Search for K+ decays into the π+e+e−e+e− final state
(2023) Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics — Vol. 846 (2023)
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- The first search for ultra-rare <math altimg="si1.svg"><msup><mrow><mi>K</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup></math> decays into the <math altimg="si15.svg"><msup><mrow><mi>π</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo></mrow></msup></math> final state is reported, using a dataset collected by the NA62 experiment at CERN in 2017–2018. An upper limit of <math altimg="si3.svg"><mn>1.4</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo><mn>8</mn></mrow></msup></math> at 90% CL is obtained for the branching ratio of the <math altimg="si20.svg"><msup><mrow><mi>K</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo></mrow></msup></math> decay, predicted in the Standard Model to be <math altimg="si24.svg"><mo stretchy="false">(</mo><mn>7.2</mn><mo>±</mo><mn>0.7</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo><mn>11</mn></mrow></msup></math>. Upper limits at 90% CL are obtained at the level of <math altimg="si6.svg"><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo><mn>9</mn></mrow></msup></math> for the branching ratios of two prompt decay chains involving pair-production of hidden-sector mediators: <math altimg="si34.svg"><msup><mrow><mi>K</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><mi>a</mi><mi>a</mi></math>, <math altimg="si8.svg"><mi>a</mi><mo stretchy="false">→</mo><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo></mrow></msup></math> and <math altimg="si32.svg"><msup><mrow><mi>K</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><mi>S</mi></math>, <math altimg="si10.svg"><mi>S</mi><mo stretchy="false">→</mo><msup><mrow><mi>A</mi></mrow><mrow><mo>′</mo></mrow></msup><msup><mrow><mi>A</mi></mrow><mrow><mo>′</mo></mrow></msup></math>, <math altimg="si11.svg"><msup><mrow><mi>A</mi></mrow><mrow><mo>′</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo></mrow></msup></math>.
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Citations
Cortina Gil, E., Minucci, E., Padolski, S., Rumenov Petrov, P., Jerhot, J., Volpe, R., Kleimenova, A., Shaikhiev, A., Lurkin, N., NA62, & et al. (2023). Search for K+ decays into the π+e+e−e+e− final state. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 846. https://doi.org/10.1016/j.physletb.2023.138193 (Original work published 2023)