Observation of four top quark production in proton-proton collisions at <math altimg="si1.svg"><msqrt><mrow><mi>s</mi></mrow></msqrt><mo linebreak="goodbreak" linebreakstyle="after">=</mo><mn>13</mn><mspace width="0.2em"/><mtext>TeV</mtext></math>

Benecke, Anna;Bruno, Giacomo;Caputo, Claudio;Delaere, Christophe;Bethani, Agni;et.al.
(2023) Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics — Vol. 847 (2023)

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Abstract
The observation of the production of four top quarks in proton-proton collisions is reported, based on a data sample collected by the CMS experiment at a center-of-mass energy of 13 TeV in 2016–2018 at the CERN LHC and corresponding to an integrated luminosity of 138<math altimg="si2.svg"><mspace width="0.2em"/><msup><mrow><mtext>fb</mtext></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo><mn>1</mn></mrow></msup></math>. Events with two same-sign, three, or four charged leptons (electrons and muons) and additional jets are analyzed. Compared to previous results in these channels, updated identification techniques for charged leptons and jets originating from the hadronization of b quarks, as well as a revised multivariate analysis strategy to distinguish the signal process from the main backgrounds, lead to an improved expected signal significance of 4.9 standard deviations above the background-only hypothesis. Four top quark production is observed with a significance of 5.6 standard deviations, and its cross section is measured to be <math altimg="si3.svg"><mn>17.7</mn><mspace width="0.2em"/><msubsup><mrow/><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo><mn>3.5</mn></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo><mn>3.7</mn></mrow></msubsup><mspace width="0.2em"/><mtext>(stat)</mtext><mspace width="0.2em"/><msubsup><mrow/><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo><mn>1.9</mn></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo><mn>2.3</mn></mrow></msubsup><mspace width="0.2em"/><mtext>(syst)</mtext><mrow><mspace width="0.20em"/><mtext>fb</mtext></mrow></math>, in agreement with the available standard model predictions.
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Benecke, A., Bruno, G., Caputo, C., Delaere, C., Donertas, I. S., Giammanco, A., Jaffel, K., Jain, S., Lemaitre, V., Lidrych, J., Mastrapasqua, P., Mondal, K., Tran, T. T., Wertz, S., CMS, Bethani, A., & et al. (2023). Observation of four top quark production in proton-proton collisions at <math altimg=“si1.svg”><msqrt><mrow><mi>s</mi></mrow></msqrt><mo linebreak=“goodbreak” linebreakstyle=“after”>=</mo><mn>13</mn><mspace width=“0.2em”/><mtext>TeV</mtext></math>. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 847. https://doi.org/10.1016/j.physletb.2023.138290 (Original work published 2023)