Catalog · Kaon · K008

K008 $K_L \to pi0 e^+ e^-$

Long-lived neutral-kaon rare semileptonic electron mode

Status REVIEWED VERIFIED High Code: NO Priority Medium

PDG / equivalent values

Observable	Value	Year	Experiment / source	Provenance
PDG/API $BR(K_L \to $ pi0 e+ e-) canonical limit	<2.8e-10 branching fraction	2026	Particle Data Group 2026 pdgLive listing S013.20 / S013R34	source ↑
KTeV 1999-2000 standalone $BR(K_L \to $ pi0 e+ e-) limit	<3.5e-10 branching fraction	2004	KTeV 2004 arXiv hep-ex/0309072	source ↑
KTeV 1999-2000 observed candidates	1 events	2004	KTeV 2004 arXiv hep-ex/0309072	source ↑
KTeV 1999-2000 expected background	0.99 events	2004	KTeV 2004 arXiv hep-ex/0309072	source ↑
PDG-listed CP-conserving part inferred from $K_L \to $ pi0 $\gamma\gamma$	0.0047e-10 branching fraction	2026	Particle Data Group 2026 pdgLive listing S013.20 / LAI 2002B	source ↑
PDG / NA48 $BR(K_S \to $ pi0 e+ e-) for $m_{ee}$ > 0.165 GeV	3.0e-9 branching fraction	2026	Particle Data Group 2026 pdgLive listing S012.10 / NA48	source ↑
NA48 $K_S \to $ pi0 e+ e- dilepton-mass selection	0.165 GeV	2003	Particle Data Group 2026 pdgLive listing S012.10 / NA48	source ↑
NA48 full-region extrapolated $BR(K_S \to $ pi0 e+ e-)	5.8e-9 branching fraction	2003	Particle Data Group 2026 pdgLive listing S012.10 / NA48	source ↑
KTeV theory-context Standard-Model branching-ratio order	3e-11 branching fraction	2004	KTeV 2004 arXiv hep-ex/0309072 introduction	source ↑
KTeV theory-context total CP-violating branching-ratio range	8e-12 to 45e-12 branching fraction	2004	KTeV 2004 arXiv hep-ex/0309072 introduction	source ↑
KTeV theory-context direct-CP branching-ratio estimate	3e-12 to 6e-12 branching fraction	2004	KTeV 2004 arXiv hep-ex/0309072 introduction	source ↑
KTeV theory-context direct-CP interference contribution	40 percent	2004	KTeV 2004 arXiv hep-ex/0309072 introduction	source ↑
Isidori-Smith-Unterdorfer formula normalization	1e-12 branching fraction normalization	2004	Isidori, Smith, Unterdorfer 2004	source ↑
Isidori-Smith-Unterdorfer electron $C_{mix}$ coefficient	15.7 $dimensionless coefficient multiplying \|a_S\|^2$	2004	Isidori, Smith, Unterdorfer 2004	source ↑
Isidori-Smith-Unterdorfer electron $C_{int}$ coefficient	6.2 dimensionless coefficient multiplying \|a_S\|	2004	Isidori, Smith, Unterdorfer 2004	source ↑
Isidori-Smith-Unterdorfer electron $C_{dir}$ coefficient	2.4 dimensionless coefficient	2004	Isidori, Smith, Unterdorfer 2004	source ↑
Isidori-Smith-Unterdorfer electron $C_{CPC}$ coefficient	0 approximately dimensionless coefficient	2004	Isidori, Smith, Unterdorfer 2004	source ↑
Isidori-Smith-Unterdorfer $\|a_S\|$ input	1.2 dimensionless	2004	Isidori, Smith, Unterdorfer 2004	source ↑
Isidori-Smith-Unterdorfer SM $Im(\lambda_t)/1e-4$ input	1.36 dimensionless ratio	2004	Isidori, Smith, Unterdorfer 2004	source ↑

Why this constrains the RS scan

This decay probes $s\to d e^+e^-$ electroweak-penguin and semileptonic contact structures rather than the $\Delta F=2$ KK-gluon lane already present in the repository. In anarchic or warped models it is a diagnostic for flavor-changing $Z$ couplings, heavy neutral gauge exchange, and dipole or photon-penguin effects. The KTeV theory summary quotes a Standard-Model rate of order $3\times10^{-11}$, a CP-violating range of $8$--$45\times10^{-12}$, a direct-CP estimate of $3$--$6\times10^{-12}$, and a 40\% direct-CP interference contribution (ktev2004\_kl\_pi0ee\_arxiv.txt). The present experimental limit is therefore above, but near, the scale where short-distance effects become interesting.

What's changed since the original paper

No post-2008 experiment in the author snapshot supersedes the KTeV/PDG $K_L\to\pi^0 e^+e^-$ limit. The important developments are interpretive. The PDG 2026 listing records the CP-conserving contribution inferred from $K_L\to\pi^0\gamma\gamma$ as $(0.0047^{+0.0022}_{-0.0018})\times10^{-10}$ (pdg2026\_kl\_pi0ee\_pdgLive.txt), supporting the standard view that the electron mode is CPV dominated. The supporting $K_S\to\pi^0e^+e^-$ input for the indirect-CP amplitude remains the NA48 value $(3.0^{+1.5}_{-1.2}\pm0.2)\times10^{-9}$ for $m_{ee}>0.165\,{\rm GeV}$, with an extrapolated full-region value $5.8^{+2.9}_{-2.4}\times10^{-9}$ (na48\_ks\_pi0ee\_pdgLive.txt). Since 2008, lattice work has begun addressing long-distance $K\to\pi\ell^+\ell^-$ amplitudes (ChristEtAl2016:KPiLLLattice), and the Snowmass rare-kaon white paper keeps $K_{L,S}\to\pi^0\ell^+\ell^-$ branching ratios and $q^2$ spectra in the short-distance rare-kaon program (AebischerBurasKumar2022:RareKaons).

