| Decay | Limit at 90% CL x106 | Experiment | Reference | 
|---|
|  | 
| γe+νe | 130.0 | BESIII | M. Ablikim et al., Phys. Rev. D99 (2019) 072002 | 
|  | 
| π+e+e- | 270.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
| 22.0 | CLEO | P. Rubin et al., Phys. Rev. D82 (2010) 092007 | 
| 13.0 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 5.5 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| π+μ+μ- | 430.0 | E653 | K. Kodama et al., Phys. Lett. B345 (1995) 85 | 
| 140.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
| 43.0 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 26.0 | Focus | J.M. Link et al., Phys. Lett. B572 (2003) 21 | 
| 0.18 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| K+e+e- | 1600.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
| 52.0 | CLEO | P. Rubin et al., Phys. Rev. D82 (2010) 092007 | 
| 4.9 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
| 3.7 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
|  | 
| K+μ+μ- | 140.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
| 36.0 | Focus | J.M. Link et al., Phys. Lett. B572 (2003) 21 | 
| 21.0 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 0.14 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| K*+(892)μ+μ- | 1400.0 | E653 | K. Kodama et al., Phys. Lett. B345 (1995) 85 | 
|  | 
| π+e±μ∓ | 610.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
|  | 
| π+e+μ- | 12.0 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 1.1 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| π+μ+e- | 20.0 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 0.94 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| K+e±μ∓ | 630.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
|  | 
| K+e+μ- | 14.0 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 0.79 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| K+μ+e- | 9.7 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 0.56 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| π-e+e+ | 690.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
| 18.0 | CLEO | P. Rubin et al., Phys. Rev. D82 (2010) 092007 | 
| 4.1 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 1.4 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| π-μ+μ+ | 430.0 | E653 | K. Kodama et al., Phys. Lett. B345 (1995) 85 | 
| 82.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
| 29.0 | Focus | J.M. Link et al., Phys. Lett. B572 (2003) 21 | 
| 14.0 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 0.086 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| π-e+μ+ | 730.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
| 0.63 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| K-e+e+ | 630.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
| 17.0 | CLEO | P. Rubin et al., Phys. Rev. D82 (2010) 092007 | 
| 5.2 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 0.77 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| K-μ+μ+ | 590.0 | E653 | K. Kodama et al., Phys. Lett. B345 (1995) 85 | 
| 180.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
| 13.0 | BaBar | J.P. Lees et al., Phys. Rev. D84 (2011) 072006 | 
| 0.026 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| K-e+μ+ | 680.0 | E791 | E.M. Aitala et al., Phys. Lett. B462 (1999) 401 | 
| 0.26 | LHCb | R. Aaij et al., arXiv:2011.00217 | 
|  | 
| K*-(892)μ+μ+ | 1400.0 | E653 | K. Kodama et al., Phys. Lett. B345 (1995) 85 |