt(s) = 13 TeV
L33: measurement value: < 1.5 E-10
L34: confidence_level: 90.0
L35: footnote: Corresponds to a 95% CL upper limit of <1.9E-10.
L36:

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L32: title: Measurement of the B0_s -> mu+ mu- decay properties and search for the B0 -> mu+ mu- decay in proton-proton collisions at sqrt(s) = 13 TeV
L33: measurement value: < 1.5 E-10
L34: confidence_level: 90.0
L35: footnote: Corresponds to a 95% CL upper limit of <1.9E-10.
L36: 
L37: Other recent input rows retained for provenance:
L38: AAIJ 2022, Phys. Rev. Lett. 128 041801, LHCb: (1.2 +0.8 -0.7 +-0.1) E-10; corresponds to a 95% CL upper limit of <2.6E-10.

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L35: footnote: Corresponds to a 95% CL upper limit of <1.9E-10.
L36: 
L37: Other recent input rows retained for provenance:
L38: AAIJ 2022, Phys. Rev. Lett. 128 041801, LHCb: (1.2 +0.8 -0.7 +-0.1) E-10; corresponds to a 95% CL upper limit of <2.6E-10.
L39: AABOUD 2019L, JHEP 1904 098, ATLAS: (-1.9 +-1.6) E-10; corresponds to a 95% CL upper limit of <2.1E-10.

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L36: 
L37: Other recent input rows retained for provenance:
L38: AAIJ 2022, Phys. Rev. Lett. 128 041801, LHCb: (1.2 +0.8 -0.7 +-0.1) E-10; corresponds to a 95% CL upper limit of <2.6E-10.
L39: AABOUD 2019L, JHEP 1904 098, ATLAS: (-1.9 +-1.6) E-10; corresponds to a 95% CL upper limit of <2.1E-10.

fallback_value_uncertainty BR(B0 -> mu+ mu-) / BR(B_s0 -> mu+ mu-) < 0.081 dimensionless ratio 90% CL

AMBIGUOUS

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L10: Relevant table extract:
L11: Experiment: Average
L12: Measurement units: 10^-2
L13: Average: < 8.1
L14: 
L15: Experiment: LHCb
L16: Measurement units: 10^-2

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L14: 
L15: Experiment: LHCb
L16: Measurement units: 10^-2
L17: Measurement: < 8.1
L18: Reference: Phys. Rev. D 105, 012010 (2022)
L19: 
L20: Table note:

fallback_value_uncertainty SM BR(B_d -> mu+ mu-) = (1.06 +- 0.09)e-10

AMBIGUOUS

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L12: Relevant extracted result:
L13: The paper gives updated Standard Model predictions for B_q -> l+ l- branching ratios.
L14: For the muonic B_d mode:
L15: B_d,mu x 10^10 = (1.06 +- 0.02) R_talpha R_d = 1.06 +- 0.09.
L16: 
L17: Interpreted value for this catalog:
L18: B(B_d -> mu+ mu-)_SM = (1.06 +- 0.09) x 10^-10.

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L15: B_d,mu x 10^10 = (1.06 +- 0.02) R_talpha R_d = 1.06 +- 0.09.
L16: 
L17: Interpreted value for this catalog:
L18: B(B_d -> mu+ mu-)_SM = (1.06 +- 0.09) x 10^-10.

fallback_value_uncertainty BR(B0 -> mu+ mu-) < 1.5e-10

AMBIGUOUS

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L5: Access date: 2026-05-16
L6: Journal: Phys. Lett. B 842 (2023) 137955
L7: DOI: 10.1016/j.physletb.2023.137955
L8: Local snapshot purpose: primary CMS result used by PDG for B0 -> mu+ mu-.
L9: 
L10: Title:
L11: Measurement of the B0_s -> mu+ mu- decay properties and search for the B0 -> mu+ mu- decay in proton-proton collisions at sqrt(s) = 13 TeV

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L8: Local snapshot purpose: primary CMS result used by PDG for B0 -> mu+ mu-.
L9: 
L10: Title:
L11: Measurement of the B0_s -> mu+ mu- decay properties and search for the B0 -> mu+ mu- decay in proton-proton collisions at sqrt(s) = 13 TeV
L12: 
L13: Dataset:
L14: CMS pp collisions at sqrt(s) = 13 TeV, 2016-2018, integrated luminosity 140 fb^-1.

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L14: CMS pp collisions at sqrt(s) = 13 TeV, 2016-2018, integrated luminosity 140 fb^-1.
L15: 
L16: Relevant extracted result:
L17: No evidence for the B0 -> mu+ mu- decay was found.
L18: The 90% and 95% confidence-level upper limits from the CLs criterion are:
L19: B(B0 -> mu+ mu-) < 1.5 x 10^-10 at 90% CL.
L20: B(B0 -> mu+ mu-) < 1.9 x 10^-10 at 95% CL.

