Evidence of off-shell Higgs boson production from ZZ leptonic decay channels and constraints on its total width with the ATLAS detector
Georges Aad, B. Abbott, K. Abeling, S.H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A.C. Abusleme Hoffman, B.S. Acharya, C. Adam Bourdarios, L. Adamczyk, L. Adamek, S.V. Addepalli, J. Adelman, A. Adiguzel, S. Adorni, T. Adye, A.A. Affolder, Y. Afik, M.N. Agaras, J. Agarwala, A. Aggarwal, C. Agheorghiesei, J.A. Aguilar-Saavedra, A. Ahmad, F. Ahmadov, W.S. Ahmed, S. Ahuja, X. Ai, G. Aielli, M. Ait Tamlihat, B. Aitbenchikh, I. Aizenberg, M. Akbiyik, T.P.A. Åkesson, A.V. Akimov, N.N. Akolkar, K. Al Khoury, G.L. Alberghi, J. Albert, P. Albicocco, S. Alderweireldt, M. Aleksa, I.N. Aleksandrov, C. Alexa, T. Alexopoulos, A. Alfonsi, F. Alfonsi, M. Alhroob, B. Ali, S. Ali, M. Aliev, G. Alimonti, W. Alkakhi, C. Allaire, B.M.M. Allbrooke, C.A. Allendes Flores, P.P. Allport, A. Aloisio, F. Alonso, C. Alpigiani, M. Alvarez Estevez, A. Alvarez Fernandez, M.G. Alviggi, M. Aly, Y. Amaral Coutinho, A. Ambler, C. Amelung, M. Amerl, C.G. Ames, D. Amidei, S.P. Amor Dos Santos, K.R. Amos, V. Ananiev, C. Anastopoulos, T. Andeen, J.K. Anders, S.Y. Andrean, A. Andreazza, S. Angelidakis, A. Angerami, A.V. Anisenkov, A. Annovi, C. Antel, M.T. Anthony, E. Antipov, M. Antonelli, D.J.A. Antrim, F. Anulli, M. Aoki, T. Aoki, J.A. Aparisi Pozo, M.A. Aparo, L. Aperio Bella, C. Appelt, N. Aranzabal, V. Araujo Ferraz, C. Arcangeletti, A.T.H. Arce
Abstract
This Letter reports on a search for off-shell production of the Higgs boson using 139 fb−1 of pp collision data at s= 13 TeV collected by the ATLAS detector at the Large Hadron Collider. The signature is a pair of Z bosons, with contributions from both the production and subsequent decay of a virtual Higgs boson and the interference of that process with other processes. The two observable final states are ZZ→4ℓ and ZZ→2ℓ2ν with ℓ=e or μ. In the ZZ→4ℓ final state, a dense Neural Network is used to enhance analysis sensitivity with respect to matrix element-based discrimination. The background-only hypothesis is rejected with an observed (expected) significance of 3.3 (2.2) standard deviations, representing experimental evidence for off-shell Higgs boson production. Assuming that no new particles enter the production of the virtual Higgs boson, its total width can be deduced from the measurement of its off-shell production cross-section. The measured total width of the Higgs boson is 4.5−2.5+3.3 MeV, and the observed (expected) upper limit on the total width is found to be 10.5 (10.9) MeV at 95% confidence level.