Validity and model dependence

Class: long-distance-limited, CP-decomposition-dependent, and not yet a clean single-Wilson-coefficient bound. A useful implementation must keep the indirect CPV piece tied to $K_S\to\pi^0e^+e^-$, the direct CPV short-distance piece, their sign-dependent interference, and the small two-photon CPC component separate. The Isidori--Smith--Unterdorfer decomposition gives $C_{\rm mix}^e=(15.7\pm0.3)|a_S|^2$, $C_{\rm int}^e=(6.2\pm0.3)|a_S|$, $C_{\rm dir}^e=2.4\pm0.2$, $C_{\rm CPC}^e\simeq0$, $|a_S|=1.2\pm0.2$, and $({\rm Im}\lambda_t/10^{-4})_{\rm SM}=1.36\pm0.12$, entering the rate in units of $10^{-12}$ (isidori\_smith\_unterdorfer2004\_kl\_pi0ll\_arxiv.txt).

Code coverage in this repo

NO. Targeted the author greps over quarkConstraints/, qcd/, flavorConstraints/, neutrinos/, yukawa/, warpConfig/, solvers/, scanParams/, and tests/ found no $K_L\to\pi^0 e^+e^-$, $K_S\to\pi^0e^+e^-$, $a_S$, or $s\to d e^+e^-$ implementation. Existing kaon coverage is $\Delta F=2$ only, e.g. quarkConstraints/deltaf2.py:209 and quarkConstraints/modern/phenomenology.py:23.

Implementation difficulty

HIGH. K008 requires a new $\Delta S=1$ semileptonic observable, short-distance matching to $s\to d e^+e^-$, treatment of indirect/direct CP separation and interference, and long-distance inputs from $K_S$ and $K_L\to\pi^0\gamma\gamma$. The existing $\Delta F=2$ operator basis is not sufficient.

Reason: Requires a new $\Delta S = 1$ semileptonic rare-kaon observable, short-distance $s \to d$ e+e- matching, indirect/direct CP separation with interference, and long-distance inputs from $K_S \to \pi^0$ e+e- and $K_L \to \pi^0 \gamma \gamma$. Existing $\Delta F = 2$ SLL/SLR/VLL/VRR/LR machinery does not cover this mode.

Key references

Process-local source keys before bibliography consolidation: PDG2026:K008, KTeV2004:KLPi0EE, NA482003:KSPi0EE, IsidoriSmithUnterdorfer2004:KLPi0LL, CFW2008:RSFlavor, ChristEtAl2016:KPiLLLattice, and AebischerBurasKumar2022:RareKaons. Numeric claims above are tied to the sidecar-listed local snapshots.

value <2.8e-10

AMBIGUOUS

Match 1 of 5 snapshot line 13

L10: Mode number: 32
L11: Section: Linear parametrization assuming mu-e universality K_L decay form
L12: factors; CP- or LF-violating modes, or DeltaS = 1 weak neutral current modes.
L13: PDG value: <2.8 E-10
L14: Confidence level: 90%
L15: Type: OUR AVERAGE
L16:

Match 2 of 5 snapshot line 36

L33: Technique: KTEV
L34: Comment: combined result
L35: Confidence level: 90%
L36: Value: <2.8E-10
L37: Used in average: true
L38: Footnote: Combined result of ALAVI-HARATI 2004A 1999-2000 data set and
L39: ALAVI-HARATI 2001 1997 data set.

Match 3 of 5 snapshot line 42

L39: ALAVI-HARATI 2001 1997 data set.
L40: 
L41: Other listed measurements/provenance:
L42: ALAVI-HARATI 2004A standalone KTEV 1999-2000 value: <3.5E-10 at 90% CL.
L43: LAI 2002B, PL B536 229, NA48, CP-conserving part: (0.0047 +0.0022 -0.0018) E-10.
L44: Footnote: LAI 2002B uses the absence of a signal in K0L --> pi0 gamma gamma
L45: with m(gamma gamma) < m(pi0) and their a(V) value to predict this value.

Match 4 of 5 snapshot line 43

L40: 
L41: Other listed measurements/provenance:
L42: ALAVI-HARATI 2004A standalone KTEV 1999-2000 value: <3.5E-10 at 90% CL.
L43: LAI 2002B, PL B536 229, NA48, CP-conserving part: (0.0047 +0.0022 -0.0018) E-10.
L44: Footnote: LAI 2002B uses the absence of a signal in K0L --> pi0 gamma gamma
L45: with m(gamma gamma) < m(pi0) and their a(V) value to predict this value.
L46: ALAVI-HARATI 2001, PRL 86 397, KTEV 1997 value: <5.1E-10 at 90% CL.

