Catalog · Beauty · B012

B012 $B\to K^*(892)\gamma$

Exclusive radiative B $ \to K* \gamma$

Status REVIEWED VERIFIED High Code: NO Priority Medium

PDG / equivalent values

Observable	Value	Year	Experiment / source	Provenance
B(B0 $ \to $ K*(892)0 $\gamma$)	0.00004163 branching fraction	2024	HFLAV rare decays, end-of-year 2024	source ↑
B(B+ $ \to $ K*(892)+ $\gamma$)	0.0000395 branching fraction	2024	HFLAV rare decays, end-of-year 2024	source ↑
$\Delta_0+(B \to K* \gamma$)	0.059 dimensionless	2024	HFLAV rare decays, end-of-year 2024	source ↑
$A_{CP}(B \to K* \gamma$)	-0.004 dimensionless	2024	HFLAV rare decays, end-of-year 2024	source ↑
$S_{K(892)0 \gamma}(B0 \to $ K(892)0 $\gamma$)	-0.08 dimensionless	2025	PDG pdgLive 2025	source ↑
$C_{K(892)0 \gamma}(B0 \to $ K(892)0 $\gamma$)	0.03 dimensionless	2025	PDG pdgLive 2025	source ↑

Why this constrains the RS scan

This is the exclusive radiative complement to the inclusive $B\to X_s\gamma$ entry. The inclusive rate mostly constrains the size of the electromagnetic dipole combination, while $S_{K^*\gamma}$ is a chirality test: a large right-handed dipole coefficient $C_7'$ can enhance the mixing-induced asymmetry even when the total rate remains near the SM value. Anarchic RS models can generate chirality-flipped dipoles through KK-fermion, KK-gauge, or Higgs-sector loops, so this process directly probes a direction not covered by the present $\Delta F=2$ scan.

What's changed since the original paper

Since the arXiv:0804.1954 flavor-baseline era (cfw\_2008\_rs\_flavor), BaBar produced a high-statistics branching-fraction, direct-CP, and isospin-asymmetry measurement in 2009 (babar\_2009\_btokstargamma); Belle reported evidence for isospin violation in 2017 (belle\_2017\_isospin\_cp); LHCb observed photon polarization in $b\to s\gamma$ using $B^\pm\to K^\pm\pi^\mp\pi^\pm\gamma$ (lhcb\_2014\_photon\_polarization); and Belle II added $B\to K^*\gamma$ measurements now entering HFLAV (belleii\_2024\_btokstargamma). PDG 2025 also includes a new Belle/Belle II input in the $S_{K^*\gamma}$ average (pdglive\_2025\_kstargamma\_cp).

Validity and model dependence

The branching fractions are measured cleanly but are less theory-clean than the inclusive rate because exclusive form factors and spectator effects enter the SM comparison. The time-dependent asymmetry is a sharper null-test of photon helicity, but its present uncertainty is still statistics-limited. Translating the entry into an RS bound requires a convention-matched $C_7,C_7'$ and $C_8,C_8'$ pipeline plus exclusive-amplitude inputs; the measured averages alone should not be treated as a standalone likelihood.

Code coverage in this repo

NO. The required greps over quarkConstraints/, qcd/, flavorConstraints/, neutrinos/, yukawa/, warpConfig/, solvers/, scanParams/, and tests/ found no $B\to K^*\gamma$, $C_7'$, photon-polarization, or right-handed $b\to s\gamma$ implementation. The modern quark surface is limited to neutral-meson mixing systems at quarkConstraints/modern/phenomenology.py:23; the only dipole code found is the unrelated lepton-sector $\mu\to e\gamma$ check at flavorConstraints/muToEGamma.py:75.

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

Implementation difficulty

HIGH. Production use needs new dipole matching, RG evolution for $C_7,C_7'$ and $C_8,C_8'$, exclusive $B\to K^*$ form-factor handling, and a time-dependent CP/helicity observable. None of that is supplied by the current $\Delta F=2$ operator basis.

Reason: Requires new $b \to s \gamma$ dipole matching and RG for C7/C7' and C8/C8', exclusive $B \to K*$ form-factor treatment, and a time-dependent CP/helicity observable likelihood absent from the $\Delta F = 2$ code.

Key references

Process-local keys before bibliography consolidation: hflav\_rare\_decays\_dec2024\_btokstargamma, pdglive\_2025\_kstargamma\_cp, belleii\_2024\_btokstargamma, belle\_2017\_isospin\_cp, babar\_2009\_btokstargamma, lhcb\_2014\_photon\_polarization, and cfw\_2008\_rs\_flavor.

fallback_value_uncertainty B(B0 -> K*(892)0 gamma) = (4.163 +- 0.092)e-5

RESOLVED

Match snapshot line 27

L24:   CLEO [242]      45.5 +7.2 -6.8 +/- 3.4
L25:   LHCb [206], [184] ratios used in HFLAV fit
L26: Average columns:
L27:   HFLAV: 41.63 +/- 0.92
L28:   PDG:   41.77 +/- 2.48
L29: 
L30: Table 76: Isospin asymmetry in B radiative and FCNC decays.

