We report the results of a search for the <math><mrow><mi>B</mi><mo>→</mo><mi>Y</mi><mo>(</mo><mn>4260</mn><mo>)</mo><mi>K</mi></mrow></math>, <math><mrow><mi>Y</mi><mo>(</mo><mn>4260</mn><mo>)</mo><mo>→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> decays. This study is based on a data sample corresponding to an integrated luminosity of <math><mrow><mn>711</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>fb</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math>, collected at the <math><mrow><mi>ϒ</mi><mo>(</mo><mn>4</mn><mi>S</mi><mo>)</mo></mrow></math> resonance with the Belle detector at the KEKB asymmetric-energy <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collider. We investigate the <math><mi>J</mi><mo>/</mo><mi>ψ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> invariant mass distribution in the range 4.0 to <math><mrow><mn>4.6</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></mrow></math> using both <math><msup><mi>B</mi><mo>+</mo></msup><mo>→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><msup><mi>K</mi><mo>+</mo></msup></math> and <math><msup><mi>B</mi><mn>0</mn></msup><mo>→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><msubsup><mi>K</mi><mi>S</mi><mn>0</mn></msubsup></math> decays. We find excesses of events above the background levels, with significances of 2.1 and 0.9 standard deviations for charged and neutral <math><mi>B</mi><mo>→</mo><mi>Y</mi><mo>(</mo><mn>4260</mn><mo>)</mo><mi>K</mi></math> decays, respectively, taking into account the systematic uncertainties. These correspond to upper limits on the product of branching fractions, <math><mi>B</mi><mo>(</mo><msup><mi>B</mi><mo>+</mo></msup><mo>→</mo><mi>Y</mi><mo>(</mo><mn>4260</mn><mo>)</mo><msup><mi>K</mi><mo>+</mo></msup><mo>)</mo><mo>×</mo><mi>B</mi><mo>(</mo><mi>Y</mi><mo>(</mo><mn>4260</mn><mo>)</mo><mo>→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mo>)</mo><mo>&lt;</mo><mn>1.4</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></math> and <math><mi>B</mi><mo>(</mo><msup><mi>B</mi><mn>0</mn></msup><mo>→</mo><mi>Y</mi><mo>(</mo><mn>4260</mn><mo>)</mo><msup><mi>K</mi><mn>0</mn></msup><mo>)</mo><mo>×</mo><mi>B</mi><mo>(</mo><mi>Y</mi><mo>(</mo><mn>4260</mn><mo>)</mo><mo>→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mo>)</mo><mo>&lt;</mo><mn>1.7</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></math> at the 90% confidence level.

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United States

Russia

Germany

Czechia

Slovenia

Poland

Taiwan

France

Australia

China

Georgia

Italy

Search for the <math><mrow><mi>B</mi><mo>→</mo><mi>Y</mi><mo>(</mo><mn>4260</mn><mo>)</mo><mi>K</mi></mrow></math>, <math><mrow><mi>Y</mi><mo>(</mo><mn>4260</mn><mo>)</mo><mo>→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> decays