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L16: Relevant extracted result:
L17: No evidence for the B0 -> mu+ mu- decay was found.
L18: The 90% and 95% confidence-level upper limits from the CLs criterion are:
L19: B(B0 -> mu+ mu-) < 1.5 x 10^-10 at 90% CL.
L20: B(B0 -> mu+ mu-) < 1.9 x 10^-10 at 95% CL.
L21: 
L22: PDG linkage:

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L17: No evidence for the B0 -> mu+ mu- decay was found.
L18: The 90% and 95% confidence-level upper limits from the CLs criterion are:
L19: B(B0 -> mu+ mu-) < 1.5 x 10^-10 at 90% CL.
L20: B(B0 -> mu+ mu-) < 1.9 x 10^-10 at 95% CL.
L21: 
L22: PDG linkage:
L23: PDG live/API listing S042.7 marks TUMASYAN 2023A (CMS) as used in the average/fit for the canonical <1.5E-10 90% CL limit.

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L20: B(B0 -> mu+ mu-) < 1.9 x 10^-10 at 95% CL.
L21: 
L22: PDG linkage:
L23: PDG live/API listing S042.7 marks TUMASYAN 2023A (CMS) as used in the average/fit for the canonical <1.5E-10 90% CL limit.

fallback_value_uncertainty BR(B0 -> mu+ mu-) < 2.3e-10

AMBIGUOUS

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L4: PDF inspected transiently from: https://arxiv.org/pdf/2108.09283
L5: Access date: 2026-05-16
L6: Journal: Phys. Rev. Lett. 128 (2022) 041801 / Phys. Rev. D 105 (2022) 012010 listing context
L7: Local snapshot purpose: primary LHCb B0 -> mu+ mu- input and HFLAV ratio input.
L8: 
L9: Title:
L10: Measurement of the B0_s -> mu+ mu- decay properties and search for the B0 -> mu+ mu- and B0_s -> mu+ mu- gamma decays

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L7: Local snapshot purpose: primary LHCb B0 -> mu+ mu- input and HFLAV ratio input.
L8: 
L9: Title:
L10: Measurement of the B0_s -> mu+ mu- decay properties and search for the B0 -> mu+ mu- and B0_s -> mu+ mu- gamma decays
L11: 
L12: Dataset:
L13: LHCb pp collisions at sqrt(s) = 7, 8, and 13 TeV, integrated luminosities 1, 2, and 6 fb^-1.

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L13: LHCb pp collisions at sqrt(s) = 7, 8, and 13 TeV, integrated luminosities 1, 2, and 6 fb^-1.
L14: 
L15: Relevant extracted results:
L16: No significant signal for B0 -> mu+ mu- was found.
L17: B(B0 -> mu+ mu-) < 2.3 x 10^-10 at 90% CL.
L18: B(B0 -> mu+ mu-) < 2.6 x 10^-10 at 95% CL.
L19: Ratio R_{mu+mu-} = B(B0 -> mu+ mu-) / B(B_s0 -> mu+ mu-) < 0.081 at 90% CL and <0.095 at 95% CL.

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L14: 
L15: Relevant extracted results:
L16: No significant signal for B0 -> mu+ mu- was found.
L17: B(B0 -> mu+ mu-) < 2.3 x 10^-10 at 90% CL.
L18: B(B0 -> mu+ mu-) < 2.6 x 10^-10 at 95% CL.
L19: Ratio R_{mu+mu-} = B(B0 -> mu+ mu-) / B(B_s0 -> mu+ mu-) < 0.081 at 90% CL and <0.095 at 95% CL.
L20:

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L15: Relevant extracted results:
L16: No significant signal for B0 -> mu+ mu- was found.
L17: B(B0 -> mu+ mu-) < 2.3 x 10^-10 at 90% CL.
L18: B(B0 -> mu+ mu-) < 2.6 x 10^-10 at 95% CL.
L19: Ratio R_{mu+mu-} = B(B0 -> mu+ mu-) / B(B_s0 -> mu+ mu-) < 0.081 at 90% CL and <0.095 at 95% CL.
L20: 
L21: PDG linkage:

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L16: No significant signal for B0 -> mu+ mu- was found.
L17: B(B0 -> mu+ mu-) < 2.3 x 10^-10 at 90% CL.
L18: B(B0 -> mu+ mu-) < 2.6 x 10^-10 at 95% CL.
L19: Ratio R_{mu+mu-} = B(B0 -> mu+ mu-) / B(B_s0 -> mu+ mu-) < 0.081 at 90% CL and <0.095 at 95% CL.
L20: 
L21: PDG linkage:
L22: PDG live/API listing S042.7 includes AAIJ 2022 with value (1.2 +0.8 -0.7 +-0.1) E-10 and notes the 95% CL upper limit <2.6E-10.