Match 5 of 5 snapshot line 46

L43: LAI 2002B, PL B536 229, NA48, CP-conserving part: (0.0047 +0.0022 -0.0018) E-10.
L44: Footnote: LAI 2002B uses the absence of a signal in K0L --> pi0 gamma gamma
L45: with m(gamma gamma) < m(pi0) and their a(V) value to predict this value.
L46: ALAVI-HARATI 2001, PRL 86 397, KTEV 1997 value: <5.1E-10 at 90% CL.

value <3.5e-10

AMBIGUOUS

Match 1 of 2 snapshot line 15

L12: The KTeV/E799 experiment at Fermilab searched for KL -> pi0 e+ e-. This mode
L13: is expected to have a significant CP-violating component. For the 1999-2000
L14: data set, one event was observed with an expected background of 0.99 +/- 0.35
L15: events. KTeV set a 90% CL limit BR(KL -> pi0 e+ e-) < 3.5 x 10^-10. Combining
L16: with the 1997 KTeV result yielded the final KTeV limit:
L17: BR(KL -> pi0 e+ e-) < 2.8 x 10^-10 at 90% CL.
L18:

Match 2 of 2 snapshot line 17

L14: data set, one event was observed with an expected background of 0.99 +/- 0.35
L15: events. KTeV set a 90% CL limit BR(KL -> pi0 e+ e-) < 3.5 x 10^-10. Combining
L16: with the 1997 KTeV result yielded the final KTeV limit:
L17: BR(KL -> pi0 e+ e-) < 2.8 x 10^-10 at 90% CL.
L18: 
L19: The paper states that in the Standard Model there are direct and indirect CPV
L20: contributions to the amplitude plus an interference term. The indirect

value 1

AMBIGUOUS

Match 1 of 10 snapshot line 4

L1: Source: arXiv text extraction from KTeV paper
L2: URL: https://arxiv.org/abs/hep-ex/0309072
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ex/0309072
L4: Accessed: 2026-05-16
L5: arXiv: hep-ex/0309072
L6: Published as: Phys. Rev. Lett. 93, 021805 (2004)
L7: DOI: 10.1103/PhysRevLett.93.021805

Match 2 of 10 snapshot line 6

L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ex/0309072
L4: Accessed: 2026-05-16
L5: arXiv: hep-ex/0309072
L6: Published as: Phys. Rev. Lett. 93, 021805 (2004)
L7: DOI: 10.1103/PhysRevLett.93.021805
L8: Title: Search for the Rare Decay KL -> pi0 e+ e-
L9: Collaboration: KTeV

Match 3 of 10 snapshot line 7

L4: Accessed: 2026-05-16
L5: arXiv: hep-ex/0309072
L6: Published as: Phys. Rev. Lett. 93, 021805 (2004)
L7: DOI: 10.1103/PhysRevLett.93.021805
L8: Title: Search for the Rare Decay KL -> pi0 e+ e-
L9: Collaboration: KTeV
L10:

Match 4 of 10 snapshot line 13

L10: 
L11: Relevant abstract and introduction extraction:
L12: The KTeV/E799 experiment at Fermilab searched for KL -> pi0 e+ e-. This mode
L13: is expected to have a significant CP-violating component. For the 1999-2000
L14: data set, one event was observed with an expected background of 0.99 +/- 0.35
L15: events. KTeV set a 90% CL limit BR(KL -> pi0 e+ e-) < 3.5 x 10^-10. Combining
L16: with the 1997 KTeV result yielded the final KTeV limit:

Match 5 of 10 snapshot line 15

L12: The KTeV/E799 experiment at Fermilab searched for KL -> pi0 e+ e-. This mode
L13: is expected to have a significant CP-violating component. For the 1999-2000
L14: data set, one event was observed with an expected background of 0.99 +/- 0.35
L15: events. KTeV set a 90% CL limit BR(KL -> pi0 e+ e-) < 3.5 x 10^-10. Combining
L16: with the 1997 KTeV result yielded the final KTeV limit:
L17: BR(KL -> pi0 e+ e-) < 2.8 x 10^-10 at 90% CL.
L18:

Match 6 of 10 snapshot line 16

L13: is expected to have a significant CP-violating component. For the 1999-2000
L14: data set, one event was observed with an expected background of 0.99 +/- 0.35
L15: events. KTeV set a 90% CL limit BR(KL -> pi0 e+ e-) < 3.5 x 10^-10. Combining
L16: with the 1997 KTeV result yielded the final KTeV limit:
L17: BR(KL -> pi0 e+ e-) < 2.8 x 10^-10 at 90% CL.
L18: 
L19: The paper states that in the Standard Model there are direct and indirect CPV

Match 7 of 10 snapshot line 17

L14: data set, one event was observed with an expected background of 0.99 +/- 0.35
L15: events. KTeV set a 90% CL limit BR(KL -> pi0 e+ e-) < 3.5 x 10^-10. Combining
L16: with the 1997 KTeV result yielded the final KTeV limit:
L17: BR(KL -> pi0 e+ e-) < 2.8 x 10^-10 at 90% CL.
L18: 
L19: The paper states that in the Standard Model there are direct and indirect CPV
L20: contributions to the amplitude plus an interference term. The indirect

Match 8 of 10 snapshot line 22

L19: The paper states that in the Standard Model there are direct and indirect CPV
L20: contributions to the amplitude plus an interference term. The indirect
L21: component is known from KS -> pi0 e+ e- and appears to dominate. The direct
L22: component was estimated to be about 3 to 6 x 10^-12, and the two CPV
L23: contributions together give BR(KL -> pi0 e+ e-)_CPV in the range
L24: 8 to 45 x 10^-12. The CP-conserving amplitude proceeds through
L25: pi0 gamma* gamma* states and can be determined from KL -> pi0 gamma gamma.

