Search for a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>μ</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>μ</mml:mi><mml:mo>−</mml:mo></mml:msup></mml:math> resonance in four-muon final states at Belle II
I. Adachi, K. Adamczyk, L. Aggarwal, H. Ahmed, H. Aihara, Н. Акопов, A. Aloisio, N. Anh Ky, D. M. Asner, H. Atmacan, V. Aushev, M. Aversano, R. Ayad, V. Babu, H. Bae, S. Bahinipati, P. Bambade, Sw. Banerjee, S. Bansal, M. Barrett, J. Baudot, A. Baur, A. Beaubien, F. Becherer, J. Becker, J. V. Bennett, F. U. Bernlochner, V. Bertacchi, M. Bertemes, E. Bertholet, M. Bessner, S. Bettarini, B. Bhuyan, F. Bianchi, T. Bilka, S. Bilokin, D. Biswas, A. Bobrov, D. Bodrov, A. E. Bolz, A. Bożek, M. Bračko, P. Branchini, T. E. Browder, A. Budano, S. Bussino, M. Campajola, L. Cao, G. Casarosa, C. Cecchi, J. Cerasoli, M.-C. Chang, P. Chang, R. Cheaib, P. Cheema, B. G. Cheon, K. Chilikin, K. Chirapatpimol, H.-E. Cho, K. Cho, S.-J. Cho, S. -J. Cho, S. Choudhury, L. Corona, L. Cremaldi, S. Das, F. Dattola, E. De La Cruz–Burelo, S. A. De La Motte, G. De Nardo, M. De Nuccio, G. De Pietro, R. de Sangro, M. Destefanis, R. Dhamija, A. Di Canto, F. Di Capua, J. Dingfelder, Z. Doležal, T. V. Dong, M. Dorigo, K. Dort, S. Dreyer, S. Dubey, G. Dujany, P. Ecker, M. Eliachevitch, D. Epifanov, P. Feichtinger, T. Ferber, D. Ferlewicz, T. Fillinger, C. Finck, G. Finocchiaro, A. Fodor, F. Forti, A. Frey, B. G. Fulsom, A. Gabrielli, E. Ganiev
Abstract
We report on a search for a resonance <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>X</a:mi></a:math> decaying to a pair of muons in <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:msup><c:mi>e</c:mi><c:mo>+</c:mo></c:msup><c:msup><c:mi>e</c:mi><c:mo>−</c:mo></c:msup><c:mo stretchy="false">→</c:mo><c:msup><c:mi>μ</c:mi><c:mo>+</c:mo></c:msup><c:msup><c:mi>μ</c:mi><c:mo>−</c:mo></c:msup><c:mi>X</c:mi></c:math> events in the <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"><f:mrow><f:mn>0.212</f:mn><f:mi>–</f:mi><f:mn>9.000</f:mn><f:mtext> </f:mtext><f:mtext> </f:mtext><f:mi>GeV</f:mi><f:mo>/</f:mo><f:msup><f:mrow><f:mi>c</f:mi></f:mrow><f:mrow><f:mn>2</f:mn></f:mrow></f:msup></f:mrow></f:math> mass range, using <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mn>178</h:mn><h:mtext> </h:mtext><h:mtext> </h:mtext><h:msup><h:mi>fb</h:mi><h:mrow><h:mo>−</h:mo><h:mn>1</h:mn></h:mrow></h:msup></h:math> of data collected by the Belle II experiment at the SuperKEKB collider at a center of mass energy of 10.58 GeV. The analysis probes two different models of <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:mi>X</j:mi></j:math> beyond the standard model: a <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:msup><l:mi>Z</l:mi><l:mo>′</l:mo></l:msup></l:math> vector boson in the <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:msub><n:mi>L</n:mi><n:mi>μ</n:mi></n:msub><n:mo>−</n:mo><n:msub><n:mi>L</n:mi><n:mi>τ</n:mi></n:msub></n:math> model and a muonphilic scalar. We observe no evidence for a signal and set exclusion limits at the 90% confidence level on the products of cross section and branching fraction for these processes, ranging from 0.046 fb to 0.97 fb for the <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:msub><p:mi>L</p:mi><p:mi>μ</p:mi></p:msub><p:mo>−</p:mo><p:msub><p:mi>L</p:mi><p:mi>τ</p:mi></p:msub></p:math> model and from 0.055 fb to 1.3 fb for the muonphilic scalar model. For masses below <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:mrow><r:mn>6</r:mn><r:mtext> </r:mtext><r:mtext> </r:mtext><r:mi>GeV</r:mi><r:mo>/</r:mo><r:msup><r:mrow><r:mi>c</r:mi></r:mrow><r:mn>2</r:mn></r:msup></r:mrow></r:math>, the corresponding constraints on the couplings of these processes to the standard model range from 0.0008 to 0.039 for the <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:msub><t:mi>L</t:mi><t:mi>μ</t:mi></t:msub><t:mo>−</t:mo><t:msub><t:mi>L</t:mi><t:mi>τ</t:mi></t:msub></t:math> model and from 0.0018 to 0.040 for the muonphilic scalar model. These are the first constraints on the muonphilic scalar from a dedicated search. Published by the American Physical Society 2024