The rare decay was studied with the dataset taken at the J-PARC KOTO experiment in 2016, 2017, and 2018. With a single event sensitivity of , three candidate events were observed in the signal region. After unveiling them, contaminations from and scattered decays were studied, and the total number of background events was estimated to be . We conclude that the number of observed events is statistically consistent with the background expectation. For this dataset, we set an upper limit of on the branching fraction of at the 90% confidence level.
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"titles": [
{
"source": "APS",
"title": "Study of the <math><msub><mi>K</mi><mi>L</mi></msub><mo>\u2192</mo><msup><mi>\u03c0</mi><mn>0</mn></msup><mi>\u03bd</mi><mover><mi>\u03bd</mi><mo>\u00af</mo></mover></math> Decay at the J-PARC KOTO Experiment"
}
],
"dois": [
{
"value": "10.1103/PhysRevLett.126.121801"
}
],
"publication_info": [
{
"journal_volume": "126",
"journal_title": "Physical Review Letters",
"material": "article",
"journal_issue": "12",
"year": 2021
}
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"value": "The rare decay <math><msub><mi>K</mi><mi>L</mi></msub><mo>\u2192</mo><msup><mi>\u03c0</mi><mn>0</mn></msup><mi>\u03bd</mi><mover><mi>\u03bd</mi><mo>\u00af</mo></mover></math> was studied with the dataset taken at the J-PARC KOTO experiment in 2016, 2017, and 2018. With a single event sensitivity of <math><mrow><mo>(</mo><mn>7.20</mn><mo>\u00b1</mo><mn>0.0</mn><msub><mrow><mn>5</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>\u00b1</mo><mn>0.6</mn><msub><mrow><mn>6</mn></mrow><mrow><mi>syst</mi></mrow></msub><mo>)</mo><mo>\u00d7</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>\u2212</mo><mn>10</mn></mrow></msup></mrow></math>, three candidate events were observed in the signal region. After unveiling them, contaminations from <math><msup><mi>K</mi><mo>\u00b1</mo></msup></math> and scattered <math><msub><mi>K</mi><mi>L</mi></msub></math> decays were studied, and the total number of background events was estimated to be <math><mn>1.22</mn><mo>\u00b1</mo><mn>0.26</mn></math>. We conclude that the number of observed events is statistically consistent with the background expectation. For this dataset, we set an upper limit of <math><mn>4.9</mn><mo>\u00d7</mo><msup><mn>10</mn><mrow><mo>\u2212</mo><mn>9</mn></mrow></msup></math> on the branching fraction of <math><msub><mi>K</mi><mi>L</mi></msub><mo>\u2192</mo><msup><mi>\u03c0</mi><mn>0</mn></msup><mi>\u03bd</mi><mover><mi>\u03bd</mi><mo>\u00af</mo></mover></math> at the 90% confidence level."
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