Match 9 of 10 snapshot line 24

L21: component is known from KS -> pi0 e+ e- and appears to dominate. The direct
L22: component was estimated to be about 3 to 6 x 10^-12, and the two CPV
L23: contributions together give BR(KL -> pi0 e+ e-)_CPV in the range
L24: 8 to 45 x 10^-12. The CP-conserving amplitude proceeds through
L25: pi0 gamma* gamma* states and can be determined from KL -> pi0 gamma gamma.
L26: The paper quotes a Standard-Model branching ratio around 3 x 10^-11, dominated
L27: by CPV, with a 40% contribution from direct CPV through the interference term.

Match 10 of 10 snapshot line 26

L23: contributions together give BR(KL -> pi0 e+ e-)_CPV in the range
L24: 8 to 45 x 10^-12. The CP-conserving amplitude proceeds through
L25: pi0 gamma* gamma* states and can be determined from KL -> pi0 gamma gamma.
L26: The paper quotes a Standard-Model branching ratio around 3 x 10^-11, dominated
L27: by CPV, with a 40% contribution from direct CPV through the interference term.

value 0.99 0.35

RESOLVED

Match snapshot line 14

L11: Relevant abstract and introduction extraction:
L12: The KTeV/E799 experiment at Fermilab searched for KL -> pi0 e+ e-. This mode
L13: is expected to have a significant CP-violating component. For the 1999-2000
L14: data set, one event was observed with an expected background of 0.99 +/- 0.35
L15: events. KTeV set a 90% CL limit BR(KL -> pi0 e+ e-) < 3.5 x 10^-10. Combining
L16: with the 1997 KTeV result yielded the final KTeV limit:
L17: BR(KL -> pi0 e+ e-) < 2.8 x 10^-10 at 90% CL.

value 0.0047e-10 +0.0022e-10 -0.0018e-10

AMBIGUOUS

Match 1 of 5 snapshot line 13

L10: Mode number: 32
L11: Section: Linear parametrization assuming mu-e universality K_L decay form
L12: factors; CP- or LF-violating modes, or DeltaS = 1 weak neutral current modes.
L13: PDG value: <2.8 E-10
L14: Confidence level: 90%
L15: Type: OUR AVERAGE
L16:

Match 2 of 5 snapshot line 36

L33: Technique: KTEV
L34: Comment: combined result
L35: Confidence level: 90%
L36: Value: <2.8E-10
L37: Used in average: true
L38: Footnote: Combined result of ALAVI-HARATI 2004A 1999-2000 data set and
L39: ALAVI-HARATI 2001 1997 data set.

Match 3 of 5 snapshot line 42

L39: ALAVI-HARATI 2001 1997 data set.
L40: 
L41: Other listed measurements/provenance:
L42: ALAVI-HARATI 2004A standalone KTEV 1999-2000 value: <3.5E-10 at 90% CL.
L43: LAI 2002B, PL B536 229, NA48, CP-conserving part: (0.0047 +0.0022 -0.0018) E-10.
L44: Footnote: LAI 2002B uses the absence of a signal in K0L --> pi0 gamma gamma
L45: with m(gamma gamma) < m(pi0) and their a(V) value to predict this value.

Match 4 of 5 snapshot line 43

L40: 
L41: Other listed measurements/provenance:
L42: ALAVI-HARATI 2004A standalone KTEV 1999-2000 value: <3.5E-10 at 90% CL.
L43: LAI 2002B, PL B536 229, NA48, CP-conserving part: (0.0047 +0.0022 -0.0018) E-10.
L44: Footnote: LAI 2002B uses the absence of a signal in K0L --> pi0 gamma gamma
L45: with m(gamma gamma) < m(pi0) and their a(V) value to predict this value.
L46: ALAVI-HARATI 2001, PRL 86 397, KTEV 1997 value: <5.1E-10 at 90% CL.

Match 5 of 5 snapshot line 46

L43: LAI 2002B, PL B536 229, NA48, CP-conserving part: (0.0047 +0.0022 -0.0018) E-10.
L44: Footnote: LAI 2002B uses the absence of a signal in K0L --> pi0 gamma gamma
L45: with m(gamma gamma) < m(pi0) and their a(V) value to predict this value.
L46: ALAVI-HARATI 2001, PRL 86 397, KTEV 1997 value: <5.1E-10 at 90% CL.

value 3.0e-9 +1.5e-9 -1.2e-9 stat; +/-0.2e-9 syst

AMBIGUOUS

Match 1 of 5 snapshot line 10

L7: PDG identifier and summary:
L8: PDGID: S012.10
L9: Description: K0S --> pi0 e+ e-
L10: PDG value: (3.0 +1.5 -1.2) E-9
L11: 
L12: Listing block:
L13: Related PDGID: S012R10

Match 2 of 5 snapshot line 28

L25: Technique: NA48
L26: Event count: 7
L27: Comment: m(ee)>0.165 GeV
L28: Value: (3.0 +1.5 -1.2 +-0.2) E-9
L29: Statistical error: +1.5E-9 / -1.2E-9
L30: Systematic error: +-0.2E-9
L31: Used in average: true

Match 3 of 5 snapshot line 29

L26: Event count: 7
L27: Comment: m(ee)>0.165 GeV
L28: Value: (3.0 +1.5 -1.2 +-0.2) E-9
L29: Statistical error: +1.5E-9 / -1.2E-9
L30: Systematic error: +-0.2E-9
L31: Used in average: true
L32: Footnote: BATLEY 2003 extrapolate also to the full kinematical region using