fallback_value_uncertainty B(B+ -> K*(892)+ gamma) = (3.95 +- 0.1)e-5

RESOLVED

Match snapshot line 15

L12:   BaBar [241]     42.2 +/- 1.4 +/- 1.6
L13:   CLEO [242]      37.6 +8.9 -8.3 +/- 2.8
L14: Average columns:
L15:   HFLAV: 39.5 +/- 1.0
L16:   PDG:   39.2 +/- 2.2
L17: 
L18: Table 62: Branching fractions of B0 radiative and FCNC decays with leptons, units 10^-6.

fallback_value_uncertainty Delta_0+(B -> K* gamma) = 0.059 +- 0.014

RESOLVED

Match snapshot line 37

L34:   Belle II [240]  0.050 +/- 0.020 +/- 0.015
L35:   BaBar [241]     0.066 +/- 0.021 +/- 0.022
L36: Average columns:
L37:   HFLAV: 0.059 +/- 0.014
L38:   PDG:   0.063 +/- 0.017
L39: HFLAV caution: these averages are computed naively and should be treated with caution.
L40:

fallback_value_uncertainty A_CP(B -> K* gamma) = -0.004 +- 0.011

AMBIGUOUS

Match 1 of 2 snapshot line 44

L41: Table 96: CP asymmetries of charmless hadronic B+ / B0 admixture.
L42: Parameter: A_CP(B -> K* gamma)
L43: Measurements:
L44:   Belle [239]     -0.004 +/- 0.014 +/- 0.003
L45:   BaBar [241]     -0.003 +/- 0.017 +/- 0.007
L46: Average:
L47:   -0.004 +/- 0.011

Match 2 of 2 snapshot line 47

L44:   Belle [239]     -0.004 +/- 0.014 +/- 0.003
L45:   BaBar [241]     -0.003 +/- 0.017 +/- 0.007
L46: Average:
L47:   -0.004 +/- 0.011
L48: 
L49: Reference lines relevant to these rows:
L50: [239] Belle collaboration, T. Horiguchi et al., Evidence for Isospin Violation and Measurement of CP Asymmetries in B -> K*(892) gamma, Phys. Rev. Lett. 119 (2017) 191802, arXiv:1707.00394.

fallback_value_uncertainty S_{K*(892)0 gamma}(B0 -> K*(892)0 gamma) = -0.08 +- 0.17

AMBIGUOUS

Match 1 of 2 snapshot line 12

L9: Collapsed B0 listing entries:
L10:   A_CP(B0 -> K*(892)0 gamma) = -0.006 +/- 0.011
L11:   C_{K*(892)0 gamma}(B0 -> K*(892)0 gamma) = 0.03 +/- 0.10
L12:   S_{K*(892)0 gamma}(B0 -> K*(892)0 gamma) = -0.08 +/- 0.17
L13: 
L14: S042SX4 data block:
L15: Observable: S_{K*(892)0 gamma}(B0 -> K*(892)0 gamma)

Match 2 of 2 snapshot line 16

L13: 
L14: S042SX4 data block:
L15: Observable: S_{K*(892)0 gamma}(B0 -> K*(892)0 gamma)
L16:   OUR AVERAGE: -0.08 +/- 0.17
L17: Inputs used by PDG:
L18:   ADACHI 2025, Belle:      0.00 +0.27 -0.26 +/- 0.03
L19:   AUBERT 2008BA, BaBar:   -0.03 +/- 0.29 +/- 0.03

fallback_value_uncertainty C_{K*(892)0 gamma}(B0 -> K*(892)0 gamma) = 0.03 +- 0.1

AMBIGUOUS

Match 1 of 3 snapshot line 11

L8: 
L9: Collapsed B0 listing entries:
L10:   A_CP(B0 -> K*(892)0 gamma) = -0.006 +/- 0.011
L11:   C_{K*(892)0 gamma}(B0 -> K*(892)0 gamma) = 0.03 +/- 0.10
L12:   S_{K*(892)0 gamma}(B0 -> K*(892)0 gamma) = -0.08 +/- 0.17
L13: 
L14: S042SX4 data block:

Match 2 of 3 snapshot line 18

L15: Observable: S_{K*(892)0 gamma}(B0 -> K*(892)0 gamma)
L16:   OUR AVERAGE: -0.08 +/- 0.17
L17: Inputs used by PDG:
L18:   ADACHI 2025, Belle:      0.00 +0.27 -0.26 +/- 0.03
L19:   AUBERT 2008BA, BaBar:   -0.03 +/- 0.29 +/- 0.03
L20:   USHIRODA 2006, Belle:   -0.32 +0.36 -0.33 +/- 0.05
L21: Older inputs listed but not used:

Match 3 of 3 snapshot line 19

L16:   OUR AVERAGE: -0.08 +/- 0.17
L17: Inputs used by PDG:
L18:   ADACHI 2025, Belle:      0.00 +0.27 -0.26 +/- 0.03
L19:   AUBERT 2008BA, BaBar:   -0.03 +/- 0.29 +/- 0.03
L20:   USHIRODA 2006, Belle:   -0.32 +0.36 -0.33 +/- 0.05
L21: Older inputs listed but not used:
L22:   AUBERT,B 2005P, BaBar:  -0.21 +/- 0.40 +/- 0.05; replaced by AUBERT 2008BA