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L19: Ratio R_{mu+mu-} = B(B0 -> mu+ mu-) / B(B_s0 -> mu+ mu-) < 0.081 at 90% CL and <0.095 at 95% CL.
L20: 
L21: PDG linkage:
L22: PDG live/API listing S042.7 includes AAIJ 2022 with value (1.2 +0.8 -0.7 +-0.1) E-10 and notes the 95% CL upper limit <2.6E-10.

fallback_value_uncertainty BR(B0 -> mu+ mu-) < 4.3e-10

AMBIGUOUS

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L5: Access date: 2026-05-16
L6: Journal: JHEP 04 (2019) 098
L7: DOI: 10.1007/JHEP04(2019)098
L8: Local snapshot purpose: primary ATLAS post-2008 input for B0 -> mu+ mu-.
L9: 
L10: Title:
L11: Study of the rare decays of B0_s and B0 mesons into muon pairs using data collected during 2015 and 2016 with the ATLAS detector

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L8: Local snapshot purpose: primary ATLAS post-2008 input for B0 -> mu+ mu-.
L9: 
L10: Title:
L11: Study of the rare decays of B0_s and B0 mesons into muon pairs using data collected during 2015 and 2016 with the ATLAS detector
L12: 
L13: Relevant extracted results:
L14: Using 26.3 fb^-1 of 13 TeV pp data, ATLAS obtains:

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L12: 
L13: Relevant extracted results:
L14: Using 26.3 fb^-1 of 13 TeV pp data, ATLAS obtains:
L15: B(B0 -> mu+ mu-) < 4.3 x 10^-10 at 95% CL.
L16: 
L17: Combined with the Run 1 ATLAS result:
L18: B(B0 -> mu+ mu-) < 2.1 x 10^-10 at 95% CL.

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L15: B(B0 -> mu+ mu-) < 4.3 x 10^-10 at 95% CL.
L16: 
L17: Combined with the Run 1 ATLAS result:
L18: B(B0 -> mu+ mu-) < 2.1 x 10^-10 at 95% CL.
L19: 
L20: PDG linkage:
L21: PDG live/API listing S042.7 includes AABOUD 2019L with value (-1.9 +-1.6) E-10 and notes the 95% CL upper limit <2.1E-10.

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L18: B(B0 -> mu+ mu-) < 2.1 x 10^-10 at 95% CL.
L19: 
L20: PDG linkage:
L21: PDG live/API listing S042.7 includes AABOUD 2019L with value (-1.9 +-1.6) E-10 and notes the 95% CL upper limit <2.1E-10.

dataset_numerical_claims[0].fallback_value_uncertainty CMS Run 2 integrated luminosity for the B_s0/B0 -> mu+ mu- analysis = 140 fb^-1

RESOLVED

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L11: Measurement of the B0_s -> mu+ mu- decay properties and search for the B0 -> mu+ mu- decay in proton-proton collisions at sqrt(s) = 13 TeV
L12: 
L13: Dataset:
L14: CMS pp collisions at sqrt(s) = 13 TeV, 2016-2018, integrated luminosity 140 fb^-1.
L15: 
L16: Relevant extracted result:
L17: No evidence for the B0 -> mu+ mu- decay was found.

dataset_numerical_claims[1].fallback_value_uncertainty proton-proton center-of-mass energy for the CMS Run 2 B_s0/B0 -> mu+ mu- analysis = 13 TeV

AMBIGUOUS

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L3: URL: https://arxiv.org/abs/2212.10311
L4: PDF inspected transiently from: https://arxiv.org/pdf/2212.10311
L5: Access date: 2026-05-16
L6: Journal: Phys. Lett. B 842 (2023) 137955
L7: DOI: 10.1016/j.physletb.2023.137955
L8: Local snapshot purpose: primary CMS result used by PDG for B0 -> mu+ mu-.
L9:

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L4: PDF inspected transiently from: https://arxiv.org/pdf/2212.10311
L5: Access date: 2026-05-16
L6: Journal: Phys. Lett. B 842 (2023) 137955
L7: DOI: 10.1016/j.physletb.2023.137955
L8: Local snapshot purpose: primary CMS result used by PDG for B0 -> mu+ mu-.
L9: 
L10: Title:

Match 3 of 4 snapshot line 11

L8: Local snapshot purpose: primary CMS result used by PDG for B0 -> mu+ mu-.
L9: 
L10: Title:
L11: Measurement of the B0_s -> mu+ mu- decay properties and search for the B0 -> mu+ mu- decay in proton-proton collisions at sqrt(s) = 13 TeV
L12: 
L13: Dataset:
L14: CMS pp collisions at sqrt(s) = 13 TeV, 2016-2018, integrated luminosity 140 fb^-1.

Match 4 of 4 snapshot line 14

L11: Measurement of the B0_s -> mu+ mu- decay properties and search for the B0 -> mu+ mu- decay in proton-proton collisions at sqrt(s) = 13 TeV
L12: 
L13: Dataset:
L14: CMS pp collisions at sqrt(s) = 13 TeV, 2016-2018, integrated luminosity 140 fb^-1.
L15: 
L16: Relevant extracted result:
L17: No evidence for the B0 -> mu+ mu- decay was found.