Match 4 of 5 snapshot line 30

L27: Comment: m(ee)>0.165 GeV
L28: Value: (3.0 +1.5 -1.2 +-0.2) E-9
L29: Statistical error: +1.5E-9 / -1.2E-9
L30: Systematic error: +-0.2E-9
L31: Used in average: true
L32: Footnote: BATLEY 2003 extrapolate also to the full kinematical region using
L33: a constant form factor and a vector matrix element. The resulting branching

Match 5 of 5 snapshot line 34

L31: Used in average: true
L32: Footnote: BATLEY 2003 extrapolate also to the full kinematical region using
L33: a constant form factor and a vector matrix element. The resulting branching
L34: ratio is 5.8 +2.9 -2.4 E-9.

value 0.165

RESOLVED

Match snapshot line 27

L24: Title: Observation of the Rare Decay K0S --> pi0 e+ e-
L25: Technique: NA48
L26: Event count: 7
L27: Comment: m(ee)>0.165 GeV
L28: Value: (3.0 +1.5 -1.2 +-0.2) E-9
L29: Statistical error: +1.5E-9 / -1.2E-9
L30: Systematic error: +-0.2E-9

value 5.8e-9 +2.9e-9 -2.4e-9

AMBIGUOUS

Match 1 of 5 snapshot line 10

L7: PDG identifier and summary:
L8: PDGID: S012.10
L9: Description: K0S --> pi0 e+ e-
L10: PDG value: (3.0 +1.5 -1.2) E-9
L11: 
L12: Listing block:
L13: Related PDGID: S012R10

Match 2 of 5 snapshot line 28

L25: Technique: NA48
L26: Event count: 7
L27: Comment: m(ee)>0.165 GeV
L28: Value: (3.0 +1.5 -1.2 +-0.2) E-9
L29: Statistical error: +1.5E-9 / -1.2E-9
L30: Systematic error: +-0.2E-9
L31: Used in average: true

Match 3 of 5 snapshot line 29

L26: Event count: 7
L27: Comment: m(ee)>0.165 GeV
L28: Value: (3.0 +1.5 -1.2 +-0.2) E-9
L29: Statistical error: +1.5E-9 / -1.2E-9
L30: Systematic error: +-0.2E-9
L31: Used in average: true
L32: Footnote: BATLEY 2003 extrapolate also to the full kinematical region using

Match 4 of 5 snapshot line 30

L27: Comment: m(ee)>0.165 GeV
L28: Value: (3.0 +1.5 -1.2 +-0.2) E-9
L29: Statistical error: +1.5E-9 / -1.2E-9
L30: Systematic error: +-0.2E-9
L31: Used in average: true
L32: Footnote: BATLEY 2003 extrapolate also to the full kinematical region using
L33: a constant form factor and a vector matrix element. The resulting branching

Match 5 of 5 snapshot line 34

L31: Used in average: true
L32: Footnote: BATLEY 2003 extrapolate also to the full kinematical region using
L33: a constant form factor and a vector matrix element. The resulting branching
L34: ratio is 5.8 +2.9 -2.4 E-9.

value 3e-11

AMBIGUOUS

Match 1 of 9 snapshot line 2

L1: Source: arXiv text extraction from KTeV paper
L2: URL: https://arxiv.org/abs/hep-ex/0309072
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ex/0309072
L4: Accessed: 2026-05-16
L5: arXiv: hep-ex/0309072

Match 2 of 9 snapshot line 3

L1: Source: arXiv text extraction from KTeV paper
L2: URL: https://arxiv.org/abs/hep-ex/0309072
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ex/0309072
L4: Accessed: 2026-05-16
L5: arXiv: hep-ex/0309072
L6: Published as: Phys. Rev. Lett. 93, 021805 (2004)

Match 3 of 9 snapshot line 5

L2: URL: https://arxiv.org/abs/hep-ex/0309072
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ex/0309072
L4: Accessed: 2026-05-16
L5: arXiv: hep-ex/0309072
L6: Published as: Phys. Rev. Lett. 93, 021805 (2004)
L7: DOI: 10.1103/PhysRevLett.93.021805
L8: Title: Search for the Rare Decay KL -> pi0 e+ e-

Match 4 of 9 snapshot line 6

L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ex/0309072
L4: Accessed: 2026-05-16
L5: arXiv: hep-ex/0309072
L6: Published as: Phys. Rev. Lett. 93, 021805 (2004)
L7: DOI: 10.1103/PhysRevLett.93.021805
L8: Title: Search for the Rare Decay KL -> pi0 e+ e-
L9: Collaboration: KTeV

Match 5 of 9 snapshot line 7

L4: Accessed: 2026-05-16
L5: arXiv: hep-ex/0309072
L6: Published as: Phys. Rev. Lett. 93, 021805 (2004)
L7: DOI: 10.1103/PhysRevLett.93.021805
L8: Title: Search for the Rare Decay KL -> pi0 e+ e-
L9: Collaboration: KTeV
L10:

Match 6 of 9 snapshot line 14

L11: Relevant abstract and introduction extraction:
L12: The KTeV/E799 experiment at Fermilab searched for KL -> pi0 e+ e-. This mode
L13: is expected to have a significant CP-violating component. For the 1999-2000
L14: data set, one event was observed with an expected background of 0.99 +/- 0.35
L15: events. KTeV set a 90% CL limit BR(KL -> pi0 e+ e-) < 3.5 x 10^-10. Combining
L16: with the 1997 KTeV result yielded the final KTeV limit:
L17: BR(KL -> pi0 e+ e-) < 2.8 x 10^-10 at 90% CL.

Match 7 of 9 snapshot line 15

L12: The KTeV/E799 experiment at Fermilab searched for KL -> pi0 e+ e-. This mode
L13: is expected to have a significant CP-violating component. For the 1999-2000
L14: data set, one event was observed with an expected background of 0.99 +/- 0.35
L15: events. KTeV set a 90% CL limit BR(KL -> pi0 e+ e-) < 3.5 x 10^-10. Combining
L16: with the 1997 KTeV result yielded the final KTeV limit:
L17: BR(KL -> pi0 e+ e-) < 2.8 x 10^-10 at 90% CL.
L18:

Match 8 of 9 snapshot line 22

L19: The paper states that in the Standard Model there are direct and indirect CPV
L20: contributions to the amplitude plus an interference term. The indirect
L21: component is known from KS -> pi0 e+ e- and appears to dominate. The direct
L22: component was estimated to be about 3 to 6 x 10^-12, and the two CPV
L23: contributions together give BR(KL -> pi0 e+ e-)_CPV in the range
L24: 8 to 45 x 10^-12. The CP-conserving amplitude proceeds through
L25: pi0 gamma* gamma* states and can be determined from KL -> pi0 gamma gamma.

Match 9 of 9 snapshot line 26

L23: contributions together give BR(KL -> pi0 e+ e-)_CPV in the range
L24: 8 to 45 x 10^-12. The CP-conserving amplitude proceeds through
L25: pi0 gamma* gamma* states and can be determined from KL -> pi0 gamma gamma.
L26: The paper quotes a Standard-Model branching ratio around 3 x 10^-11, dominated
L27: by CPV, with a 40% contribution from direct CPV through the interference term.

value 8e-12 to 45e-12

AMBIGUOUS

Match 1 of 2 snapshot line 22

L19: The paper states that in the Standard Model there are direct and indirect CPV
L20: contributions to the amplitude plus an interference term. The indirect
L21: component is known from KS -> pi0 e+ e- and appears to dominate. The direct
L22: component was estimated to be about 3 to 6 x 10^-12, and the two CPV
L23: contributions together give BR(KL -> pi0 e+ e-)_CPV in the range
L24: 8 to 45 x 10^-12. The CP-conserving amplitude proceeds through
L25: pi0 gamma* gamma* states and can be determined from KL -> pi0 gamma gamma.

Match 2 of 2 snapshot line 24

L21: component is known from KS -> pi0 e+ e- and appears to dominate. The direct
L22: component was estimated to be about 3 to 6 x 10^-12, and the two CPV
L23: contributions together give BR(KL -> pi0 e+ e-)_CPV in the range
L24: 8 to 45 x 10^-12. The CP-conserving amplitude proceeds through
L25: pi0 gamma* gamma* states and can be determined from KL -> pi0 gamma gamma.
L26: The paper quotes a Standard-Model branching ratio around 3 x 10^-11, dominated
L27: by CPV, with a 40% contribution from direct CPV through the interference term.

value 3e-12 to 6e-12

AMBIGUOUS

Match 1 of 2 snapshot line 22

L19: The paper states that in the Standard Model there are direct and indirect CPV
L20: contributions to the amplitude plus an interference term. The indirect
L21: component is known from KS -> pi0 e+ e- and appears to dominate. The direct
L22: component was estimated to be about 3 to 6 x 10^-12, and the two CPV
L23: contributions together give BR(KL -> pi0 e+ e-)_CPV in the range
L24: 8 to 45 x 10^-12. The CP-conserving amplitude proceeds through
L25: pi0 gamma* gamma* states and can be determined from KL -> pi0 gamma gamma.

Match 2 of 2 snapshot line 24

L21: component is known from KS -> pi0 e+ e- and appears to dominate. The direct
L22: component was estimated to be about 3 to 6 x 10^-12, and the two CPV
L23: contributions together give BR(KL -> pi0 e+ e-)_CPV in the range
L24: 8 to 45 x 10^-12. The CP-conserving amplitude proceeds through
L25: pi0 gamma* gamma* states and can be determined from KL -> pi0 gamma gamma.
L26: The paper quotes a Standard-Model branching ratio around 3 x 10^-11, dominated
L27: by CPV, with a 40% contribution from direct CPV through the interference term.

value 40

RESOLVED

Match snapshot line 27

L24: 8 to 45 x 10^-12. The CP-conserving amplitude proceeds through
L25: pi0 gamma* gamma* states and can be determined from KL -> pi0 gamma gamma.
L26: The paper quotes a Standard-Model branching ratio around 3 x 10^-11, dominated
L27: by CPV, with a 40% contribution from direct CPV through the interference term.

value 1e-12

AMBIGUOUS

Match 1 of 10 snapshot line 2

L1: Source: arXiv text extraction
L2: URL: https://arxiv.org/abs/hep-ph/0404127
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ph/0404127
L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127

Match 2 of 10 snapshot line 3

L1: Source: arXiv text extraction
L2: URL: https://arxiv.org/abs/hep-ph/0404127
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ph/0404127
L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127
L6: Published as: Eur. Phys. J. C 36, 57-66 (2004)

Match 3 of 10 snapshot line 4

L1: Source: arXiv text extraction
L2: URL: https://arxiv.org/abs/hep-ph/0404127
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ph/0404127
L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127
L6: Published as: Eur. Phys. J. C 36, 57-66 (2004)
L7: DOI: 10.1140/epjc/s2004-01879-0

Match 4 of 10 snapshot line 5

L2: URL: https://arxiv.org/abs/hep-ph/0404127
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ph/0404127
L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127
L6: Published as: Eur. Phys. J. C 36, 57-66 (2004)
L7: DOI: 10.1140/epjc/s2004-01879-0
L8: Title: The rare decay KL -> pi0 mu+ mu- within the SM

Match 5 of 10 snapshot line 7

L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127
L6: Published as: Eur. Phys. J. C 36, 57-66 (2004)
L7: DOI: 10.1140/epjc/s2004-01879-0
L8: Title: The rare decay KL -> pi0 mu+ mu- within the SM
L9: Authors: Gino Isidori, Christopher Smith, Rene Unterdorfer
L10:

Match 6 of 10 snapshot line 15

L12: The paper writes the neutral-kaon dilepton rate in terms of mixing, direct,
L13: interference, and CP-conserving pieces:
L14: B(KL -> pi0 l+ l-) =
L15: [C_mix^l +/- C_int^l (Im lambda_t / 10^-4)
L16:  + C_dir^l (Im lambda_t / 10^-4)^2 + C_CPC^l] x 10^-12.
L17: 
L18: For the electron mode, the coefficients quoted are:

Match 7 of 10 snapshot line 16

L13: interference, and CP-conserving pieces:
L14: B(KL -> pi0 l+ l-) =
L15: [C_mix^l +/- C_int^l (Im lambda_t / 10^-4)
L16:  + C_dir^l (Im lambda_t / 10^-4)^2 + C_CPC^l] x 10^-12.
L17: 
L18: For the electron mode, the coefficients quoted are:
L19: C_mix^e = (15.7 +/- 0.3) |a_S|^2

Match 8 of 10 snapshot line 19

L16:  + C_dir^l (Im lambda_t / 10^-4)^2 + C_CPC^l] x 10^-12.
L17: 
L18: For the electron mode, the coefficients quoted are:
L19: C_mix^e = (15.7 +/- 0.3) |a_S|^2
L20: C_int^e = (6.2 +/- 0.3) |a_S|
L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0

Match 9 of 10 snapshot line 24

L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0
L23: 
L24: The same paragraph gives |a_S| = 1.2 +/- 0.2 and
L25: (Im lambda_t / 10^-4)_SM = 1.36 +/- 0.12. The paper reports both signs of the
L26: interference because the sign of a_S was not fixed model-independently, while
L27: noting that theoretical arguments point toward constructive interference. For

Match 10 of 10 snapshot line 25

L22: C_CPC^e approx 0
L23: 
L24: The same paragraph gives |a_S| = 1.2 +/- 0.2 and
L25: (Im lambda_t / 10^-4)_SM = 1.36 +/- 0.12. The paper reports both signs of the
L26: interference because the sign of a_S was not fixed model-independently, while
L27: noting that theoretical arguments point toward constructive interference. For
L28: the electron mode it states that the decay is completely dominated by the CPV

value 15.7 0.3

RESOLVED

Match snapshot line 19

L16:  + C_dir^l (Im lambda_t / 10^-4)^2 + C_CPC^l] x 10^-12.
L17: 
L18: For the electron mode, the coefficients quoted are:
L19: C_mix^e = (15.7 +/- 0.3) |a_S|^2
L20: C_int^e = (6.2 +/- 0.3) |a_S|
L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0

value 6.2 0.3

RESOLVED

Match snapshot line 20

L17: 
L18: For the electron mode, the coefficients quoted are:
L19: C_mix^e = (15.7 +/- 0.3) |a_S|^2
L20: C_int^e = (6.2 +/- 0.3) |a_S|
L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0
L23:

value 2.4 0.2

RESOLVED

Match snapshot line 21

L18: For the electron mode, the coefficients quoted are:
L19: C_mix^e = (15.7 +/- 0.3) |a_S|^2
L20: C_int^e = (6.2 +/- 0.3) |a_S|
L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0
L23: 
L24: The same paragraph gives |a_S| = 1.2 +/- 0.2 and

value 0

AMBIGUOUS

Match 1 of 16 snapshot line 2

L1: Source: arXiv text extraction
L2: URL: https://arxiv.org/abs/hep-ph/0404127
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ph/0404127
L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127

Match 2 of 16 snapshot line 3

L1: Source: arXiv text extraction
L2: URL: https://arxiv.org/abs/hep-ph/0404127
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ph/0404127
L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127
L6: Published as: Eur. Phys. J. C 36, 57-66 (2004)

Match 3 of 16 snapshot line 4

L1: Source: arXiv text extraction
L2: URL: https://arxiv.org/abs/hep-ph/0404127
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ph/0404127
L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127
L6: Published as: Eur. Phys. J. C 36, 57-66 (2004)
L7: DOI: 10.1140/epjc/s2004-01879-0

Match 4 of 16 snapshot line 5

L2: URL: https://arxiv.org/abs/hep-ph/0404127
L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ph/0404127
L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127
L6: Published as: Eur. Phys. J. C 36, 57-66 (2004)
L7: DOI: 10.1140/epjc/s2004-01879-0
L8: Title: The rare decay KL -> pi0 mu+ mu- within the SM

Match 5 of 16 snapshot line 6

L3: PDF used transiently through stdout only: https://arxiv.org/pdf/hep-ph/0404127
L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127
L6: Published as: Eur. Phys. J. C 36, 57-66 (2004)
L7: DOI: 10.1140/epjc/s2004-01879-0
L8: Title: The rare decay KL -> pi0 mu+ mu- within the SM
L9: Authors: Gino Isidori, Christopher Smith, Rene Unterdorfer

Match 6 of 16 snapshot line 7

L4: Accessed: 2026-05-16
L5: arXiv: hep-ph/0404127
L6: Published as: Eur. Phys. J. C 36, 57-66 (2004)
L7: DOI: 10.1140/epjc/s2004-01879-0
L8: Title: The rare decay KL -> pi0 mu+ mu- within the SM
L9: Authors: Gino Isidori, Christopher Smith, Rene Unterdorfer
L10:

Match 7 of 16 snapshot line 8

L5: arXiv: hep-ph/0404127
L6: Published as: Eur. Phys. J. C 36, 57-66 (2004)
L7: DOI: 10.1140/epjc/s2004-01879-0
L8: Title: The rare decay KL -> pi0 mu+ mu- within the SM
L9: Authors: Gino Isidori, Christopher Smith, Rene Unterdorfer
L10: 
L11: Relevant extraction:

Match 8 of 16 snapshot line 14

L11: Relevant extraction:
L12: The paper writes the neutral-kaon dilepton rate in terms of mixing, direct,
L13: interference, and CP-conserving pieces:
L14: B(KL -> pi0 l+ l-) =
L15: [C_mix^l +/- C_int^l (Im lambda_t / 10^-4)
L16:  + C_dir^l (Im lambda_t / 10^-4)^2 + C_CPC^l] x 10^-12.
L17:

Match 9 of 16 snapshot line 15

L12: The paper writes the neutral-kaon dilepton rate in terms of mixing, direct,
L13: interference, and CP-conserving pieces:
L14: B(KL -> pi0 l+ l-) =
L15: [C_mix^l +/- C_int^l (Im lambda_t / 10^-4)
L16:  + C_dir^l (Im lambda_t / 10^-4)^2 + C_CPC^l] x 10^-12.
L17: 
L18: For the electron mode, the coefficients quoted are:

Match 10 of 16 snapshot line 16

L13: interference, and CP-conserving pieces:
L14: B(KL -> pi0 l+ l-) =
L15: [C_mix^l +/- C_int^l (Im lambda_t / 10^-4)
L16:  + C_dir^l (Im lambda_t / 10^-4)^2 + C_CPC^l] x 10^-12.
L17: 
L18: For the electron mode, the coefficients quoted are:
L19: C_mix^e = (15.7 +/- 0.3) |a_S|^2

Match 11 of 16 snapshot line 19

L16:  + C_dir^l (Im lambda_t / 10^-4)^2 + C_CPC^l] x 10^-12.
L17: 
L18: For the electron mode, the coefficients quoted are:
L19: C_mix^e = (15.7 +/- 0.3) |a_S|^2
L20: C_int^e = (6.2 +/- 0.3) |a_S|
L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0

Match 12 of 16 snapshot line 20

L17: 
L18: For the electron mode, the coefficients quoted are:
L19: C_mix^e = (15.7 +/- 0.3) |a_S|^2
L20: C_int^e = (6.2 +/- 0.3) |a_S|
L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0
L23:

Match 13 of 16 snapshot line 21

L18: For the electron mode, the coefficients quoted are:
L19: C_mix^e = (15.7 +/- 0.3) |a_S|^2
L20: C_int^e = (6.2 +/- 0.3) |a_S|
L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0
L23: 
L24: The same paragraph gives |a_S| = 1.2 +/- 0.2 and

Match 14 of 16 snapshot line 22

L19: C_mix^e = (15.7 +/- 0.3) |a_S|^2
L20: C_int^e = (6.2 +/- 0.3) |a_S|
L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0
L23: 
L24: The same paragraph gives |a_S| = 1.2 +/- 0.2 and
L25: (Im lambda_t / 10^-4)_SM = 1.36 +/- 0.12. The paper reports both signs of the

Match 15 of 16 snapshot line 24

L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0
L23: 
L24: The same paragraph gives |a_S| = 1.2 +/- 0.2 and
L25: (Im lambda_t / 10^-4)_SM = 1.36 +/- 0.12. The paper reports both signs of the
L26: interference because the sign of a_S was not fixed model-independently, while
L27: noting that theoretical arguments point toward constructive interference. For

Match 16 of 16 snapshot line 25

L22: C_CPC^e approx 0
L23: 
L24: The same paragraph gives |a_S| = 1.2 +/- 0.2 and
L25: (Im lambda_t / 10^-4)_SM = 1.36 +/- 0.12. The paper reports both signs of the
L26: interference because the sign of a_S was not fixed model-independently, while
L27: noting that theoretical arguments point toward constructive interference. For
L28: the electron mode it states that the decay is completely dominated by the CPV

value 1.2 0.2

RESOLVED

Match snapshot line 24

L21: C_dir^e = 2.4 +/- 0.2
L22: C_CPC^e approx 0
L23: 
L24: The same paragraph gives |a_S| = 1.2 +/- 0.2 and
L25: (Im lambda_t / 10^-4)_SM = 1.36 +/- 0.12. The paper reports both signs of the
L26: interference because the sign of a_S was not fixed model-independently, while
L27: noting that theoretical arguments point toward constructive interference. For

value 1.36 0.12

RESOLVED

Match snapshot line 25

L22: C_CPC^e approx 0
L23: 
L24: The same paragraph gives |a_S| = 1.2 +/- 0.2 and
L25: (Im lambda_t / 10^-4)_SM = 1.36 +/- 0.12. The paper reports both signs of the
L26: interference because the sign of a_S was not fixed model-independently, while
L27: noting that theoretical arguments point toward constructive interference. For
L28: the electron mode it states that the decay is completely dominated by the CPV